Climate scientists have warned that melting polar ice sheets could cause sea levels to rise twice as much as predicted.
A 2007 report by the Intergovernmental Panel on Climate Change (IPCC) projected a sea level rise of seven to 23 inches by the end of the century.
But experts presenting the latest research on global warming at a meeting in Copenhagen on Tuesday dismissed those estimates as too conservative, saying that new data suggests that sea levels could rise by over 39 inches.
Organisers of the three-day congress hosted by the University of Copenhagen said in a statement: 'This means that, if the emissions of greenhouse gases is not reduced quickly and substantially, even the best-case scenario will hit low-lying coastal areas housing one-tenth of humans on the planet hard.'
The melting of polar ice sheets and of glaciers are two big factors that will affect sea levels, they added.
Australian Weather and Climate Research Centre spokesman John Church said: 'Unless we undertake urgent and significant mitigation actions, the climate could cross a threshold during the 21st century, committing the world to a sea level rise of metres.'
The conclusions of the conference will be presented to politicians meeting in Copenhagen in December to discuss a new global agreement on greenhouse gas emissions to replace the Kyoto Protocol, which expires in 2012.
IPCC chairman Rajendra Pachauri said that, while scientists can analyse the dangers associated with global warming, it's up to politicians to do something about it.