Furthermore the forests in the region are less effective in soaking up greenhouse gases than previously believed.

Snow and ice are melting earlier, according to the scientists, from the University of Jena in eastern Germany who used data from European, Japanese and US satellites.

Because of the rise in temperatures in the taiga (coniferous forests) there has been an increase in the release of organic carbon from decomposition and in the production of methane, a greenhouse gas.

"All that leads us to believe that the taiga overall absorbs less greenhouse gas than we were supposing until now," Professor Christiane Schmullius said.

She thought her team's findings could also apply to other major northern hemisphere forests such as those in Canada and the United States.

The taiga only soaks up 20 percent of Russia's output of carbon dioxide of human origin and only 10 percent of European output, according to Martin Heimann of the Max-Planck Institute.

The scientists say their findings contradict the idea put forward by supporters of the Kyoto agreement on cutting greenhouse gases that tree planting could help.

The Kyoto protocol, agreed in 1997 but shunned by the United States, the world's biggest producer of greenhouse gases, aims to cut emissions by five percent by 2012 from their 1990 levels.

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