Alister Doyle, Reuters 22 Jan 09;
ROTHERA BASE, Antarctica (Reuters) - Sea levels will rise at widely varying rates around the world because of a quirk of the earth's gravity linked to global warming, a leading glaciologist said.
"Everyone thinks sea level rises the same around the world," David Vaughan, of the British Antarctic Survey, told Reuters on Tuesday at the Rothera Base on the Antarctic Peninsula. "But it doesn't".
Rises could vary by tens of centimeters (inches) from region to region if seas gained by an average of one meter by 2100 as temperatures rise, he said. Worst-affected nations would have to budget billions of dollars more than others on coastal defences.
Vaughan said big ice sheets on Antarctica and on Greenland have a gravitational pull that lifts the seas around them -- water levels around Antarctica, for instance, are higher than if the frozen continent were an open ocean.
As ice thaws, Antarctica would get smaller and its gravitational tug would diminish. In some places around the continent, the level of the Southern Ocean might even drop despite a flood of fresh water into the oceans.
The effect means that seas will paradoxically rise least where thawing ice pours into the sea and most further away from the point of melt, he said.
"Ice lost from Antarctica has a bigger impact on European sea level rise than ice lost from the European Alps, tonne for tonne," Vaughan said.
SYDNEY, BEIJING
Buenos Aires or Sydney will suffer less sea level rise if ice melts quickest from Antarctica than San Francisco or Beijing, for instance. And if Greenland melts fastest, South Pacific islands will suffer more than New York or London.
"If there's a meter of sea level rise over the next century, the difference will probably be tens of centimeters if it comes from Greenland or it comes from Antarctica," Vaughan said.
Vaughan said that governments, trying to work out a new U.N. treaty by the end of 2009 to fight global warming, needed to work out where ice was most likely to thaw.
The U.N. Climate Panel projected in 2007 that average world sea levels would rise by between 18 and 59 centimeters (7-24 inches) by 2100, mainly because of a warming spurred by human emissions of greenhouse gases from burning fossil fuels.
Vaughan, who was a co-leader of a chapter about the world's polar regions in the Panel's report, said recent studies indicated an accelerating rate of loss from both Greenland and parts of Antarctica.
"There is increasing evidence that Greenland and Antarctica are contributing more water than before," he said. The average sea level rise this century could be closer to a meter than the Panel's prediction.
Temperatures on the Antarctic Peninsula have risen by about 3 Celsius (5.4 Fahrenheit) in the past 50 years -- the fastest rate in the Southern Hemisphere. Most of Antarctica, however, is a deep freeze that shows no sign of warming.
But even a tiny melt of Antarctica would affect sea levels -- its ice is equivalent to an additional 57 meters of sea level. The far smaller Greenland ice sheet would raise sea levels by about 7 meters if it ever all thawed.
(Editing by Angus MacSwan)
