High-latitude faunal migrations have been documented during a rapid warming event near the Paleocene-Eocene boundary (the latest Paleocene thermal maximum, LPTM). The migrations are difficult to explain from a climate perspective. Climate along these routes is at present too harsh to support the migrations, and no mechanism has yet proved adequate to explain the past high-latitude warmth required by such migrations. A large negative excursion in the δ13C record at the LPTM suggests that a large quantity of CH4 was released into the atmosphere at this time. High concentrations of atmospheric CH4 have been linked to the formation of polar stratospheric clouds. We used an atmospheric general circulation model to explore early Cenozoic climate response to the combined effects of high atmospheric CH4 levels and polar stratospheric clouds, a unique combination of forcing factors in paleoclimate modeling studies. Our interests are in understanding if the climate response to this forcing may explain the high-latitude faunal migrations. Model results indicate that high-latitude winter warming with high methane levels and polar stratospheric clouds is sufficient to facilitate the high-latitude migrations. Temperatures along high-latitude migration routes remained above freezing year-round and thus permitted exchanges of fauna between Asia, North America, and Europe. On the basis of our results, we suggest that other Paleogene migrations may be correlated with LPTM-like events with high concentrations of greenhouse gases and polar stratospheric clouds.

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