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Global Warming

Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun’s energy varied. But in the past century, another force has started to influence Earth’s climate: humanity.

(NASA astronaut photograph ISS022-E-6674. )

What is Global Warming?

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century primarily due to the greenhouse gases released by people burning fossil fuels.

How Does Today’s Warming Compare to Past Climate Change?

Earth has experienced climate change in the past without help from humanity. But the current climatic warming is occurring much more rapidly than past warming events.

Why Do Scientists Think Current Warming Isn’t Natural?

In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes unrelated to human activity. These natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.

How Much More Will Earth Warm?

Models predict that as the world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with them. Based on plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century. Some of this warming will occur even if future greenhouse gas emissions are reduced, because the Earth system has not yet fully adjusted to environmental changes we have already made.

How Will Earth Respond to Warming Temperatures?

The impact of global warming is far greater than just increasing temperatures. Warming modifies rainfall patterns, amplifies coastal erosion, lengthens the growing season in some regions, melts ice caps and glaciers, and alters the ranges of some infectious diseases. Some of these changes are already occurring.

References and Related Resources

Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun’s energy varied. But in the past century, another force has started to influence Earth’s climate: humanity

How does this warming compare to previous changes in Earth’s climate? How can we be certain that human-released greenhouse gases are causing the warming? How much more will the Earth warm? How will Earth respond? Answering these questions is perhaps the most significant scientific challenge of our time.

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century primarily due to the greenhouse gases released as people burn fossil fuels. The global average surface temperature rose 0.6 to 0.9 degrees Celsius (1.1 to 1.6° F) between 1906 and 2005, and the rate of temperature increase has nearly doubled in the last 50 years. Temperatures are certain to go up further.

Despite ups and downs from year to year, global average surface temperature is rising. By the beginning of the 21st century, Earth’s temperature was roughly 0.5 degrees Celsius above the long-term (1951–1980) average. (NASA figure adapted from Goddard Institute for Space Studies Surface Temperature Analysis. )

Earth’s natural greenhouse effect

Earth’s temperature begins with the Sun. Roughly 30 percent of incoming sunlight is reflected back into space by bright surfaces like clouds and ice. Of the remaining 70 percent, most is absorbed by the land and ocean, and the rest is absorbed by the atmosphere. The absorbed solar energy heats our planet.

As the rocks, the air, and the seas warm, they radiate “heat” energy (thermal infrared radiation). From the surface, this energy travels into the atmosphere where much of it is absorbed by water vapor and long-lived greenhouse gases such as carbon dioxide and methane.

When they absorb the energy radiating from Earth’s surface, microscopic water or greenhouse gas molecules turn into tiny heaters— like the bricks in a fireplace, they radiate heat even after the fire goes out. They radiate in all directions. The energy that radiates back toward Earth heats both the lower atmosphere and the surface, enhancing the heating they get from direct sunlight.

This absorption and radiation of heat by the atmosphere—the natural greenhouse effect—is beneficial for life on Earth. If there were no greenhouse effect, the Earth’s average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today.

See Climate and Earth’s Energy Budget to read more about how sunlight fuels Earth’s climate.

The enhanced greenhouse effect

What has scientists concerned now is that over the past 250 years, humans have been artificially raising the concentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels, but also from cutting down carbon-absorbing forests. Since the Industrial Revolution began in about 1750, carbon dioxide levels have increased nearly 38 percent as of 2009 and methane levels have increased 148 percent.

Increases in concentrations of carbon dioxide (top) and methane (bottom) coincided with the start of the Industrial Revolution in about 1750. Measurements from Antarctic ice cores (green lines) combined with direct atmospheric measurements (blue lines) show the increase of both gases over time. (NASA graphs by Robert Simmon, based on data from the NOAA Paleoclimatology and Earth System Research Laboratory. )

The atmosphere today contains more greenhouse gas molecules, so more of the infrared energy emitted by the surface ends up being absorbed by the atmosphere. Since some of the extra energy from a warmer atmosphere radiates back down to the surface, Earth’s surface temperature rises. By increasing the concentration of greenhouse gases, we are making Earth’s atmosphere a more efficient greenhouse.

How is Today’s Warming Different from the Past?

Earth has experienced climate change in the past without help from humanity. We know about past climates because of evidence left in tree rings, layers of ice in glaciers, ocean sediments, coral reefs, and layers of sedimentary rocks. For example, bubbles of air in glacial ice trap tiny samples of Earth’s atmosphere, giving scientists a history of greenhouse gases that stretches back more than 800,000 years. The chemical make-up of the ice provides clues to the average global temperature.

See the Earth Observatory’s series Paleoclimatology for details about how scientists study past climates.

Glacial ice and air bubbles trapped in it (top) preserve an 800,000-year record of temperature & carbon dioxide. Earth has cycled between ice ages (low points, large negative anomalies) and warm interglacials (peaks). (Photograph courtesy National Snow & Ice Data Center. NASA graph by Robert Simmon, based on data from Jouzel et al., 2007. )

Using this ancient evidence, scientists have built a record of Earth’s past climates, or “paleoclimates.” The paleoclimate record combined with global models shows past ice ages as well as periods even warmer than today. But the paleoclimate record also reveals that the current climatic warming is occurring much more rapidly than past warming events.

As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming.

Temperature histories from paleoclimate data (green line) compared to the history based on modern instruments (blue line) suggest that global temperature is warmer now than it has been in the past 1,000 years, and possibly longer. (Graph adapted from Mann et al., 2008. )

Models predict that Earth will warm between 2 and 6 degrees Celsius in the next century. When global warming has happened at various times in the past two million years, it has taken the planet about 5,000 years to warm 5 degrees. The predicted rate of warming for the next century is at least 20 times faster. This rate of change is extremely unusual.

Is Current Warming Natural?

In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes not related to human activity. Most often, global climate has changed because of variations in sunlight. Tiny wobbles in Earth’s orbit altered when and where sunlight falls on Earth’s surface. Variations in the Sun itself have alternately increased and decreased the amount of solar energy reaching Earth. Volcanic eruptions have generated particles that reflect sunlight, brightening the planet and cooling the climate. Volcanic activity has also, in the deep past, increased greenhouse gases over millions of years, contributing to episodes of global warming.

A biographical sketch of Milutin Milankovitch describes how changes in Earth’s orbit affects its climate.

These natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades. We know this because scientists closely monitor the natural and human activities that influence climate with a fleet of satellites and surface instruments.

Remote meteorological stations (left) and orbiting satellites (right) help scientists monitor the causes and effects of global warming. [Images courtesy NOAA Network for the Detection of Atmospheric Composition Change (left) and Environmental Visualization Laboratory (right).]

NASA satellites record a host of vital signs including atmospheric aerosols (particles from both natural sources and human activities, such as factories, fires, deserts, and erupting volcanoes), atmospheric gases (including greenhouse gases), energy radiated from Earth’s surface and the Sun, ocean surface temperature changes, global sea level, the extent of ice sheets, glaciers and sea ice, plant growth, rainfall, cloud structure, and more.

On the ground, many agencies and nations support networks of weather and climate-monitoring stations that maintain temperature, rainfall, and snow depth records, and buoys that measure surface water and deep ocean temperatures. Taken together, these measurements provide an ever-improving record of both natural events and human activity for the past 150 years.

Scientists integrate these measurements into climate models to recreate temperatures recorded over the past 150 years. Climate model simulations that consider only natural solar variability and volcanic aerosols since 1750—omitting observed increases in greenhouse gases—are able to fit the observations of global temperatures only up until about 1950. After that point, the decadal trend in global surface warming cannot be explained without including the contribution of the greenhouse gases added by humans.

Though people have had the largest impact on our climate since 1950, natural changes to Earth’s climate have also occurred in recent times. For example, two major volcanic eruptions, El Chichon in 1982 and Pinatubo in 1991, pumped sulfur dioxide gas high into the atmosphere. The gas was converted into tiny particles that lingered for more than a year, reflecting sunlight and shading Earth’s surface. Temperatures across the globe dipped for two to three years.

Although Earth’s temperature fluctuates naturally, human influence on climate has eclipsed the magnitude of natural temperature changes over the past 120 years. Natural influences on temperature—El Niño, solar variability, and volcanic aerosols—have varied approximately plus and minus 0.2° C (0.4° F), (averaging to about zero), while human influences have contributed roughly 0.8° C (1° F) of warming since 1889. (Graphs adapted from Lean et al., 2008.)

Although volcanoes are active around the world, and continue to emit carbon dioxide as they did in the past, the amount of carbon dioxide they release is extremely small compared to human emissions. On average, volcanoes emit between 130 and 230 million tonnes of carbon dioxide per year. By burning fossil fuels, people release in excess of 100 times more, about 26 billion tonnes of carbon dioxide, into the atmosphere every year (as of 2005). As a result, human activity overshadows any contribution volcanoes may have made to recent global warming.

Changes in the brightness of the Sun can influence the climate from decade to decade, but an increase in solar output falls short as an explanation for recent warming. NASA satellites have been measuring the Sun’s output since 1978. The total energy the Sun radiates varies over an 11-year cycle. During solar maxima, solar energy is approximately 0.1 percent higher on average than it is during solar minima.

The transparent halo known as the solar corona changes between solar maximum (left) and solar minimum (right). (NASA Extreme Ultraviolet Telescope images from the SOHO Data Archive. )

Each cycle exhibits subtle differences in intensity and duration. As of early 2010, the solar brightness since 2005 has been slightly lower, not higher, than it was during the previous 11-year minimum in solar activity, which occurred in the late 1990s. This implies that the Sun’s impact between 2005 and 2010 might have been to slightly decrease the warming that greenhouse emissions alone would have caused.

Satellite measurements of daily (light line) and monthly average (dark line) total solar irradiance since 1979 have not detected a clear long-term trend. (NASA graph by Robert Simmon, based on data from the ACRIM Science Team. )

Scientists theorize that there may be a multi-decadal trend in solar output, though if one exists, it has not been observed as yet. Even if the Sun were getting brighter, however, the pattern of warming observed on Earth since 1950 does not match the type of warming the Sun alone would cause. When the Sun’s energy is at its peak (solar maxima), temperatures in both the lower atmosphere (troposphere) and the upper atmosphere (stratosphere) become warmer. Instead, observations show the pattern expected from greenhouse gas effects: Earth’s surface and troposphere have warmed, but the stratosphere has cooled.

Satellite measurements show warming in the troposphere (lower atmosphere, green line) but cooling in the stratosphere (upper atmosphere, red line). This vertical pattern is consistent with global warming due to increasing greenhouse gases, but inconsistent with warming from natural causes. (Graph by Robert Simmon, based on data from Remote Sensing Systems, sponsored by the NOAA Climate and Global Change Program.)

The stratosphere gets warmer during solar maxima because the ozone layer absorbs ultraviolet light; more ultraviolet light during solar maxima means warmer temperatures. Ozone depletion explains the biggest part of the cooling of the stratosphere over recent decades, but it can’t account for all of it. Increased concentrations of carbon dioxide in the troposphere and stratosphere together contribute to cooling in the stratosphere.

To further explore the causes and effects of global warming and to predict future warming, scientists build climate models—computer simulations of the climate system. Climate models are designed to simulate the responses and interactions of the oceans and atmosphere, and to account for changes to the land surface, both natural and human-induced. They comply with fundamental laws of physics—conservation of energy, mass, and momentum—and account for dozens of factors that influence Earth’s climate.

Though the models are complicated, rigorous tests with real-world data hone them into powerful tools that allow scientists to explore our understanding of climate in ways not otherwise possible. By experimenting with the models—removing greenhouse gases emitted by the burning of fossil fuels or changing the intensity of the Sun to see how each influences the climate—scientists use the models to better understand Earth’s current climate and to predict future climate.

The models predict that as the world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with them. Based on a range of plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century.

Model simulations by the Intergovernmental Panel on Climate Change estimate that Earth will warm between two and six degrees Celsius over the next century, depending on how fast carbon dioxide emissions grow. Scenarios that assume that people will burn more and more fossil fuel provide the estimates in the top end of the temperature range, while scenarios that assume that greenhouse gas emissions will grow slowly give lower temperature predictions. The orange line provides an estimate of global temperatures if greenhouse gases stayed at year 2000 levels. (©2007 IPCC WG1 AR-4.)

Climate Feedbacks

Greenhouse gases are only part of the story when it comes to global warming. Changes to one part of the climate system can cause additional changes to the way the planet absorbs or reflects energy. These secondary changes are called climate feedbacks, and they could more than double the amount of warming caused by carbon dioxide alone. The primary feedbacks are due to snow and ice, water vapor, clouds, and the carbon cycle.

Snow and ice

Perhaps the most well known feedback comes from melting snow and ice in the Northern Hemisphere. Warming temperatures are already melting a growing percentage of Arctic sea ice, exposing dark ocean water during the perpetual sunlight of summer. Snow cover on land is also dwindling in many areas. In the absence of snow and ice, these areas go from having bright, sunlight-reflecting surfaces that cool the planet to having dark, sunlight-absorbing surfaces that bring more energy into the Earth system and cause more warming.

Canada’s Athabasca Glacier has been shrinking by about 15 meters per year. In the past 125 years, the glacier has lost half its volume and has retreated more than 1.5 kilometers. As glaciers retreat, sea ice disappears, and snow melts earlier in the spring, the Earth absorbs more sunlight than it would if the reflective snow and ice remained. (Photograph ©2005 Hugh Saxby. )

Water Vapor

The largest feedback is water vapor. Water vapor is a strong greenhouse gas. In fact, because of its abundance in the atmosphere, water vapor causes about two-thirds of greenhouse warming, a key factor in keeping temperatures in the habitable range on Earth. But as temperatures warm, more water vapor evaporates from the surface into the atmosphere, where it can cause temperatures to climb further.

The question that scientists ask is, how much water vapor will be in the atmosphere in a warming world? The atmosphere currently has an average equilibrium or balance between water vapor concentration and temperature. As temperatures warm, the atmosphere becomes capable of containing more water vapor, and so water vapor concentrations go up to regain equilibrium. Will that trend hold as temperatures continue to warm?

The amount of water vapor that enters the atmosphere ultimately determines how much additional warming will occur due to the water vapor feedback. The atmosphere responds quickly to the water vapor feedback. So far, most of the atmosphere has maintained a near constant balance between temperature and water vapor concentration as temperatures have gone up in recent decades. If this trend continues, and many models say that it will, water vapor has the capacity to double the warming caused by carbon dioxide alone.

Closely related to the water vapor feedback is the cloud feedback. Clouds cause cooling by reflecting solar energy, but they also cause warming by absorbing infrared energy (like greenhouse gases) from the surface when they are over areas that are warmer than they are. In our current climate, clouds have a cooling effect overall, but that could change in a warmer environment.

Clouds can both cool the planet (by reflecting visible light from the sun) and warm the planet (by absorbing heat radiation emitted by the surface). On balance, clouds slightly cool the Earth. (NASA Astronaut Photograph STS31-E-9552 courtesy Johnson space Center Earth Observations Lab. )

If clouds become brighter, or the geographical extent of bright clouds expands, they will tend to cool Earth’s surface. Clouds can become brighter if more moisture converges in a particular region or if more fine particles (aerosols) enter the air. If fewer bright clouds form, it will contribute to warming from the cloud feedback.

See Ship Tracks South of Alaska to learn how aerosols can make clouds brighter.

Clouds, like greenhouse gases, also absorb and re-emit infrared energy. Low, warm clouds emit more energy than high, cold clouds. However, in many parts of the world, energy emitted by low clouds can be absorbed by the abundant water vapor above them. Further, low clouds often have nearly the same temperatures as the Earth’s surface, and so emit similar amounts of infrared energy. In a world without low clouds, the amount of emitted infrared energy escaping to space would not be too different from a world with low clouds.

Clouds emit thermal infrared (heat) radiation in proportion to their temperature, which is related to altitude. This image shows the Western Hemisphere in the thermal infrared. Warm ocean and land surface areas are white and light gray; cool, low-level clouds are medium gray; and cold, high-altitude clouds are dark gray and black. (NASA image courtesy GOES Project Science. )

High cold clouds, however, form in a part of the atmosphere where energy-absorbing water vapor is scarce. These clouds trap (absorb) energy coming from the lower atmosphere, and emit little energy to space because of their frigid temperatures. In a world with high clouds, a significant amount of energy that would otherwise escape to space is captured in the atmosphere. As a result, global temperatures are higher than in a world without high clouds.

If warmer temperatures result in a greater amount of high clouds, then less infrared energy will be emitted to space. In other words, more high clouds would enhance the greenhouse effect, reducing the Earth’s capability to cool and causing temperatures to warm.

See Clouds and Radiation for a more complete description.

Scientists aren’t entirely sure where and to what degree clouds will end up amplifying or moderating warming, but most climate models predict a slight overall positive feedback or amplification of warming due to a reduction in low cloud cover. A recent observational study found that fewer low, dense clouds formed over a region in the Pacific Ocean when temperatures warmed, suggesting a positive cloud feedback in this region as the models predicted. Such direct observational evidence is limited, however, and clouds remain the biggest source of uncertainty--apart from human choices to control greenhouse gases—in predicting how much the climate will change.

The Carbon Cycle

Increased atmospheric carbon dioxide concentrations and warming temperatures are causing changes in the Earth’s natural carbon cycle that also can feedback on atmospheric carbon dioxide concentration. For now, primarily ocean water, and to some extent ecosystems on land, are taking up about half of our fossil fuel and biomass burning emissions. This behavior slows global warming by decreasing the rate of atmospheric carbon dioxide increase, but that trend may not continue. Warmer ocean waters will hold less dissolved carbon, leaving more in the atmosphere.

About half the carbon dioxide emitted into the air from burning fossil fuels dissolves in the ocean. This map shows the total amount of human-made carbon dioxide in ocean water from the surface to the sea floor. Blue areas have low amounts, while yellow regions are rich in anthropogenic carbon dioxide. High amounts occur where currents carry the carbon-dioxide-rich surface water into the ocean depths. (Map adapted from Sabine et al., 2004.)

See The Ocean’s Carbon Balance on the Earth Observatory.

On land, changes in the carbon cycle are more complicated. Under a warmer climate, soils, especially thawing Arctic tundra, could release trapped carbon dioxide or methane to the atmosphere. Increased fire frequency and insect infestations also release more carbon as trees burn or die and decay.

On the other hand, extra carbon dioxide can stimulate plant growth in some ecosystems, allowing these plants to take additional carbon out of the atmosphere. However, this effect may be reduced when plant growth is limited by water, nitrogen, and temperature. This effect may also diminish as carbon dioxide increases to levels that become saturating for photosynthesis. Because of these complications, it is not clear how much additional carbon dioxide plants can take out of the atmosphere and how long they could continue to do so.

The impact of climate change on the land carbon cycle is extremely complex, but on balance, land carbon sinks will become less efficient as plants reach saturation, where they can no longer take up additional carbon dioxide, and other limitations on growth occur, and as land starts to add more carbon to the atmosphere from warming soil, fires, and insect infestations. This will result in a faster increase in atmospheric carbon dioxide and more rapid global warming. In some climate models, carbon cycle feedbacks from both land and ocean add more than a degree Celsius to global temperatures by 2100.

Emission Scenarios

Scientists predict the range of likely temperature increase by running many possible future scenarios through climate models. Although some of the uncertainty in climate forecasts comes from imperfect knowledge of climate feedbacks, the most significant source of uncertainty in these predictions is that scientists don’t know what choices people will make to control greenhouse gas emissions.

The higher estimates are made on the assumption that the entire world will continue using more and more fossil fuel per capita, a scenario scientists call “business-as-usual.” More modest estimates come from scenarios in which environmentally friendly technologies such as fuel cells, solar panels, and wind energy replace much of today’s fossil fuel combustion.

It takes decades to centuries for Earth to fully react to increases in greenhouse gases. Carbon dioxide, among other greenhouse gases, will remain in the atmosphere long after emissions are reduced, contributing to continuing warming. In addition, as Earth has warmed, much of the excess energy has gone into heating the upper layers of the ocean. Like a hot water bottle on a cold night, the heated ocean will continue warming the lower atmosphere well after greenhouse gases have stopped increasing.

These considerations mean that people won’t immediately see the impact of reduced greenhouse gas emissions. Even if greenhouse gas concentrations stabilized today, the planet would continue to warm by about 0.6°C over the next century because of greenhouses gases already in the atmosphere.

See Earth’s Big Heat Bucket, Correcting Ocean Cooling, and Climate Q&A: If we immediately stopped emitting greenhouse gases, would global warming stop? to learn more about the ocean heat and global warming.

How Will Global Warming Change Earth?

The impact of increased surface temperatures is significant in itself. But global warming will have additional, far-reaching effects on the planet. Warming modifies rainfall patterns, amplifies coastal erosion, lengthens the growing season in some regions, melts ice caps and glaciers, and alters the ranges of some infectious diseases. Some of these changes are already occurring.

Global warming will shift major climate patterns, possibly prolonging and intensifying the current drought in the U.S. Southwest. The white ring of bleached rock on the once-red cliffs that hold Lake Powell indicate the drop in water level over the past decade—the result of repeated winters with low snowfall. (Photograph ©2006 Tigresblanco. )

Changing Weather

For most places, global warming will result in more frequent hot days and fewer cool days, with the greatest warming occurring over land. Longer, more intense heat waves will become more common. Storms, floods, and droughts will generally be more severe as precipitation patterns change. Hurricanes may increase in intensity due to warmer ocean surface temperatures.

Apart from driving temperatures up, global warming is likely to cause bigger, more destructive storms, leading to an overall increase in precipitation. With some exceptions, the tropics will likely receive less rain (orange) as the planet warms, while the polar regions will receive more precipitation (green). White areas indicate that fewer than two-thirds of the climate models agreed on how precipitation will change. Stippled areas reveal where more than 90 percent of the models agreed. (©2007 IPCC WG1 AR-4.)

It is impossible to pin any single unusual weather event on global warming, but emerging evidence suggests that global warming is already influencing the weather. Heat waves, droughts, and intense rain events have increased in frequency during the last 50 years, and human-induced global warming more likely than not contributed to the trend.

Rising Sea Levels

The weather isn’t the only thing global warming will impact: rising sea levels will erode coasts and cause more frequent coastal flooding. Some island nations will disappear. The problem is serious because up to 10 percent of the world’s population lives in vulnerable areas less than 10 meters (about 30 feet) above sea level.

Between 1870 and 2000, the sea level increased by 1.7 millimeters per year on average, for a total sea level rise of 221 millimeters (0.7 feet or 8.7 inches). And the rate of sea level rise is accelerating. Since 1993, NASA satellites have shown that sea levels are rising more quickly, about 3 millimeters per year, for a total sea level rise of 48 millimeters (0.16 feet or 1.89 inches) between 1993 and 2009.

Sea levels crept up about 20 centimeters (7.9 inches) during the twentieth century. Sea levels are predicted to go up between 18 and 59 cm (7.1 and 23 inches) over the next century, though the increase could be greater if ice sheets in Greenland and Antarctica melt more quickly than predicted. Higher sea levels will erode coastlines and cause more frequent flooding. (Graph ©2007 Robert Rohde. )

The Intergovernmental Panel on Climate Change (IPCC) estimates that sea levels will rise between 0.18 and 0.59 meters (0.59 to 1.9 feet) by 2099 as warming sea water expands, and mountain and polar glaciers melt. These sea level change predictions may be underestimates, however, because they do not account for any increases in the rate at which the world’s major ice sheets are melting. As temperatures rise, ice will melt more quickly. Satellite measurements reveal that the Greenland and West Antarctic ice sheets are shedding about 125 billion tons of ice per year—enough to raise sea levels by 0.35 millimeters (0.01 inches) per year. If the melting accelerates, the increase in sea level could be significantly higher.

Impacting Ecosystems

More importantly, perhaps, global warming is already putting pressure on ecosystems, the plants and animals that co-exist in a particular climate zone, both on land and in the ocean. Warmer temperatures have already shifted the growing season in many parts of the globe. The growing season in parts of the Northern Hemisphere became two weeks longer in the second half of the 20th century. Spring is coming earlier in both hemispheres.

This change in the growing season affects the broader ecosystem. Migrating animals have to start seeking food sources earlier. The shift in seasons may already be causing the lifecycles of pollinators, like bees, to be out of synch with flowering plants and trees. This mismatch can limit the ability of both pollinators and plants to survive and reproduce, which would reduce food availability throughout the food chain.

See Buzzing About Climate Change to read more about how the lifecycle of bees is synched with flowering plants.

Warmer temperatures also extend the growing season. This means that plants need more water to keep growing throughout the season or they will dry out, increasing the risk of failed crops and wildfires. Once the growing season ends, shorter, milder winters fail to kill dormant insects, increasing the risk of large, damaging infestations in subsequent seasons.

In some ecosystems, maximum daily temperatures might climb beyond the tolerance of indigenous plant or animal. To survive the extreme temperatures, both marine and land-based plants and animals have started to migrate towards the poles. Those species, and in some cases, entire ecosystems, that cannot quickly migrate or adapt, face extinction. The IPCC estimates that 20-30 percent of plant and animal species will be at risk of extinction if temperatures climb more than 1.5° to 2.5°C.

Impacting People

The changes to weather and ecosystems will also affect people more directly. Hardest hit will be those living in low-lying coastal areas, and residents of poorer countries who do not have the resources to adapt to changes in temperature extremes and water resources. As tropical temperature zones expand, the reach of some infectious diseases, such as malaria, will change. More intense rains and hurricanes and rising sea levels will lead to more severe flooding and potential loss of property and life.

One inevitable consequence of global warming is sea-level rise. In the face of higher sea levels and more intense storms, coastal communities face greater risk of rapid beach erosion from destructive storms like the intense nor’easter of April 2007 that caused this damage. (Photograph ©2007 metimbers2000. )

Hotter summers and more frequent fires will lead to more cases of heat stroke and deaths, and to higher levels of near-surface ozone and smoke, which would cause more ‘code red’ air quality days. Intense droughts can lead to an increase in malnutrition. On a longer time scale, fresh water will become scarcer, especially during the summer, as mountain glaciers disappear, particularly in Asia and parts of North America.

On the flip side, there could be “winners” in a few places. For example, as long as the rise in global average temperature stays below 3 degrees Celsius, some models predict that global food production could increase because of the longer growing season at mid- to high-latitudes, provided adequate water resources are available. The same small change in temperature, however, would reduce food production at lower latitudes, where many countries already face food shortages. On balance, most research suggests that the negative impacts of a changing climate far outweigh the positive impacts. Current civilization—agriculture and population distribution—has developed based on the current climate. The more the climate changes, and the more rapidly it changes, the greater the cost of adaptation.

Ultimately, global warming will impact life on Earth in many ways, but the extent of the change is largely up to us. Scientists have shown that human emissions of greenhouse gases are pushing global temperatures up, and many aspects of climate are responding to the warming in the way that scientists predicted they would. This offers hope. Since people are causing global warming, people can mitigate global warming, if they act in time. Greenhouse gases are long-lived, so the planet will continue to warm and changes will continue to happen far into the future, but the degree to which global warming changes life on Earth depends on our decisions now.

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• Joint Science Academies. (2005). Joint Science Academies’ Statement: Global Response to Climate Change. June 2005.
• Jouzel, J., Masson-Delmotte, V., Cattani, O., Dreyfus, G., Falourd, S., Hoffmann, G., Minster, B., et al. (2007). Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years. Science , 317(5839), 793-796.
• Labitzke, K., Butchart, N., Knight, J., Takahashi, M., Nakamoto, M., Nagashima, T., Haigh, J., et al. (2002). The global signal of the 11-year solar cycle in the stratosphere: observations and models. Journal of Atmospheric and Solar-Terrestrial Physics, 64(2), 203-210.
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What Is Climate Change?

Climate change refers to long-term shifts in temperatures and weather patterns. Such shifts can be natural, due to changes in the sun’s activity or large volcanic eruptions. But since the 1800s, human activities have been the main driver of climate change , primarily due to the burning of fossil fuels like coal, oil and gas.

Burning fossil fuels generates greenhouse gas emissions that act like a blanket wrapped around the Earth, trapping the sun’s heat and raising temperatures.

The main greenhouse gases that are causing climate change include carbon dioxide and methane. These come from using gasoline for driving a car or coal for heating a building, for example. Clearing land and cutting down forests can also release carbon dioxide. Agriculture, oil and gas operations are major sources of methane emissions. Energy, industry, transport, buildings, agriculture and land use are among the main sectors  causing greenhouse gases.

Humans are responsible for global warming

Climate scientists have showed that humans are responsible for virtually all global heating over the last 200 years. Human activities like the ones mentioned above are causing greenhouse gases that are warming the world faster than at any time in at least the last two thousand years.

The average temperature of the Earth’s surface is now about 1.2°C warmer than it was in the late 1800s (before the industrial revolution) and warmer than at any time in the last 100,000 years. The last decade (2011-2020) was the warmest on record , and each of the last four decades has been warmer than any previous decade since 1850.

Many people think climate change mainly means warmer temperatures. But temperature rise is only the beginning of the story. Because the Earth is a system, where everything is connected, changes in one area can influence changes in all others.

The consequences of climate change now include, among others, intense droughts, water scarcity, severe fires, rising sea levels, flooding, melting polar ice, catastrophic storms and declining biodiversity.

People are experiencing climate change in diverse ways

Climate change can affect our health , ability to grow food, housing, safety and work. Some of us are already more vulnerable to climate impacts, such as people living in small island nations and other developing countries. Conditions like sea-level rise and saltwater intrusion have advanced to the point where whole communities have had to relocate, and protracted droughts are putting people at risk of famine. In the future, the number of people displaced by weather-related events is expected to rise.

Every increase in global warming matters

In a series of UN reports , thousands of scientists and government reviewers agreed that limiting global temperature rise to no more than 1.5°C would help us avoid the worst climate impacts and maintain a livable climate. Yet policies currently in place point to a 3°C temperature rise by the end of the century.

The emissions that cause climate change come from every part of the world and affect everyone, but some countries produce much more than others .The seven biggest emitters alone (China, the United States of America, India, the European Union, Indonesia, the Russian Federation, and Brazil) accounted for about half of all global greenhouse gas emissions in 2020.

Everyone must take climate action, but people and countries creating more of the problem have a greater responsibility to act first.

We face a huge challenge but already know many solutions

Many climate change solutions can deliver economic benefits while improving our lives and protecting the environment. We also have global frameworks and agreements to guide progress, such as the Sustainable Development Goals , the UN Framework Convention on Climate Change and the Paris Agreement . Three broad categories of action are: cutting emissions, adapting to climate impacts and financing required adjustments.

Switching energy systems from fossil fuels to renewables like solar or wind will reduce the emissions driving climate change. But we have to act now. While a growing number of countries is committing to net zero emissions by 2050, emissions must be cut in half by 2030 to keep warming below 1.5°C. Achieving this means huge declines in the use of coal, oil and gas: over two-thirds of today’s proven reserves of fossil fuels need to be kept in the ground by 2050 in order to prevent catastrophic levels of climate change.

Adapting to climate consequences protects people, homes, businesses, livelihoods, infrastructure and natural ecosystems. It covers current impacts and those likely in the future. Adaptation will be required everywhere, but must be prioritized now for the most vulnerable people with the fewest resources to cope with climate hazards. The rate of return can be high. Early warning systems for disasters, for instance, save lives and property, and can deliver benefits up to 10 times the initial cost.

We can pay the bill now, or pay dearly in the future

Climate action requires significant financial investments by governments and businesses. But climate inaction is vastly more expensive. One critical step is for industrialized countries to fulfil their commitment to provide $100 billion a year to developing countries so they can adapt and move towards greener economies.

To get familiar with some of the more technical terms used in connection with climate change, consult the Climate Dictionary .

Learn more about…

The facts on climate and energy

Climate change is a hot topic – with myths and falsehoods circulating widely. Find some essential facts here .

The science

See the latest climate reports from the United Nations as well as climate action facts .

Causes and Effects

Fossil fuels are by far the largest contributor to the greenhouse gas emissions that cause climate change, which poses many risks to all forms of life on Earth. Learn more .

From the Secretary-General

Read the UN Chief’s latest statements on climate action.

What is net zero? Why is it important? Our  net-zero page  explains why we need steep emissions cuts now and what efforts are underway.

Renewable energy – powering a safer future

What is renewable energy and why does it matter? Learn more about why the shift to renewables is our only hope for a brighter and safer world.

How will the world foot the bill? We explain the issues and the value of financing climate action.

What is climate adaptation? Why is it so important for every country? Find out how we can protect lives and livelihoods as the climate changes.

Climate Issues

Learn more about how climate change impacts are felt across different sectors and ecosystems.

Why women are key to climate action

Women and girls are on the frontlines of the climate crisis and uniquely situated to drive action. Find out why it’s time to invest in women.

Facts and figures

• What is climate change?
• Causes and effects
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Cutting emissions

• Explaining net zero
• High-level expert group on net zero
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• Greenwashing
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• Renewable energy – key to a safer future
• What is renewable energy
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ENCYCLOPEDIC ENTRY

Climate change.

Climate change is a long-term shift in global or regional climate patterns. Often climate change refers specifically to the rise in global temperatures from the mid-20th century to present.

Earth Science, Climatology

Fracking tower

Fracking is a controversial form of drilling that uses high-pressure liquid to create cracks in underground shale to extract natural gas and petroleum. Carbon emissions from fossils fuels like these have been linked to global warming and climate change.

Photograph by Mark Thiessen / National Geographic

Climate is sometimes mistaken for weather. But climate is different from weather because it is measured over a long period of time, whereas weather can change from day to day, or from year to year. The climate of an area includes seasonal temperature and rainfall averages, and wind patterns. Different places have different climates. A desert, for example, is referred to as an arid climate because little water falls, as rain or snow, during the year. Other types of climate include tropical climates, which are hot and humid , and temperate climates, which have warm summers and cooler winters.

Climate change is the long-term alteration of temperature and typical weather patterns in a place. Climate change could refer to a particular location or the planet as a whole. Climate change may cause weather patterns to be less predictable. These unexpected weather patterns can make it difficult to maintain and grow crops in regions that rely on farming because expected temperature and rainfall levels can no longer be relied on. Climate change has also been connected with other damaging weather events such as more frequent and more intense hurricanes, floods, downpours, and winter storms.

In polar regions, the warming global temperatures associated with climate change have meant ice sheets and glaciers are melting at an accelerated rate from season to season. This contributes to sea levels rising in different regions of the planet. Together with expanding ocean waters due to rising temperatures, the resulting rise in sea level has begun to damage coastlines as a result of increased flooding and erosion.

The cause of current climate change is largely human activity, like burning fossil fuels , like natural gas, oil, and coal. Burning these materials releases what are called greenhouse gases into Earth’s atmosphere . There, these gases trap heat from the sun’s rays inside the atmosphere causing Earth’s average temperature to rise. This rise in the planet's temperature is called global warming. The warming of the planet impacts local and regional climates. Throughout Earth's history, climate has continually changed. When occuring naturally, this is a slow process that has taken place over hundreds and thousands of years. The human influenced climate change that is happening now is occuring at a much faster rate.

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October 19, 2023

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Newsroom Post

Climate change widespread, rapid, and intensifying – ipcc.

GENEVA, Aug 9 – Scientists are observing changes in the Earth’s climate in every region and across the whole climate system, according to the latest Intergovernmental Panel on Climate Change (IPCC) Report, released today. Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years, and some of the changes already set in motion—such as continued sea level rise—are irreversible over hundreds to thousands of years.

However, strong and sustained reductions in emissions of carbon dioxide (CO 2 ) and other greenhouse gases would limit climate change. While benefits for air quality would come quickly, it could take 20-30 years to see global temperatures stabilize, according to the IPCC Working Group I report, Climate Change 2021: the Physical Science Basis , approved on Friday by 195 member governments of the IPCC, through a virtual approval session that was held over two weeks starting on July 26.

The Working Group I report is the first instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.

“This report reflects extraordinary efforts under exceptional circumstances,” said Hoesung Lee, Chair of the IPCC. “The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making.”

Faster warming

The report provides new estimates of the chances of crossing the global warming level of 1.5°C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.

The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming. This assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.

“This report is a reality check,” said IPCC Working Group I Co-Chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”

Every region facing increasing changes

Many characteristics of climate change directly depend on the level of global warming, but what people experience is often very different to the global average. For example, warming over land is larger than the global average, and it is more than twice as high in the Arctic.

“Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.

The report projects that in the coming decades climate changes will increase in all regions. For 1.5°C of global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons. At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.

But it is not just about temperature. Climate change is bringing multiple different changes in different regions – which will all increase with further warming. These include changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans. For example:

• Climate change is intensifying the water cycle. This brings more intense rainfall and associated flooding, as well as more intense drought in many regions.
• Climate change is affecting rainfall patterns. In high latitudes, precipitation is likely to increase, while it is projected to decrease over large parts of the subtropics. Changes to monsoon precipitation are expected, which will vary by region.
• Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion. Extreme sea level events that previously occurred once in 100 years could happen every year by the end of this century.
• Further warming will amplify permafrost thawing, and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice.
• Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence. These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century.
• For cities, some aspects of climate change may be amplified, including heat (since urban areas are usually warmer than their surroundings), flooding from heavy precipitation events and sea level rise in coastal cities.

For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.

This regional information can be explored in detail in the newly developed Interactive Atlas interactive-atlas.ipcc.ch as well as regional fact sheets, the technical summary, and underlying report.

Human influence on the past and future climate

“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” said Masson-Delmotte. Yet the new report also reflects major advances in the science of attribution – understanding the role of climate change in intensifying specific weather and climate events such as extreme heat waves and heavy rainfall events.

The report also shows that human actions still have the potential to determine the future course of climate. The evidence is clear that carbon dioxide (CO 2 ) is the main driver of climate change, even as other greenhouse gases and air pollutants also affect the climate.

“Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO 2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” said Zhai.

For more information contact:

IPCC Press Office [email protected] , +41 22 730 8120

Katherine Leitzell [email protected]

Nada Caud (French) [email protected]

Notes for Editors

Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change

The Working Group I report addresses the most updated physical understanding of the climate system and climate change, bringing together the latest advances in climate science, and combining multiple lines of evidence from paleoclimate, observations, process understanding, global and regional climate simulations. It shows how and why climate has changed to date, and the improved understanding of human influence on a wider range of climate characteristics, including extreme events. There will be a greater focus on regional information that can be used for climate risk assessments.

The Summary for Policymakers of the Working Group I contribution to the Sixth Assessment Report (AR6) as well as additional materials and information are available at https://www.ipcc.ch/report/ar6/wg1/

Note : Originally scheduled for release in April 2021, the report was delayed for several months by the COVID-19 pandemic, as work in the scientific community including the IPCC shifted online. This is first time that the IPCC has conducted a virtual approval session for one of its reports.

AR6 Working Group I in numbers

234 authors from 66 countries

• 31 – coordinating authors
• 167 – lead authors
• 36 – review editors
• 517 – contributing authors

Over 14,000 cited references

A total of 78,007 expert and government review comments

(First Order Draft 23,462; Second Order Draft 51,387; Final Government Distribution: 3,158)

More information about the Sixth Assessment Report can be found here .

About the IPCC

The Intergovernmental Panel on Climate Change (IPCC) is the UN body for assessing the science related to climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide political leaders with periodic scientific assessments concerning climate change, its implications and risks, as well as to put forward adaptation and mitigation strategies. In the same year the UN General Assembly endorsed the action by the WMO and UNEP in jointly establishing the IPCC. It has 195 member states.

Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, IPCC scientists volunteer their time to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.

The IPCC has three working groups: Working Group I , dealing with the physical science basis of climate change; Working Group II , dealing with impacts, adaptation and vulnerability; and Working Group III , dealing with the mitigation of climate change. It also has a Task Force on National Greenhouse Gas Inventories that develops methodologies for measuring emissions and removals. As part of the IPCC, a Task Group on Data Support for Climate Change Assessments (TG-Data) provides guidance to the Data Distribution Centre (DDC) on curation, traceability, stability, availability and transparency of data and scenarios related to the reports of the IPCC.

IPCC assessments provide governments, at all levels, with scientific information that they can use to develop climate policies. IPCC assessments are a key input into the international negotiations to tackle climate change. IPCC reports are drafted and reviewed in several stages, thus guaranteeing objectivity and transparency. An IPCC assessment report consists of the contributions of the three working groups and a Synthesis Report. The Synthesis Report integrates the findings of the three working group reports and of any special reports prepared in that assessment cycle.

About the Sixth Assessment Cycle

At its 41st Session in February 2015, the IPCC decided to produce a Sixth Assessment Report (AR6). At its 42nd Session in October 2015 it elected a new Bureau that would oversee the work on this report and the Special Reports to be produced in the assessment cycle.

Global Warming of 1.5°C , an IPCC special report on the impacts of global warming of 1.5 degrees Celsius above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty was launched in October 2018.

Climate Change and Land , an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems was launched in August 2019, and the Special Report on the Ocean and Cryosphere in a Changing Climate was released in September 2019.

In May 2019 the IPCC released the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories , an update to the methodology used by governments to estimate their greenhouse gas emissions and removals.

The other two Working Group contributions to the AR6 will be finalized in 2022 and the AR6 Synthesis Report will be completed in the second half of 2022.

For more information go to www.ipcc.ch

The website includes outreach materials including videos about the IPCC and video recordings from outreach events conducted as webinars or live-streamed events.

Most videos published by the IPCC can be found on our YouTube and Vimeo channels.

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• View all journals

Climate change articles from across Nature Portfolio

Climate change refers to a statistically defined change in the average and/or variability of the climate system, this includes the atmosphere, the water cycle, the land surface, ice and the living components of Earth. The definition does not usually require the causes of change to be attributed, for example to human activity, but there are exceptions.

Rising atmospheric carbon dioxide widens yield gaps

Rising atmospheric carbon dioxide concentrations and temperature unevenly affect the two main rice subspecies, which is predicted to increase the yield gap between low-income and middle- to high-income countries later this century.

• Irakli Loladze

Climate feedbacks from coastal erosion

The erosion of melting permafrost in the coastal Arctic Ocean is projected to lower the ocean’s capacity to absorb carbon dioxide, triggering unexpected carbon–climate feedbacks in the Arctic region.

• Manfredi Manizza

Coral giants sound the alarm for the Great Barrier Reef

Ocean warming has repeatedly led to mass coral bleaching on the Great Barrier Reef in the past 20 years, threatening its existence. Coral skeletons show that reef temperatures reached historical highs during this period.

• Miriam Pfeiffer

Related Subjects

• Attribution
• Climate and Earth system modelling
• Climate-change impacts
• Climate-change mitigation
• Projection and prediction

Latest Research and Reviews

Dissecting the vital role of dietary changes in food security assessment under climate change

Dietary changes can potentially alleviate climate change’s impact on global food supply, benefiting up to 42% of the global population and potentially addressing the food security crisis, according to assessment of dietary changes’ impact on food security.

• Zhentao Zhang
• Xiaoguang Yang

The carbon emission reduction effect of China’s national high-tech industrial development zones

Projected changes in extreme hot summer events in Asian monsoon regions

• Reshmita Nath
• Debashis Nath

The atmospheric connection between the Arctic and Eurasia is underestimated in simulations with prescribed sea ice

Incorporating turbulent heat fluxes from reanalysis data in numerical simulations of Arctic sea ice loss enhances heat transfer and reproduces the Arctic-Eurasian connection, despite underestimation in models with prescribed sea ice concentrations, according to results from numerical simulations of sea ice forcing experiments.

• Wenqing Zhang

Dedicated climate ministries help to reduce carbon emissions

• Julian Limberg
• Yves Steinebach
• Jacob Nyrup

Deep learning for detecting and characterizing oil and gas well pads in satellite imagery

This work uses deep learning on satellite imagery to map well pads and storage tanks in two major U.S. basins. The resulting data fills large gaps in existing databases, a crucial step for improving methane emission estimates and source attribution.

• Neel Ramachandran
• Jeremy Irvin
• Robert B. Jackson

News and Comment

What is the hottest temperature humans can survive? These labs are redefining the limit

The threshold for survival in heat is lower than thought — researchers are using state-of-the-art climate chambers to explore when blistering conditions threaten life.

• Carissa Wong

Who is legally responsible for climate harms? The world’s top court will now decide

The International Court of Justice will clarify states’ legal responsibility for impacts of climate change. Although non-binding, its opinion will matter for thousands of climate lawsuits.

Caution in the use of populism to describe distributional considerations of climate policy

• R. M. Colvin

National policies to accelerate climate action in US healthcare

US healthcare contributes 8.5% of national greenhouse gas emissions, but its policies to guide mitigation and waste reduction are underdeveloped. We recommend national policies to streamline the adoption of best practices, address implementation challenges to achieve net-zero goals and serve as useful exemplars for other nations.

• Elizabeth Cerceo
• Hardeep Singh

Priorities for net-zero web services

The complexity of the infrastructure underpinning the modern Internet has led to a lack of clarity on how to measure the energy consumption of web services and achieve sustainable web design. It is now crucial to redirect sustainability efforts in the sector towards more effective interventions.

• Mohit Arora
• Iain McClenaghan
• Lydia Wozniak

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Learn about the causes and effects of global warming.

global warming , Increase in the global average surface temperature resulting from enhancement of the greenhouse effect, primarily by air pollution . In 2007 the UN Intergovernmental Panel on Climate Change forecast that by 2100 global average surface temperatures would increase 3.2–7.2 °F (1.8–4.0 °C), depending on a range of scenarios for greenhouse gas emissions, and stated that it was now 90 percent certain that most of the warming observed over the previous half century could be attributed to greenhouse gas emissions produced by human activities (i.e., industrial processes and transportation). Many scientists predict that such an increase in temperature would cause polar ice caps and mountain glaciers to melt rapidly, significantly raising the levels of coastal waters, and would produce new patterns and extremes of drought and rainfall, seriously disrupting food production in certain regions. Other scientists maintain that such predictions are overstated. The 1992 Earth Summit and the 1997 Kyoto Protocol to the United Nations Framework Convention on Climate Change attempted to address the issue of global warming, but in both cases the efforts were hindered by conflicting national economic agendas and disputes between developed and developing nations over the cost and consequences of reducing emissions of greenhouse gases.

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Talking about Climate Change and Global Warming

Maurice lineman.

College of Natural Sciences, Department of Biological Sciences, Pusan National University, Busan, South Korea

Ji Yoon Kim

Gea-jae joo.

Conceived and designed the experiments: YD GJJ. Performed the experiments: ML YD. Analyzed the data: ML YD. Contributed reagents/materials/analysis tools: JK YD. Wrote the paper: ML YD GJJ.

Associated Data

All relevant data are within the paper.

The increasing prevalence of social networks provides researchers greater opportunities to evaluate and assess changes in public opinion and public sentiment towards issues of social consequence. Using trend and sentiment analysis is one method whereby researchers can identify changes in public perception that can be used to enhance the development of a social consciousness towards a specific public interest. The following study assessed Relative search volume (RSV) patterns for global warming (GW) and Climate change (CC) to determine public knowledge and awareness of these terms. In conjunction with this, the researchers looked at the sentiment connected to these terms in social media networks. It was found that there was a relationship between the awareness of the information and the amount of publicity generated around the terminology. Furthermore, the primary driver for the increase in awareness was an increase in publicity in either a positive or a negative light. Sentiment analysis further confirmed that the primary emotive connections to the words were derived from the original context in which the word was framed. Thus having awareness or knowledge of a topic is strongly related to its public exposure in the media, and the emotional context of this relationship is dependent on the context in which the relationship was originally established. This has value in fields like conservation, law enforcement, or other fields where the practice can and often does have two very strong emotive responses based on the context of the problems being examined.

Introduction

Identifying trends in the population, used to be a long and drawn out process utilizing surveys and polls and then collating the data to determine what is currently most popular with the population [ 1 , 2 ]. This is true for everything that was of merit to the political organizations present, regarding any issue of political or public interest.

Recently, the use of the two terms ‘Climate Change’ and ‘Global Warming’ have become very visible to the public and their understanding of what is happening with respect to the climate [ 3 ]. The public response to all of the news and publicity about climate has been a search for understanding and comprehension, leading to support or disbelief. The two terms while having similarity in meaning are used in slightly different semantic contexts. The press in order to expand their news readership/viewer lists has chosen to use this ambiguity to their favor in providing news to the public [ 4 ]. Within the news releases, the expression ‘due to climate change’ has been used to explain phenomological causality.

These two terms “global warming–(GW)” and “climate change–(CC)” both play a role in how the public at large views the natural world and the changes occurring in it. They are used interactively by the news agencies, without a thought towards their actual meaning [ 3 , 4 ]. Therefore, the public in trying to identify changes in the news and their understanding of those changes looks for the meaning of those terms online. The extent of their knowledge can be examined by assessing the use of the terms in online search queries. Information searches using the internet are increasing, and therefore can indicate public or individual interest.

Internet search queries can be tracked using a variety of analytic engines that are independent of, or embedded into, the respective search engines (google trend, naver analytics) and are used to determine the popularity of a topic in terms of internet searches [ 5 ]. The trend engines will look for selected keywords from searches, keywords chosen for their relevance to the field or the query being performed.

The process of using social media to obtain information on public opinion is a practice that has been utilized with increasing frequency in modern research for subjects ranging from politics [ 6 , 7 ] to linguistics [ 8 – 10 ] complex systems [ 11 , 12 ] to environment [ 13 ]. This variety of research belies the flexibility of the approach, the large availability of data availability for mining in order to formulate a response to public opinion regarding the subject being assessed. In modern society understanding how the public responds regarding complex issues of societal importance [ 12 ].

While the two causally connected terms GW and CC are used interchangeably, they describe entirely different physical phenomena [ 14 ]. These two terms therefore can be used to determine how people understand the parallel concepts, especially if they are used as internet search query terms in trend analysis. However, searching the internet falls into two patterns, searches for work or for personal interest, neither of which can be determined from the trend engines. The By following the searches, it is possible to determine the range of public interest in the two terms, based on the respective volumes of the search queries. Previously in order to mine public opinion on a subject, government agencies had to revert to polling and surveys, which while being effective did not cover a very large component of the population [ 15 – 17 ].

Google trend data is one method of measuring popularity of a subject within the population. Individuals searching for a topic use search keywords to obtain the desired information [ 5 , 18 ]. These keywords are topic sensitive, and therefore indicate the level of knowledge regarding the searched topic. The two primary word phrases here “climate change” and “global warming” are unilateral terms that indicate a level of awareness about the issue which is indicative of the individuals interest in that subject [ 5 , 19 , 20 ]. Google trend data relates how often a term is searched, that is the frequency of a search term can be identified from the results of the Google® trend analysis. While frequency is not a direct measure of popularity, it does indicate if a search term is common or uncommon and the value of that term to the public at large. The relationship between frequency and popularity lies in the volume of searches by a large number of individuals over specific time duration. Therefore, by identifying the number of searches during a specific period, it is possible to come to a proximate understanding of how popular or common a term is for the general population [ 21 ]. However, the use of trend data is more appropriately used to identify awareness of an issue rather than its popularity.

This brings us to sentiment analysis. Part of the connection between the search and the populations’ awareness of an issue can be measured using how they refer to the subject in question. This sentiment, is found in different forms of social media, or social networking sites sites i.e. twitter®, Facebook®, linked in® and personal blogs [ 7 , 22 – 24 ]. Thus, the original information, which was found on the internet, becomes influenced by personal attitudes and opinions [ 25 ]and then redistributed throughout the internet, accessible to anyone who has an internet connection and the desire to search. This behavior affects the information that now provides the opportunity to assess public sentiment regarding the prevailing attitudes regarding environmental issues [ 26 , 27 ]. To assess this we used Google® and Twitter® data to understand public concerns related to climate change and global warming. Google trend was used to trace changes in interest between the two phenomena. Tweets (comments made on Twitter®) were analyzed to identify negative or positive emotional responses.

Comparatively, twitter data is more indicative of how people refer to topics of interest [ 28 – 31 ], in a manner that is very linguistically restricted. As well, twitter is used as a platform for verbal expression of emotional responses. Due to the restrictions on tweet size (each tweet can only be 140 characters in length), it is necessary to be more direct in dealing with topics of interest to the tweeter. Therefore, the tweets are linguistically more emotionally charged and can be used to define a level of emotional response by the tweeter.

The choice of target words for the tweets and for the Google trend searches were the specific topic phrases [ 32 , 33 ]. These were chosen because of the descriptive nature of the phrases. Scientific literature is very specific in its use and therefore has very definitive meanings. The appropriation of these words by the population as a method for describing their response to the variation in the environment provides the basis for the choice as target words for the study. The classification of the words as being positive versus negative lies in the direction provided by Frank Lutz. This politicization of a scientific word as a means of directing public awareness, means the prescription of one phrase (climate change) as being more positive than the other (global warming).

Global warming is defined as the long-term trend of increasing average global temperatures; alternatively, climate change is defined as a change in global or regional climate patterns, in particular a change apparent from the mid to late 20 th century onwards and attributed to the increased levels of atmospheric carbon dioxide arising from the use of fossil fuels. Therefore, the search keywords were chosen based on their scientific value and their public visibility. What is important about the choice of these search terms is that due to their scientific use, they describe a distinctly identifiable state. The more specific these words are, the less risk of the algorithm misinterpreting the keyword and thus having the results misinterpreted [ 34 – 36 ].

The purpose of the following study was to identify trends within search parameters for two specific sets of trend queries. The second purpose of the study was to identify how the public responds emotionally to those same queries. Finally, the purpose of the study was to determine if the two had any connections.

Data Collection

Public awareness of the terms climate change and global warming was identified using Google Trends (google.com/trends) and public databases of Google queries [ 37 ]. To specify the exact searches we used the two terms ‘climate change’ and ‘global warming’ as query phrases. Queries were normalized using relative search volume (RSV) to the period with the highest proportion of searches going to the focal terms (i.e. RSV = 100 is the period with the highest proportion for queries within a category and RSV = 50 when 50% of that is the highest search proportion). Two assumptions were necessary for this study. The first is, of the two terms, climate change and global warming, that which draws more search results is considered more interesting to the general population. The second assumption is that changes in keyword search patterns are indicators of the use of different forms of terminology used by the public. To analyze sentiments related to climate change and global warming, tweets containing acronyms for climate change and global warming were collected from Twitter API for the period from October 12 to December 12, 2013. A total of 21,182 and 26,462 tweets referencing the terms climate change and global warming were collected respectively. When duplicated tweets were identified, they were removed from the analysis. The remaining tweets totaled 8,465 (climate change) and 8,263 (global warming) were compiled for the sentiment analysis.

Data Analysis

In Twitter® comments are emotionally loaded, due to their textually shortened nature. Sentiment analysis, which is in effect opinion mining, is how opinions in texts are assessed, along with how they are expressed in terms of positive, neutral or negative content [ 36 ]. Nasukawa and Yi [ 10 ]state that sentiment analysis identifies statements of sentiment and classifies those statements based on their polarity and strength along with their relationship to the topic.

Sentiment analysis was conducted using Semantria® software ( www.semantria.com ), which is available as an MS Excel spreadsheet application plugin. The plugin is broken into parts of speech (POS), the algorithm within the plugin then identifies sentiment-laden phrases and then scores them from -10 to 10 on a logarithmic scale, and finally the scores for each POS are tabulated to identify the final score for each phrase. The tweets are then via statistical inferences tagged with a numerical value from -2 to 2 and given a polarity, which is classified as positive, neutral or negative [ 36 ]. Semantria®, the program utilized for this study, has been used since 2011 to perform sentiment analyses [ 7 , 22 ].

For the analysis, an identity column was added to the dataset to enable analysis of individual tweets with respect to sentiment. A basic sentiment analysis was conducted on the dataset using the Semantria® plugin. The plugin uses a cloud based corpus of words tagged with sentimental connotations to analyze the dataset. Through statistical inference, each tweet is tagged with a sentiment value from -2 to +2 and a polarity of (i) negative, (ii) neutral, or (iii) positive. Positive nature increases with increasing positive sentiment. The nature of the language POS assignation is dependent upon the algorithmic classification parameters defined by the Semantria® program. Determining polarity for each POS is achieved using the relationship between the words as well as the words themselves. By assigning negative values to specific negative phrases, it limits the use of non-specific negation processes in language; however, the program has been trained to assess non-specific linguistic negations in context.

A tweet term frequency dictionary was computed using the N-gram method from the corpus of climate change and global warming [ 38 ]. We used a combination of unigrams and bigrams, which has been reported to be effective [ 39 ]. Before using the N-gram method, typological symbols were removed using the open source code editor (i.e. Notepad) or Microsoft Words’ “Replace” function.

Differences in RSV’s for the terms global warming and climate change for the investigation period were identified using a paired t-test. Pettitt and Mann-Kendall tests were used to identify changes in distribution, averages and the presence of trends within the weekly RSV’s. The Pettitt and MK tests, which assume a stepwise shift in the mean (a break point) and are sensitive to breaks in the middle of a time series, were applied to test for homogeneity in the data [ 40 ]. Temporal trends within the time series were analyzed with Spearman’s non-parametric correlation analysis. A paired t-test and Spearman’s non-parametric correlation analysis were conducted using SPSS software (version 17.0 SPSS In corp. Chicago IL) and Pettitt and MK tests were conducted using XLSTAT (version 7.0).

To determine the accuracy and reliability of the Sentiment analysis, a Pearson’s chi-square analysis was performed. This test identifies the difference ratio for each emotional response group, and then compares them to determine reliance and probability of interactions between the variables, in this case the terms global warming and climate change.

According to Google trend ( Fig 1 ) from 2004–2014, people searched for the term global warming (n = 8,464; mean ± S.D = 25.33 ± 2.05) more frequently than climate change (n = 8,283; mean ± S.D. = 7.97±0.74). Although the Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment Report in 2007 and was awarded the Nobel Prize, interest in the term global warming as used in internet searches has decreased significantly since 2010 (K = 51493, t = 2010-May-23, P<0.001). Further the change in RSV also been indicative of the decreased pattern (Kendall’s tau = -0.336, S = -44563, P<0.001). The use of the term “climate change” has risen marginally since 2006 (K = 38681, t = 2006-Oct-08, P<0.001), as indicated by a slight increase (Kendall’s tau = -0.07, S = 9068, P<0.001). These findings show that the difference in usage of the two terms climate change and global warming has recently been reduced.

The sentiment analysis of tweets ( Fig 2 ) shows that people felt more negative about the term global warming (sentiment index = -0.21±0.34) than climate change (-0.068±0.36). Global warming tweets reflecting negative sentiments via descriptions such as, “bad, fail, crazy, afraid and catastrophe,” represented 52.1% of the total number of tweets. As an example, the tweet, “Supposed to snow here in the a.m.! OMG. So sick of already, but Saturday says 57 WTF!” had the lowest score at -1.8. Another observation was that 40.7% of tweets, including “agree, recommend, rescue, hope, and contribute,” were regarded as neutral. While 7.2% of tweets conveyed positive messages such as, “good, accept, interesting, and truth.” One positive global warming tweet, read, “So if we didn’t have global warming, would all this rain be snow!”. The results from the Pearson’s chi-square analysis showed that the relationship between the variables was significant (Pearson’s chi-square –763.98, d.f. = 2, P<0.001). Negative climate change tweets represented 33.1% of the total while neutral tweets totaled 49.8%, while positive climate change tweets totaled 17.1%.

Understandably, global warming and climate change are the terms used most frequently to describe each phenomenon, respectively, as revealed by the N-gram analysis ( Table 1 ). When people tweeted about global warming, they repeatedly used associated such as, “ice, snow, Arctic, and sea.” In contrast, tweets referring to climate change commonly used, “report, IPCC, world, science, environment, and scientist.” People seem to think that climate change as a phenomenon is revealed by scientific investigation.

Rank	Global warming		Climate change
	Words	Frequency	Words	Frequency
1	Global warming	821	Climate change	802
2	Climate change	507	Global warming	267
3	Ice	177	Ow	177
4	Years	158	Report	167
5	Snow	143	IPCC	143
6	Arctic	136	World	136
7	Scientist	124	Science	119
8	Sea	119	Environment	105
9	Cause	114	Scientist	101
10	Ow	109	Help	100
11	Time	101	Action	97
12	Show	97	Impacts	85
13	Report	94	Arctic	82
14	Science	91	Time	79
15	Data	88	Australia	77
16	World	85	Study	75
17	Earth	82	Caused	72
18	Environment	75	Talk	70
19	Coverage	70	Human	68
20	Percent	68	Need	65
21	Human	67	People	63
22	Study	65	Deniers	60
23	Satellite	63	Huff	58
24	IPCC	60	Risk	57
25	EPA	56	Fight	56
26	Expert	54	Years	54
27	Stop	53	Make	53
28	Fight	52	Politics	52
29	Million	51	Nations	51
30	People	50	Carbon	49

Internet searches are one way of understanding the popularity of an idea or meme within the public at large. Within that frame of reference, the public looks at these two terms global warming and climate change and their awareness of the roles of the two phenomena [ 41 ]. From 2004 to 2008, the search volumes for the term global warming far exceeded the term climate change. The range for the term global warming in Relative search volumes (RSV) was more than double that of climate change in this period ( Fig 1 ). From 2008 on the RSV’s began to steadily decrease until in 2014 when the RSV’s for the term global warming were nearly identical to those for the term climate change. From 2008 there was an increase in the RSVs for CC until 2010 at which point the RSVs also began to decline for the term climate change. The decline in the term climate change for the most part paralleled that of the term global warming from 2010 on to the present.

While we are seeing the increases and decreases in RSVs for both the terms global warming and climate change, the most notable changes occur when the gap between the terms was the greatest, from 2008 through to 2010. During this period, there was a very large gap found between the RSVs for the terms global warming and climate change; however, searches for the term climate change was increasing while searches for the tem global warming were decreasing. The counter movement of the RSV’s for the two terms shows that there is a trend happening with respect to term recognition. At this point, there was an increase in the use of the CC term while there was a corresponding decrease in the use of the GW term. The change in the use of the term could have been due to changes in the publicity of the respective terms, since at this point, the CC term was being used more visibly in the media, and therefore the CC term was showing up in headlines and the press, resulting in a larger number of searches for the CC term. Correspondingly, the decrease in the use of the GW term is likely due to the changes in how the term was perceived by the public. The public press determines how a term is used, since they are the body that consistently utilizes a term throughout its visible life. The two terms, regardless of how they differ in meaning, are used with purpose in a scientific context, yet the public at large lacks this definition and therefore has no knowledge of the variations in the terms themselves [ 42 ]. Therefore, when searching for a term, the public may very well, choose the search term that they are more comfortable with, resulting in a search bias, since they do not know the scientific use of the term.

The increase in the use of the CC term, could be a direct result of the release of the fourth assessment report for the IPCC in 2007 [ 43 ]. The publicity related to the release of this document, which was preceded by the release of the Al Gore produced documentary “An Inconvenient Truth”, both of which were followed by the selection by the Nobel committee of Al Gore and the IPCC scientists for the Nobel Prize in 2007 [ 43 ]. These three acts individually may not have created the increased media presence of the CC term; however, at the time the three events pushed the CC term and increased its exposure to the public which further drove the public to push for positive environmental change at the political level [ 44 , 45 ]. This could very well have resulted in the increases in RSV’s for the CC term. This point is more likely to depict accurately the situation, since in 2010 the use of the two terms decline at almost the same rate, with nearly the same patterns.

Thus with respect to trend analysis, what is interesting is that RSVs are paralleling the press for specific environmental events that have predetermined value according to the press. The press in increasing the visibility of the term may drive the increases in the RSV’s for that term. Prior to 2007, the press was using the GW term indiscriminately whenever issues affecting the global climate arose; however, after the movie, the report and then the Nobel prize the terminology used by the press switched and the CC term became the word du jour. This increased the visibility of the word to the public, thereby it may be that increasing public awareness of the word, but not necessarily its import, is the source for the increases in RSV’s between 2008 and 2010.

The decline in the RSV’s then is a product of the lack of publicity about the issue. As the terms become more familiar, there would be less necessity to drive the term publicly into the spotlight; however, occasionally events/situations arise that refocus the issue creating a resurgence in the terms even though they have reached their peak visibility between 2008 and 2010.

Since these terms have such an impact on the daily lives of the public via local regional national and global weather it is understandable that they have an emotional component to them [ 46 ]. Every country has its jokes about the weather, where they come up with cliché’s about the weather (i.e. if you don’t like the weather wait 10minutes) that often show their discord and disjunction with natural climatological patterns [ 47 ]. Furthermore, some sectors of society (farmers) have a direct relationship with the climate and their means of living; bad weather is equal to bad harvests, which means less money. To understand how society represents this love hate relationship with the weather, the twitter analysis was performed. Twitter, a data restricted social network system, has a limited character count to relay information about any topic the sender chooses to relate. These tweets can be used to assess the sentiment of the sender towards a certain topic. As stated previously, the sentiment is defined by the language of the tweet within the twitter system. Sentiment analysis showed that the two terms differed greatly. Based on the predefined algorithm for the sentiment analysis, certain language components carried a positive sentiment, while others carried a negative sentiment. Tweets about GW and CC were subdivided based on their positive, neutral and negative connotations within the tweet network. These emotions regardless of their character still play a role in how humans interacts with surroundings including other humans [ 48 , 49 ] As seen in Fig 2 the different terms had similar distributions, although with different ranges in the values. Global warming showed a much smaller positive tweet value than did climate change. Correspondent to this the respective percentage of positive sentiments for CC was more than double that of GW. Comparatively, the neutral percentiles were more similar for each term with a small difference. However, the negative sentiments for the two terms again showed a greater disparity, with negative statements about GW nearly double those of climate change.

These differences show that there is a perceptive difference in how the public relates to the two terms Global Warming and Climate Change [ 50 , 51 ]. Climate change is shown in a more positive light than global warming simply based on the tweets produced by the public. The difference in how people perceive climate change and global warming is possibly due to the press, personal understanding of the terms, or level of education. While this in itself is indefinable, since by nature tweets are linguistically restrictive, the thing to take from it is that there is a measurable difference in how individuals respond to climatological changes that they are experiencing daily. These changes have a describable effect on how the population is responding to the publicity surrounding the two terms to the point where it can be used to manipulate governmental policy [ 52 ].

Sentiment analysis is a tool that can be used to determine how the population feels about a topic; however, the nature of the algorithm makes it hard to effectively determine how this is being assessed. For the current study, the sentiment analysis showed that there was a greater negative association with the term global warming than with the term climate change. This difference, which while being an expression of individual like or dislike at the time the tweet was created, denotes that the two terms were either not understood in their true form, or that individuals may have a greater familiarity with one term over the other, which may be due to a longer exposure to the term (GW) or the negative press associated with the term (GW).

Conclusions

Trend analysis identified that the public is aware of the terminology used to describe climatological variation. The terminology showed changes in use over time with global warming starting as the more well-known term, and then its use decreased over time. At the same time, the more definitive term climate change had less exposure early on; however, with the increase of press exposure, the public became increasingly aware of the term and its more accurate definition. This increase appeared to be correspondent with the increasing publicity around three very powerful press exposure events (a documentary, a scientific report release and a Nobel Prize). The more the term was used the more people came to use it, this included searches on the internet.

Comparatively sentiment analysis showed that the two terms had differential expressions in the population. With climate change being seen in a more positive frame than global warming. The use of sentiment analysis as a tool to evaluate how the population is responding to a feature is an important tool. However, it is a tool that measures, it does not define.

Social network systems and internet searches are effective tools in identifying changes in both public awareness and public perception of an issue. However, in and of itself, these are bell ringers they can be used to determine the importance of an issue, but not the rationale behind the why it is important. This is an important fact to remember when using analytical tools that evaluate social network systems and their use by the public.

Acknowledgments

This study was financially supported by the 2015 Post-Doc. Development Program of Pusan National University

Funding Statement

This study was financially supported by the 2015 Post-Doc Development Program of Pusan National University.

Data Availability

Global warming frequently asked questions

] Earth’s average surface temperature has risen by 1.8°F (1.0°C) since the late 1800s, an average rate of 0.13° F (0.07° C) per decade. Since 1981, the rate of warming has more than doubled to 0.32°F (0.18°C) per decade. The six warmest years in the 1880–2020 record have all occurred since 2014, while 19 of the 20 warmest years have occurred since 2001.  ] With significant reductions in the emissions of greenhouse gases, the annual global surface temperature rise this century could be limited to 3.6°F (2°C) or less. Without major reductions in these emissions, the increase in annual average global temperatures relative to preindustrial times could reach 9°F (5°C) or more by the end of this century. ] Learn more and .

] Thanks to natural climate variability, volcanic eruptions, and to a smaller extent, low solar activity, the rate of average global warming from 1998–2013 was slower than it had been over the two preceding decades. Such varations in the rate of warming from decade to decade are common. ] Meanwhile, excess heat continued to accumulate in the deeper layers of the ocean, contributing to marine heat waves and sea level rise. ] The slowdown in surface warming was only temporary, however, as the six warmest years in recorded history have all occurred after 2013. ] Learn more and

. and and . . ] Carbon dioxide, methane, nitrous oxide, ozone, and various chlorofluorocarbons are all human-emitted . Among these, carbon dioxide is of greatest concern to scientists because it exerts a larger overall warming influence than the .

At present, humans are putting an estimated 9.5 billion metric tons of carbon into the atmosphere each year by burning fossil fuels, and another 1.5 billion through deforestation and other land cover changes. Of this human-produced carbon, forests and other vegetation absorb around 3.2 billion metric tons per year, while the ocean absorbs about 2.5 billion metric tons per year. A net 5 billion metric tons of human-produced carbon remain in the atmosphere each year, raising the global average carbon dioxide concentrations by about 2.3 parts per million per year. Since 1750, humans have increased the abundance of carbon dioxide in the atmosphere by nearly 50 percent. ]  .

and ?

generally refers to the long-term increase in global average temperature as a result of human activity. Climate change is a much broader term that covers changes in multiple parts of the climate system, from temperature to precipitation to wind patterns. Climate change can be local, regional, or global, and it can have natural or human causes. Global warming is a type of climate change; however, not all climate change is global warming. .

] When different teams of climate scientists in different agencies (e.g., NOAA and NASA) and in other countries (e.g., the U.K.’s Hadley Centre) average these data together, they all find essentially the same result: Earth’s average surface temperature has risen by about 1.8°F (1.0°C) since 1880. ]

In addition to our surface station data, we have many different lines of evidence that Earth is warming ( ). Birds are migrating earlier, and their migration patterns are changing. and are moving north. Plants are blooming earlier in the spring. Mountain glaciers are melting and snow cover is declining in the Northern Hemisphere (Learn more and ). Greenland’s ice sheet—which holds about 8 percent of Earth’s fresh water—is melting at an accelerating rate ( ). Mean global sea level is rising ( ). Arctic sea ice is declining rapidly in both thickness and extent ( ).

We know this warming is largely caused by human activities because the key role that carbon dioxide plays in maintaining Earth’s natural greenhouse effect has been understood since the mid-1800s. Unless it is offset by some equally large cooling influence, more atmospheric carbon dioxide will lead to warmer surface temperatures. Since 1800, the amount of carbon dioxide in the atmosphere from about 280 parts per million to 410 ppm in 2019. We know from both its rapid increase and its isotopic “fingerprint” that the source of this new carbon dioxide is fossil fuels, and not natural sources like forest fires, volcanoes, or outgassing from the ocean.

Finally, no other known climate influences have changed enough to account for the observed warming trend. Taken together, these and other lines of evidence point squarely to human activities as the cause of recent global warming.

] In addition, fossil fuels are the only source of carbon consistent with the of the carbon present in today’s atmosphere. That analysis indicates it must be coming from terrestrial plant matter, and it must be very, very old. These and other lines of evidence leave no doubt that fossil fuels are the primary source of the carbon dioxide building up in Earth’s atmosphere.

] [ ] [ ] [ ]

This scientific consensus is clearly summarized in the climate assessment reports of the U.S. Global Change Research Program and the Intergovernmental Panel on Climate Change. ] [ ] [ ] NOAA scientists played lead roles in authoring and editing both sets of reports.

Additionally, the United States’ foremost science agencies and organizations have all recognized global warming as a human-caused problem that threatens human and natural systems and, therefore, should be addressed. These agencies and organizations include (but are not limited to) ; the ; the ; the ; the ; the ; the ; the ; the ; and the .

is the short-term atmospheric conditions at a given location on a specific day and time. is usually described as the long-term average weather at a given place, but it the range of weather conditions that are possible at a given place, including the types and historical frequency of extreme events that occur there. By analogy, if the outcome of any given at-bat is like the weather, then a baseball player’s career batting average is like the climate. There’s an old saying: “Climate is what you expect; weather is what you get.”

Another way to think about the difference between weather and climate is to say that a region’s climate is the background conditions that give rise to a location’s weather events. Because all weather occurs within Earth’s climate system, changes in the background state of the climate system can make different weather outcomes more or less likely to happen. For example, during the period from 1997-2018, the percentage area of the globe that experienced record-setting warm temperatures dwarfed the percentage area of the globe that experienced record-setting cold temperatures. ] This was a predictable set of weather outcomes due to global warming. .

conditions and climate is about conditions. Climate models are not trying, for example, to forecast the daytime high temperature in Chicago, IL, on August 15, 2035. They are trying to forecast the daytime high temperature for the of August over the entire of the 2030s. And while the exact weather conditions at a given location can change dramatically from hour to hour, the average changes much less from year to year or even decade to decade. The difference in time scale means that our ability to predict future climate doesn’t depend on our ability to predict next week’s weather.

Not only are weather models predicting different things than climate models, they require different kinds of starting information. Modelers call weather forecasting an problem because, at short time scales, the future atmospheric conditions depend mostly on the initial atmospheric conditions. The accuracy of your forecast for a given location depends heavily on how well you can describe these initial conditions, especially in the surrounding area.

In contrast, most modelers describe a climate projection as a problem because at long time scales (years to decades), future climate depends mostly on big-picture characteristics of the Earth system that don’t vary from day to day: the amount of land and ocean surface, the height and location of mountain ranges, the geometry of Earth’s orbit, and—crucially—the composition of the global atmosphere. These things define the boundaries of the climate system, the relatively narrow range of outcomes that are possible over long time frames.

These fundamental differences between weather models and climate models, in both what they are trying to predict and what those predictions depend on, mean that the quality of a weather forecast two weeks out isn’t a good test of how well we can predict the climate two decades out.

since the mid-1800s. The more greenhouse gases in the atmosphere, the more heat energy the atmosphere traps near the surface ( ), causing Earth’s surface temperature to rise.

The initial warming due to increasing carbon dioxide kicks off several feedback loops: more water vapor, which is a powerful greenhouse gas; permafrost thaw and decomposition, which releases more methane and carbon dioxide; loss of sea ice and snow, which reduces the amount of sunlight the Earth reflects; and outgassing of additional carbon dioxide from the ocean. Together, these feedback loops make the actual warming two or more times larger than it would be due to carbon dioxide increases alone. ]

] So in terms of total warming, water vapor is the most important greenhouse gas. But without the background warmth provided by carbon dioxide—which doesn’t condense and rain out of the atmosphere as water vapor does—the atmosphere would be too cold to support much water vapor, and the entire greenhouse effect would collapse. Models indicate Earth would likely freeze over everywhere but the equator. ] So in terms of making the greenhouse effect , carbon dioxide is the most important greenhouse gas.

As the most abundant of the non-condensing , carbon dioxide is the main control knob—the thermostat—of Earth’s greenhouse effect. ] Increases in atmospheric carbon dioxide from human activities are turning the thermostat up. As surface temperatures rise, more water evaporates, enhancing the initial warming. This water vapor feedback loop is powerful, at least doubling the warming provided by carbon dioxide alone. ] [ ] [ ] But water vapor can’t act on its own to cause climate change; it can only amplify a change caused by the non-condensing greenhouse gases or other climate influences, such as variations in incoming sunlight. That means that when it comes to causing global warming, carbon dioxide is without question the most important greenhouse gas.

]  ]  ]  ] It was partly through their attempts to understand previous ice ages that climate scientists came to understand the dominant role that carbon dioxide plays in Earth’s climate system, and the role it is playing in current global warming. Learn more and .

Over at least the past million years, have been triggered by in how much sunlight reaches the Northern Hemisphere in the summer, which are driven by small variations in the geometry of Earth’s orbit around the Sun. But these fluctuations in sunlight aren’t enough on their own to bring about full-blown ice ages and interglacials. They trigger several that amplify the original warming or cooling. During an interglacial,

These feedbacks until the Earth’s orbit goes through a phase during which the amount of Northern Hemisphere summer sunlight is minimized. Then these feedbacks operate in reverse, reinforcing the cooling trend.

During all the ice ages that have occurred over at least the past million years, these opposing branches of the carbon cycle have kept the atmospheric carbon dioxide level at or below 300 parts per million (ppm). ] , that level is close to 410 ppm. Not only is this the highest carbon dioxide has been during all of human civilization, it has reached these levels virtually instantaneously in geologic time frames. During ice age cycles of the past, a change this large would likely have taken thousands of years to occur.

This extremely rapid build-up of carbon dioxide is happening because humans are putting carbon dioxide into the atmosphere faster than natural sinks can remove it. By burning fossil fuels, we have essentially taken millions of years of carbon uptake by plants and returned it to the atmosphere in . ]

] to perhaps as much as 0.6 billion metric tons ], whereas human activities have been releasing more than 30 billion metric tons of carbon dioxide per year ] 

up to 0.1°C of the 1.0°C (1.8°F) of warming observed since the pre-industrial era. ] However, there has been no significant net change in the Sun’s energy output from the late 1970s to the present, which is when we have observed the most rapid global warming. .

A second reason that scientists have ruled out a significant role for the Sun in global warming is that if the Sun’s energy output had intensified, we would expect all layers of Earth’s atmosphere to have warmed. But we don’t see that. Rather, satellites and observations from weather balloons show warming in the lower atmosphere (troposphere) and cooling in the upper stratosphere (stratosphere)—which is exactly what we would expect to see as a result of increasing greenhouse gases trapping heat in the lower atmosphere. ] Scientists regard this piece of evidence as one of several “smoking guns” linking today’s global warming to human-emitted, heat-trapping gases.

are smaller than the warming influence of the heat-trapping gases humans put into the air. ]

Our greatest cooling influence comes from particulate pollution (aerosols) we produce. We put plumes of aerosols into the air from power plants and industrial smokestacks; smoke and gases from biomass burning; windblown dust from deforested areas, dried wetlands, and crop fields; exhaust from ships’ smokestacks; tailpipe emissions from cars, trucks, buses, and trains; etc. Aerosol particles absorb and reflect the sun’s rays, thereby reducing the amount of sunlight reaching Earth’s surface. They also interact with clouds, in many cases making them brighter and longer-lived, also reducing the amount of sunlight reaching the surface. .

Whereas aerosols linger in the atmosphere from days to a few weeks, heat-trapping gases that we add to the atmosphere linger from decades to centuries. Plus, when scientists discovered that our aerosol emissions were causing other undesired harmful side effects—such as acid rain and human respiratory diseases and deaths—we began to regulate and reduce their emission. Thus, the warming effect of our heat-trapping gases is ultimately winning out over the cooling influence of our particle pollution. .

makes it harder for shell-building marine life—including commercially and culturally valuable species such as coral, crabs, and oysters—to build and maintain their shells. ]

Because of its tremendous volume and high heat capacity, the ocean has absorbed more than 90 percent of all excess heat trapped in Earth's climate system by greenhouse gases. Currents mix much of that heat into deeper layers of the ocean, delaying the full impact of surface warming we would otherwise expect. However, the heating of deeper layers of the ocean still contributes to sea level rise, sea ice retreat, marine heatwaves, oxygen depletion and expanding dead zones, shifts in the ranges of several marine species, and accelerating loss of polar ice shelves. ]

and not necessarily in all seasons. It’s like your grades—if you get Bs and Cs in your first semester and in the next semester you get all As and Cs, your overall grade point average rises even though you didn’t improve in every class. Differences in exposure to sunlight, cloud cover, atmospheric circulation patterns, aerosol concentrations, atmospheric humidity, land surface cover, etc., all vary from place to place which, in turn, influence whether and how much a location is warming or cooling. Learn more , , , and .

Generally speaking, an extreme event is any event that ranks in the highest or lowest 5 percent or 10 percent of all historical observations of that type of event. The percentage threshold is arbitrary and is designated by a researcher to provide context on a given event or set of events.

Scientists sometimes describe extreme events in terms of their “sigmas” (or their “standard deviation”), which is a measure of how far removed an individual value is from the average of all observations in a data set. So, if a climate expert describes a heavy rain event as a “5-sigma event,” s/he is talking about rainfall so extreme that it was 5 standard deviations away from the average rainfall for that location—way out at the tail end of the range of all values that have ever been observed. .

Another way of characterizing an extreme event is by describing the probability of occurrence in a given span of time. Based on historical observations, experts to estimate the range of all possible events that we would eventually expect to observe if our data record was long enough. From this range of all possible values, they can pinpoint how frequently a particular value would be expected to recur within a given amount of time. For example, 100-year event means an event is so extreme that it has only a 1 percent chance (1 divided by 100) of happening in any given year. A thousand-year event has a 0.1 percent chance of happening in any single year (1 divided by 1,000). .

 by global warming. However, over the past decade, that climate change due to global warming has made many extreme events more likely, more intense, longer-lasting, or larger in scale than they would have been without it. For many of the events that have been studied, global warming has been identified as the primary driver of the event, not just a supporting player. And a number of recent studies have concluded that certain heat-related extreme events would not have been possible without human-caused global warming. Learn more   and  .

is the science of figuring out what caused a given extreme weather or climate event, and weighting the relative influence of global warming versus natural variability. The biggest collection of research dedicated to understanding the causes of extreme events is published annually in a special issue of the Bulletin of the American Meteorological Society. The most recent edition of the report, , was the eighth in the series. (The report covering a selection of events from 2019 is soon to be released). Together, these eight reports have documented 168 attribution studies, 73 percent of which identified a substantial link between an extreme event and human-caused climate change, whereas 27 percent did not. To learn more, go   and 

]

Today’s warming is occurring much more quickly than previous interglacial episodes. In transitions from an ice age to an interglacial, it took 5,000–10,000 years for the temperature to rise between 5 and 9° Fahrenheit (3–5° Celsius). Humans could witness the same amount of global warming within the next 80 years if we continue emitting heat-trapping gases at today’s rate. ]

Finally, if we cause our world to warm by 2.7°F (1.5°C) or more compared to the temperatures before the start of the Industrial Revolution, scientists warn that there will be harmful repercussions for human health, the economy, infrastructure, and agriculture and natural resources. ] The greater the warming above that threshold, the more widespread and severe the impacts are likely to be. Human and natural systems that cannot adapt quickly enough may be overwhelmed.

from year to year. In a geological context, a global-scale warming of 1.8°F (1°C) in less than 150 years is an unusually large temperature change in a relatively short span of time.

It's also important to recognize that Earth is not warming uniformly, nor is it expected to. Middle and high latitudes in general will warm more than the tropics, and land surface temperatures will rise more than ocean temperatures. Over the long term, land masses at the latitude of the United States are expected to warm much more than the global average.  ] If global warming continues at an increasing rate, in several decades the world is likely to be warmer than it's been for over a million years, with unpredictable consequences for humans and the natural resources we depend on.

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In terms of biodiversity, adaptable species with wide geographic ranges—such as white-tailed deer and feral hogs—are likely to continue to thrive. But those species that depend on particular habitats—polar and alpine species, coral reefs, coldwater fishes—are vulnerable, as are the communities that depend on them culturally and economically. ] According to the Fourth National Climate Assessment, “[S]pecies, including many iconic species, may disappear from regions where they have been prevalent or become extinct, altering some regions so much that their mix of plant and animal life will become almost unrecognizable.” ]

Food and forage production will decline in agricultural regions experiencing increased frequency and duration of drought. Even without drought, higher temperatures will increase evaporation of soil moisture, increasing crop stress and water demand—further stressing U.S. surface and groundwater supplies used for irrigation. And even with irrigation, many commodity crops are likely to experience declines in average yield as temperatures rise beyond their preferred heat tolerance range. Milder winters and shifts in precipitation are likely to increase the incidence of pests and diseases for crops and livestock, while extreme heat—especially nighttime heat—will reduce livestock productivity. Impacts will vary from region to region, depending on the extent of warming and the level of adaptation. ]

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] and the trend is likely to continue as many extreme events become more frequent and severe. The economic impacts of extreme events include not just the direct damages, but also the loss of productivity and interruption of essential services and supply chains that can reach deep into the national economy. ]

In many parts of the country, existing infrastructure—septic and stormwater systems, roads, bridges, the energy grid—was not designed to cope with current and future sea level and climate extremes, and current levels of investment aren’t enough to cover necessary repairs and upgrades. ]  ]

Beyond extreme events, human-caused climate change is likely to disrupt many sectors of the U.S. economy and the communities that depend on them, including commercial and recreational fisheries, tourism and recreation, and agriculture. ]  ]  ]

In the short term, farmers in some regions may benefit from the earlier onset of spring and from a longer warm season that is suitable for growing crops. Also, studies show that, up to a certain point, crops and other plants grow better in the presence of higher carbon dioxide levels and seem to be more drought-tolerant. ] But this benefit is a two-edged sword: weeds, many invasive plant species, and insect pests will also thrive in a warmer world. Water availability will be impacted in drier agricultural areas that need irrigation. At some point, the benefits to crops of increased carbon dioxide will likely be overwhelmed by the negative impacts of heat stress and drought.

In the long term, shipping commerce will benefit from the opening of the Northwest Passage for longer periods of the year due to the loss of Arctic sea ice. However, in the long run, if a "business as usual" approach to emitting heat-trapping gases is maintained at the present rate, or faster, then the negative costs and impacts of global warming are very likely to far outweigh the benefits over the course of this century, with increased potential for catastrophic impacts from more extreme events. ] In part, this is because any substantial change, whether warmer or colder, would challenge the societal infrastructure that has developed under the current climate.

]

If all human emissions of heat-trapping gases were to stop today, Earth’s temperature would continue to rise for a few decades as ocean currents bring excess heat stored in the deep ocean back to the surface. Once this excess heat radiated out to space, Earth’s temperature would stabilize. Experts think the additional warming from this “hidden” heat is unlikely to exceed 0.9° Fahrenheit (0.5°Celsius). ] With no further human influence, natural processes would begin to slowly remove the excess carbon dioxide from the atmosphere, and global temperatures would gradually begin to decline.

It’s true that without dramatic action in the next couple of decades, we are unlikely to keep global warming in this century below 2.7° Fahrenheit (1.5° Celsius) compared to pre-industrial temperatures—a threshold that experts say offers a lower risk of serious negative impacts. ] But the more we overshoot that threshold, the more serious and widespread the negative impacts will be, which means that it is never “too late” to take action.

it is likely many strategies working together will be needed. Generally speaking, here are some examples of mitigation strategies we can use to slow or stop the human-caused global warming ( ):

techniques.

Note that NOAA doesn’t advocate for or against particular climate policies. Instead, NOAA’s role is to provide data and scientific information about climate, including how it has changed and is likely to change in the future depending on different climate policies or actions society may or may not take. Learn more  and .

):

Note that NOAA doesn’t advocate for or against particular climate policies. Instead, NOAA’s role is to provide data and scientific information about climate, including how it has changed and is likely to change in the future depending on different climate policies or actions society may or may not take. Learn more  and .

NOAA is helping to improve the nation’s resilience to changes in climate and weather. Specifically, NOAA is working to…

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U.S. Global Change Research Program, Washington, DC, USA, pp. 391–437. doi: 10.7930/NCA4.2018.CH10 NOAA National Centers for Environmental Information (NCEI). (2020).  . [Accessed October 23, 2020]. DOI:  Maxwell, K., S. Julius, A. Grambsch, A. Kosmal, L. Larson, and N. Sonti. (2018). Built Environment, Urban Systems, and Cities. In   [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 438–478. doi: 10.7930/NCA4.2018.CH11 Jacobs, J.M., M. Culp, L. Cattaneo, P. Chinowsky, A. Choate, S. DesRoches, S. Douglass, and R. Miller. (2018). Transportation. In   [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 479–511. doi: 10.7930/NCA4.2018.CH12 Clarke, L., L. Nichols, R. Vallario, M. Hejazi, J. Horing, A.C. Janetos, K. Mach, M. Mastrandrea, M. Orr, B.L. Preston, P. Reed, R.D. Sands, and D.D. White. (2018). Sector Interactions, Multiple Stressors, and Complex Systems. In   [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 638–668. doi: 10.7930/NCA4.2018.CH17 Allen, M.R., O.P. Dube, W. Solecki, F. Aragón-Durand, W. Cramer, S. Humphreys, M. Kainuma, J. Kala, N. Mahowald, Y. Mulugetta, R. Perez, M.Wairiu, and K. Zickfeld (2018 Framing and Context. In: [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press. Wuebbles, D.J., D.R. Easterling, K. Hayhoe, T. Knutson, R.E. Kopp, J.P. Kossin, K.E. Kunkel, A.N. LeGrande, C. Mears, W.V. Sweet, P.C. Taylor, R.S. Vose, and M.F. Wehner, 2017: Our globally changing climate. In: [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 35-72, doi: . Aquila, V., Swartz, W. H., Waugh, D. W., Colarco, P. R., Pawson, S., Polvani, L. M., & Stolarski, R. S. (2016). Isolating the roles of different forcing agents in global stratospheric temperature changes using model integrations with incrementally added single forcings. s, 121(13), 8067–8082. Snyder, C. W. (2016). Evolution of global temperature over the past two million years. 538(7624), 226–228. Tierney, J. E., Zhu, J., King, J., Malevich, S. B., Hakim, G. J., & Poulsen, C. J. (2020). Glacial cooling and climate sensitivity revisited. 584(7822), 569–573. Cuffey, K. M., Clow, G. D., Steig, E. J., Buizert, C., Fudge, T. J., Koutnik, M., Waddington, E. D., Alley, R. B., & Severinghaus, J. P. (2016). Deglacial temperature history of West Antarctica. 113(50), 14249–14254.

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What’s the difference between climate change and global warming?

The terms “global warming” and “climate change” are sometimes used interchangeably, but "global warming" is only one aspect of climate change.

“Global warming” refers to the long-term warming of the planet. Global temperature shows a well-documented rise since the early 20th century and most notably since the late 1970s. Worldwide since 1880, the average surface temperature has risen about 1 ° C (about 2 ° F), relative to the mid-20th century baseline (of 1951-1980). This is on top of about an additional 0.15 ° C of warming from between 1750 and 1880.

“Climate change” encompasses global warming, but refers to the broader range of changes that are happening to our planet. These include rising sea levels; shrinking mountain glaciers; accelerating ice melt in Greenland, Antarctica and the Arctic; and shifts in flower/plant blooming times. These are all consequences of warming, which is caused mainly by people burning fossil fuels and putting out heat-trapping gases into the air.

• Overview: Weather, Global Warming and Climate Change

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How global warming is disrupting life on Earth

The signs of global warming are everywhere, and are more complex than just climbing temperatures.

Our planet is getting hotter. Since the Industrial Revolution—an event that spurred the use of fossil fuels in everything from power plants to transportation—Earth has warmed by 1 degree Celsius, about 2 degrees Fahrenheit.  

That may sound insignificant, but 2023 was the hottest year on record , and all 10 of the hottest years on record have occurred in the past decade.  

Global warming and climate change are often used interchangeably as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems.  

Climate change encompasses not only rising average temperatures but also natural disasters, shifting wildlife habitats, rising seas , and a range of other impacts. All of these changes are emerging as humans continue to add heat-trapping greenhouse gases , like carbon dioxide and methane, to the atmosphere.

What causes global warming?

When fossil fuel emissions are pumped into the atmosphere, they change the chemistry of our atmosphere, allowing sunlight to reach the Earth but preventing heat from being released into space. This keeps Earth warm, like a greenhouse, and this warming is known as the greenhouse effect .  

Carbon dioxide is the most commonly found greenhouse gas and about 75 percent of all the climate warming pollution in the atmosphere. This gas is a product of producing and burning oil, gas, and coal. About a quarter of Carbon dioxide also results from land cleared for timber or agriculture.  

Methane is another common greenhouse gas. Although it makes up only about 16 percent of emissions, it's roughly 25 times more potent than carbon dioxide and dissipates more quickly. That means methane can cause a large spark in warming, but ending methane pollution can also quickly limit the amount of atmospheric warming. Sources of this gas include agriculture (mostly livestock), leaks from oil and gas production, and waste from landfills.  

What are the effects of global warming?  

One of the most concerning impacts of global warming is the effect warmer temperatures will have on Earth's polar regions and mountain glaciers. The Arctic is warming four times faster than the rest of the planet. This warming reduces critical ice habitat and it disrupts the flow of the jet stream, creating more unpredictable weather patterns around the globe.  

( Learn more about the jet stream. )

A warmer planet doesn't just raise temperatures. Precipitation is becoming more extreme as the planet heats. For every degree your thermometer rises, the air holds about seven percent more moisture. This increase in moisture in the atmosphere can produce flash floods, more destructive hurricanes, and even paradoxically, stronger snow storms.  

The world's leading scientists regularly gather to review the latest research on how the planet is changing. The results of this review is synthesized in regularly published reports known as the Intergovernmental Panel on Climate Change (IPCC) reports.  

A recent report outlines how disruptive a global rise in temperature can be:

• Coral reefs are now a highly endangered ecosystem. When corals face environmental stress, such as high heat, they expel their colorful algae and turn a ghostly white, an effect known as coral bleaching . In this weakened state, they more easily die.  
• Trees are increasingly dying from drought , and this mass mortality is reshaping forest ecosystems.
• Rising temperatures and changing precipitation patterns are making wildfires more common and more widespread. Research shows they're even moving into the eastern U.S. where fires have historically been less common.
• Hurricanes are growing more destructive and dumping more rain, an effect that will result in more damage. Some scientists say we even need to be preparing for Cat 6 storms . (The current ranking system ends at Cat 5.)

How can we limit global warming?  

Limiting the rising in global warming is theoretically achievable, but politically, socially, and economically difficult.  

Those same sources of greenhouse gas emissions must be limited to reduce warming. For example, oil and gas used to generate electricity or power industrial manufacturing will need to be replaced by net zero emission technology like wind and solar power. Transportation, another major source of emissions, will need to integrate more electric vehicles, public transportation, and innovative urban design, such as safe bike lanes and walkable cities.  

( Learn more about solutions to limit global warming. )

One global warming solution that was once considered far fetched is now being taken more seriously: geoengineering. This type of technology relies on manipulating the Earth's atmosphere to physically block the warming rays of the sun or by sucking carbon dioxide straight out of the sky.

Restoring nature may also help limit warming. Trees, oceans, wetlands, and other ecosystems help absorb excess carbon—but when they're lost, so too is their potential to fight climate change.  

Ultimately, we'll need to adapt to warming temperatures, building homes to withstand sea level rise for example, or more efficiently cooling homes during heat waves.  

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Climate Change

Evidence and causes: update 2020.

Climate change is one of the defining issues of our time. It is now more certain than ever, based on many lines of evidence, that humans are changing Earth's climate. The Royal Society and the US National Academy of Sciences, with their similar missions to promote the use of science to benefit society and to inform critical policy debates, produced the original Climate Change: Evidence and Causes in 2014. It was written and reviewed by a UK-US team of leading climate scientists. This new edition, prepared by the same author team, has been updated with the most recent climate data and scientific analyses, all of which reinforce our understanding of human-caused climate change.

Scientific information is a vital component for society to make informed decisions about how to reduce the magnitude of climate change and how to adapt to its impacts. This booklet serves as a key reference document for decision makers, policy makers, educators, and others seeking authoritative answers about the current state of climate-change science.

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Open Access

Peer-reviewed

Research Article

Talking about Climate Change and Global Warming

Contributed equally to this work with: Maurice Lineman, Yuno Do

Affiliation College of Natural Sciences, Department of Biological Sciences, Pusan National University, Busan, South Korea

* E-mail: [email protected]

• Maurice Lineman, 
• Yuno Do, 
• Ji Yoon Kim, 
• Gea-Jae Joo

• Published: September 29, 2015
• https://doi.org/10.1371/journal.pone.0138996
• Reader Comments

The increasing prevalence of social networks provides researchers greater opportunities to evaluate and assess changes in public opinion and public sentiment towards issues of social consequence. Using trend and sentiment analysis is one method whereby researchers can identify changes in public perception that can be used to enhance the development of a social consciousness towards a specific public interest. The following study assessed Relative search volume (RSV) patterns for global warming (GW) and Climate change (CC) to determine public knowledge and awareness of these terms. In conjunction with this, the researchers looked at the sentiment connected to these terms in social media networks. It was found that there was a relationship between the awareness of the information and the amount of publicity generated around the terminology. Furthermore, the primary driver for the increase in awareness was an increase in publicity in either a positive or a negative light. Sentiment analysis further confirmed that the primary emotive connections to the words were derived from the original context in which the word was framed. Thus having awareness or knowledge of a topic is strongly related to its public exposure in the media, and the emotional context of this relationship is dependent on the context in which the relationship was originally established. This has value in fields like conservation, law enforcement, or other fields where the practice can and often does have two very strong emotive responses based on the context of the problems being examined.

Citation: Lineman M, Do Y, Kim JY, Joo G-J (2015) Talking about Climate Change and Global Warming. PLoS ONE 10(9): e0138996. https://doi.org/10.1371/journal.pone.0138996

Editor: Hayley J. Fowler, Newcastle University, UNITED KINGDOM

Received: August 18, 2014; Accepted: September 8, 2015; Published: September 29, 2015

Copyright: © 2015 Lineman et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Data Availability: All relevant data are within the paper.

Funding: This study was financially supported by the 2015 Post-Doc Development Program of Pusan National University.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Identifying trends in the population, used to be a long and drawn out process utilizing surveys and polls and then collating the data to determine what is currently most popular with the population [ 1 , 2 ]. This is true for everything that was of merit to the political organizations present, regarding any issue of political or public interest.

Recently, the use of the two terms ‘Climate Change’ and ‘Global Warming’ have become very visible to the public and their understanding of what is happening with respect to the climate [ 3 ]. The public response to all of the news and publicity about climate has been a search for understanding and comprehension, leading to support or disbelief. The two terms while having similarity in meaning are used in slightly different semantic contexts. The press in order to expand their news readership/viewer lists has chosen to use this ambiguity to their favor in providing news to the public [ 4 ]. Within the news releases, the expression ‘due to climate change’ has been used to explain phenomological causality.

These two terms “global warming–(GW)” and “climate change–(CC)” both play a role in how the public at large views the natural world and the changes occurring in it. They are used interactively by the news agencies, without a thought towards their actual meaning [ 3 , 4 ]. Therefore, the public in trying to identify changes in the news and their understanding of those changes looks for the meaning of those terms online. The extent of their knowledge can be examined by assessing the use of the terms in online search queries. Information searches using the internet are increasing, and therefore can indicate public or individual interest.

Internet search queries can be tracked using a variety of analytic engines that are independent of, or embedded into, the respective search engines (google trend, naver analytics) and are used to determine the popularity of a topic in terms of internet searches [ 5 ]. The trend engines will look for selected keywords from searches, keywords chosen for their relevance to the field or the query being performed.

The process of using social media to obtain information on public opinion is a practice that has been utilized with increasing frequency in modern research for subjects ranging from politics [ 6 , 7 ] to linguistics [ 8 – 10 ] complex systems [ 11 , 12 ] to environment [ 13 ]. This variety of research belies the flexibility of the approach, the large availability of data availability for mining in order to formulate a response to public opinion regarding the subject being assessed. In modern society understanding how the public responds regarding complex issues of societal importance [ 12 ].

While the two causally connected terms GW and CC are used interchangeably, they describe entirely different physical phenomena [ 14 ]. These two terms therefore can be used to determine how people understand the parallel concepts, especially if they are used as internet search query terms in trend analysis. However, searching the internet falls into two patterns, searches for work or for personal interest, neither of which can be determined from the trend engines. The By following the searches, it is possible to determine the range of public interest in the two terms, based on the respective volumes of the search queries. Previously in order to mine public opinion on a subject, government agencies had to revert to polling and surveys, which while being effective did not cover a very large component of the population [ 15 – 17 ].

Google trend data is one method of measuring popularity of a subject within the population. Individuals searching for a topic use search keywords to obtain the desired information [ 5 , 18 ]. These keywords are topic sensitive, and therefore indicate the level of knowledge regarding the searched topic. The two primary word phrases here “climate change” and “global warming” are unilateral terms that indicate a level of awareness about the issue which is indicative of the individuals interest in that subject [ 5 , 19 , 20 ]. Google trend data relates how often a term is searched, that is the frequency of a search term can be identified from the results of the Google® trend analysis. While frequency is not a direct measure of popularity, it does indicate if a search term is common or uncommon and the value of that term to the public at large. The relationship between frequency and popularity lies in the volume of searches by a large number of individuals over specific time duration. Therefore, by identifying the number of searches during a specific period, it is possible to come to a proximate understanding of how popular or common a term is for the general population [ 21 ]. However, the use of trend data is more appropriately used to identify awareness of an issue rather than its popularity.

This brings us to sentiment analysis. Part of the connection between the search and the populations’ awareness of an issue can be measured using how they refer to the subject in question. This sentiment, is found in different forms of social media, or social networking sites sites i.e. twitter®, Facebook®, linked in® and personal blogs [ 7 , 22 – 24 ]. Thus, the original information, which was found on the internet, becomes influenced by personal attitudes and opinions [ 25 ]and then redistributed throughout the internet, accessible to anyone who has an internet connection and the desire to search. This behavior affects the information that now provides the opportunity to assess public sentiment regarding the prevailing attitudes regarding environmental issues [ 26 , 27 ]. To assess this we used Google® and Twitter® data to understand public concerns related to climate change and global warming. Google trend was used to trace changes in interest between the two phenomena. Tweets (comments made on Twitter®) were analyzed to identify negative or positive emotional responses.

Comparatively, twitter data is more indicative of how people refer to topics of interest [ 28 – 31 ], in a manner that is very linguistically restricted. As well, twitter is used as a platform for verbal expression of emotional responses. Due to the restrictions on tweet size (each tweet can only be 140 characters in length), it is necessary to be more direct in dealing with topics of interest to the tweeter. Therefore, the tweets are linguistically more emotionally charged and can be used to define a level of emotional response by the tweeter.

The choice of target words for the tweets and for the Google trend searches were the specific topic phrases [ 32 , 33 ]. These were chosen because of the descriptive nature of the phrases. Scientific literature is very specific in its use and therefore has very definitive meanings. The appropriation of these words by the population as a method for describing their response to the variation in the environment provides the basis for the choice as target words for the study. The classification of the words as being positive versus negative lies in the direction provided by Frank Lutz. This politicization of a scientific word as a means of directing public awareness, means the prescription of one phrase (climate change) as being more positive than the other (global warming).

Global warming is defined as the long-term trend of increasing average global temperatures; alternatively, climate change is defined as a change in global or regional climate patterns, in particular a change apparent from the mid to late 20 th century onwards and attributed to the increased levels of atmospheric carbon dioxide arising from the use of fossil fuels. Therefore, the search keywords were chosen based on their scientific value and their public visibility. What is important about the choice of these search terms is that due to their scientific use, they describe a distinctly identifiable state. The more specific these words are, the less risk of the algorithm misinterpreting the keyword and thus having the results misinterpreted [ 34 – 36 ].

The purpose of the following study was to identify trends within search parameters for two specific sets of trend queries. The second purpose of the study was to identify how the public responds emotionally to those same queries. Finally, the purpose of the study was to determine if the two had any connections.

Data Collection

Public awareness of the terms climate change and global warming was identified using Google Trends (google.com/trends) and public databases of Google queries [ 37 ]. To specify the exact searches we used the two terms ‘climate change’ and ‘global warming’ as query phrases. Queries were normalized using relative search volume (RSV) to the period with the highest proportion of searches going to the focal terms (i.e. RSV = 100 is the period with the highest proportion for queries within a category and RSV = 50 when 50% of that is the highest search proportion). Two assumptions were necessary for this study. The first is, of the two terms, climate change and global warming, that which draws more search results is considered more interesting to the general population. The second assumption is that changes in keyword search patterns are indicators of the use of different forms of terminology used by the public. To analyze sentiments related to climate change and global warming, tweets containing acronyms for climate change and global warming were collected from Twitter API for the period from October 12 to December 12, 2013. A total of 21,182 and 26,462 tweets referencing the terms climate change and global warming were collected respectively. When duplicated tweets were identified, they were removed from the analysis. The remaining tweets totaled 8,465 (climate change) and 8,263 (global warming) were compiled for the sentiment analysis.

Data Analysis

In Twitter® comments are emotionally loaded, due to their textually shortened nature. Sentiment analysis, which is in effect opinion mining, is how opinions in texts are assessed, along with how they are expressed in terms of positive, neutral or negative content [ 36 ]. Nasukawa and Yi [ 10 ]state that sentiment analysis identifies statements of sentiment and classifies those statements based on their polarity and strength along with their relationship to the topic.

Sentiment analysis was conducted using Semantria® software ( www.semantria.com ), which is available as an MS Excel spreadsheet application plugin. The plugin is broken into parts of speech (POS), the algorithm within the plugin then identifies sentiment-laden phrases and then scores them from -10 to 10 on a logarithmic scale, and finally the scores for each POS are tabulated to identify the final score for each phrase. The tweets are then via statistical inferences tagged with a numerical value from -2 to 2 and given a polarity, which is classified as positive, neutral or negative [ 36 ]. Semantria®, the program utilized for this study, has been used since 2011 to perform sentiment analyses [ 7 , 22 ].

For the analysis, an identity column was added to the dataset to enable analysis of individual tweets with respect to sentiment. A basic sentiment analysis was conducted on the dataset using the Semantria® plugin. The plugin uses a cloud based corpus of words tagged with sentimental connotations to analyze the dataset. Through statistical inference, each tweet is tagged with a sentiment value from -2 to +2 and a polarity of (i) negative, (ii) neutral, or (iii) positive. Positive nature increases with increasing positive sentiment. The nature of the language POS assignation is dependent upon the algorithmic classification parameters defined by the Semantria® program. Determining polarity for each POS is achieved using the relationship between the words as well as the words themselves. By assigning negative values to specific negative phrases, it limits the use of non-specific negation processes in language; however, the program has been trained to assess non-specific linguistic negations in context.

A tweet term frequency dictionary was computed using the N-gram method from the corpus of climate change and global warming [ 38 ]. We used a combination of unigrams and bigrams, which has been reported to be effective [ 39 ]. Before using the N-gram method, typological symbols were removed using the open source code editor (i.e. Notepad) or Microsoft Words’ “Replace” function.

Differences in RSV’s for the terms global warming and climate change for the investigation period were identified using a paired t-test. Pettitt and Mann-Kendall tests were used to identify changes in distribution, averages and the presence of trends within the weekly RSV’s. The Pettitt and MK tests, which assume a stepwise shift in the mean (a break point) and are sensitive to breaks in the middle of a time series, were applied to test for homogeneity in the data [ 40 ]. Temporal trends within the time series were analyzed with Spearman’s non-parametric correlation analysis. A paired t-test and Spearman’s non-parametric correlation analysis were conducted using SPSS software (version 17.0 SPSS In corp. Chicago IL) and Pettitt and MK tests were conducted using XLSTAT (version 7.0).

To determine the accuracy and reliability of the Sentiment analysis, a Pearson’s chi-square analysis was performed. This test identifies the difference ratio for each emotional response group, and then compares them to determine reliance and probability of interactions between the variables, in this case the terms global warming and climate change.

According to Google trend ( Fig 1 ) from 2004–2014, people searched for the term global warming (n = 8,464; mean ± S.D = 25.33 ± 2.05) more frequently than climate change (n = 8,283; mean ± S.D. = 7.97±0.74). Although the Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment Report in 2007 and was awarded the Nobel Prize, interest in the term global warming as used in internet searches has decreased significantly since 2010 (K = 51493, t = 2010-May-23, P<0.001). Further the change in RSV also been indicative of the decreased pattern (Kendall’s tau = -0.336, S = -44563, P<0.001). The use of the term “climate change” has risen marginally since 2006 (K = 38681, t = 2006-Oct-08, P<0.001), as indicated by a slight increase (Kendall’s tau = -0.07, S = 9068, P<0.001). These findings show that the difference in usage of the two terms climate change and global warming has recently been reduced.

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https://doi.org/10.1371/journal.pone.0138996.g001

The sentiment analysis of tweets ( Fig 2 ) shows that people felt more negative about the term global warming (sentiment index = -0.21±0.34) than climate change (-0.068±0.36). Global warming tweets reflecting negative sentiments via descriptions such as, “bad, fail, crazy, afraid and catastrophe,” represented 52.1% of the total number of tweets. As an example, the tweet, “Supposed to snow here in the a.m.! OMG. So sick of already, but Saturday says 57 WTF!” had the lowest score at -1.8. Another observation was that 40.7% of tweets, including “agree, recommend, rescue, hope, and contribute,” were regarded as neutral. While 7.2% of tweets conveyed positive messages such as, “good, accept, interesting, and truth.” One positive global warming tweet, read, “So if we didn’t have global warming, would all this rain be snow!”. The results from the Pearson’s chi-square analysis showed that the relationship between the variables was significant (Pearson’s chi-square –763.98, d.f. = 2, P<0.001). Negative climate change tweets represented 33.1% of the total while neutral tweets totaled 49.8%, while positive climate change tweets totaled 17.1%.

https://doi.org/10.1371/journal.pone.0138996.g002

Understandably, global warming and climate change are the terms used most frequently to describe each phenomenon, respectively, as revealed by the N-gram analysis ( Table 1 ). When people tweeted about global warming, they repeatedly used associated such as, “ice, snow, Arctic, and sea.” In contrast, tweets referring to climate change commonly used, “report, IPCC, world, science, environment, and scientist.” People seem to think that climate change as a phenomenon is revealed by scientific investigation.

https://doi.org/10.1371/journal.pone.0138996.t001

Internet searches are one way of understanding the popularity of an idea or meme within the public at large. Within that frame of reference, the public looks at these two terms global warming and climate change and their awareness of the roles of the two phenomena [ 41 ]. From 2004 to 2008, the search volumes for the term global warming far exceeded the term climate change. The range for the term global warming in Relative search volumes (RSV) was more than double that of climate change in this period ( Fig 1 ). From 2008 on the RSV’s began to steadily decrease until in 2014 when the RSV’s for the term global warming were nearly identical to those for the term climate change. From 2008 there was an increase in the RSVs for CC until 2010 at which point the RSVs also began to decline for the term climate change. The decline in the term climate change for the most part paralleled that of the term global warming from 2010 on to the present.

While we are seeing the increases and decreases in RSVs for both the terms global warming and climate change, the most notable changes occur when the gap between the terms was the greatest, from 2008 through to 2010. During this period, there was a very large gap found between the RSVs for the terms global warming and climate change; however, searches for the term climate change was increasing while searches for the tem global warming were decreasing. The counter movement of the RSV’s for the two terms shows that there is a trend happening with respect to term recognition. At this point, there was an increase in the use of the CC term while there was a corresponding decrease in the use of the GW term. The change in the use of the term could have been due to changes in the publicity of the respective terms, since at this point, the CC term was being used more visibly in the media, and therefore the CC term was showing up in headlines and the press, resulting in a larger number of searches for the CC term. Correspondingly, the decrease in the use of the GW term is likely due to the changes in how the term was perceived by the public. The public press determines how a term is used, since they are the body that consistently utilizes a term throughout its visible life. The two terms, regardless of how they differ in meaning, are used with purpose in a scientific context, yet the public at large lacks this definition and therefore has no knowledge of the variations in the terms themselves [ 42 ]. Therefore, when searching for a term, the public may very well, choose the search term that they are more comfortable with, resulting in a search bias, since they do not know the scientific use of the term.

The increase in the use of the CC term, could be a direct result of the release of the fourth assessment report for the IPCC in 2007 [ 43 ]. The publicity related to the release of this document, which was preceded by the release of the Al Gore produced documentary “An Inconvenient Truth”, both of which were followed by the selection by the Nobel committee of Al Gore and the IPCC scientists for the Nobel Prize in 2007 [ 43 ]. These three acts individually may not have created the increased media presence of the CC term; however, at the time the three events pushed the CC term and increased its exposure to the public which further drove the public to push for positive environmental change at the political level [ 44 , 45 ]. This could very well have resulted in the increases in RSV’s for the CC term. This point is more likely to depict accurately the situation, since in 2010 the use of the two terms decline at almost the same rate, with nearly the same patterns.

Thus with respect to trend analysis, what is interesting is that RSVs are paralleling the press for specific environmental events that have predetermined value according to the press. The press in increasing the visibility of the term may drive the increases in the RSV’s for that term. Prior to 2007, the press was using the GW term indiscriminately whenever issues affecting the global climate arose; however, after the movie, the report and then the Nobel prize the terminology used by the press switched and the CC term became the word du jour. This increased the visibility of the word to the public, thereby it may be that increasing public awareness of the word, but not necessarily its import, is the source for the increases in RSV’s between 2008 and 2010.

The decline in the RSV’s then is a product of the lack of publicity about the issue. As the terms become more familiar, there would be less necessity to drive the term publicly into the spotlight; however, occasionally events/situations arise that refocus the issue creating a resurgence in the terms even though they have reached their peak visibility between 2008 and 2010.

Since these terms have such an impact on the daily lives of the public via local regional national and global weather it is understandable that they have an emotional component to them [ 46 ]. Every country has its jokes about the weather, where they come up with cliché’s about the weather (i.e. if you don’t like the weather wait 10minutes) that often show their discord and disjunction with natural climatological patterns [ 47 ]. Furthermore, some sectors of society (farmers) have a direct relationship with the climate and their means of living; bad weather is equal to bad harvests, which means less money. To understand how society represents this love hate relationship with the weather, the twitter analysis was performed. Twitter, a data restricted social network system, has a limited character count to relay information about any topic the sender chooses to relate. These tweets can be used to assess the sentiment of the sender towards a certain topic. As stated previously, the sentiment is defined by the language of the tweet within the twitter system. Sentiment analysis showed that the two terms differed greatly. Based on the predefined algorithm for the sentiment analysis, certain language components carried a positive sentiment, while others carried a negative sentiment. Tweets about GW and CC were subdivided based on their positive, neutral and negative connotations within the tweet network. These emotions regardless of their character still play a role in how humans interacts with surroundings including other humans [ 48 , 49 ] As seen in Fig 2 the different terms had similar distributions, although with different ranges in the values. Global warming showed a much smaller positive tweet value than did climate change. Correspondent to this the respective percentage of positive sentiments for CC was more than double that of GW. Comparatively, the neutral percentiles were more similar for each term with a small difference. However, the negative sentiments for the two terms again showed a greater disparity, with negative statements about GW nearly double those of climate change.

These differences show that there is a perceptive difference in how the public relates to the two terms Global Warming and Climate Change [ 50 , 51 ]. Climate change is shown in a more positive light than global warming simply based on the tweets produced by the public. The difference in how people perceive climate change and global warming is possibly due to the press, personal understanding of the terms, or level of education. While this in itself is indefinable, since by nature tweets are linguistically restrictive, the thing to take from it is that there is a measurable difference in how individuals respond to climatological changes that they are experiencing daily. These changes have a describable effect on how the population is responding to the publicity surrounding the two terms to the point where it can be used to manipulate governmental policy [ 52 ].

Sentiment analysis is a tool that can be used to determine how the population feels about a topic; however, the nature of the algorithm makes it hard to effectively determine how this is being assessed. For the current study, the sentiment analysis showed that there was a greater negative association with the term global warming than with the term climate change. This difference, which while being an expression of individual like or dislike at the time the tweet was created, denotes that the two terms were either not understood in their true form, or that individuals may have a greater familiarity with one term over the other, which may be due to a longer exposure to the term (GW) or the negative press associated with the term (GW).

Conclusions

Trend analysis identified that the public is aware of the terminology used to describe climatological variation. The terminology showed changes in use over time with global warming starting as the more well-known term, and then its use decreased over time. At the same time, the more definitive term climate change had less exposure early on; however, with the increase of press exposure, the public became increasingly aware of the term and its more accurate definition. This increase appeared to be correspondent with the increasing publicity around three very powerful press exposure events (a documentary, a scientific report release and a Nobel Prize). The more the term was used the more people came to use it, this included searches on the internet.

Comparatively sentiment analysis showed that the two terms had differential expressions in the population. With climate change being seen in a more positive frame than global warming. The use of sentiment analysis as a tool to evaluate how the population is responding to a feature is an important tool. However, it is a tool that measures, it does not define.

Social network systems and internet searches are effective tools in identifying changes in both public awareness and public perception of an issue. However, in and of itself, these are bell ringers they can be used to determine the importance of an issue, but not the rationale behind the why it is important. This is an important fact to remember when using analytical tools that evaluate social network systems and their use by the public.

Acknowledgments

This study was financially supported by the 2015 Post-Doc. Development Program of Pusan National University

Author Contributions

Conceived and designed the experiments: YD GJJ. Performed the experiments: ML YD. Analyzed the data: ML YD. Contributed reagents/materials/analysis tools: JK YD. Wrote the paper: ML YD GJJ.

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Should we change the term we use for “climate change”? Evidence from a national U.S. terminology experiment

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• Published: 12 August 2024
• Volume 177 , article number  129 , ( 2024 )

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• Wändi Bruine de Bruin   ORCID: orcid.org/0000-0002-1601-789X 1 , 2 ,
• Laurel Kruke   ORCID: orcid.org/0009-0005-0467-375X 3 ,
• Gale M. Sinatra   ORCID: orcid.org/0000-0002-6545-587X 2 , 3 &
• Norbert Schwarz   ORCID: orcid.org/0000-0002-8868-7067 2 , 4 , 5  

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The terms “global warming,” “climate crisis,” “climate emergency,” and “climate justice” each draw attention to different aspects of climate change. Psychological theories of attitude formation suggest that people’s attitudes can be influenced by such variations in terminology. In a national experiment, we randomly assigned a national sample of 5,137 U.S. residents to “climate change,” “global warming,” “climate crisis,” “climate emergency,” or “climate justice” and examined their responses. Overall, “climate change” and “global warming” were rated as most familiar and most concerning, and “climate justice” the least, with ratings for “climate crisis” and “climate emergency” falling in between. Moreover, we find no evidence for “climate crisis” or “climate emergency” eliciting more perceived urgency than “climate change” or “global warming.” Rated willingness to support climate-friendly policies and eat less red meat were less affected by presented terms, but they were lowest for “climate justice.” Although effects of terms on rated familiarity, concern, and perceived urgency varied by political leaning, “climate justice” generally received the lowest ratings on these variables among Democrats, Republicans, and Independent/others. Auxiliary analyses found that when terms were unfamiliar, participants were generally less likely to express concern, urgency, policy support, or willingness to eat less red meat. We therefore recommend sticking with familiar terms, conclude that changing terminology is likely not the key solution for promoting climate action, and suggest alternative communication strategies.

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1 Introduction

1.1 words matter.

Psychological theories of attitude formation suggest that attitudes about a topic are influenced by topic-related information that comes to mind in the moment (Schwarz 2007 ; Sudman et al. 1996 ). In line with those theories, survey design research has been showing for decades that words that draw attention to different aspects of a topic can sway public opinion about that topic (Cantril 1944 ; Payne 1951 ). Similarly, classic psychological studies have found that seemingly slight variations in how options are framed can affect people’s judgments and decisions (Tversky and Kahneman 1981 ; Levin et al. 1988 ). For example, food without meat and dairy is more likely to be chosen when it is labeled “plant-based” rather than “vegan” -- and becomes even more popular when labels say “healthy” or “sustainable” to emphasize the benefits of eating food without meat and dairy (Sleboda et al. 2024 ). While “healthy” and “sustainable” are not exactly synonyms of the term “vegan,” vegan food does tend to be more healthy and sustainable than non-vegan food (Sleboda et al. 2024 ). Hence, there is reason to suspect that the terms that have been proposed to emphasize different aspects of “climate change” may affect people’s responses, including their concern about the topic, and their willingness to do something about it (e.g. Schuldt et al. 2011 ). The present paper therefore examines public responses to the terms “climate change,” “global warming,” “climate crisis,” “climate emergency,” and “climate justice,” among Democrats, Republicans, and Independents/others (see Sect. 1.6).

1.2 Terms used to discuss “climate change” emphasize different aspects of the phenomenon

Terms like “climate change” and “global warming” have long been used to describe the climate impacts of increasing anthropogenic greenhouse gases in the atmosphere (Penz 2017 ). Although “climate change” and “global warming” are often used interchangeably in the public discourse (Benjamin 2017 ), they are not synonyms and emphasize different aspects of the phenomenon. Specifically, “climate change” refers to diverse changes in the climate that may or may not be due to human activity while “global warming” refers to increasing global surface temperatures and implies that humans are actively warming the planet (Penz 2017 ). Indeed, the term “climate change” was initially popularized by an advisor to the Bush administration to de-emphasize the role of human activity (Penz 2017 ). Google Trends between 2004 and 2014 found that, as an internet search term, “climate change” was initially less popular than “global warming” (Lineman et al. 2015 ). Consistent with this trend, a 2003 public perception study in South England found that “climate change” was less familiar than “global warming,” while also raising less concern or calls for action (Whitmarsh 2009 ). However, “climate change” and “global warming” were similarly likely to be searched in 2014, and “climate change” had overtaken “global warming” in 2016 (Penz 2017 ).

In addition to “climate change” and “global warming,” other terms have been introduced to focus the public discourse on other aspects of the phenomenon. Like “global warming,” none of these terms are synonyms of “climate change,” but they emphasize aspects of climate change to try to increase public responsiveness. In 2019, The Guardian newspaper switched to using “climate crisis” and “climate emergency” in an effort to raise concern and convey urgency (Schäfer et al. 2023 ). Additionally, the term “climate justice” has been introduced by left-leaning grassroot organizations to draw attention to climate change as a human rights challenge (Dutta 2019 ). That is, disadvantaged communities will suffer the most from the effects of climate change despite being the least responsible for causing it (Dutta 2019 ; Schlosberg and Collins 2014 ; Saraswat and Kumar 2016 ). It has been suggested that linking climate policy to justice may increase public support (Bergquist et al. 2020 ).

1.3 Political polarization in public responses to “climate change” and “global warming”

Americans who lean Republican are traditionally more skeptical about climate change than Americans who lean Democrat (Pew Research Center 2023a ), in agreement with political parties’ stance on the issue. In part, this reflects Americans’ tendency to support the views of their political party and devalue the views of the other political party (van Boven et al. 2018 ).

Since the early 2000s, national experiments have been examining whether the words used for “climate change” affect this partisan divide (e.g., Akerlof and Maibach 2011 ; Schuldt et al. 2011 ; Villar and Krosnick 2011 ). In the early 2000’s, Republicans in the United States (U.S.) reported being more skeptical when they were asked about “global warming” than when they were asked about “climate change,” perhaps because Republicans tended to question “global warming” during unseasonably cold weather (Schuldt et al. 2011 , 2015 ; Morin-Chassé et al. 2020 ). A Republican senator even brought a snowball into U.S. Congress in 2015 to highlight how cold it was and to question “global warming” (Fisher et al. 2015 ).

In line with this finding, Republicans used to consider “climate change” as more serious than “global warming” (Villar and Krosnick 2011 ). In contrast, Democrats considered “global warming” more serious than “climate change” (Villar and Krosnick 2011 ), perhaps because the former suggests the contribution of human activity (Penz 2017 ). When asked to choose between “climate change” and “global warming,” most Americans had no preference, though Democrats slightly preferred “global warming” (Akerlof and Maibach 2011 ). However, Democrats and Independents/others showed relatively less skepticism than Republicans, independent of the presented terms (Schuldt et al. 2011 ).

Over time, partisan differences in responses to the terms “climate change” and “global warming” have faded (Schuldt et al. 2020 ). In 2018, about 75% of Republicans and 95% of Democrats indicated that they thought “climate change” and “global warming” were real, thus no longer showing an effect of terminology on reported concerns (Schuldt et al. 2020 ). However, the influence of saying “climate change” or “global warming” may be stronger on concerns than on willingness to act, and on Independents/others who do not have strong opinions about the phenomenon (Benjamin et al. 2017 ).

1.4 Political polarization in public responses to newer terms

Few studies have examined public responses to “climate crisis” and “climate emergency,” which were introduced to raise public concern and emphasize urgency (Schäfer et al. 2023 ). One study with a U.S. national sample found no differences in willingness to support specific policies after reading news stories mentioning “climate crisis,” “climate emergency” or “climate change,” and there were no partisan differences in responses to those terms (Feldman and Hart 2021 ). However, perceived credibility and newsworthiness were generally worse for “climate emergency” than for “climate change” (Feldman and Hart 2021 ). Two other studies also examined public responses to the “climate crisis,” but not whether they varied by political leaning (Jaskuslky and Besel 2013 ; Hung and Bayrak 2020 ). The first study found that American undergraduate students expressed the least concern about rising temperatures after reading a news story about the “climate crisis,” as compared to “climate change,” or “global warming” (Jaskulsky and Besel 2013 ). The second study was conducted with Taiwanese adults, and found no differences in their reported concerns or willingness to act when they were asked about the “climate crisis” or “climate change” (Hung and Bayrak 2020 ). However, people with individualistic or hierarchical world views reported relatively less willingness to act on the “climate crisis” than on “climate change” (Hung and Bayrak 2020 ). While these findings suggest that saying “climate crisis” or “climate emergency” could potentially be counterproductive (Jaskulsky and Besel 2013 ; Hung and Bayrak 2020 ; Feldman and Hart 2021 ), public responses to terms change over time (Schuldt et al. 2020 ; Benjamin et al. 2017 ).

We found no national experiments that examined the relative benefits of using the term “climate justice” as compared to other terms. As noted, the term “climate justice” was introduced by left-leaning grassroots organizations to emphasize the unfairness of unequal vulnerabilities to climate change (Dutta 2019 ; Schlosberg and Collins 2014 ), and linking climate policy to justice may improve public support (Bergquist et al. 2020 ). However, one study that examined U.S. residents’ familiarity with the concept found that only 37–44% was aware that climate change affects “some groups more than others” (Schuldt and Pearson 2023 ). Moreover, a study in the United Kingdom found that narratives that focus on “climate justice” are politically polarizing because they resonate with left-leaning audiences and are off-putting to right-leaning audiences (Whitmarsh and Corner 2017 ). It remains an open question how the term “climate justice” will be received by U.S. residents with different political leanings.

1.5 The current study

Here, we aimed to examine public responses to terms that emphasize different aspects of climate change, and whether these responses differed by respondents’ political leaning. Specifically, we conducted a national terminology experiment in which we randomly assigned a nationally representative sample of 5,137 U.S. adults to survey questions about the terms “climate change,” “global warming,” “climate crisis,” “climate emergency,” and “climate justice.” Our first research aim was to examine the effect of terminology on participants’ ratings of familiarity, concern, perceived urgency, willingness to support policies, and willingness to eat less red meat. Thus, we incorporated measures of beliefs and intentions to act, in recognition of previous findings suggesting that the use of different terms is more likely to affect beliefs than intentions to act (Benjamin et al. 2017 ). Willingness to eat less red meat was included because the IPCC ( 2019 ; 2022 ) has recommended this dietary shift as a major opportunity for reducing greenhouse gas emissions, which would, in turn, curb climate change and its disproportionate impact on vulnerable communities. Our second research aim was to examine whether the effects of the randomly assigned terms on ratings of familiarity, concern, urgency, willingness to support climate-friendly policies, and willingness to eat less red meat were moderated by Democratic, Republican, or Independent/other political leaning.

Our sample includes 5,137 participants of the Understanding America Study, a national survey panel directed by the University of Southern California’s Understanding America Study (UAS), including 1,852 Democrats, 1,697 Republicans, and 1,588 Independent/others. Panel members were recruited from randomly selected U.S. addresses, sampling probabilities were adjusted for underrepresented populations, and internet-connected tablets were provided to interested individuals if needed. They are regularly invited to complete surveys and receive $20 for each 30 minutes of participation.

Initially, 7,607 participants were invited to complete a survey that asked about their political leaning. Only those 5,763 (75%) who reported their political leaning were eligible for our survey. Of those, 5,137 (89%) completed our survey, thus retaining 68% of original invitees. Figure S1 shows the flowchart of participants’ pathway through the surveys. Table  1 compares sample demographics to 2022 population statistics from the U.S. Census, before and after applying post-stratification weights. These post-stratification weights, generated through a raking algorithm, were used in all analyses to align the sample to the U.S. adult population, in terms of age, gender, race/ethnicity, education, and geographic location (see www.uasdata.usc.edu/page/Weights ).

2.2 Procedure

Participants were randomly assigned to receive questions about “climate change” (unweighted N  = 1,071), “global warming” (unweighted N  = 1,009), “climate crisis” (unweighted N  = 1,037), “climate emergency” (unweighted N  = 1,014), and “climate justice” (unweighted N  = 1,006). Table S1 shows demographic characteristics of participants who completed our questions about each randomized term. Participants received five questions about their assigned term (Table  2 ). The questions about willingness to support policies and willingness to eat less red meat were preceded by a sentence that mentioned the assigned term (Table  2 ). Survey design research suggests that people take into account such preceding sentences when interpreting survey questions (Schwarz 1999 ). As is common practice on the UAS, we also offered a Spanish version of our survey (Table S3 ), even though few UAS participants tend to select it. Indeed, most American residents of Hispanic origin are proficient in English (Pew Research Center 2023b ).

Our survey was conducted in June-August 2023 (survey #556 of the Understanding America Study; https://uasdata.usc.edu/index.php ). In December 2022-February 2023, participants had been asked “regardless of how you are registered to vote, are you more closely aligned with…” (survey #500 of the Understanding America Study; https://uasdata.usc.edu/index.php ). They could indicate Democrat, Republican, Independent (no party), Libertarian, Green Party, some other party, or not aligned with any party. Participants indicating the latter five responses were classified as Independents/others. Table S2 shows that self-reported political leaning was significantly associated with each demographic characteristic, with Republicans being the least likely to indicate wanting the Spanish survey version, or being 65 or younger, female, college-educated, or from a racial/ethnic minority group.

2.3 Analyses

For ease of interpretation, we present the percent of participants who gave a positive response by using the top half of the 4-point rating scale for each of our dependent variables (Table  3 ). Terms’ mean ratings of familiarity, concern, perceived urgency, willingness to support policies, and willingness to eat less red meat appear in Figs.  1 and 2 . Our main analyses treated each rating as a continuous variable. For each rating, we conducted a separate Analysis of Covariance in which we examined the effect of terminology (“climate change,” “global warming,” “climate crisis,” “climate emergency,” or “climate justice”) and political leaning (Democrat, Republican, or Independent/other) as well as their interaction (Table 4 ). Because demographic characteristics were associated with political leaning (Table S2 ), covariates included selecting the Spanish (vs. English) survey version, being aged 65 or older (vs. not), being female (vs. not), having a college degree (vs. not), and identifying with the three largest race/ethnicity groups, including Hispanic (vs. not), Non-Hispanic White (vs. not) or Non-Hispanic Black (vs. not). Overall conclusions were unaffected by including or excluding these covariates. We computed partial η 2 to assess the effect size for each main effect and the interaction. For partial η 2 , 0.01 reflects a small effect size, 0.06 a medium effect size, and 0.14 a large effect size (Cohen 1969 ). We treated significant effects with a partial η 2  < 0.01 as showing no meaningful difference.

Mean reported ( A ) familiarity, ( B ) concern, ( C ) urgency, ( D ) willingness to support policies, and ( E ) willingness to eat less red meat by term

Note: Survey questions and response scales are described in Table  2 . Poststratification weights were used in these analyses. Error bars reflect standard errors. Significance tests of pairwise comparisons between terms are reported in Table S4

Mean reported ( A ) familiarity, ( B ) concern, ( C ) urgency, ( D ) willingness to support policies, and ( E ) willingness to eat less red meat, by term and political leaning

Note: Survey questions and response scales are described in Table  2 . Poststratification weights were used in these analyses. Error bars reflect standard errors. Significance tests of pairwise comparisons between terms are reported in Table S5 - S7

To address our first research aim, we examined the main effect of the randomly assigned term on participants’ ratings of familiarity, concern, perceived urgency, willingness to support policies, and willingness to eat less red meat elicited by the terms (Table 4 ). We also conducted pairwise comparisons of terms with Bonferroni-corrected p -values to adjust for the number of tests (Table S4 ).

To address our second research aim, we examined the interaction effect of the randomly assigned term and participants’ political leaning, on ratings of familiarity, concern, urgency, willingness to support climate-friendly policies, and willingness to eat less red meat (Table 4 ). To better understand these interactions, we conducted a separate Analyses of Covariance on each rating to examine the effect of terms among Democrats, Republicans, and Independents/others, using the same covariates (Table 5 ). For these analyses, we also report effect sizes (Table 5 ) and pairwise comparisons with Bonferroni-corrected p -values (Table S5 - S7 ).

In auxiliary analyses, we examined the role familiarity played in reported urgency, willingness to support climate-friendly policies, and willingness to eat less red meat. This involved an Analyses of Covariance in which we added familiarity and its interactions with the randomly assigned term, political leaning, or both, using the same covariates as mentioned above (Table 6 ). We also conducted separate Analyses of Covariance to examine the effect of familiarity by term and political leaning (Table S8 - S9 ). Familiarity was dichotomized for these auxiliary analyses to facilitate interpretations of these auxiliary analyses, treating “somewhat familiar” and “very familiar” as familiar and treating “not familiar at all” and “not that familiar” as unfamiliar. As noted, post-stratification weights were used in all analyses (see www.uasdata.usc.edu/page/Weights ).

3.1 Familiarity

A majority of participants indicated being very familiar or somewhat familiar with “climate change,” “global warming,” “climate crisis,” or “climate emergency,” but not “climate justice” (Table  3 ). However, ratings of familiarity varied across terms (Fig.  1 A), seen in a significant main effect with a large effect size (Table 4 ). “Climate change” and “global warming” received the highest ratings of familiarity (Fig.  1 A), with pairwise comparisons suggesting that both terms were rated as similarly familiar and significantly more familiar than each of the other terms (Table S4 ). “Climate justice” was rated as the least familiar (Fig.  1 A), and significantly less familiar than each of the other terms (Table S4 ). The other two terms fell in between (Fig.  1 A), with “climate crisis” rated as significantly more familiar than “climate emergency” (Table S4 ).

A breakdown by political leaning showed that a large majority of Democrats, Republicans, and Independents/others were familiar with the terms “climate change,” and “global warming” (Table  3 ). A somewhat smaller majority in each group reported being familiar with the terms “climate crisis,” and “climate emergency” (Table  3 ). In each political group, “climate justice” was the least familiar, with the majority rating it as unfamiliar rather than familiar (Table  3 ). Ratings of familiarity also showed this relative pattern across terms (Fig.  2 A). Democrats and Independents/others were generally somewhat more familiar with the terms than Republicans (Fig.  2 A), seen in a significant main effect of political leaning on familiarity ratings with a small effect size (Table 4 ). More importantly, we found a significant interaction between terms and political leaning with a small effect size (Table 4 ): The effect of terms on familiarity ratings was somewhat more pronounced for, in order, Republicans, Independents/others, and Democrats (Table 5 ). “Climate crisis,” “climate emergency” and “climate justice” were each significantly less familiar than “climate change” and “global warming” for each political leaning (Table S5 - S7 ), but “climate justice” was especially unfamiliar to Republicans (Fig.  2 A).

3.2 Concern

A majority of participants expressed being very concerned or somewhat concerned with “climate change,” “climate change,” “climate crisis,” or “climate emergency,” but not “climate justice” (Table  3 ). Ratings of concern varied across terms (Fig.  1 B), resulting in a significant main effect with a medium effect size (Table  6 ). “Climate change” and “global warming” were rated as eliciting the most concern (Fig.  1 B), with pairwise comparisons suggesting that both terms elicited similar concern and at least somewhat more concern than each of the other terms (Table S4 ). “Climate justice” was rated as the least concerning (Fig.  1 B) and received significantly lower ratings of concern than each of the other terms (Table S4 ). The other two terms fell in between (Fig.  1 B), with “climate crisis” raising similar concern as “climate emergency” (Table S4 ).

A breakdown by political leaning shows that most Democrats and Independents/others were concerned about each term, except for “climate justice,” which only raised concern among a majority of Democrats (Table  3 ). No term raised enough concern to reach a majority among Republicans (Table  3 ). Indeed, we found a significant main effect of political leaning on ratings of concern with a large effect size (Table  4 ): Concern was generally highest among Democrats and lowest among Republicans, with Independents/others falling in between (Fig.  2 B). There was no significant interaction between terms and political leaning (Table  4 ): For every political leaning, “climate justice” consistently elicited the least concern (Fig.  2 B), and received significantly lower ratings of concern than every other term (Table S5 - S7 ).

3.3 Urgency

Most participants felt that it was somewhat urgent or very urgent to do something about “climate change,” “global warming,” “climate crisis,” “climate emergency,” and “climate justice” (Table  3 ). Ratings of urgency varied across terms (Fig.  1 C), as seen in a significant main effect with a relatively small effect size (Table  4 ). “Climate change,” “global warming,” climate crisis,” and “climate emergency” were all rated as similarly urgent, except that “global warming” was rated as slightly more urgent than “climate crisis” (Table S4 ). “Climate justice” was rated as significantly less urgent than all other terms (Table S4 ).

A majority of Democrats and Independents/others perceived urgency to do something about each term– but not Republicans (Table  3 ). Indeed, there was a significant main effect of political leaning on urgency ratings with a large effect size (Table 4 ): Perceived urgency was highest among Democrats and lowest among Republicans (Fig.  2 C). More importantly, the effect of terms on ratings of urgency varied by political leaning (Fig.  2 C), as seen in a significant interaction between terms and political leaning with a large effect size, F (2, 4441) = 2.97, partial η 2  = 0.26, p  < 0.01. The effect of terms on urgency ratings showed a medium effect size among Democrats, and a small effect size among Republicans, with Independent/others falling in between (Table 5 ). Both Democrats and Independent/others rated each term as significantly more urgent than “climate justice,” while Democrats also rated “global warming” as significantly more urgent than “climate emergency” (Table S5 - S7 ). Republicans’ ratings of urgency showed few significant differences between terms, except that they rated “global warming” and “climate emergency” as somewhat more urgent than “climate justice” (Table S6 ).

3.4 Willingness to support policies

A majority of participants reported being somewhat willing or very willing to support policies to do something about “climate change,” “global warming,” “climate crisis,” “climate emergency,” and “climate justice” (Table  3 ). Ratings of policy support did not vary meaningfully across terms (Fig.  1 D), as seen in a significant main effect with a very small effect size (Table 4 ). Pairwise comparisons suggested that ratings of policy support were mostly similar across terms, except that “global warming” received significantly higher ratings of policy support than “climate justice” despite the difference being small (Table S4 ).

A majority of Democrats and Independents/others supported policies to do something about each term (Table  3 ). Even among Republicans, a slight majority indicated willingness to support policies to do something about each term, with the lowest support still being at 50% for “climate change” (Table  3 ). Yet, there was a significant main effect of political leaning on ratings of willingness to support policies with a large effect size (Table 4 ): Democrats showed the highest and Republicans the lowest willingness to support policies. There was no significant interaction between terms and political leaning (Table 4 ). Pairwise comparisons of terms within each political group found no significant differences, except that Independent/others responded slightly more positively to “global warming” than to “climate crisis” (Table S5 - S7 ).

3.5 Willingness to eat less red meat

A majority of participants reported being somewhat willing or very willing to eat less red meat to do something about “climate change,” “climate change,” “climate crisis,” “climate emergency,” and “climate justice” (Table  3 ). Ratings of willingness to eat less red meat did not vary meaningfully across terms (Fig.  1 E), as seen in a significant main effect with a very small effect size (Table  4 ). Indeed, pairwise comparisons found only two small significant differences, suggesting that “global warming” and “climate emergency” received somewhat higher ratings for willingness to eat less red meat, compared to “climate justice” (Table S4 ).

A majority of Democrats and Independents/others, but not Republicans, indicated being willing to eat less red meat independent of the term that was used (Table  3 ). Rated willingness to eat less red meat was indeed highest among Democrats and lowest among Republicans (Fig.  2 E), as confirmed in a significant main effect of political leaning with a large effect size (Table  4 ). There was no significant interaction between terms and political leaning (Table  4 ). Indeed, pairwise comparisons of terms within each political group found no significant differences, except that Democrats responded slightly more positively to “global warming” than to “climate justice” (Table S5 - S7 ).

3.6 Auxiliary analysis

Among participants who found a term unfamiliar (vs. familiar), ratings of concern, urgency, willingness to support climate-friendly policies, and willingness to eat less red meat were generally lower (Fig.  3 ). Familiarity had a significant effect on each of these dependent variables, with a medium effect size for concern, and a smaller effect size for perceived urgency, willingness to support policies, and willingness to eat less red meat (Table  6 ). The effect of familiarity did not significantly vary with the randomized term, with two exceptions: There was a significant interaction with a small effect size for willingness to support climate-friendly policies and for willingness to eat less red meat (Table 6 ), which suggested that the effect of familiarity was the least pronounced for “climate justice” (Fig.  3 ; Table S8 ).

Mean reported ( A ) concern, ( B ) urgency, ( C ) willingness to support policies, and ( D ) willingness to eat less red meat by term and familiarity

Note: Familiarity was dichotomized, treating “somewhat familiar” and “very familiar” as familiar and treating “not familiar at all” and “not that familiar” as unfamiliar. Survey questions and response scales are described in Table  2 . Poststratification weights were used in these analyses. Error bars reflect standard errors. Significance tests are reported in Table S8

The effect of familiarity did significantly vary by political leaning, seen in a significant interaction with a small effect size for each dependent variable (Table  6 ). Specifically, while familiarity tended to make no difference for Republicans, Democrats and Independents/others generally responded more strongly if a term was familiar (Figure S2 - S4 ), with effect sizes typically being largest among Democrats (Table S9 ). Three-way interactions between familiarity, randomized term and political leaning had a very small effect size for each dependent variable (Table  6 ), suggesting no meaningful variation.

4 Discussion

Psychological theories of attitude formation suggest that attitudes about a topic are influenced by topic-related information that comes to mind in the moment (Schwarz 2007 ; Sudman et al. 1996 ). Therefore, it has been posited that changing terms to emphasize different aspects of “climate change” may influence public concern and willingness to act (e.g. Schuldt et al. 2011 ). In a national terminology experiment, we therefore compared public responses to the term “climate change” as well as alternative terms that emphasize different aspects of the phenomenon: “global warming,” “climate crisis,” “climate emergency,” and “climate justice.” Although the terms “climate change” and “global warming” are often used interchangeably in public discourse, “climate change” refers to diverse changes in the climate while seemingly de-emphasizing human activity, and “global warming” refers to increasing global surface temperatures and implies that this is due to humans actively warming the planet (Penz 2017 ). The terms “climate crisis,” “climate emergency,” and “climate justice” have more recently been introduced to emphasize urgency (Schäfer et al. 2023 ). The term “climate justice” has been used by left-leaning grassroots organizations to emphasize the unfairness of unequal vulnerabilities (Dutta 2019 ; Schlosberg and Collins 2014 ).

Across a national U.S. sample, we found that the more traditional terms “climate change” and “global warming” were rated as more familiar than the relatively newer terms “climate crisis” and “climate emergency.” Perhaps due to being less familiar, the terms “climate crisis” and “climate justice,” which were introduced to emphasize urgency (Schäfer et al. 2023 ), actually elicited somewhat less concern. Moreover, "climate crisis" or "climate emergency" did not elicit greater perceptions of urgency than “climate change” and “global warming.” The term “climate justice” was least familiar and generally performed most poorly on all dependent measures. This may, in part, reflect low familiarity with the idea that climate change disproportionally affects vulnerable communities (Schuldt and Pearson 2023 ). Additionally, the term “climate justice” may resonate less with people than the other terms.

Respondents’ willingness to support policies and willingness to eat less red meat were generally less affected by the presented terms than their ratings of concern and urgency. This finding is in line with previous suggestions that terminology effects are stronger for beliefs than for willingness to act, with the latter having a higher threshold (Benjamin et al. 2017 ). However, our study suggested that both willingness to support policies and willingness to eat less red meat were lowest in response to “climate justice.” If people are unaware of the disproportionate effect of climate change on vulnerable communities (Schuldt and Pearson 2023 ), they may find it harder to see the need to act on it even if they have heard of the term “climate justice.”

Because of demonstrated partisan differences in responses to terminology, we also examined how responses to terms varied between individuals who leaned Democrat, Republican, or Independent/other (e.g., Akerlof and Maibach 2011 ; Schuldt et al. 2011 ; Villar and Krosnick 2011 ). Effects of terms varied by participants’ political leaning, but only for ratings of familiarity, concern, and perceived urgency– with willingness to act only showing main effects of terms and of political leaning. All political groups were familiar with the more traditional terms “climate change” and “global warming,” relatively less familiar with “climate crisis” and “climate emergency,” and least familiar with “climate justice.” Those terminology effects on familiarity were most pronounced among Republicans, who were especially unfamiliar with “climate justice.” For ratings of concern and perceived urgency, terminology effects showed large effect sizes. Terminology effects on ratings of concern and perceived urgency were most pronounced for Democrats, with a relatively larger benefit of using the traditional terms “climate change” or “global warming” instead of “climate justice.” Thus, unlike in the United Kingdom (Whitmarsh and Corner 2017 ), “climate justice” did not appear to polarize American audiences much along political lines– perhaps because the issue is currently not yet that familiar in the U.S. (Schuldt and Pearson 2023 ).

Nevertheless, a consistent finding across all political groups was that “climate change” and “global warming” performed similarly well, and about as well or better than alternative terms on all outcome variables. Even though the terms “climate change” and “global warming” were differentially favored by Democrats and Republicans in the past, there is a growing trend to treat these two terms as interchangeable (Benjamin et al. 2017 ). Even among Independents/others we now find that these two terms elicit similar responses, while in 2012 they were the last group to respond differentially (and more positively) to “climate change” vs. “global warming” (Benjamin 2017 ).

In line with psychological theories of attitude formation (Schwarz 2007 ; Sudman et al. 1996 ), these findings suggest that it matters somewhat which terms we use for climate change. Specifically, “climate change” and “global warming” are likely the most effective terms to use, followed by “climate crisis” and “climate emergency,” with “climate justice” being the least effective. However, our findings also suggest a need to temper the conclusion that climate terms matter, for two reasons. First, the effect of terms was less strong for willingness to support policies and willingness to eat less red meat, than for expressed concern, and perceived urgency. This finding is in line with previous reports that terminology effects tend to be smaller for willingness to act than for expressed beliefs (Benjamin et al. 2017 ). Second, the effect of political ideology was stronger than the effect of terminology for expressed concern, perceived urgency, willingness to support policies, and willingness to eat less red meat, in line with previous suggestions that Americans follow the views of their political party (van Boven et al., 2018 ). That is, Republicans generally responded most negatively to presented terms. The relative advantage of using the terms “climate change” or “global warming” was also the lowest among Republicans. Hence, changing the terms we use is likely not the key solution for promoting climate action.

4.1 Limitations

Like any study, ours has limitations. First, our study presents only one snapshot in time, and the popularity and effectiveness of terms may change over time (Penz 2017 ; Schuldt et al. 2020 ; Benjamin et al. 2017 ). The term “climate justice” may increase willingness to act, as it becomes more familiar. Yet, it is possible that “climate justice” will become politically polarizing as it becomes more familiar, following findings from the United Kingdom, where the “justice” framing resonates with left-leaning audiences while right-leaning audiences find it off-putting (Whitmarsh and Corner 2017 ). Second, we did not assess how participants interpreted each term, or the reasoning behind their responses. It is possible that those who said that they were familiar with a term did not know what it meant, or that those who said that they were unfamiliar with a term were nevertheless able to make an educated guess that affected their responses. Moreover, people may have perceived “climate change” as the main concern, and “climate justice” as a secondary outcome. Third, we presented terms without further explanation, to test the effect of their mere usage on public responses. Providing definitions of less familiar terms like “climate justice” is likely needed to raise public awareness that climate change affects some more than others (Schuldt and Pearson 2023 ). Many people are also unaware that eating less red meat can reduce greenhouse gas emissions (Kause et al. 2019 ), and may therefore benefit from information about how eating less red meat could curb climate change and its impacts on vulnerable communities. Fourth, questions about willingness to support policies and willingness to eat less red meat were preceded by a sentence that mentioned the randomly assigned term (Table  2 ). However, survey design research suggests that people do take into account such preceding sentences when interpreting survey questions (Schwarz 1999 ). Fifth, we only examined willingness to eat less red meat as a personal action, and not willingness to engage in other actions to reduce carbon emissions. Sixth, our study was conducted during an exceptionally hot summer that brought unprecedented heat waves, droughts, and wildfires across the U.S. Because the term “global warming” tends to elicit thoughts of these hot weather events, participants may have expressed relatively more concern about “global warming” than they might have otherwise (Whitmarsh 2009 ). Seventh, in line with most previous studies, we focused on how terminology effects varied with participants’ political leaning (e.g., Schuldt et al. 2011 ; Vilnar et al. 2011). However, participants’ climate change beliefs may be more complex (Benjamin et al. 2017 ), and that complexity may affect how they respond to presented terms. Eighth, our study only focused on the U.S., and different terms may be more effective for communicating about climate change in other countries. For example, people in Africa may be more likely to indicate that they are perceiving long-term severe weather changes than that they are perceiving climate change (Bruine de Bruin and Dugan 2022 ).

4.2 Conclusion

The terms we use to talk about climate change matter, but only somewhat. The traditional terms “climate change” and “global warming” are generally familiar, among Democrats, Republicans, and Independents/others. The newer terms “climate crisis,” “climate emergency,” and “climate justice” are generally less familiar, and may not raise as much concern as the traditional terms “climate change” and “global warming.” Sticking with familiar terms is advisable because public responsiveness may be lower when terms are unfamiliar. Although we did not test the term “climate upheaval,” which has recently been introduced to emphasize the sudden worrisome change associated with climate change (Chen 2024 ), we suspect that it will be more effective to stick with the familiar terms “climate change” and “global warming.” Indeed, interviews with climate-concerned and climate-ambivalent Americans found that they wanted climate change communications to use familiar terms (Bruine de Bruin et al. 2021 ). This finding was replicated in Germany (Wege et al. 2024 ).

However, terms’ effects on willingness to act were small at best, and Republicans were often unresponsive. Climate change communications may therefore need to go beyond terminology to promote willingness to act. For example, effective communication strategies include using compelling everyday language, presenting clear graphs, emphasizing social norms, and making climate-friendly actions the default (Bruine de Bruin et al. 2021 ; Bruine de Bruin et al. 2024; Constantino et al. 2022 ; Nisa et al. 2019 ; Sleboda et al. 2024 ; Wege et al. 2024 ). Moreover, efforts to reach Republicans may require messages from Conservative spokespeople, and involving the private sector in climate change mitigation (Goldberg et al. 2021 ; Gillis et al. 2021 ).

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Acknowledgements

We thank the team of the Understanding America Study at the University of Southern California’s Center for Economic and Social Research for data collection, especially Jill Darling and Bart Orriens.

We gratefully acknowledge funding from the University of Southern California’s Wrigley Institute for Environmental Studies. Bruine de Bruin was additionally supported by a gift from the Golden Belt Community Foundation.

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Bruine de Bruin, W., Kruke, L., Sinatra, G.M. et al. Should we change the term we use for “climate change”? Evidence from a national U.S. terminology experiment. Climatic Change 177 , 129 (2024). https://doi.org/10.1007/s10584-024-03786-3

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