Climate change experts clash over sea-rise ‘apocalypse’

Critics say an influential prediction of a 6ft rise in sea levels is flawed
Jonathan Leake

Climate science faces a new controversy after the Met Office denounced research from the Copenhagen summit which suggested that global warming could raise sea levels by 6ft by 2100.
The research, published by the Potsdam Institute for Climate Impact Research in Germany, created headline news during the United Nations summit on climate change in Denmark last month.
It predicted an apocalyptic century in which rising seas could threaten coastal communities from England to Bangladesh and was the latest in a series of studies from Potsdam that has gained wide acceptance among governments and environmental campaigners.
Besides underpinning the Copenhagen talks, the research is also likely to be included in the next report of the Intergovernmental Panel on Climate Change. This would elevate it to the level of global policy-making.

However, the studies, led by Stefan Rahmstorf, professor of ocean physics at Potsdam, have caused growing concern among other experts. They say his methods are flawed and that the real increase in sea levels by 2100 is likely to be far lower than he predicts.
Jason Lowe, a leading Met Office climate researcher, said: "These predictions of a rise in sea level potentially exceeding 6ft have got a huge amount of attention, but we think such a big rise by 2100 is actually incredibly unlikely. The mathematical approach used to calculate the rise is simplistic and unsatisfactory."
The row comes just weeks after the so-called climategate affair when emails leaked from the University of East Anglia's Climate Research Unit revealed how scientists tried to withhold data from public scrutiny.
The new controversy, which has no connection with Climategate, dates back to January 2007, when Science magazine published a research paper by Rahmstorf linking the 7in rise in sea levels from 1881-2001 with a 0.7C rise in global temperature over the same period.
Most scientists accept those data and agree that sea levels will continue to rise. However, Rahmstorf then parted company from colleagues by extrapolating the findings to 2100 — when the world is projected to have warmed by up to 6.4C unless greenhouse gas emissions can be reduced.
Based on the 7in increase in 1881-2001, Rahmstorf calculated that such a spike in temperature would raise sea levels by up to 74in — a jump that stunned other experts.
They say it is unsafe to use the relatively small increases in sea levels seen in the 19th and 20th centuries to predict such extreme changes in future.
Another critic is Simon Holgate, a sea-level expert at the Proudman Oceanographic Laboratory, Merseyside. He has written to Science magazine, attacking Rahmstorf's work as "simplistic".
"Rahmstorf is very good at publishing extreme papers just before big conferences like Copenhagen when they are guaranteed attention," said Holgate. "The problem is that his methods are biased to generate large numbers for sea-level rise which cannot be justified but which attract headlines."
One key problem cited by Holgate is that much of the 1881-2001 sea-level rise came from small glaciers melting in regions such as the Alps and Himalayas. Such glaciers are, however, disappearing fast and will be largely gone by 2050. It means further rises in sea levels would have to come from increased melting of the Antarctic and Greenland ice sheets.
These hold enough water to raise global sea levels by more than 200ft, but their recent contribution to sea-level rise has been negligible. Jonathan Gregory, a sea-level specialist at the Met Office, said: "We do not know enough about the physics of large ice sheets to predict how global temperature rise will affect them. My concern about these extreme predictions is that they could discredit the whole process because they are not backed up by solid science and that is vital in such a political area of research.”
Rahmstorf said he accepted the criticisms but his work was "the best system we have got". He added: “I agree that there has been too little research into the behaviour of ice sheets but that is exactly why I did this research. It uses simple measurements of historic changes in the real world to show a direct relationship between temperature rise and sea level increase and it works stunningly well.”
Rahmstorf said the last decade had, however, seen preliminary evidence suggesting that the ice sheets of Greenland and West Antarctica were becoming unstable. He said: "In my heart I hope my critics are right because a rise of the kind my work predicts would be catastrophic," he said. "But as a scientist I have to look at the evidence . . . my figures for sea-level rise are likely to be an underestimate of what the world will face by 2100."