New Scientist.com
Planting northern forests would increase global warming
19:00 11 July 01
Fred Pearce, Amsterdam
Talks to salvage the Kyoto Protocol could be undermined before they even start by research suggesting that planting forests to curb global warming could backfire.
The world's nations are due to meet in Bonn from 16 July to thrash out ways to combat climate change. The protocol gives governments the option to plant trees to soak up carbon dioxide, rather than cutting emissions of the greenhouse gas.
But this provision is deeply flawed, warns Richard Betts of Britain's Meteorological Office. He says it does not take into account other ways that new forests can affect climate. "Carbon accounting alone will overestimate the contribution of afforestation to reducing climate warming," he told New Scientist.
On Tuesday, Betts presented the first detailed calculations showing that planting trees across the snow-covered swathes of Siberia and North America will heat the planet rather than cool it. And even away from the tundra, the cooling potential of forests is much less than previously supposed, he told a climate conference in Amsterdam.
Green on white
His findings may further undermine support for the Kyoto Protocol. Several industrialised countries are wavering following the withdrawal of the US from the proposed treaty earlier in 2001.
Green forest canopies reflect much less solar radiation than most other land surfaces. They also absorb more, heating the Earth's surface. This effect is greatest where forests replace snowy tundra, which normally reflects large amounts of solar radiation.
Betts calculates that at northern latitudes, warming as a result of planting forests will overwhelm any cooling effect due to the trees soaking up CO2.
Both Canada and Russia want to plant forests in their empty tundras to help meet their Kyoto commitments, because a hectare of immature forest can absorb more than 100 tonnes of carbon each year, despite growing slowly.
But Betts calculates that the net warming effect of heat-absorbent forests in both regions is equivalent to an annual emission of 75 tonnes of carbon per hectare.
His new calculations also halve estimates for the carbon sink potential of western European forests.
"Even in places where the cooling effect is still dominant," says Betts, "the cooling influence is generally much smaller than expected when considering carbon sequestration alone."
So should some countries be destroying forests instead? "I am not suggesting that we deforest," says Betts. "But afforestation is not always an effective alternative to cutting fossil fuel emissions."
19:00 11 July 01
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