US: The rate of ice melting in the Arctic is increasing and a panel of researchers says it sees no natural process likely to change the trend.
Within a century the melting could lead to a summertime ice-free ocean - conditions not seen in the area in a million years, the group said.
Melting of land-based glaciers could take much longer, but could raise the sea levels, potentially affecting coastal regions worldwide.
Changes to subsurface layers of frozen soil could undermine buildings, drain water into bogs and release more carbon into the atmosphere.
"What really makes the Arctic different from the rest of the non-polar world is the permanent ice in the ground, in the ocean, and on land," said Jonathan Overpeck, chairman of the American National Science Foundation's Arctic system science committee that issued the report.
"We see all of that ice melting already, and we envision that it will melt back much more dramatically in the future, as we move towards this more permanent ice-free state," Mr Overpeck said.
The panel's findings were published in Eos, the weekly newspaper of the American Geophysical Union.
The report comes just days after environmental ministers and officials from 23 countries met in Greenland to call on governments to start acting on global warming.
The session was held in the town of Ilulissat, near the edge of the Sermeq Kujalleq glacier, which has retreated nearly seven miles since 1960 and has become a symbol of global warming fears.
The report was issued following a week-long meeting of scientists who examined how the Arctic environment and climate interact and how that system would respond as global temperatures rise.
The scientists said they did not see any natural mechanism that could stop the loss of ice.
Mr Overpeck said that in addition to sea ice and land ice melting, the frozen soil layer called permafrost would melt and eventually disappear in some areas. This could release additional greenhouse gases stored in the permafrost for thousands of years.