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Scientists appear to have solved the mystery of where huge quantities of man-made carbon dioxide are ending up after being pumped into the atmosphere, writes Kam Patel.

Tropical forests were declared a major sink for "missing carbon" at a meeting yesterday to discuss findings of a five-year global environment research programme.

John Lawton, director of the Natural Environment Research Council's centre for population biology at Imperial College, London, explained that the burning of fossil fuels releases about seven gigatonnes of carbon dioxide into the atmosphere a year.

While this release is a major driver for global warming, the problem is not as bad as it could be. Only about half stays in the atmosphere while much of the rest dissolves in the oceans. But the sink for a significant amount, around one to two gigatonnes, has been unknown up to now.

NERC's TIGER research programme has led to British and Brazilian scientists showing that forests in Amazonia, Cameroon and Canada are all accumulating carbon, and at a rate far greater that anticipated. In Amazonia alone the uptake is enough to account for the missing sink. The carbon is stored up as wood, leaves and dead organic matter and acts, in effect, as a fertiliser.

Professor Lawton says: "The finding that tropical forests are most likely the 'missing sink' is a major achievement that is contrary to expectations. Most scientists thought the forests were in equilibrium. Quite apart from other reasons for conserving tropical forests, this finding indicates that their further large-scale destruction will inevitably have a damaging impact on their ability to absorb carbon dioxide."