NEW YORK • For half a century, climate scientists have seen the West Antarctic ice sheet, a remnant of the last Ice Age, as a sword of Damocles hanging over human civilisation.
The great ice sheet, larger than Mexico, is thought to be potentially vulnerable to disintegration from a relatively small amount of global warming, and capable of raising the sea level by 3.6m or more should it break up. But researchers long assumed that the worst effects would take hundreds - if not thousands - of years to occur.
Now, new research suggests the disaster scenario could play out much sooner.
Continued high emissions of heat-trapping gases could launch a disintegration of the ice sheet within decades, according to a study published on Wednesday, heaving enough water into the ocean to raise the sea level by as much as 1m by the end of this century.
With ice melting in other regions too, the total sea level rise could reach almost 2m by 2100, the researchers found. That is roughly twice the increase reported as a plausible worst-case scenario by a United Nations panel just three years ago, and so high that it would likely provoke a deep crisis within the lifetime of children being born now.
Singapore's efforts at tackling rising waters
SINGAPORE • The first phase of a national climate change study which was completed last year projects the mean sea level to rise by up to 0.76m by the end of the century, the Building and Construction Authority (BCA) said earlier this year.
An ongoing "coastal adaptation study", which is expected to be completed by next year, would spell out what needs to be done to prepare for that predicted rise in sea level.
Meanwhile, Singapore is adequately protected from coastal floods for the immediate future, although experts have warned that rising sea levels will have a devastating impact on Singapore.
In 2011, the reclamation height was raised from 3m to 4m above the mean sea level.
About 70 per cent to 80 per cent of Singapore's coastal areas already have hard walls or stone embankments, which help protect against coastal erosion, a BCA spokesman said.
Works are being carried out in Nicoll Drive to elevate the 1km, two-lane dual carriageway by up to 0.8m.
It is the Land Transport Authority's first road-raising project in anticipation of rising sea levels triggered by global warming, the authority had said.
As Nicoll Drive is located near the coastline next to Changi Beach, the works are being carried out to minimise the risk of seawater inundation as part of the Government's overall coastal protection measures for climate change adaptation.
The project, to be completed by the middle of this year, is expected to help motorists stay dry during unusually high tides.
In 1974, several parts of the city were submerged - without a single drop of rain.
The situation would become far worse beyond 2100, the researchers found, with the rise of the sea exceeding 30cm per decade by the middle of next century.
Scientists have documented such rates of increase in the geological past, when far larger ice sheets were collapsing, but most of them had long assumed that it would be impossible to reach rates so extreme with the smaller ice sheets of today.
"We are not saying this is definitely going to happen," said Dr David Pollard, a researcher at Pennsylvania State University and a co-author of the new paper.
"But I think we are pointing out that there's a danger, and it should receive a lot more attention."
The long-term effect would likely be to drown the world's coastlines, including many of its great cities.
New York is nearly 400 years old; in the worst-case scenario conjured by the research, its chances of surviving another 400 years in anything like its present form would appear to be remote. Miami, New Orleans, London, Venice, Shanghai, Hong Kong and Sydney are all just as vulnerable as New York, or more so.
In principle, coastal defences could be built to protect the densest cities, but experts believe it would be impossible to do that along all 152,888km of the American coastline, meaning that immense areas will most likely have to be abandoned to the rising sea.
The new research, published by the journal Nature, is based on an improved computerised model of Antarctica and its complex landscape of rocks and glaciers that is meant to capture factors newly recognised as imperilling the stability of the ice.
The new version of the model allowed the scientists, for the first time, to reproduce high sea levels of the past, such as a climatic period about 125,000 years ago when the seas rose to levels 6m to 9m higher than they are today.
That gave the researchers greater confidence in the model's ability to project the future sea level, although they acknowledge that they do not yet have an answer that could be called definitive.
The new research is the work of two scientists who have been at the forefront of ice sheet modelling for years. They are Dr Pollard and Professor Robert DeConto of the University of Massachusetts, Amherst.
NEW YORK TIMES