NOAA 97-009

CONTACT:  Patricia Viets            FOR IMMEDIATE RELEASE
          Barbara McGehan           2/20/97

GLOBAL CLIMATE SYSTEM MIGHT BE MORE SENSITIVE TO THE GREENHOUSE EFFECT THAN COMMONLY THOUGHT

The global climate system might be more sensitive to the greenhouse effect than many scientists think, according to a paleoclimatologist at the National Geophysical Data Center, who reports his findings in the February 20 issue of Nature magazine.

Robert S. Webb, of the Commerce Department's National Oceanic and Atmospheric Administration, and a team of scientists performed a series of global climate simulations. They found that incorporating near-modern ocean heat transports, reduced glacial atmospheric carbon dioxide levels, and large terrestrial ice sheets, together with feedback mechanisms, are sufficient to lower annual average global surface temperature by 8 degrees Centigrade (14.4 degrees Fahrenheit) and tropical sea surface temperatures by 5.5 degrees Centigrade (9.9 degrees Fahrenheit) at the Last Glacial Maximum (LGM).

"While debate continues on the role of the tropics and the ocean in climate change, our results suggest greater climate sensitivity and cooling in the past," Webb concluded. "Furthermore, the greater global cooling shown in our simulations implies a much greater climate sensitivity than previous estimates. This suggests that the expected warming from carbon dioxide doubling may be closer to 4 degrees centigrade warming, rather than more modest estimates of 2.5 degrees Centigrade."

Webb's results indicate that the new cooler tropical LGM temperatures inferred from coral material and noble gases in fossil ground waters could have resulted from the combined impacts of greenhouse effects and of ocean heat maintained at near-modern levels during the Last Glacial Maximum. The coral and ground water evidence and mechanism for tropical cooling described by Webb undercut previously posed arguments that tropical sea surface temperatures have changed little throughout the Cenozoic and that such stability will persist in the future.

In addition to Webb, the team consists of: David H. Rind and Richard J. Healy, both of NASA; Scott J. Lehman, University of Colorado; and Daniel Sigman of Woods Hole Oceanographic Institution.