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Friday, July 24, 2009

Seas rise — vast amounts of ice melt for every 1 mm gain

by Alister Doyle, 07:59 July 24th, 2009, Reuters

It takes the equivalent of a massive chunk of ice of 390 km³ (150 cubic miles) to raise world sea levels by one millimetre, according to David Carlson, director of the International Programme Office of the International Polar Year.

As an example, he says that works out as a lump 39 km long, 10 wide and 1 km thick. Or I reckon it could be a blockbuster ice cube with sides 7.3 km long — that would smother most of a large city such as Paris (top left — you can see the Eiffel Tower in the middle).

David’s numbers give an idea of the scale of the thaw under way — seas have been rising at about 3 mm/year in recent years in a trend that almost all climate scientists blame on global warming caused by human activities. That’s equivalent to a rate of 30 cm a century.

And it’s also a lot faster than a rise of 1.8 mm a year from the 1960s, according to the U.N. Climate Panel. The thaw is one of the spurs to action under plans for a new U.N. treaty to fight global warming due to be agreed in Copenhagen in December.

Some scientists reckon seas could rise by one metre this century. Most of the rise projected by 2100, however, is likely because water expands as it gets warmer, rather than because of a thaw of glaciers or of ice sheets smothering Greenland or Antarctica.

One bit of good news on the ice front is that it looks as if sea ice in the Arctic will not shrink to a new record low this summer [BLOGGER'S NOTE: the author fails to point out that sea ice extent figures do not show that the ice this year is less than half as thick as it was last year, thus only half as much ice is up there, despite any sea extent recovery, a virtually meaningless number at this point], after 2007 marked the smallest since satellite records began in the 1970s (and probably a lot longer than that).

Ice shrinks to its annual low in September before freezing out again: so far the ice is still far bigger than in 2007 at the same time although it is also far smaller than the 1979-2000 average, according to the U.S. National Snow and Ice Data Center. And ice floating on the sea doesn’t really contribute to raising sea levels — it’s effectively part of the water already.

(Picture: undated satellite image of the Eiffel Tower and the surrounding area in Paris, France. REUTERS/DigitalGlobe TZ)


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