*EPF317 12/12/2001
Text: NAS Report Cites Possibility of Abrupt Climate Change
(Periods of abrupt change marked by severe floods and droughts) (1300)

The National Academy of Sciences has released a report citing evidence that warming caused by greenhouse gases and other pollutants could trigger large, abrupt climate changes marked by periods of severe floods and droughts.

A December 11 press release says the new report by the National Academies' National Research Council provides a different view from recent climate change studies that have focused on the risks of a gradual rise in the Earth's temperature.

Using historical observations and computer modeling analyses going back hundreds of centuries, the researchers found evidence that periods of gradual change in Earth's past were punctuated by episodes of abrupt change, including temperature changes of about 10 degrees Celsius in only a decade in some places.

The researchers said examples of abrupt change in the past century include the U.S. Dust Bowl drought of the 1930s and the rapid warming of the North Atlantic from 1920 to 1930 -- a warming that was accompanied by significant climate changes across the globe, including flooding and drought.

The committee that wrote the report added, however, that there is no need for undue alarm about the possibility of sudden climate change because societies have learned to adapt to these changes through the course of human history. It also emphasized that not enough is known about such events to accurately predict them, so surprises are inevitable.

The committee said proactive policies might be beneficial regardless of whether abrupt climate change occurs, including reducing greenhouse gas emissions to slow global warming, improving climate forecasting, slowing biodiversity loss, and improving water, land and air quality.

The entire report, entitled "Abrupt Climate Change: Inevitable Surprises," can be found at the following Web site: http://www.nap.edu

Following is the text of the press release:

(begin text)

NATIONAL ACADEMY OF SCIENCES

Dec. 11, 2001

Possibility of Abrupt Climate Change Needs Research and Attention

Most climate-change research has focused on gradual changes, such as the processes by which emissions of greenhouse gases lead to warming of the planet. But new evidence shows that periods of gradual change in Earth's past were punctuated by episodes of abrupt change, including temperature changes of about 10 degrees Celsius, or 18 degrees Fahrenheit, in only a decade in some places. Severe floods and droughts also marked periods of abrupt change.

A new report from the National Academies' National Research Council says greenhouse warming and other human alterations of the climate system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events. Researchers do not know enough about such events to accurately predict them, so surprises are inevitable.

If the planet's climate is being forced to change -- as is currently the case -- it increases the number of possible mechanisms that can trigger abrupt events, the report says. And the more rapid the forced change that is taking place, the more likely it is that abrupt events will occur on a time scale that has immediate human and ecological consequences.

There is no need for undue alarm, however, about the possibility of sudden climate change, because societies have learned to adapt to these changes over the course of human history, said the committee that wrote the report. Nevertheless, the committee said research into the causes, patterns, and likelihood of abrupt climate change is the best way to reduce its impact. Overall, research should be aimed at improving modeling and statistical analysis of abrupt changes. An important focus of the research should be on mechanisms that lead to sudden climate changes during warm periods, with an eye to providing realistic estimates of the likelihood of extreme events. Poor countries may need more help preparing for abrupt climate change since they lack scientific and economic resources.

The planet's past climate record also needs to be understood better, according to the report. Scientists have a variety of means to study what the climate was like thousands of years ago. For example, researchers look at tree rings to examine the frequency of droughts and analyze gas bubbles trapped in ice cores to measure past atmospheric conditions. With such techniques, scientists have discovered repeated instances of especially large and abrupt climate changes over the last 100,000 years during the slide into and climb out of the most recent ice age. For instance, the warming at the end of the last ice age triggered an abrupt cooling period, which finished with an especially abrupt warming about 12,000 years ago. Since then, less dramatic -- though still rapid -- climate changes have occurred, affecting precipitation, hurricanes, and the El Ni�� events that occasionally disrupt temperatures in the tropical Pacific. Examples of abrupt change in the past century include a rapid warming of the North Atlantic from 1920 to 1930 and the Dust Bowl drought of the 1930s.

Simulating abrupt climate changes using computer models is particularly difficult because most climate models respond in a linear manner in which a doubling of the factor forcing change -- greenhouse gases, for instance -- doubles the response. However, abrupt climate changes show that a small forcing may cause a small change, or may force the climate system across a threshold and trigger huge change. A massive discharge of fresh water from lakes dammed by melting ice sheets, which suddenly changes climate conditions worldwide, is an example of threshold-crossing. Chaotic behavior in the climate also may push it across a threshold without any apparent external forcing.

The collapse of some ancient civilizations has been associated with abrupt climate changes, especially severe droughts, but humans have shown great resilience as well. Fast changes make adaptation more difficult, so research should be pursued to identify strategies that reduce vulnerabilities and increase the adaptability of economic and ecological systems, the committee said. It noted that many proactive policies might provide benefits regardless of whether abrupt climate change occurs. Some steps that deserve careful scrutiny include reducing emissions to slow global warming, improving climate forecasting, slowing biodiversity loss, and improving water, land, and air quality.

The report was sponsored by the U.S. Global Change Research Program, with additional support from the National Bureau of Economic Research Program on International Environmental Economics at Yale University. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.

Read the full text of Abrupt Climate Change: Inevitable Surprises on the Internet at .

NATIONAL RESEARCH COUNCIL Division on Earth and Life Studies Board on Atmospheric Sciences and Climate Ocean Studies Board Polar Research Board

Committee on Abrupt Climate Change: Implications for Science and Public Policy

Richard B. Alley (chair)

Evan Pugh: Professor of Geosciences, and Associate Professor of the Environment Institute College of Earth and Mineral Sciences Pennsylvania State University, University Park

Jochem Marotzke: Professor Southampton Oceanography Centre Southampton, England

William D. Nordhaus: A. Whitney Griswold Professor of Economics Yale University New Haven, Conn.

Jonathan T. Overpeck: Professor and Director Institute for the Study of Planet Earth University of Arizona Tucson

Dorothy M. Peteet: Senior Research Scientist NASA Goddard Institute for Space Science, and Adjunct Senior Research Scientist Lamont Doherty Earth Observatory Columbia University New York City

Roger A. Pielke Jr.: Scientist National Center for Atmospheric Research Boulder, Colo.

Raymond T. Pierrehumbert: Professor of Geophysical Sciences University of Chicago Chicago

Peter B. Rhines: Professor of Oceanography and Atmospheric Sciences University of Washington Seattle

Thomas F. Stocker: Professor of Climate and Environmental Physics University of Bern Physics Institute Switzerland

Lynne D. Talley: Professor Scripps Institute of Oceanography La Jolla, Calif.

John M. Wallace: Professor of Atmospheric Sciences University of Washington Seattle

RESEARCH COUNCIL STAFF

Alexandra Isern Co-study Director

Chris Elfring Co-study Director

(end text)

(Distributed by the Office of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)

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