Role of orbitally induced changes in tundra area in the onset of glaciation

THE link between glacial-interglacial cycles and changes in insolation due to variations in the Earth's orbital parameters is well established(1-4). But of the attempts to simulate incipient glaciation using three-dimensional general circulation models (GCMs) driven by orbital forcing alone(5-10), only one(10) has been successful. GCM experiments(7,11) show that reduced summer insolation 115,000 years ago (during an interglacial-to-glacial climate shift) produces sufficient high-latitude cooling to clause expansion of tundra at the expense of boreal forest(11), which in turn can induce more cooling(11-14). Here we show, using a global climate model, that the increase in surface albedo (under snow-covered conditions) that results from a biome model estimate(11) of tundra expansion 115,000 years ago is sufficient to induce glaciation over extreme-northeastern Canada. If the additional cooling from this estimated tundra expansion induces further expansion, then widespread glaciation occurs at latitudes above 65 degrees N. These results suggest that the climate feedback from high-latitude tundra expansion might have contributed to the onset of the most recent glaciation.