CONTACT:  Patricia Viets                      IMMEDIATE RELEASE
          Barbara McGehan                     12/4/96
          Jonathan Overpeck

ABRUPT CLIMATE CHANGE DURING LAST GLACIAL PERIOD COULD BE TIED TO DUST-INDUCED REGIONAL WARMING

Preliminary new evidence suggests that periodic increases in atmospheric dust concentrations during the glacial periods of the last 100,000 years may have resulted in significant regional warming, and that this warming may have triggered the abrupt climatic changes observed in paleoclimate records, according to a scientist at the Commerce Department's National Oceanic and Atmospheric Administration. Current scientific thinking is that the dust concentrations contributed to global cooling.

Jonathan T. Overpeck, head of the Paleoclimatology Program at NOAA's National Geophysical Data Center in Boulder, Colo., and a team of scientists report the preliminary findings of their recent climate research in the Dec. 5 issue of Nature magazine. They point out the need for additional climate research, including additional ice-core and geological data to improve our understanding of aerosols and their impact on climate change.

Overpeck and the team conducted global climate model simulations to examine the potential role of tropospheric dust in glacial climates. Comparing "modern dust" with "glacial dust" conditions, they found patterns of regional warming that increased at progressively higher latitudes. The warming was greatest (up to 4.4 degrees Celsius) in regions with dust over snow- and ice-covered areas.

The team conducted another set of simulations using interactive sea surface temperatures. The mid- to high-latitude warming was reduced from 4.4 degrees C to 2.4 degrees C, but the main regions of significant warming remained concentrated in areas where the dust loading coincides with snow- or ice-covered land areas. The authors point out that their results are conservative in several respects, and that the regional warming may have been significantly greater than 2.4 degrees during some extreme dust events.

The scientists found that mineral dust appears to have been the most globally distributed aerosol during glacial periods, with the largest radiative effect over snow- and ice-covered regions. Episodic dust loading may have provided the warming needed to trigger the ice, ocean and atmospheric changes associated with abrupt climatic events during the past 100,000 years, they wrote.

Many abrupt climatic events of the last 100,000 years, which included dramatic reorganization of the Earth's atmosphere-ocean system, are still poorly understood. The new results regarding the possible impacts of high atmospheric dust concentrations shed new light on the mechanisms behind these climate reorganizations, and hence on how the coupled atmosphere-ocean system may respond in the future.

In addition to Overpeck, the scientists are David Rind and Andrew Lacis of the NASA Goddard Institute for Space Studies, and Richard Healy of Columbia University's Center for Climate Systems Research.

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