Sunday, March 25, 2007

Melting ice sheets and glaciers

A number of apocalyptic news stories recently might have led the uninitiated to believe that the ice sheets of Greenland and Antarctica are melting, and that this melting is wholly responsible for rising sea levels. Well, in fact, the size of the Antarctic ice sheet is currently increasing, and the climate models currently suggest that snowfall over both the ice caps will increase in the 21st century.

Moreover, an interesting news article in this week's New Scientist reveals that "Ice shed from the giant sheets covering Antarctica and Greenland is responsible for only 12 per cent of the rise in global sea levels...melting ice contributes 0.35 millimetres to the annual 3 mm rise in sea levels. The remaining 88 per cent is due to water expanding as it warms, and the melting of mountain glaciers and ice caps outside Greenland and Antarctica...measurements since 1993 show that the thermal expansion of water is responsible for 1.6 mm of the annual rise and other melting glaciers and ice caps for 0.77 mm." Duncan Wingham reports that "It has become very clear over the past five years that these sheets are not losing most of their mass through melting. They are losing it because the ice is flowing into the ocean faster than the snow is replacing it."

The melting of glaciers and ice sheets is therefore, at present, 'poorly understood'. The wiser members of the Intergovernmental Panel on Climate Change (IPCC) recognise this, and restrict their comments to those aspects of global warming which are more certain.

Curiously, I don't recall having seen this latest research reported on the BBC last week. Must have been an oversight, because the BBC are a paragon of impartiality, and seek only to keep the viewer fully informed.

2 comments:

clare said...

Just wondering about your view on that terrifying scenario I heard about a few months ago ...of bottom-most layer of ice melting underneath the Greenland ice sheet enabling the whole lot to slip into the ocean.

Gordon McCabe said...

It's certainly an interesting suggestion, and one which deserves to be properly investigated.