"Sea levels rising faster than predicted"

Rises in sea levels during the coming decades could be much higher than previously believed, say experts. A new report by a consortium of scientists from the National Oceanography Centre in Southampton, UK, and research centres in Germany and the US says that sea levels rose by an average of 1.6 m every hundred years when the Earth was last as warm as it is predicted to be by the end of the present century.

The report, published in the journal Nature Geoscience in December, suggests that current predictions of sea level rises may be too optimistic. In the last 20 years, the rising of sea levels has become one of the most ominous indications of climate change and one of the most frequent subjects for environmental debate.

In the last interglacial period (134 000 to 119 000 years ago), sea levels reached around 6 m above the present rate because of the melting of ice sheets in Greenland and Antarctica. The consortium’s results provide the first hard evidence of the sea’s rise to these levels.

Such new studies are providing proof that sea levels are rising higher than scientists had previously believed, and it is becoming clear that governments have to act faster to mitigate the effects of climate change. In the last century, the Earth experienced a warming of 0.7°C, and between 1993 and 2006 sea levels rose by 3.3 mm a year on average, whereas the 2001 IPCC (the UN’s Intergovernmental Panel on Climate Change) report predicted an annual rise of less than 2 mm.

Professor Eelco Rohling of the University of Southampton’s School of Ocean and Earth Science, said: ‘There is currently much debate about how fast future sea-level rises might be. Several researchers have made strong theoretical cases that the rates of rise projected from models in the recent IPCC Fourth Assessment are too low. This is because the IPCC estimates mainly concern thermal expansion and surface ice melting, while not quantifying the impact of dynamic ice-sheet processes. Until now, there have been no data that sufficiently constrain the full rate of past sea-level rises above the present level.

'We have exploited a new method of sea level reconstruction which we have pioneered since 1998, to look at rates of rise during the last interglacial. At that time, Greenland was 3°C to 5°C warmer than today, similar to the warming expected 50 to 100 years from now. Our analysis suggests that accompanying rates of sea level rise due to ice volume loss on Greenland and Antarctica were very high indeed.'

The researchers found that the average rate of rise of 1.6 m per century is approximately twice as high as maximum estimates in the IPCC Fourth Assessment report. As larger areas of the polar ice sheets melt, a sea rise approaching 1 m would threaten vast tracts of low-lying land, including major world cities such as New York, London and Tokyo.

The new findings offer strong evidence that climate change is causing potentially catastrophic changes to the Earth. Worldwide governmental action on climate change is urgent, as is more research and a better understanding of ice sheet dynamics.