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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