CO2 from forest destruction overestimated?

The carbon dioxide emissions caused by the destruction of tropical forests have been significantly overestimated, according to a new study. The work could undermine attempts to pay poor countries to protect forests as a cost-effective way to tackle global warming.

The loss of forests in countries such as Brazil and Indonesia is widely assumed to account for about 20% of all carbon dioxide produced by human activity – more than the world's transport system. The 20% figure was published by the Intergovernmental Panel on Climate Change in 2007 and was widely quoted after being highlighted by the Stern review on the economics of the problem. It is repeatedly used by Prince Charles and others as an incentive to push efforts to include forests in carbon trading.

Curbing emissions from deforestation is one of the main issues being discussed at a UN climate meeting in Barcelona this week, before crucial talks in Copenhagen next month.

But researchers led by Guido van der Werf, an earth scientist at VU University in Amsterdam, say that figure is an overestimate and that the true figure is closer to 12%. Publishing their analysis in the journal Nature Geoscience, they say the 20% figure was based on inaccurate and out-of-date information. "It's a tough message because everybody would like to see forests better protected and it is difficult to tell them that carbon dioxide emissions are less important than assumed. Still, the good news of lower emissions is no bad news for the forests," said Van der Werf.

The lower figure could make it harder to agree ways to reward forest protection, he said. "If you want to put a price on carbon [in forests] then you would get less carbon for your money now."

The study showed previous assessments exaggerated the rate of tropical deforestation. It also took into account soaring emissions from fossil fuel burning since 2000, which reduces the relative role of deforestation. The scientists say 12% is an estimate, and the figure could be between 6% and 17%, but that the original 20% figure was equally uncertain.

Van der Werf said an important finding of the research was the previously unquantified emissions from tropical peatlands, which they say could be as high as 3% of global CO₂ – more than the aviation industry. "The total contribution of deforestation and peatlands is about 15% and is still a substantial contribution to global CO₂ emissions, and therefore remains a significant opportunity for global CO₂ reduction," he said.