The risk of rising sea levels engulfing Britain’s coasts has been overstated* but the evidence for other devastating impacts of climate change is growing, according to the first major review of the science of global warming since the “climategate”* affair.

Apocalyptic claims about the slowing down of the Atlantic Ocean conveyor belt*, popularly known as the Gulf Stream, have also been exaggerated, the review found. But the study by a group of Britain’s leading climate science institutions found that some risks posed by a warming climate were greater than had been stated by the Intergovernmental Panel on Climate Change (IPCC).

Public confidence in climate science was shaken this year after the IPCC admitted grossly exaggerating the risk of Himalayan glaciers melting. E-mails hacked from the University of East Anglia’s Climatic Research Unit also suggested that climate scientists had conspired to withhold information from climate sceptics.

The most recent IPCC report, published in 2007, had predicted that the Arctic would frequently be ice-free in summer between 2080 and 2100.
The latest observations of thinning ice indicate that ships could sail routinely across the North Pole in summer months as early as the 2060s, according to the review by the Met Office, the Grantham Institute for Climate Change at Imperial College and the Tyndall Centre for Climate Change Research.

Released in Cancun to coincide with the arrival of environment ministers and a handful of national leaders at the UN climate change conference, the study concluded: “There is overwhelming agreement on the fundamentals — that our climate is changing and this represents a real and urgent problem.”

The authors conceded that there was no evidence that the Gulf Stream was shutting down. The Gulf Stream brings warm water from the tropics and raises European temperatures by 5-10C (41-50F) on average. If it stopped flowing it could plunge North America and Western Europe into a mini ice age, the scenario dramatised in the disaster movie The Day After Tomorrow.

The National Oceanography Centre at the University of Southampton had claimed in 2005 that the flow rate had declined by 30 per cent since the 1950s.
But one recent study by Nasa, based on satellite measurements and 3,000 robotic floats, suggests it has actually accelerated in the past two decades.
The review concluded that the observed changes were the result of natural variability in ocean currents, not man-made emissions.
It said: “Ocean circulation is highly variable and improved observations cast doubt on previously reported evidence of recent slowdown.”
The review dismissed claims that the sea level could rise by more than 2m (7ft) by 2100 as “very unlikely”. It said “an increase of more than 1m is currently viewed as unlikely.” If the sea rose only 1m, the Thames Barrier and hundreds of other flood defences around Britain could probably cope. A 2m rise would require huge investment in new barriers. Predictions about sea level rise depend on assumptions made about the melting rate of the Greenland and Antarctic ice sheets. While some studies suggest the melt rate in Greenland is increasing, others suggest the Antarctic ice sheet is growing.

The review found new evidence that tropical forests were more susceptible to drought than previously thought. It also found that old forests continued to absorb carbon even though the trees were mature.

This finding has implications for the debate in Cancún about rewarding countries for preserving their forests. Some rainforest countries argue that palm oil and paper plantations should be included in the reward scheme because all trees absorb carbon as they grow.

The review suggested cutting down old trees could accelerate climate change even if they were replaced with plantation trees.
It said there was stronger evidence that thawing permafrost was contributing to emissions. Permafrost regions, such as Siberia, contain double the amount of carbon in the world’s atmosphere.

Evidence from new computer models suggested emissions of methane, a greenhouse gas 20 times more potent than carbon dioxide, would increase by up to 35 per cent for every degree of global temperature increase. These findings strengthen the claim that a warming climate will trigger a vicious circle of rising emissions from the thawing and drying of landscapes.

The review predicted that the intensity of tropical storms would increase but admitted that it is unclear whether such storms would become more frequent.
It suggested that bouts of extreme weather, such as intense rainfall, could become more frequent. But it added: “At present, we have poor skill in quantifying the local changes in extremes.”
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