"This is very alarming," said Svein Tveidtal, a prominent scientist with the United Nations Environment Program. "The Arctic is an area where temperature changes are going to cause tremendous problems."

Permafrost is land that stays frozen throughout the year and there are vast expanses of it in the Antarctic and the northernmost Arctic.

For thousands of years, the permafrost has mopped up carbon dioxide from the atmosphere and stored it in its soil, mainly because the decomposition of dead vegetation is extremely slow in such low temperatures.

However, with rising temperatures in the Arctic, microbes decompose dead plant matter at a higher rate, releasing carbon dioxide that then adds to the problem of global warming.

U.N. scientists say the vicious cycle appears to have already begun.

"There are indications that at least some parts of the Arctic have switched from being sinks of carbon dioxide to being sources," scientists monitoring the melting of the permafrost said in a recent report.

Tveidtal conceded that investigations were still at a very early stage but the consequences of global warming on the Arctic permafrost were serious, not just for the environment but also for human settlements.

Rising temperatures can turn the permafrost from a solid structure of frozen soil into a soft, slurry-like material that can lead to subsidence and damage to buildings and structures.

Tveidtal said the problems might also have a significant impact on Arctic wildlife such as reindeer populations, as well as on the traditional lifestyles of indigenous people. Some 200,000 indigenous people live in Arctic Russia alone.