19 January 2007David Adam
Mist and pollution over the City of London. Photograph: Matthew Fearn/PA
New figures from dozens of measuring stations across the world reveal that concentrations of CO2, the main greenhouse gas, rose at record levels during 2006 - 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 we had little over a decade to tackle rising emissions to avoid the worst effects of climate change.
David Hofmann of the US National Oceanic and Atmospheric Administration (Noaa), which published the figures, said: "Over this last decade the growth rates in carbon dioxide have been higher. I don't think we can plausibly say what's causing it. It's something we're going to look at."
Peter Cox, a climate change expert at Exeter University, said: " The concern is that climate change itself will affect the ability of the land to absorb our emissions." 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.
Professor Cox added: "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."
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 according to the latest figures, last year saw a rise of 2.6ppm. And 2006 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 Niño weather pattern, centred on the Pacific Ocean. But the last El Niño was in 1998, when it resulted in a record annual increase in carbon dioxide of 2.9ppm. If the current trend continues, this year's predicted El Niño could see the annual rise in carbon dioxide pass the 3ppm level for the first time.
Prof 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. Such events are predicted to become more frequent with rising global temperatures. He admitted "the jury is still out" on whether the recent spike is evidence of a significant change, although some computer models predict that the Earth will start to absorb less carbon dioxide some time this decade.
"Over the past few years carbon dioxide has been going up faster than we would expect, based on the rate that emissions are increasing," Prof Cox said.
Figures presented to a recent UN climate conference in Nairobi showed that carbon dioxide emissions produced by the worldwide burning of fossil fuels increased by 3.2% from 2000 to 2005.
From 1990 to 1999 the emissions increase was 0.8%. But other experts think rising emissions could yet account for the anomaly. Pieter Tans of Noaa cited contrasting figures from the US Department of Energy, which show much sharper annual emissions increases, up to 4.5% in recent years. The Intergovernmental Panel on Climate Change is expected to announce more robust emissions data when it reports next month.
http://environment.guardian.co.uk/climatechange/story/0,,1994071,00.html
