Notes on Long-Term Forcing of Arctic Climate

Explanations for Cenozoic cooling of the Arctic tend to focus on proximal causes such as slow northward drift of circum-Arctic land masses or changes in meridional fluxes of heat and moisture through narrow gateways to the Arctic Ocean. Recent studies suggest that an important part of the forcing may lie in lower middle latitudes far from the Arctic. Uplift of massive plateaus in southern Asia and the American west appears to have fundamentally rearranged planetary-scale atmospheric circulation, including jet stream meanders and subtropical monsoons, with resulting climatic effects on all circum-Arctic lands. The onset and progressive intensification of strong monsoons in southeast Asia and elsewhere may have increased chemical weathering of freshly exposed rocks including silicates, causing a drawdown of atmospheric CO2 and thus a global cooling.