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The finding published recently is crucial, because it means that more of the CO₂ we release will end up affecting the climate in the atmosphere rather than being safely locked away in trees or soil.

The results may partly explain recent studies suggesting that the amount of CO₂ in the atmosphere is increasing faster than expected.

If higher temperatures mean less carbon is soaked up by plants and microbes, global warming will accelerate.

The Intergovernmental Panel on Climate Change, which shared the Nobel peace prize with Al Gore, has concluded that humanity has eight years left to prevent the worst effects of global warming. Carbon uptake by land and sea is crucial to predictions about future warming.

“We are currently getting a 50 per cent discount on the climatic impact of our fossil fuel emissions,” the climate scientist John Miller of the University of Colorado wrote in a commentary on the research in the journal Nature — meaning that half of what we put out is sucked up by the oceans and ecosystems on land.

“Unfortunately, we have no guarantee that the 50 per cent discount will continue, and if it disappears we will feel the full climatic brunt of our unrelenting emission of CO₂ from fossil fuels.”

The surprise rethink concerns abundant evidence from around the world that winter is starting later and spring earlier.

In northern latitudes, spring and autumn temperatures have risen by 1.1C and 0.8C respectively in the past two decades.

That means a longer growing season for plants, which scientists thought should be a good thing for slowing warming.

This increased growth is even visible from space, with satellite measurements indicating a greening of the land. As plants take up more CO₂, that should put a break on CO₂ increases.

The data, which goes back to 1980, charts the levels of CO₂ in the local atmosphere. This is a product of both uptake by plants during photosynthesis and release of CO₂ by plants and microbes during respiration.

The team focused particularly on the date in autumn at which the forests switched from being a net sink for carbon into a net source.

Instead of moving later in the year as they had expected, this date actually got earlier — in some places by a few days, but in others by a few weeks.

“This means potentially a bigger warming effect,” said Timo Vesala at the University of Helsinki, who led the study.

The research could partly explain results by the Global Carbon Project, which confirmed that the rise in CO₂ levels in the atmosphere is accelerating. — Guardian Newspapers Limited 2008

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