It said human impact on the climate was melting glaciers from the Andes to the Himalayas, bringing longer-term threats of higher sea levels that could swamp island states.

Officials from 180 nations will meet in Milan on December 1-12 to discuss international efforts to rein in a rise in global temperatures, blamed by scientists on emissions of gases from factories and cars that are blanketing the planet.

"Simulations project that a 4.0 Celsius (8.0 F) rise in temperature would eliminate nearly all of the world's glaciers" by the end of the century, WWF said.

Himalayan glaciers feed seven great rivers of Asia that run through China and India, the world's most populous nations, ensuring a year-round water supply to two billion people.

WWF said that nations most at risk also included Ecuador, Peru and Bolivia, where melt water from Andean glaciers supplies millions during dry seasons.

Island states like Tuvalu in the Pacific, meanwhile, could be submerged by rising sea levels triggered by melting glaciers.

Sea levels could rise even further if two of the world's largest ice caps, in Antarctica and Greenland, melt substantially, though the report left them out of its reckoning because of their unpredictability.