Even if global concentrations of greenhouse gases in the atmosphere had been stabilized in the year 2000, we are “already committed to further global warming of about another half degree and an additional 320% sea level rise caused by thermal expansion by the end of the 21st century.” That is the finding of a new paper in the journal Science.
The paper’s authors, led by Gerald A. Meehl of the National Center for Atmospheric Research in Boulder, Colorado, ran two different models to predict temperature change and sea level rise under a variety of different scenarios: one in which atmospheric concentrations held at 2000 levels, and three that involved low, medium, and high estimates of 2100 levels.

The researchers found that, at the end of the 21st century, the low-level scenario would produce warming of 1.1 and 1.5 degrees Celsius, with sea level rising to 13 to 18 cm above year 1999 levels. The medium-range scenario produces a warming at the end of the 21st century of between 1.9- and 2.6 degrees C, with between 18 and 25 cm of sea level rise in the two models. For the high-estimate scenario, warming at 2100 is about 2.2- and 3.5 degrees C, and sea level rise is 19 to 30 cm. If greenhouse gas concentrations were then held level at 2100 levels, sea level rise would continue apace: by a further 12 to 21 cm by 2200, and by an additional 10 to 21 cm between 2200 and 2300. Sea level rise would continue for at least two centuries beyond 2300, even with greenhouse gas concentrations stabilized at 2100 levels.

The paper’s authors note that these calculations of sea level rise are based solely on thermal expansion of the ocean, and do not consider possible glacial or ice sheet melting in Greenland or Antarctica. As a result, they note, their results should be considered “the minimum values of sea level rise. Contributions from future ice sheet and glacier melting could perhaps at least double the projected sea level rise produced by thermal expansion.

Source: Meehl, G.A., et al. 2005. How much more global warming and sea level rise? Science307: 1769-1772.

Contact: Gerald A. Meehl, National Center for Atmospheric Research, Post Office Box 3000, Boulder, CO 80307, USA. E-mail: meehl@ncar.ucar.edu