It is established that glacial–interglacial cycles are driven in the first instance by
oscillations in solar irradiance received by the Earth, oscillations due to cyclic
changes in the Earth’s rotation and its orbit around the sun. These are termed
Milankovitch cycles, after Milutin Milankovitch, a Serbian mathematician who
worked on the problem of estimating combined effects of Earth’s rotational and
orbital variations. Glaciers grow or recede depending upon the balance between
winter snow accumulation and summer melting rates. Since glaciers always form in
and advance from regions that are cold all winter, every winter, and they receive snow
addition every year. The amount is only weakly affected by temperature variation.
However, the response of summer melting to temperature variation is strong. A few
degrees of temperature increase can switch condtions from leaving some of last
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