by Fred Pearce, NewScientist.com news service, 7 July 2008

Pacific nations threatened with disappearing beneath the waves as sea levels rise have been
given a partial reprieve – for a few decades at least. But Europe and North America could be at much greater risk of floods than previously appreciated. So claims the first systematic analysis of what will happen to the water from melting Greenland ice.

In the past five years, research has suggested that sea levels could rise by more than a metre in the coming century, as rising temperatures cause Greenland's ice to slide into the oceans and melt. This would be enough to entirely engulf coral-island nations like Kiribati and Tuvalu.

But now Detlaf Stammer of Hamburg University, Germany, says that most of the melted water will stay in the Atlantic for at least 50 years, where sea levels will rise much faster as a result. Only small amounts will make it into the Pacific Ocean in that time.

Slow wave

"It is often assumed that sea levels will rise instantaneously, but that is unlikely, given what we know about ocean dynamics," says Stammer. "The Greenland ice cap is much less of a threat to tropical islands in the Pacific than it is for the coasts of North America and Europe."

Stammer plugged data about the amounts of meltwater released from the Greenland ice sheet since 1948 into a computer model. This then calculated how that water spread around the oceans over 50 years.

He shows that meltwater forms a "wave" of rising sea levels that gradually works its way south from Greenland, down the American coast, reaching the tip of southern Africa after about a decade.

After that, it slowly spills east through the Indian Ocean. According to Stammer, the "additional" water only reaches the Pacific after about 30 years.

US at risk

Fifty years after the meltwater is released from Greenland, Stammer's model predicts, sea-level rise could be 30 times greater around Greenland and down the eastern side of North America, including the Gulf of Mexico, than in the Pacific Ocean.

Meanwhile, sea-level rises in Europe are around six times that of the Pacific, but only a fifth as great as on the opposite shore of the Atlantic.

This does not mean that the Pacific Islands or other low-lying areas like Bangladesh in the Indian Ocean, are safe. The thermal expansion of water as a result of global warming is already causing waters to rise around the world. But the delay does buy these vulnerable nations some time.

Stammer's model indicates that meltwater from Antarctica's ice sheets would spread more slowly still. The strong currents in the Southern Ocean could prevent substantial sea-level rise from reaching much of the world for centuries. He found that after 50 years, rises from Antarctic meltwater in the northern Atlantic and Pacific would be "barely measurable."

Journal reference: Journal of Geophysical Research (DOI: 10.1029/2006JC004079)

Link to article: http://environment.newscientist.com/article/dn14264-greenland-meltwater-will-take-slow-wave-around-globe.html