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Climate Change Science Overview

Earth’s climate is changing in ways that affect our weather, oceans, snow, ice, ecosystems, and society.

Natural causes alone cannot explain all of these changes. Human activities are contributing to climate change, primarily by releasing billions of tons of carbon dioxide (CO2) and other heat-trapping gases, known as greenhouse gases, into the atmosphere every year. [1]

Climate changes will continue into the future. The more greehouse gases we emit, the larger future climate changes will be.

Photo of cars on a highwayPhotograph of clear-cut forest with standing trees in the distance.Photograph of smokestacks and power lines.

Human activities, like driving, manufacturing, electricity generation, and the clearing of forests contribute to greenhouse gas emissions and warm the planet.
Sources: EPA 2010, EPA 2011, USGCRP 2008

Changes in the climate system affect our health, environment, and economy. We can prepare for some of the impacts of climate change to reduce their effects on our well-being.

Earth’s climate is changing

The global average temperature increased by more than 1.3°F over the last century.[2] The average temperature in the Arctic rose by almost twice as much. [2] The buildup of greenhouse gases in our atmosphere and the warming of the planet are responsible for other changes, such as:

Learn more about the indicators of climate change.

Temperatures across the world in the 1880s (left) and the 1980s (right)

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These maps show temperatures across the world in the 1880s (left) and the 1980s (right), as compared to average temperatures from 1951 to 1980. This difference from average is called an anomaly. The map on the left shows that it was colder in the 1880’s in most places. The map on the right shows it was warmer in the 1980s in most places. Earth’s average surface temperature has increased almost 1.5°F during the 20th century. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.3°F-0.4°F per decade.
Source: NASA

Climate Change versus Global Warmning

Click on the image to open a pop-up that explains the differences between climate change and global warming.

The CO2 that humans have added to the atmosphere has caused an increase in the atmospheric concentration of CO2. The graph shown here, called a Keeling Curve after the scientist who first developed it, represents the record of increased global atmospheric carbon dioxide concentration.

Click on the image to open a pop-up that shows a larger version of this image, plus text that explains the differences between weather and climate.

Natural causes alone cannot explain recent changes

Line graph with a line that show the observed temperature increases, a blue band that show how the temperature would have changed over the past century due to only natural forces, and a red band that shows the combined effects of natual and human forces. The blue band that shows natural forces starts and ends the 20th century just above 56 degrees Fahrenheit. The actual observed global average temperatures closely follows the model projections that use both human and natural forces - beginning in 1900 at just above 56 degrees Fahrenheit and ending in 2000 around 58 degrees Fahrenheit.

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Models that account only for the effects of natural processes are not able to explain the warming over the past century. Models that also account for the greenhouse gases emitted by humans are able to explain this warming.
Source: USGRCP 2009

Line graph with three trend lines that represent concentration of carbon dioxide, methane, and nitrous oxide over time. The three gasses follow a very similar pattern that starts low and is steady from year zero until sometime around 1900 where the concentration of all three gasses start increasing dramatically. In the first 1900 years carbon dioxide and nitrous oxide remain at levels around 280 parts per million and 250 parts per billion, respectively. By 2000, carbon dioxide measures around 380 parts per million and nitrous oxide measures around 320 parts per billion. Similarly methane remains at approximately 700 parts per billion until around 1800. By 2000, methane concentrations measure close to 2000 parts per billion.

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This graph shows the increase in greenhouse gas (GHG) concentrations in the atmosphere over the last 2,000 years. Increases in concentrations of these gases since 1750 are due to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion molecules of air.
Source: USGCRP 2009

Natural processes such as changes in the sun’s energy, shifts in ocean currents, and others affect Earth’s climate. However, they do not explain the warming that we have observed over the last half-century. [1]

Human causes can explain these changes

Most of the warming of the past half century has been caused by human emissions of greenhouse gases. [1] Greenhouse gases come from a variety of human activities, including: burning fossil fuels for heat and energy, clearing forests, fertilizing crops, storing waste in landfills, raising livestock, and producing some kinds of industrial products.

Greenhouse gas emissions are not the only way that people can change the climate. Activities such as agriculture or road construction can change the reflectivity of Earth’s surface, leading to local warming or cooling. This effect is observed in urban centers, which are often warmerthan surrounding, less populated areas. Emissions of small particles, known as aerosols, into the air can also lead to reflection or absorption of the sun’s energy.

Learn more about past and present climate trends and their causes.

Climate will continue to change unless we reduce our emissions

During the 21st century, global warming is projected to continue and climate changes are likely to intensify. Scientists have used climate models to project different aspects of future climate, including temperature, precipitation, snow and ice, ocean level, and ocean acidity. Depending on future emissions of greenhouse gases and how the climate responds, average global temperatures are projected to increase worldwide by 2°F to 11.5°F by 2100. [1] Learn more about the projections of future climate change.

Climate change impacts our health, environment, and economy

Climate change affects our environment and natural resources, and impacts our way of life in many ways. For example:

  • Warmer temperatures increase the frequency, intensity, and duration of heat waves, which can pose health risks, particularly for young children and the elderly.
  • Rising sea levels threaten coastal communities and ecosystems.
  • Changes in the patterns and amount of rainfall, as well as changes in the timing and amount of stream flow, can affect water supplies and water quality and the production of hydroelectricity.
  • Changing ecosystems influence geographic ranges of many plant and animal species and the timing of their lifecycle events, such as migration and reproduction.
  • Increases in the frequency and intensity of extreme weather events, such as heat waves, droughts, and floods, can increase losses to property, cause costly disruptions to society, and reduce the availability and affordability of insurance.

We can prepare for some of the likely climate change impacts to reduce their effect on ecosystem and human well-being. Making such preparations is known as adaptation. Examples of adaptation include strengthening water conservation programs, upgrading stormwater systems, developing early warning systems for extreme heat events, and preparing for stronger storms through better emergency preparation and response strategies.

Learn more about how climate change impacts are expected to affect different U.S. regions and sectors and how we can prepare.

Temperature increases and other climate changes may directly impact our food and water supply, ecosystems, coasts, and human health. The bars in the bottom box indicate what temperatures and impacts are expected under the high and low emissions scenarios, which are determined by our actions.

This slideshow describes some of the projected climate change impacts to key sectors, among other topics. Click the image above to play the slideshow.

References:

[1] NRC (2010). Advancing the Science of Climate Change Exit EPA Disclaimer . National Research Council. The National Academies Press, Washington, DC, USA.

[2] IPCC (2007). Climate Change 2007: Synthesis Report Exit EPA Disclaimer . Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Pachauri, R.K. and A. Reisinger (eds.)]. Geneva, Switzerland.

[3] IPCC (2012) Exit EPA Disclaimer . Summary for Policymakersin: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[4] Le Treut, H., R. Somerville, U. Cubasch, Y. Ding, C. Mauritzen, A. Mokssit, T. Peterson and M. Prather (2007). Historical Overview of Climate Change Science. In: Climate Change 2007: The Physical Science Basis Exit EPA Disclaimer .Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change[Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Basic InformationGreenhouse Gas EmissionsScienceWhat EPA is Source: United States Environmental Protection Agency, “Climate Change Science Overview” http://www.epa.gov website. Accessed November 24, 2015. http://www.epa.gov/climatechange/science/overview.html

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