THE RESPONSE OF NORTHERN-HEMISPHERE EXTRATROPICAL CLIMATE AND VEGETATION TO ORBITALLY INDUCED CHANGES IN INSOLATION DURING THE LAST INTERGLACIATION

The last interglaciation (substage 5e) provides an opportunity to exam ine the effects of extreme orbital changes on regional climates. We ha ve made two atmospheric general circulation model experiments: P+T+ ap proximated the northern hemisphere seasonality maximum near the beginn ing of 5e; P-T- approximated the minimum near the end of 5e. Simulated regional climate changes have been translated into biome changes usin g a physiologically based model of global vegetation types. Major clim atic and vegetational changes were simulated for the northern hemisphe re extratropics, due to radiational effects that were both amplified a nd modified by atmospheric circulation changes and sea-ice feedback. P +T+ showed mid-continental summers up to 8 degrees C warmer than prese nt. Mid-latitude winters were 2-4 degrees C cooler than present but in the Arctic, summer warmth reduced sea-ice extent and thickness, produ cing winters 2-8 degrees C warmer than present, The tundra and taiga b iomes were displaced poleward, while warm-summer steppes expanded in t he mid latitudes due to drought, P-T- showed summers up to 5 degrees C cooler than present, especially in mid latitudes. Sea ice and snowpac k were thicker and lasted longer; polar desert, tundra, and taiga biom es were displaced equatorward, while cool-summer steppes and semideser ts expanded due to the cooling. A slight winter warming in mid latitud es, however, caused warm-temperate evergreen forests and scrub to expa nd poleward. Such qualitative contrasts in the direction of climate an d vegetation change during 5e should be identifiable in the paleorecor d. (C) 1995 University of Washington.