Science: New Research Reduces Projected Rise is Sea Levels

Columbia Glacier, Alaska.

Some models of sea level fluctuations predict a rise of two meters or more by the year 2100, caused by global warming and the disintegration of Greenland and Antarctic ice. But in the latest issue of Science, a group of U.S. researchers argue that such an increase is actually a worst-case scenario, and they say that a more accurate estimate would be somewhere between 0.8 and two meters.

Even at the low end of that estimate, said the group headed by W. Tad Pfeffer from the University of Colorado, the impact would be devastating for millions of people living in low-lying coastal areas around the world. For example, they write, raising the California Central Valley levees by only 0.15 meters would cost more than $1 billion. In other areas, the rising seas could force whole populations to relocate away from coastal areas.

Researchers in many different scientific fields have addressed the issue of rising sea levels over the next hundred years due to climate change, but their predictions vary greatly. Some models of sea level fluctuation predict a rise of 0.5 meters—about 1.5 feet—by 2100, while others suggest the seas could rise a full 3.5 meters in that span.

Pfeffer, who specializes in glacier physics, and a small group of researchers from the University of Montana and the University of California-San Diego, reached their conclusions about sea level rise after performing a study on ice discharge from Greenland and Antarctica. But unlike most assessments in the past that have attempted to total the estimates of individual sources into the sea, their experiment approached the issue from a different angle.

Pfeffer and colleagues began with the predicted sea level rise of two meters, and then worked backwards.

They first calculated how much ice discharge from Greenland and Antarctica would be required to produce various rates of sea level rise, including the estimated two meters. Then, the researchers evaluated just how realistic those discharge rates actually were.

Their findings suggest that current discharge rates from the two sources in question are not enough to add up to a two-meter rise in sea level by 2100. They show that, for the sea to rise two meters in that time frame, more ice would need to be melted or expelled from Greenland and Antarctica than has ever been reported before. Although Pfeffer and his team acknowledge that discharge rates could potentially reach levels sufficient to cause the two-meter rise, they maintain that that projection is a worst-case scenario and not a reliable guide for public policy.

In their report, the researchers propose three other possible scenarios of ice discharge that they believe to be more likely. The three different scenarios incorporate current rates of ice discharge from Greenland and Antarctica, along with various adjusted rates, and provide a framework that the researchers believe to be more realistic.

Accurate predictions of sea level rise are necessary for planning constructive and cost-effective adaptation efforts. Underestimation will cause inadequate preparation and response, while overestimating the situation could lead to a waste of resources.

The Pfeffer report is published in the 5 September issue of Science, the journal of AAAS.

Brandon Bryn

5 September 2008