Saturday, December 5, 2009

The ice is not melting

Melting and climate

On July 21, 1983, the lowest reliably measured temperature ever recorded on Earth was at Vostok with -89.2 °C. The highest recorded temperature at Vostok is -19° C, which occurred in January 1992, and during the month of July 1987 the temperature never rose above -72.2° C. At these temperatures ice cannot flow under the pressures that prevail near the surface. Warming has no effect at such low temperatures because ice will not flow faster at -60°C than at -70° C.

In the case of ice sheets it may take many thousands of years for ice to flow from the accumulation area to the melting area. That is why meteorites such as the one from Antarctica that was thought to contain Martian fossils take thousands of years to reach places where they can be collected from the surface. The balance between movement and melting therefore does not relate to today's climate, but to the climate thousands of years ago.

Glaciers and precipitation

We have seen that glaciers and ice sheets are in a state of quasiequilibrium, governed by rates of melting and rates of accumulation. For a glacier to maintain its present size it must have precipitation as snowfall at its source. This leads to a slightly complex relationship with temperature. If the regional climate becomes too dry, there will be no precipitation, so the glacier will diminish. This could happen if the region became cold enough to reduce evaporation from the ocean.
If temperatures rise, evaporation is enhanced and so therefore is snowfall. Paradoxically a regional rise of temperature may lead to increased growth of glaciers and ice sheets. Today, for example, the ice sheets of both Antarctica and Greenland are growing by accumulation of snow.
More here, pp 22 - 24. A fascinating piece on glaciers, the age of the ice, how ice flows, the temperature where glaciers are, and the warming to hell of earth (OK, I lied about the warming to hell of earth bit).

Thanks to Wand.

1 comment:

Carpe Jugulum said...

Note to self - scratch Vostok from potential holiday list.