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National Geographic News (December 14, 2006) reports on a new study of potential sea level rise in this century. "[T]he physics of how ice sheets melt and how the oceans will expand in a warmer world is still poorly understood.

So Stefan Rahmstorf, an ocean physicist at Potsdam University in Germany, took a different approach: He used studied actual observations of changes in sea level collected in the 20th century to make predictions for the 21st century.

Current models don't jibe with actual sea level rise during recent decades, Rahmstorf says. So he crafted a formula based on a relationship between global temperature and sea level seen during the past hundred years.

'The more the temperature rises, the faster the sea level rises,' he said.

The report goes on to note uncertainty in the ice melt models: "Konrad Steffen is a professor of geography at the University of Colorado at Boulder who studies how melting ice sheets and glaciers contribute to sea level.

He said one wild card that could impact predictions is the so-called dynamic response of the ice sheets to warming.

In the last five to eight years, he noted, the speed at which Greenland's glaciers move toward the sea has sped up dramatically (explore Greenland's changing landscapes with a National Geographic Adventure magazine guide).

Scientists think that meltwater, which pools up on the ice, funnels down to the glacier bed. There, the water acts as a lubricant, allowing the ice to slip seaward more quickly.

The process may last five or ten years, or it may last decades, Steffen said.

You can read the entire report here:

Sea Level May Rise 40 Percent Higher Than Predicted, Study Says