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Concentrations of carbon dioxide rising faster than expected

Carbon dioxide is accumulating in the atmosphere much faster than scientists expected, raising fears that humankind may have less time to tackle climate change than previously thought.

New figures from dozens of measuring stations across the world reveal that concentrations of carbon dioxide, the main green-house gas, rose at record levels last year -- the fourth year in the last five to show a sharp increase.

Experts are puzzled because the spike, which follows decades of more modest annual rises, does not appear to match the pattern of steady increases in human emissions.

At its most far reaching, the finding could indicate that global temperatures are making forests, soils and oceans less able to absorb carbon dioxide -- a shift that would make it harder to tackle global warming.

Such a shift would worsen even the gloomy predictions of the Stern Review which warned that the world had little over a decade to tackle rising emissions to avoid the worst effects of climate change.

"The concern is that climate change itself will affect the ability of the land to absorb our emissions," said Peter Cox, a climate change expert at Exeter University in the UK.

At the moment around half of human carbon emissions are reabsorbed by nature, but the fear among scientists is that increasing temperatures will work to reduce this effect.

"It means our emissions would have a progressively bigger impact on climate change because more of them will remain in the air. It accelerates the rate of change so we get it sooner and we get it harder," Cox said.

Carbon dioxide concentration in the atmosphere is measured in parts per million (ppm). From 1970 to 2000 that concentration rose by about 1.5ppm each year, as human activities sent more of the gas into the atmosphere. But last year saw a rise of 2.6ppm.

And last year was not alone. A series of similar jumps in recent years means the carbon dioxide level has risen by an average 2.2ppm each year since 2001.

Above average annual rises in carbon dioxide levels have been explained by natural events such as the El Nino weather pattern, centred on the Pacific Ocean. But the last El Nino was in 1998, when it resulted in a record annual increase in carbon dioxide of 2.9ppm.

Cox said that an increase in forest fires, heatwaves across Europe and the Amazon drought of 2005 could have helped to drive up carbon dioxide levels.
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