Could forests boost global warming?
© 2000 Reuters Limited
November 8, 2000
LONDON, Nov. 8 — Global warming could happen faster than scientists expect because forests, instead of mitigating climate change, could speed it up, researchers say.
AS ENVIRONMENT MINISTERS prepare for a major climate change conference in The Hague next week, scientists at Britain’s Hadley Center for Climate Prediction and Research said planting forests to absorb carbon dioxide and reduce global warming could be counterproductive.
Two studies published in Thursday’s issue of the journal Nature using computer models of global warming show that as temperatures rise, forests, or so-called carbon sinks, are likely to emit more carbon dioxide into the atmosphere, leading to further warming of the climate.
COUNTERINTUITIVE CONCLUSION
The findings may seem counterintuitive, since green plants take in carbon dioxide and give off oxygen as a result of photosynthesis. But the researchers said increased global temperatures could change the net effect created by vegetation.
“Our initial results suggest that vegetation and soils, which currently absorb about a quarter of human-made carbon dioxide emissions, could accelerate future climate change by releasing carbon to the atmosphere as the planet warms,” said Peter Cox.
Assuming that there are no substantial changes in the current patterns of human-induced carbon-dioxide release, the terrestrial biosphere would switch from being a carbon sink to a carbon source around the year 2050, the researchers said. They said this phenomenon, added to changes in ocean carbon cycling, could exacerbate the global warming predicted in the absence of carbon-cycle feedbacks.
The findings could have important implications for the Hague meeting because the use of carbon sinks is one of the key issues that will be debated at the two-week conference.
Ministers from around the world will try to seal an international agreement to cut carbon dioxide emissions by an average of 5 percent from 1990 levels by 2008-2012 in line with a 1997 treaty forged in Kyoto, Japan.
The Kyoto treaty allows countries to plant forests to offset some of their carbon dioxide emissions.
“All we can say ... is that if you want to plant trees to absorb CO2 in order to offset additional future emissions there are a huge amount of uncertainties,” Geoff Jenkins, head of the Hadley climate change program, said in a telephone interview.
“On the other hand if you refrain from emitting carbon into the atmosphere you know where you are in terms of its effect on CO2. So there is a big difference in the uncertainty levels between those two courses of action,” he added.
CHARGES OF CHEATING
Environmental groups Greenpeace and WWF are calling for carbon sinks to be excluded from the Kyoto treaty. Both groups want industrialized countries to achieve their targets by cutting emissions.
“Claiming credit for carbon stored in trees is a blatant attempt by some countries to cheat on their Kyoto commitments,” Bill Hare, Greenpeace International’s Climate Policy Director, said in a statement.
The second study in Nature, by Hadley researcher Richard Betts, also showed that planting new forests in cold parts of the world like Siberia and Canada could be doing more harm than good.
This is because in northern countries, where the ground is covered in snow, forests absorb more of the sun’s heat than the terrain. The additional exposure to the sun has a warming influence that could offset part of the cooling effect of the carbon dioxide uptake.
Britain’s Environment Minister Michael Meacher said the research highlighted the importance of the Hague conference and the difficult negotiations ministers will face.
“These results add weight to our view that we must achieve real emission reductions to meet Kyoto targets, and confirm our concerns about sinks. We must be cautious about them,” he said in a statement.