Sea level rise may exceed worst expectations
Seas were nearly 10 metres higher than now in previous interglacial period.
By Richard A. Lovett With climate talks stalling in Copenhagen, a study suggests that one problem, sea level rise, may be even more urgent than previously thought. Robert Kopp, a palaeoclimatologist at Princeton University in New Jersey, and his colleagues examined sea level rise during the most recent previous interglacial stage, about 125,000 years ago. It was a time when the climate was similar to that predicted for our future, with average polar temperatures about 3-5°C warmer than now. Other studies have looked at this era, but most focused on sea level changes in only a few locales and local changes may not fully reflect global changes. Sea level can rise, for example, if the land is subsiding. It can also be affected by changes in the mass distribution of Earth. For example, says Kopp, ice-age glaciers have enough gravity to pull water slightly polewards. When the glaciers melt, water moves back towards the Equator. To adjust for such effects, Kopp’s team compiled sea-level data from over 30 sites across the globe. “We could go to a lot of different places and look at coral reefs or intertidal sediments or beaches that are now stranded above sea level, and build a reasonably large database of sea-level indicators,” says Kopp. The team reports in Nature today that the sea probably rose about 6.6–9.4 metres above present-day levels during the previous period between ice ages. When it was at roughly its present level, the average rate of rise was probably 56–92 centimetres a century. “[That is] faster than the current rate of sea level rise by a factor of about two or three,” Kopp says, warning that if the poles warm as expected, a similar acceleration in sea-level rise might occur in future. The study is “very sophisticated”, says Peter Clark, a geologist at Oregon State University in Corvallis. “A lot more of the existing ice sheets at the time must have melted than was thought to be the case,” he says, such as parts of Greenland and Antarctica. The implications are disconcerting, says Clark. If the world warms up to levels comparable to those 125,000 years ago, “we can expect a large fraction of the Greenland ice sheet and some part of the Antarctic ice sheet, mostly likely West Antarctica, to melt. That’s clearly in sight with where we’re heading.” Jonathan Overpeck, a climate scientist at the University of Arizona in Tucson agrees. “Earth’s polar ice sheets may be more vulnerable to climate change than commonly believed,” he says. …
