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This study originated from a White House request to help inform the Administration's ongoing review of U.S. climate change policy. In particular, the written request ( Appendix A) asked for the National Academies' “assistance in identifying the areas in the science of climate change where there are the greatest certainties and uncertainties,” and “views on whether there are any substantive differences between the IPCC [Intergovernmental Panel on Climate Change] Reports and the IPCC summaries.” In addition, based on discussions with the Administration, the following specific questions were incorporated into the statement of task for the study:

  • What is the range of natural variability in climate?

  • Are concentrations of greenhouse gases and other emissions that contribute to climate change increasing at an accelerating rate, and are different greenhouse gases and other emissions increasing at different rates?

  • How long does it take to reduce the buildup of greenhouse gases and other emissions that contribute to climate change?

  • What other emissions are contributing factors to climate change (e.g., aerosols, CO, black carbon soot), and what is their relative contribution to climate change?

  • Do different greenhouse gases and other emissions have different draw down periods?

  • Are greenhouse gases causing climate change?

  • Is climate change occurring? If so, how?

  • Is human activity the cause of increased concentrations of greenhouse gases and other emissions that contribute to climate change?

  • How much of the expected climate change is the consequence of climate feedback processes (e.g., water vapor, clouds, snow packs)?

  • By how much will temperatures change over the next 100 years and where?

  • What will be the consequences (e.g., extreme weather, health effects) of increases of various magnitudes?

  • Has science determined whether there is a “safe” level of concentration of greenhouse gases?

  • What are the substantive differences between the IPCC Reports and the Summaries?

  • What are the specific areas of science that need to be studied further, in order of priority, to advance our understanding of climate change?

The White House asked for a response “as soon as possible” but no later than early June—less than one month after submitting its formal request.

The National Academies has a mandate arising from its 1863 charter to respond to government requests when asked. In view of the critical nature of this issue, we agreed to undertake this study and to use our own funds to support it.

A distinguished committee with broad expertise and diverse perspectives on the scientific issues of climate change was therefore appointed through the National Academies' National Research Council (see Appendix B for biographical information on committee members). In early May, the committee held a conference call to discuss the specific questions and to prepare for its 2-day meeting (May 21–22, 2001) in Irvine, California. The committee reviewed the 14 questions and deter

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