Sea levels could rise twice as much as previously projected, climate scientists warned as they presented the latest research on global warming.
A 2007 report by the Intergovernmental Panel on Climate Change predicted a sea level rise of 7 to 23 inches by the end of the century.
But scientists meeting Tuesday in Copenhagen dismissed those estimates as too conservative, saying new data suggests that sea level rise could exceed 39 inches and is unlikely to be less than 20 inches.
"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," organizers said in a statement at the three-day congress hosted by the University of Copenhagen.
The melting of polar ice sheets and of glaciers are two big factors that will affect sea levels, they added.
"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 meters," said John Church of the Centre for Australian Weather and Climate Research.
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 scientists can analyze the dangers associated with global warming, but that it's up to politicians to do something about it.
"I am afraid that it is something that involves value judgment on the part of policy makers, and I am afraid that they shied away from it," he told the conference. "It is time to take action."
Some 1,600 abstracts from nearly 80 countries have been submitted to the conference, which will be attended by Nicholas Stern, the author of a British government report on the cost of climate change.