POSSIBLE ROLE OF ATMOSPHERE-BIOSPHERE INTERACTIONS IN TRIGGERING THE LAST GLACIATION

We coupled a global biome model iteratively with an atmospheric genera l circulation model to study the possible role of vegetation in the cl imate system, at the time of glacial inception 115,000 years ago. Orbi tal forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present (atmospheric co mposition, oceans, biosphere and cryosphere). Summers were however col d enough to induce major vegetation shifts in high northern latitudes. Southward migration of the boreal forest/tundra limit helped to Creat e favourable conditions for continental ice-sheet growth, with increas ing snow depth and duration in Labrador, Arctic Canada and northern/we stern Fennoscandia. These results support a role for biogeophysical fe edback in initiating glaciations.