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Tropical forests more effective than temperate forests in fighting climate change

Tropical reforestation more effective than temperate afforestation for slowing global warming.

Rainforest tree in Panama
Rainforest tree in Panama. Photo by: Rhett A. Butler.

Preserving forest cover and reforesting cleared areas in the tropics will more effectively reduce temperatures than planting trees across temperate croplands, argues a new paper published in Nature Geoscience.

Using computer models, Vivek Arora and Alvaro Montenegro estimate that converting all the world’s croplands to forests would reduce global temperatures in 2100 by only 0.45°C, a fraction of this rise forecast by scientists based on current emissions trajectories. The authors say their results indicate the importance of reducing greenhouse emissions rather than relying on afforestation in temperate regions.

“Afforestation is not a substitute for reduced greenhouse-gas emissions,” they write.

But the authors find that reforestation in the tropics has a disproportionate cooling effect relative to tree planting efforts away from the Equator, but not because of carbon sequestration. Forests in far northern and southern regions absorb more sunlight than croplands, causing local warming. Meanwhile heat absorption by tropical forests is offset by increased water transpiration, which has a cooling effect.

The net of this means that afforestation in tropical areas is about three times more effective at reducing warming than afforestation in temperate zones.

Arora and Montenegro therefore conclude that protecting and expanding tropical forests is an especially worthwhile approach to helping mitigate climate change.

“Avoided deforestation and continued afforestation in the tropics are effective forest management strategies from a climate perspective.”

Vivek K. Arora and Alvaro Montenegro. Small temperature benefits provided by realistic afforestation efforts. Nature Geoscience PUBLISHED ONLINE: 19 JUNE 2011 | DOI: 10.1038/NGEO1182

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