Sunday, February 4, 2007

Sea Level Change Underestimated by IPCC Projections

Seas Rising Faster than U.N. Predicts

Feb. 2, 2007

PARIS - Sea levels are rising faster than predicted amid global warming, a group of scientists said on Thursday in a challenge to the U.N.'s climate panel which is set to issue a report toning down the threat of rising oceans. The researchers -- from the United States, Germany, France, Australia and Britain -- wrote in the journal Science that seas have been edging up more rapidly since 1990 than at any time in more than a century, outpacing computer projections.

The data now available raise concerns that the climate system, in particular sea level, may be responding more quickly than climate models indicate," Stefan Ramstorf of Germany's Potsdam Institute for Climate Impact Research and co-authors wrote.

Still, they said it was too early to say for sure that the accelerated rise was linked to greenhouse gases from human burning of fossil fuels. It might, they said, be caused by some natural climate variation.

Rising seas, widely linked to a warming stoked by emissions of greenhouse gases, could swamp low-lying Pacific islands, large tracts of Bangladesh or the southern United States and threaten cities from Shanghai to Buenos Aires.

And governments want to plan how to confront a long-term threat that could cause billions of dollars in damage.

The scientists said the rises seemed to exceed projections made in 2001 by the Intergovernmental Panel on Climate Change (IPCC), which said sea levels were likely to rise by between 9 cm and 88 cm (3.5-34.6 inches) by 2100.

But the Science article comes on the eve of a new IPCC report, to be released in Paris, set to cut the likely range of rises to between 28 cm and 43 cm this century, based on six computer models.

HEAT

The IPCC says the range is narrower because of cuts in predictions of how quickly the oceans absorb heat -- water gets bigger as it warms. It also projects that Antarctica, by far the biggest store of frozen ice, will stay too cold to melt.

The experts writing in Science, including NASA's James Hansen, said sea levels rose by 3.3 mm (0.1299 inch) a year from 1993-2006, according to satellite measurements, against an IPCC best estimate in 2001 of below 2 mm a year.

Sea levels rose 17 cm in the 20th century. The 1993-2006 rate, if it lasted a century, would work out at 33 centimetres but many models project a quickening pace because of a buildup of greenhouse gases.

Previous projections, as summarised by the IPCC, have not exaggerated but may in some respects even have underestimated the change, in particular for sea level," the scientists wrote.

Rahmstorf declined give his best estimate of how far sea levels would rise -- he wrote a report in December saying that observations of past data indicated that seas could rise by 50-140 cms by 2100, far higher than IPCC projections.

Story by Alister Doyle, Environment Correspondent

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