Oceans may rise over 4½ feet by 2100

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By Alister Doyle, Reuters Environment Correspondent

Thursday, Dec. 14

 

OSLO (Reuters) - The world's oceans may rise up to 140 cms (4 ft 7

in) by 2100 due to global warming, a faster than expected increase

that could threaten low-lying coasts from Florida to Bangladesh, a

researcher said on Thursday.

 

" The possibility of a faster sea level rise needs to be considered

when planning adaptation measures such as coastal defenses, " Stefan

Rahmstorf of the Potsdam Institute for Climate Impact Research wrote

in the journal Science.

 

His study, based on air temperatures and past sea level changes

rather than computer models, suggested seas could rise by 50-140 cms

by 2100, well above the 9-88 cms projected by the scientific panel

that advises the United Nations.

 

A rise of one meter might swamp low-lying Pacific islands such as

Tuvalu, flood large areas of Bangladesh or Florida and threaten

cities from New York to Buenos Aires.

 

" The computer models underestimate the sea level rise that has

already occurred, " Rahmstorf told Reuters of a rise of about 20 cms

since 1900. " There are aspects of the physics we don't understand

very well. "

 

Sea level changes hinge on poorly understood factors such as the

pace of the melt of glaciers and of ice sheets in Greenland and

Antarctica. Water also expands as it gets warmer but the rate of

penetration of heat to the depths is uncertain.

 

" My main conclusion is not that my forecast is better but that the

uncertainty is much larger because of the different results you get

with reasonable methods, " he said.

 

Almost all climate scientists reckon the world is warming because of

emissions of greenhouse gases from human use of fossil fuels in

factories, power plants and cars. Rising temperatures could bring

more droughts, floods and heatwaves.

 

Rahmstorf likened his approach to predicting the height of tides

along a coast, largely based on past observations.

 

He said seas were 120 meters below present levels during the last

Ice Age 20,000 years ago and 25-35 meters higher than the present in

the Pliocene epoch 3 million years ago.

 

In the Ice Age temperatures were 4-7 Celsius (7.2-12.6 Fahrenheit)

cooler than today and 2-3 C (3.6-5.4F) warmer in the Pliocene. That

suggested sea levels change 10-30 meters per rise or fall per degree

Celsius (1.8F), over thousands of years.

 

The U.N. climate panel has projected temperatures will rise by 1.4-

5.8C (2.5-10.4F) by 2100, mainly because of human influences.

 

" Sea level is a very slow component of the climate system so what we

see by the year 2100 is just a small percentage of the total we are

causing, " Rahmstorf said.

 

There was still time for the world to cut greenhouse gas emissions

but he said the slow pace of U.N. talks on extending the U.N.'s

Kyoto Protocol beyond 2012 " gives you the impression that

governments are not very well aware of how urgent the whole problem

has become. "

 

Coastal cities in the North Atlantic -- from New York to London --

could be especially vulnerable because a possible slowdown of ocean

currents could also raise sea levels in the North Atlantic and lower

them in the southern hemisphere.

 

" Any time you change ocean currents you change the sea surface...if

you slow down the North Atlantic current you get a rise in the North

Atlantic, " Rahmstorf said.

 

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