Trees lose their appeal as panacea for global warming

Planting trees may be a bad way of trying to slow global warming, according to research from the United Nations Intergovernmental Panel on Climate Change.

Planting trees may be a bad way of trying to slow global warming, according to research from the United Nations Intergovernmental Panel on Climate Change.

It says new "carbon sink" forests will quickly become saturated with carbon and begin to return much of the carbon they contain into the atmosphere just as global warming accelerates.

The panel's report, highlighted in New Scientist magazine, undermines a key provision of the Kyoto Protocol, which requires industrialised countries to cut CO ₂ emissions. Under it, countries are allowed to offset emissions by planting trees, at home or in other countries, and count the carbon so absorbed against their industrial emissions.

The United States in particular has taken this route rather than seeking more efficient energy and generation use or developing renewable sources. Confronted with the panel's findings, the US Environmental Protection Agency has refused to comment on the issue.

But the problem of "sink saturation" will catch up with the agency at the intergovernmental meeting in Bonn next week, where it will be a big theme. Some countries, including the US, had hoped to use the meeting to complete plans for "carbon forests". But with the credibility of the idea demolished by climate scientists, it looks improbable that any agreement will be reached.

Britain in particular thinks carbon sink forests should take low priority. "The main action should be reducing emissions," said a Department of the Environment spokesman. "Sinks are much less secure than carbon and fossil fuels left unburnt, as things may change unpredictably over time."

In its last assessment in 1996 the panel concluded that "carbon fertilisation", by which elevated CO ₂ levels stimulate plant growth, would cause forests to soak up 290 million tonnes of carbon over the next century, even without new planting. With planting, that could be raised by another 100 million tonnes. The figures promised a substantial "carbon sink" into which industrial CO ₂ emissions, now 6 million tonnes a year, could vanish.