Sea-level rises could send floods driven by storm surges over London's Thames Barrier regularly by the end of the century, if nothing is done to bolster the UK's flood defences, scientists warned on Tuesday.

But around the world sea level rises from melting ice alone are likely to be "in the tens of centimetres" rather than several metres by 2100, as some outlying estimates had predicted, according to Ice2Sea, a project bringing together scientists from around Europe in order to improve predictions of sea level rises under climate change.

The scientists also said there was only a one-in-20 chance that melting ice would contribute more than 84cm to sea level rises by 2100.

Their work has helped to narrow down some of the vast differences in estimates of sea level rises. But their central estimate range is still large – that ice melting is likely to contribute between 3.5 to 36.8cm to global sea levels by 2100, which when added to the likely thermal expansion equates to a sea level rise of about 30cm to 69cm.

However, what matters more than sea-level rises alone is the effect of storm surges from the sea. The power of such surges was shown dramatically 60 years ago in Europe, when a surge in the North Sea killed more than 1,800 people in the Netherlands and more than 326 people in the UK. The waters reached nine miles inland on the UK's east coast on the night of the January storm in 1953, and it was as a result of this that the Thames Barrier was built, finally being finished in the 1980s.

The current barrier was designed to withstand the sorts of floods that occur only once in 1,000 years. But the Ice2Sea estimates show how rapidly these calculations are having to be revised.

According to the report, the sort of sea storm surge that is currently calculated as a one-in-50 year event – coming on top of the sea level rises already in store – would send waters more than 1m above current sea levels by 2100. That would overflow the current Thames Barrier, though there are plans to reinforce it.

Milder storms, which are much more frequent, would also cause more devastation because of higher sea levels, as the waters from sea surges would reach further and overtop defences less robust than the Thames Barrier. The scientists also warned that although their estimates are based on 2100, many of the effects will be felt in varying degrees before then.



Their estimates are also all based on a climate change scenario that many scientists believe is now too moderate. They are based on a mid-range of temperature rises by the end of the century of about 3-5C. Recent studies by the International Energy Agency, the World Bank and others suggest that on current trends the world is on course for a rise in temperatures of about 6C by the end of the century. Such high temperatures would not only raise sea levels even higher, but would be likely to make storms much more intense, and perhaps more frequent.

Jonathan Bamber, professor at Bristol University, said that if temperatures rose higher than the lower estimate, the consequences would be much greater. "This is not linear," he warned.

The wide range of probabilities for sea-level rises produced by Ice2Sea indicates the sheer difficulty of making predictions of such a complex system. Estimates of sea-level rise are enormously complicated, because they must take account of a large number of factors, each of which is complex in itself: the melting of ice from ice sheets based on land, such as Greenland and the Antarctic; thermal expansion of the oceans as temperatures rise; an increased frequency of storms and sea surges, among many other factors. As a result, the estimate contained in the last report of the Intergovernmental Panel on Climate Change in 2007 was admitted as "incomplete".