GLOBAL warming of only 2C could lead to sea-level rises that would submerge the Netherlands and Bangladesh, a report in the journal Nature has warned.
Scientists at Princeton and Harvard universities in the United States carried out a new analysis of the geological record of the Earth's sea level.
Their research revealed that the polar ice sheets are vulnerable to large-scale melting, even under moderate global warming scenarios. According to the analysis, an additional 2C of global warming could commit the planet to 20ft to 30ft (about six to nine metres) of sea-level rises over the long term.
Coastal areas where hundreds of millions of people live would be inundated, the US scientists warned.
It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the US east coast, much of Bangladesh and most of the Netherlands unless unprecedented coastal protection were carried out.
The researchers say the sea-level rises would take place over "centuries", but warn that, unless greenhouse gases are not abated, the Earth could be committed during this century to enough warming to trigger this outcome.
The study, "Probabilistic Assessment of Sea Level During the Last Interglacial Stage", looked at a database of geological sea level indicators for a period about 125,000 years ago, between the last two ice ages – a time when Neanderthals roamed the Earth. Polar temperatures during this stage are thought to have been up to 3C to 5C warmer than today, making it comparable to what could happen over the next century should global warming not be tackled.
Previous studies have estimated the global sea level was 13-20ft higher than today during this "interglacial" stage.
However, the researchers came to a new conclusion that there was a 95 per cent probability that global sea level reached more than 22ft (6.7m) above its present level – and a maximum of 31ft (9.4m).
Professor Michael Oppenheimer, of Princeton University, said: "Despite the uncertainties inherent in such a study, these findings should send a strong message to the governments negotiating in Copenhagen that the time to avoid disastrous outcomes may run out sooner than expected."
And Robert Kopp, of Princeton's department of geosciences, who was also involved in the research, said he found the outcomes of the scientists' research "worrisome".
"The high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures.
"Yet if the global economy continues to depend heavily on fossil fuels, we're on track to have significantly more warming by the end of the century than occurred during the last interglacial."