Faster Sea Level Rise?

14 Dec 2006

Sea level may be rising faster in the coming decades than previously expected. This is the conclusion of a new study by the German ocean expert Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research (PIK). Based on observational data for the 20th Century, Rahmstorf found a close link between the amount of global warming and the rate of sea level change: the warmer it gets, the faster sea levels rise. If this connection found for the 20th Century continues to hold in the coming 100 years, then the global sea level may be expected to rise by 50-140 cm by the year 2100. These results are published in the latest online edition of the journal Science.

As a result of global warming, global sea level has already risen by almost 20 cm in the 20th Century. Scientists have so far expected it to rise by another 9-88 cm this century, depending on how much greenhouse gases we emit and how strongly the climate system responds to that.

Rahmstorf's analysis was motivated by the fact that computer models of climate significantly underestimate the sea level rise that has already occurred. Future projections of sea level based on these climate models are therefore not yet reliable. Instead of using models, Rahmstorf's study is based on measurements of global air temperature and sea level changes.

“The fact that we get such different estimates using different methods shows how uncertain our sea level forecasts still are,” says Rahmstorf. A major reason for the uncertainty is the behaviour of the large ice sheets in Greenland and Antarctica, which is very difficult to predict. “For a given warming scenario, we may end up getting twice the sea level rise expected thus far.”

A sea level rise of one meter or more would be very bad news for major coastal cities, greatly increasing the risk of devastating storm surges. Particularly at risk are cities on North Atlantic shores like New York and London. Sea levels around the northern Atlantic may rise more than in the rest of the world if the North Atlantic Current slows down, as another study by Rahmstorf’s team showed in 2005.

Sea level rise can be limited by strongly reducing greenhouse gas emissions in the coming decades. In addition, preventive coastal protection measures can help to avoid the worst consequences.

Stefan Rahmstorf is professor of Physics of the Oceans at Potsdam University in Germany and is considered one of the leading international climate and ocean experts. He has published over 50 articles in scientific journals.

Original article:

S. Rahmstorf: A Semi-Empirical Approach to Projecting Future Sea-Level Rise, Science (express) 10.1126/science.1135456, 14 Dec. 2006.

More information:

Stefan Rahmstorf’s home page:

Background report: The Future Oceans, WBGU,

Related study: Levermann et al. 2005

Also see PIK press releases on Changes in Ocean Circulation, April 2005, and on Costs and Strategies of Global Climate Protection, March 2006

Graphics from the Science publication are available upon request from the PIK Press Office, e-mail:

Stefan Rahmstorf, Potsdam Institute for Climate Impact Research (PIK), Germany
phone: +49 (0)331 288 26 88, e-mail:

Press Office:
Uta Pohlmann, phone: +49 (0)331 288 25 07, e-mail: