THE SNOWLINE INSTABILITY AS A MECHANISM FOR RAPID CLIMATE CHANGE – APPLICATIONS TO PHANEROZOIC GLACIATIONS

Although thermohaline instabilities have been a popular explanation for rapid climate change in the Pleistocene, a different mechanism for rapid climate change has been separately discussed in the climate literature for 35 years, with relatively little penetration into the paleoclimate literature. This mechanism involves rapid changes in snow area due to albedo discontinuities at the snow-land edge. The mechanism was first discovered in energy balance models but has subsequently been found in atmospheric general circulation models and coupled energy balance/ice sheet model simulations. Applications to the paleoclimate record using the energy balance model/ice sheet model suggest that such a mechanism could have been operating during the late Proterozoic, Carboniferous, and late Cenozoic glaciations. Other work suggests something similar for the Eocene/Oligocene transition. An additional feature of such mechanisms is that they often predict higher variability near transition points in climate, a prediction that is supported by O18 data from the Eocene/Oligocene transition. Finally there is a subtler indication that the mechanism may be operating at present and, if not for anthropogenic greenhouse gas emissions, could eventually tilt the northern hemisphere into permanent midlatitude glaciation.