Northern Hemisphere ice-sheet responses to past climate warming

During ice-age glacial maxima of the last -2.6 million years, ice sheets covered large portions of the Northern Hemisphere. Records from the retreat of these ice sheets during deglaciations provide important insights into how ice sheets behave under a warming climate. During the last two deglaciations, the southernmost margins of land-based Northern Hemisphere ice sheets responded nearly instantaneously to warming caused by increased summertime solar energy reaching the Earth. Land-based ice sheets subsequently retreated at a rate commensurate with deglacial climate warming. By contrast, marine-based ice sheets experienced a delayed onset of retreat relative to warming from increased summertime solar energy, with retreat characterized by periods of rapid collapse. Both observations raise concern over the response of Earth's remaining ice sheets to carbon-dioxide-induced global warming. The almost immediate reaction of land-based ice margins to past small increases in summertime energy implies that the Greenland Ice Sheet could be poised to respond to continuing climate change. Furthermore, the prehistoric precedent of marine-based ice sheets undergoing abrupt collapses raises the potential for a less predictable response of the marine-based West Antarctic Ice Sheet to future climate change.