Proc. Natl Acad. Sci. doi: 10.1073/pnas.0608998104 104, 6550–6555 (2007)

Credit: VICTORIAN RAINFOREST NETWORK

It is often assumed that global warming can be reduced by planting trees, which soak up carbon dioxide from the atmosphere. However, trees also change the planet's surface albedo, or its ability to reflect sunshine.

Govindasamy Bala of the Lawrence Livermore National Laboratory in California and co-workers compared a deforested world with a standard world using an integrated global carbon cycle and climate model. A treeless world would be 0.3 K cooler by 2100, they claim. Although this world would have higher carbon dioxide in the atmosphere and oceans, it would reflect more sunlight, lowering the temperature.

Deforestation does not have the same cooling effect everywhere. In the tropics, clouds forming above rainforests also reflect sunlight. Their loss would cancel out any cooling effect from increased land reflectivity as a result of logging. Compared with the standard world in 2100, a world devoid of tropical forests only would be 0.7 K warmer, mainly from CO2-induced warming, whereas a world lacking only high-latitude trees would be 0.8 K cooler than the standard world.

The scientists advise against deforestation to mitigate global warming because of forests' many economic and environmental values.