Tuesday, January 19, 2010

12. The Greenland Ice Sheet

When global warming doomsayers are trying to make the effects of climate change seem frightening, a favorite trick is to point out the dire consequences of some cataclysmic event, without mentioning that the probability of said event is indistinguishable from zero. Al Gore  keeps repeating a good example: "If the Greenland ice sheet melts, the sea-level will rise 7 meters (23 feet)." This quote from his Oscar-winning slide show, An Inconvenient Truth is true but irrelevant, and quite deliberately deceptive.

What the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) actually says is that the Greenland ice sheet might begin losing mass after 2100. Until then, the higher humidity due to global warming will increase snowfall on the Greenland summit, more than compensating for melting at the coasts, and thus reducing sea-level rise due to other causes. If the temperature remains at the projected high level, melting the whole ice sheet would take thousands of years. The next glaciation of the Ice Age is virtually certain to intervene long before then.

Melting of the Antarctic ice sheet is even less probable, because the altitude of the polar plateau is more than 4 kilometers (13,000 feet), so it is much colder than in Greenland.

The actual median sea-level rise by 2100 that is projected by the IPCC is 30 cm (12 inches), mostly due to thermal expansion of water as the oceans warm. This is just 4% of the figure quoted by Mr Gore. The sea level has already risen by at least this much since the 19th century, but nobody noticed.

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