the past changes, casting uncertainties on assessments of potential future changes. Thus, it is likely that climate surprises await us.

When orbital wiggles and rising greenhouse gases warmed the earth from the last ice age, proxy records show that smooth changes were interspersed with abrupt coolings and warmings, wettings and dryings. By analogy, the expected future warming may come smoothly, but may come with jumps, short-lived or local coolings, floods or droughts, and other unexpected changes. Societies and ecosystems have an easier time dealing with slower or better-anticipated changes, so the abruptness and unpredictability of the possible changes may be disquieting.

This report considers patterns, magnitudes, mechanisms, and impacts of abrupt climate changes, possible implications for the future, and critical knowledge gaps. The potentially large impacts and prediction difficulties focus special attention on increasing the adaptability and resiliency of societies and ecosystems. The committee notes that there is no need to be fatalistic; human and natural systems have survived many abrupt changes in the past, and will continue to do so. Nonetheless, future dislocations can be minimized by taking steps to face the potential for abrupt climate change. The committee believes that increased knowledge is the best way to improve the effectiveness of response, and thus that research on abrupt climate change can help reduce vulnerabilities and increase adaptive capabilities.

I would like to thank the US Global Change Research Program and staff at the many agencies who are a part of USGCRP, for funding and participating in this study process. Thanks also to the Yale/NBER Program on International Environmental Economics for additional funding, and to committee members Bill Nordhaus and Dorothy Peteet for organizing and conducting the Impacts Workshop. The numerous participants at our workshops, the reviewers, and many other colleagues contributed valuable insights and encouragement. It has been my privilege to work with Study Director Alexandra Isern (now with the National Science Foundation), Polar Research Board Director Chris Elfring, Research Associate John Dandelski, and with Senior Project Assistants Megan Kelly, Jodi Bachim, and Ann Carlisle, of the National Research Council. I thank the Ocean Studies Board, the Polar Research Board, and the Board on Atmospheric Science and Climate for providing the impetus to do this study and oversight throughout the process.

I would especially like to extend my deep appreciation to the committee’s members for their efforts in creating this report. By exploring