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. 
Climate changes will continue into the future. The more greehouse gases we emit, the larger future climate changes will be.
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. The average temperature in the Arctic rose by almost twice as much.  The buildup of greenhouse gases in our atmosphere and the warming of the planet are responsible for other changes, such as:
- Changing precipitation patterns  
- Increases in ocean temperatures, sea level, and acidity
- Melting of glaciers and sea ice 
Learn more about the indicators of climate change.
Natural causes alone cannot explain recent changes
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. 
Human causes can explain these changes
Most of the warming of the past half century has been caused by human emissions of greenhouse gases.  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.  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.
 NRC (2010). Advancing the Science of Climate Change . National Research Council. The National Academies Press, Washington, DC, USA.
 IPCC (2007). Climate Change 2007: Synthesis Report . 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.
 IPCC (2012) . 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.
 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 .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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