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American Association for the Advancement of Science

Revising the rise of the sea

Columbia Glacier, Alaska.

As global warming continues, large sheets of ice in Greenland and Antarctica melt and fall away into the sea. Glaciers in that part of the world are cracking, and the broken chunks are adding more water into the world's oceans. To keep a close eye on these events, and to prepare for the future, researchers are constantly measuring how deep the sea is around the world. By now, every serious scientific prediction agrees that the world's sea level will continue to rise in the future. But how much will it rise?

Columbia Glacier, Alaska.

Some models of future sea levels predict that the world's oceans will rise by two full meters by the year 2100. But there is also new evidence to suggest that two meters is unrealistic, and the world's sea levels could not increase that much in the next hundred years.

W. Pfeffer and a small team of researchers say that a rise in sea level somewhere between 0.8 and two meters is actually more likely by the year 2100, but that a rise of more than two meters is very unlikely. They reached these conclusions after studying the ice and water being discharged from Greenland and Antarctic ice sheets -- but their study was different from most of the others.

Unlike most past studies that try to add up the individual sources of ice and water discharge from the glaciers into the sea, Pfeffer's experiment calculated how much ice and water lost from Greenland and Antarctica that it would take for the world's seas to raise two meters. Then, they compared those predicted rates of ice loss to what is actually happening today.

Their findings show that predictions of a two meter rise in sea level by 2100 would require more discharge from Greenland and Antarctica than has ever been reported before. So if the glaciers continue to break up and melt like they are right now for a hundred years, a two meter rise in sea level by 2100 would not be possible.

For that reason, Pfeffer and his colleagues argue that current models of sea level rise should be updated to include more realistic rates of glacier break-up and melting in Greenland and Antarctica. They argue that their prediction of a 0.8 to two meter rise in sea level by 2100 is much more realistic.


This research appears in the 5 September 2008 issue of Science.