Figures deliver stark warning of a flooded future

Scientists will warn this week that rising sea levels, triggered by global warming, pose a far greater danger to the planet than previously estimated.

There is now a major risk that many coastal areas around the world will be inundated by the end of the century because Antarctic and Greenland ice sheets are melting faster than previously estimated.

Low-lying areas, such as Bangladesh, Florida, the Maldives and the Netherlands face catastrophic flooding, while in Britain, the Thames estuary is likely to disappear by 2100. Cities like London will need new flood defences.

"It is now clear that there are going to be massive flooding disasters around the globe," said Dr David Vaughan, of the British Antarctic Survey.

"Populations are shifting to the coast, which means that more and more people are going to be threatened by sea-level rises."

The issue is set to dominate the opening sessions of the international climate change conference in Copenhagen this week, when scientists will outline their latest findings on a host of issues concerning global warming.

The meeting has been organised to set the agenda for this December's international climate talks (also to be in Copenhagen), which will draw up a treaty to replace the Kyoto protocol for limiting carbon dioxide emissions.

And key to these deliberations will be the issue of ice-sheet melting.

The International Panel on Climate Change (IPCC), when it presented its most up-to-date report on the likely impact of global warming in 2007, said sea-level rises of between 20cm and 60cm would occur by 2100.

These figures were derived from estimates of how much the sea will increase in volume as it heats up, a process called thermal expansion, and from projected increases in run-off water from melting glaciers in the Himalayas and other mountain ranges.

But the report contained an important caveat that its sea-level rise estimate contained very little input from melting ice sheets in Antarctica and Greenland. The IPCC forecast thus underestimated forthcoming changes.

"The IPCC felt the whole dynamics of polar ice-sheet melting were too poorly understood," said Vaughan.

"However, we are now getting a much better idea of what is going on in Greenland and Antarctica and can make much more accurate forecasts about ice-sheet melting and its contribution to sea-level rises." From studying satellite images, scientists have seen the sea ice that hugs the Greenland and Antarctic shores dwindle and disappear.

Sea-ice melting on its own does not cause ocean levels to rise, but it has a big effect on land ice sheets. Without sea ice to prop them up, the land sheets tip into the water and disintegrate at increasing rates, a phenomenon researchers are now studying in detail.

"It is becoming increasingly apparent from our studies of Greenland and Antarctica that changes to sea ice are being transmitted into the hearts of the land-ice sheets in a remarkably short time," said Vaughan.

These revisions suggest sea-level rises could easily top a metre by 2100 - a figure backed by the United States Geological Survey, which this year said they could reach as much as 1.5m.

And in September, a University of Colorado team published calculations using conservative, medium and extreme glaciological assumptions for sea-level rise expected from Greenland, Antarctica and the world's smaller glaciers and ice caps. They concluded that the most plausible scenario, when factoring in thermal expansion due to warming waters, will lead to a total sea level rise of 1 to 2 metres by 2100.

A commission of 20 international experts, called on by the Dutch Government to help plan its coastal defences, recently gave a range of 55cm to 1.1m for sea-level rises by 2100.

"Equally important, this commission has highlighted the fact that sea-level rise will not stop in the year 2100," said Professor Stefan Rahmstorf of Potsdam Institute for Climate Impact Research. "By 2200, they estimate a rise of 1.5 to 3.5m unless we stop the warming. This would spell the end of many of our coastal cities."

This point was backed by Dr Jason Lowe of the Hadley Centre, Britain's foremost climate change research centre. "It is still not clear exactly how much the sea will rise by the end of this century, but it is certain that rises will continue for hundreds of years beyond that - even if we do manage to stabilise carbon dioxide emissions and halt the rise in atmospheric temperature. The sea will continue to heat up and expand."

SHORT-TERM RISES
Scientists argue the most important issue is that of short-term sea-level rises: probably around 1m by 2100.

* The Maldives would be submerged, along with islands like the Sunderbans in the Bay of Bengal and Kiribati and Tuvalu in the Pacific.
* The United States - which has roughly 19,955km of coastline and more than 51,540sq km of coastal wetlands - would face a bill of around US$156 billion to protect this land.
* About 17 per cent of Bangladesh would be flooded.
* Cities such as London would require massive investments to provide defences against the rising waters.
* Rising oceans would also contaminate both surface and underground fresh water supplies, worsening the world's existing fresh-water shortage.
* Coastal farmland would be wiped out, triggering massive displacements of men, women and children.

WORRYING SCENARIO
Scientists calculate that if industrial emissions of CO2 and other greenhouse gases eventually produce a global temperature increase of around 4C, Greenland's ice covering might melt completely. It would add around 7m to the planet's sea levels. The consequence: utter devastation.

- OBSERVER