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US Climate Change Science Program provides key contributions to IPCC fourth assessment

US plays major role in IPCC Report

NOAA Research

Research conducted by scientists funded through the U.S. Climate Change Science Program (CCSP) has helped resolve key uncertainties about the causes of global climate change and has helped refine projected future changes in temperature and sea-level rise, as published in the Working Group I contribution to the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, the summary of which was issued on 2 February 2007.

CCSP assessment activities significantly contributed to the IPCC's increased confidence attributing much of the temperature increase since the mid-20th century to human activities.

U.S. observation networks, computer modeling labs, and research programs provide a strong foundation of science advancements, data, and analyses for the IPCC Report. In large part, these national efforts were coordinated through the CCSP, a body comprised of 13 federal departments and agencies and dedicated to integrating U.S. government-supported research on climate and global change.

"CCSP participates in and accepts the findings of the IPCC," said Dr. William Brennan, acting director of CCSP. "Through the focused efforts of the CCSP, we are making true breakthroughs in our understanding of how our planet's climate is continuing to change, and there is no better example than our program's contribution to the latest IPCC report which strongly links humans to climate change," said Dr. Brennan. "More than ever, research is critical to understanding the degree to which climate will change, what the impacts will be, and where we will see them."

A key report by the CCSP, the first in a series of CCSP synthesis and assessment products to be produced over the next two years, is "Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences." Prior to this synthesis and assessment product, climate scientists could not reconcile an apparent discrepancy in the rate of global surface temperature increase with a much slower rate of increase higher in the atmosphere. This study resolved this discrepancy and increased confidence in the understanding of observed climatic changes. It also showed clear evidence of human influences on the climate system due to changes in greenhouse gases, aerosols and stratospheric ozone. This report was a significant factor in IPCC increasing its confidence in the influence of anthropogenic greenhouse gases on the temperature increase since the mid-20th century from "likely" (more than 66% likelihood) to "very likely" (more than 90% likelihood).

CCSP climate modeling groups performed an unprecedented set of coordinated 20th- and 21st-century climate change experiments for the IPCC Fourth Assessment Report in addition to greenhouse gas stabilization experiments extending to the 22nd century. These model simulations were included in IPCC's analysis which concluded that "for the next two decades a warming of about 0.2°C per decade is projected for a range of... emission scenarios." Results from these and other models also led to the conclusion that "it is very likely [more than 90% likelihood] that hot extremes, heat waves, and heavy precipitation events will continue to become more frequent."

The CCSP-sponsored Climate Model Evaluation Project (CMEP) supported more than 20 studies to analyze the models' ability to simulate features of 20th-century climate. Through the international World Climate Research Programme, which is supported in part by CCSP, this modeling activity leveraged many more similar efforts from the global research community. Many of these studies were used in determining the IPCC's conclusions.

CCSP is contributing to the development and operation of several global observing and monitoring systems, including many that play an integral role in the international Global Earth Observation System of Systems (GEOSS). Based in part on these observations and the aforementioned models, IPCC concluded that "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."

CCSP's ongoing research, which is addressing key scientific uncertainties, is essential to informing effective adaptation and mitigation responses to climate change. A few examples of the critical issues being addressed by CCSP are: whether precipitation will increase or decrease over the United States; the possibility of future, abrupt changes in climate; the extent to which sea level will rise along our coasts; the likelihood that the frequency and intensity of extreme climate events (e.g., droughts) will change; the extent to which storm patterns and intensities will change; the cumulative effects of global change on ecological and human systems, and the effectiveness and trade-offs associated with various adaptation and mitigation options.


Many of the authors of the IPCC are from the United States and many of those authors are entirely or partly funded by the CCSP. In addition, CCSP managed the U.S. nomination process, which resulted in 38 U.S. Federal, academic, and non-governmental organization experts serving in lead author and editorial roles for the WG1 volume. A leading NOAA atmospheric scientist, Dr. Susan Solomon, co-chaired Working Group I, with the program providing funding to operate the Technical Support Unit based in Boulder, CO. The program also managed the Expert and Government Reviews. This ranged from a public call for comments, collection of comments, and assembly of expert panels to review comments for technical merit.

The U.S. CCSP spent approximately $1.7 billion on research in the past year. This level of funding demonstrates the program's commitment to understanding climate change and its ongoing and projected impacts in a concerted effort to improve the nation's ability to make informed decisions regarding climate change.

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