New York, London, Hong Kong business hubs to submerge by 2100?

Would towering sea waves lap over economic hubs of London, New York and Hong Kong, where the world's business transactions take place, by 2100?

Experts have warned that without efforts to curb the rise of greenhouse gases, the polar ice caps may melt far faster under the pressure of global warming than it was previously thought, threatening island states and coastal cities.

The world's ice sheets could retreat farther by the year 2100 than they have in the past 130,000 years, leading to a huge rise in sea level, experts say adding, low-lying islands such as Tuvalu and the Maldives look set to disappear.

Coastal cities will be forced to beef up their defences or else think about relocating.

The financial districts of London, New York and Hong Kong to name but three, lie barely above sea level, a report in the Nature magazine claims.

"I think sea-level rise is a huge threat," says Colin Prentice, who studies ecosystem responses to climate change at the University of Bristol, UK.

"As humans, everything we've done is set up for a stable climate. We've built huge cities within a metre of sea level and never thought they would be swamped," Prentice says. 

Researchers led by Jonathan Overpeck of the University of Arizona in Tucson and Bette Otto-Bliesner of the National Center for Atmospheric Research in Boulder, Colorado, have looked at a period known as the Last Interglaciation.

At this time, 130,000 years ago, shifts in Earth's orbit caused the Arctic to warm by 3-5 degrees Celsius and the sea level to rise by some 5 mt, the magazine says.

The team, the report adds, has worked out how Earth responded to that temperature rise in the past and asked when a similar shift might happen in the future.

The answer, it seems, is surprisingly soon.

Will the sea rise by the same amount as it did before?

"We're not saying it is going to happen exactly the same" as during the LIG, Overpeck was quoted as saying.

"If anything this is a conservative estimate of what could happen in the future," Overpeck says.

The warming that occurred during the LIG was due to Earth shifting in its orbit and tilting the Arctic region towards the Sun.

This time, warming is being caused by greenhouse gases. This means the effect will be seen at both poles, rather than being chiefly limited to the Northern Hemisphere.

"This time we're hitting it harder. It will be year-round and global," says Overpeck.

In 2001, Nature says, the Intergovernmental Panel on Climate Change predicted that sea levels would rise by a maximum of 88 cm by 2100.

It added that further warming could trigger polar ice-cap melting, which might result in sea-level rises of more than five mt by 3000.

But Overpeck and colleagues' work, published in this week's Science, indicates that metres of rise could happen much more quickly, potentially within the next 100 years.

Global warming is bringing an increase in polar snow that is making parts of both Greenland and the Antarctic bulk up, but recent research has shown that this is outweighed by melting, the report says.