Melting Ice Sheets Could Result In Sea Level Rise Twice As High As Predicted By IPCC

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Scientists in Europe and the US say that current estimates for the rise in sea levels are way too low. They predict higher levels than one metre per year, saying that current models are discounting many of the dynamic ice-sheet processes already being observed.

The scientists' estimation of historic sea level increases of 1.6 metres per century is around twice as high as the maximum estimates by the IPCC.

"Our analysis suggests that the accompanying rates of sea level rise due to ice volume loss on Greenland and Antarctica were very high indeed", the scientists say.

"There is currently much debate about how fast future sea level rise 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", said Professor Eelco Rohling of the National Oceanography Centre. He points out that the IPCC estimates mainly concern thermal expansion and melting surface ice, 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", Rohling said.

To arrive at their findings, Rohling's team used a new method for sea level reconstruction to examine rates of rise during the last interglacial (124 to 119 thousand years ago). They have experimented with this method since the late 1980s.

The scientists say it is incremental to better understand ice-sheet dynamics in a changing climate. The rate of future sea level rise is one of the crucial uncertainties in projections of future climate warming. During the last interglacial, the Earth's climate was warmer than it is today, due to a different configuration of the planet's orbit around the Sun.

During the interglacial, also known as the Eemian or Marine Isotope Stage 5e, Greenland was 3 to 5°C warmer than today. Those temperatures are expected for 50 to 100 years from now.

The interglacial was also the most recent period in which sea levels reached around six metres (20 feet) above the present, due to melt-back of ice sheets on Greenland and Antarctica. The new results provide the first robust documentation of the rates at which sea level rose to these high positions.

The study was conducted by scientists from the UK's National Oceanography Centre, research centres in Tübingen (Germany), Cambridge and New York. An article outlining the findings is published this week in the new journal Nature Geoscience.