Global warming may trigger carbon 'time bomb', scientist warns

Billions of tonnes of carbon dioxide and methane could be released from thawing Arctic soils, says climate researcher
Siberia, Russia
Siberia, Russia Photograph: Francis Latreille/© Francis Latreille/Corbis

Even modest amounts of global warming could trigger a carbon "time bomb" and release massive amounts of greenhouse gases from frozen Arctic soils, a new study has warned.

Philippe Ciais, a researcher with the Laboratory for Climate Sciences and the Environment in Gif-sur-Yvette, France, told the Copenhagen Climate Congress that billions of tonnes of carbon dioxide and methane could be freed by just a 2C average rise.

He said such a release of greenhouse gases could trigger an "explosive" reaction in the soil, with bacteria able to start decomposing giant stocks of frozen carbon. "You can call it a bacterial heat production effect if you are a pretentious scientist, or you can call it composting," he said.

Using computer models and measurements from Siberia, Ciais and his colleagues predicted a fifth of the carbon could be released by 2200, once soil temperatures reached about 8C higher than today's levels. A global average increase in air temperatures of 2C would mean significantly higher temperatures in the Arctic, and Ciais warned that a few unusually hot years could see soil temperatures reach the 8C threshhold.

He called for a global observation network to monitor permafrost, and said it was a "scandal" that there are only about 20 people measuring it worldwide.