Melting glaciers, ice sheets and snow cover could affect up to 40 percent of the world's population through rising sea levels, flooding and dwindling supplies of water for drinking and farming, a U.N. report said Monday.
The study by about 70 scientists, released before Tuesday's World Environment Day, also highlighted the risk that the receding ice cover could accelerate global warming, because the icepacks cool the planet by reflecting heat into space.
Even though much of the ice is in remote areas, such as polar regions and Greenland, the impact will be felt worldwide, U.N. Environment Program executive director Achim Steiner said.
"The report underlines that the fate of the world's snowy and icy places in a climatically challenged world should be cause for concern in every ministry, boardroom and living room across the world," Steiner said.
The report was released in the Norwegian Arctic city of Tromsoe, which is hosting the main international celebrations of World Environment Day under the theme "Melting ice - a hot topic?"
It builds on a series of reports by the Intergovernmental Panel on Climate Change released earlier this year.
The report, called "The Global Outlook for Snow and Ice," said warmer temperatures could raise sea levels by 20 to 80 centimeters (30-50 inches) this century, which could flood low-lying areas and force millions to flee, such as in Bangladesh.
Even those far from a coast could feel the impact, such as many as 1.5 billion people, mainly in Asia, who get their fresh water from the spring thaw of snow and ice.
"An estimated 40 per cent of the world's population could be affected by loss of snow and glaciers on the mountains of Asia," the UNEP said.
In the Northern Hemisphere, snow cover in March and April has declined 7-10 percent over the past 30 or 40 years, the report said.
It said over the past 30 years, the extent of sea ice has declined 6-7 percent in winter and 10-12 percent in summer, while ice thickness has declined by at least 10-15 percent. The rate at which the Greenland ice sheet is melting has doubled over the past two or three years, and glaciers are receding in most of the world.
"Melting of ice and snow will in itself have severe consequences on nature and society. But it will also reduce the reflection of sun beams from the surface of the Earth and in this way contribute to further global warming," Norwegian Environment Minister Helen Bjoernoey said.
In addition to snow and ice free areas absorbing more heat, the melting of permafrost in places like Siberia could open new bodies of water, creating "thermokast lakes" that could release enormous amounts of the powerful greenhouse gas methane.
Bjoernoey said she was especially worried by the idea that "Global warming results in further global warming."
The report said people are already adapting to the change. In China, a railroad built on permafrost includes a cooling system to prevent melting that would undermine frozen ground under the tracks.
Hunters in parts of Greenland have switched from traditional dogsleds to small boats because of changes in their ice.
Events in Tromsoe began Sunday, with South African Bishop Desmond Tutu hosting an ecumenical church service, and last through Tuesday, with a climate conference.