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Carbon dioxide being released from the soil could be making climate change worse.

Researchers warn that this phenomenon — which seems to be caused by climate change itself — means that targets for reducing man-made emissions of carbon dioxide will need an urgent rethink.

In a study published today (8 September) in Nature, a team led by Guy Kirk of Cranfield University, United Kingdom, compared the amount of carbon in soil from across England and Wales in 2003, with figures for 1978.

Until now scientists have generally assumed that carbon is largely locked away in soil permanently. But Kirk's team estimated that the upper layer of soil in the United Kingdom as a whole is losing 13 million tonnes of carbon each year.

They do not know how much of this carbon is being released into the atmosphere as carbon dioxide — the main contributor to global warming — and how much is moving further down into the earth.

Kirk's group say that the fact that soil is losing carbon irrespective of how land is used "suggests a link to climate change".

Between 1978 and 2003, the average temperature across England and Wales increased by half a degree Celsius and rainfall patterns changed.

These factors could be helping soil bacteria to decompose matter faster, releasing carbon dioxide faster than before.

"The scientific and political implications of the new findings are considerable," say Detlef Schulze and Annette Freibauer of Germany's Max-Planck Institute for Biogeochemistry in an accompanying article in Nature.

Climate policy will need to take better account of carbon sources, and ensure the protection of  'sinks' where carbon is stored naturally, they say.

They point out that the carbon losses revealed by Kirk's team equate to eight per cent of UK carbon dioxide emissions in 1990, and exceed the entire reduction in emissions achieved by the nation between then and 2002.

"The urgency of reducing fossil fuel emissions is now even greater," Kirk told SciDev.Net.

Link to full paper in Nature 

Link to full article by Schulze and Freibauer in Nature 

Reference: Nature 437, 245 (2005)