Sea levels are rising 60 percent faster than the UN's climate panel forecast in its most recent assessment, scientists reported yesterday.
At present, sea levels are increasing at an average 3.2 millimetres (0.125 inches) per year, a trio of specialists reported in the journal Environmental Research Letters.
This compares with a "best estimate" by the UN's Intergovernmental Panel on Climate Change (IPCC) in 2007, which projected that by today, the rise would be 2 mm (0.078 inches) per year.
The new figure converges with a widely-shared opinion that the world is heading for sea-level rise of around a metre (3.25 feet) by century's end, co-author Grant Foster of US firm Tempo Analytics told AFP.
"In low-lying areas where you have massive numbers of people living within a metre of sea level, like Bangladesh, it means that the land that sustains their lives disappears, and you have hundreds of millions of climate refugees, and that can lead to resource wars and all kinds of conflicts," he said.
â€œFor major coastal cities like New York, probably the principal effect would be what we saw in Hurricane Sandy.
"Every time you get a major storm, you get a storm surge, and that causes a major risk of flooding. For New York and New Jersey, three more feet of water would be even more devastating, as you can imagine," Foster added.
The investigation, led by Stefan Rahmstorf of Germany's Potsdam Institute for Climate Impact Research (PIK), gauged the accuracy of computer simulations that the IPCC used in its landmark Fourth Assessment Report in 2007.
The new study gave high marks for the document's forecast on global temperature, saying there was a "very good agreement" with what was being observed today, an overall warming trend of 0.16 degrees Celsius (0.28 degrees Fahrenheit) per decade.
But it said the IPCC's projection for sea levels was much lower than what has turned out.
Foster said the bigger-than-projected rise could be attributed to meltwater runoff from land ice, something that was a big unknown when the IPCC reported in 2007 and remains unclear today.
Other factors were technical uncertainty, he added.