The United States has based its climate change policies on the conclusions of the Intergovernmental Panel on Climate Change, which has provided an authoritative international consensus on the science of climate change.
The U.S. Global Change Research Program (USGCRP) provides a major contribution to the research base on which the IPCC assessments rely. The USGCRP was formally established by Congress in 1990 to coordinate the resources and research activities of a dozen federal agencies, especially national research activities and U.S. participation in international research activities supporting programs such as the World Climate Research Programme, the International Geosphere-Biosphere Programme, and the Human Dimensions Programme. The USGCRP coordinates a broad agenda of research, supporting the Mission to Planet Earth, ozone depletion studies, and work on the human dimensions of global change. Questions that drive the USGCRP's climate change research include:
- What is the climate's response to increasing concentrations of aerosols and greenhouse gases?
- What are the impacts of climate change on society and the environment?
- How can society mitigate future climate change or adapt to its consequences?
Based on these questions, research focuses on observing and documenting Earth system behavior; understanding the processes that influence changes in the Earth system; developing and applying models to predict climate change; evaluating the effects of climate change on agriculture, forests, water resources, coastal regions, ecosystems, and other natural resources; and improving the capabilities to mitigate adverse consequences and capitalize on any beneficial opportunities that climate change may present. Because the importance of climate change depends largely on the physical and economic impacts on human society, USGCRP has started to shift its funding toward increased evaluation of the socio-economic implications of climate change.
Recent Accomplishments of the USGCRP
- Climate models successfully simulated the transient cooling of the lower atmosphere in response to the sulfates emitted by the eruption of Mt. Pinatubo.
- The improved ability to forecast El Niņo and resulting shifts in tropical and subtropical precipitation is helping farmers in North and South America to plan better and thereby boost yields and reduce economic disruptions.
- Model simulations of changes in climate over the last 100 years match observed patterns more closely when both greenhouse gases and the regional concentrations of sulfate aerosols are taken into account.
- Combined satellite and surface measurements recently identified an unexpected absorption of 25-40 watts per square meter of radiation by the atmosphere. This new information will lead to a reanalysis of the Earth's radiation balance and the role of clouds in climate change.
- Observations show that since 1970, precipitation over the U.S. has increased by about 5 percent compared with the previous 70 years, primarily in the autumn. In addition, the frequency of extreme rainfall events (more than 2" per day) has increased throughout much of the country.
- Arctic ecosystems exposed to elevated levels of carbon dioxide only increased productivity for a few years, suggesting that the CO2 fertilization effect may be short-lived.
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U.S. Global Change Research Program (USGCRP) 
Intergovernmental Panel on Climate Change (IPPC)