| Summary: | Northern hemisphere ice sheets have played an important role in the climatic evolution of the Pleistocene. The characteristic time-scale of icesheet growth has the same order-of-magnitude as that for the orbital insolation variations. The interaction with the solid earth, the importance of the thermal conditions at the base of ice sheets and feedback on the climate system (albedo feedback, precipitation regime) make the cryospheric response to climatic forcing complicated. Feedback of surface elevation on the surface mass balance allows northern hemisphere ice sheets to grow southward when cooler summer conditions prevail. Rapid ice-sheet decay, as observed in the paleorecord, must have involved one or more powerful destabilizing mechanisms like low accumulation rates at subpolar latitudes, high ice velocities due to water-saturated sediment beds, and high calving rates in proglacial lakes and seas. In terms of radiactive forcing of the global climatic fluctuations in the Pleistocene, the effects of northern hemisphere ice sheets (albedo), varying concentration of greenhouse gases (carbon dioxide, methane) and direct effect of orbital changes (insolation) are of similar magnitude.
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