Rising sea levels pose a grave threat to the world's coastal areas unless industrial gas emissions are reduced, a United Nations report said.

"Climatic change is the most important environmental problem of the future," Peter Usher of the U.N. Environment Program (UNEP) told a Stockholm news conference.He said a scientific consensus had been reached on the "greenhouse effect," the rise in global temperatures due to industrial releases trapping solar heat near the Earth's surface.

Rising sea levels from melting ice caps would sharply increase the risk of flooding to countries with low coastlines, such as the Netherlands, China, Bangladesh and Egypt, said the report's co-author, Gordon Goodman.

"Even with moderate sea level rises, storms and tidal waves could have devastating effects," he said, adding that 50 million people in Bangladesh and 10 million in the Nile delta were at immediate risk.

Emissions of carbon dioxide from fuel burning and chlorofluorocarbons from spray cans and refrigerators were likely to result in the most dramatic temperature rises experienced in human history, he said.

A large rise in emissions would give an average temperature increase of 1.44 degrees per decade from now until the middle of the next century, while emissions at current levels would raise temperatures 0.54 degrees per decade.

Global warming could raise sea levels by between 12 inches and 4 1/2 feet by the middle of the 21st century, according to the report, "Developing Policies for Responding to Climatic Change," published jointly by UNEP and the World Meteorological Organization.

"Even an 8-inch sea level rise would put New York at risk," said co-author Jill Jaeger.