Location is key for trees to fight global warming

Everybody knows that trees are good for the climate, because they absorb greenhouse gas carbon dioxide, right? Maybe not, says a team of US and French climate experts. They say that whether or not trees help fight global warming depends on where they are.

If they are in the tropics, then investing in an "adopt a tree" scheme may be worthwhile. "Tropical forests have a net cooling effect because they take up carbon and increase cloudiness, which helps cool the planet," explains Govindasamy Bala of Lawrence Livermore National Laboratory, US.

Bala and his colleagues used computer models to predict what global temperatures would be in 2100 if all forests had been removed from the planet in 2000. Bala says their study differs from previous ones because their models do not only include the carbon-storing effects of trees. They also account for the release of water vapour into the atmosphere by trees, which promotes cloud formation, and the extra heat absorbed from the Sun by foliage, which is usually darker than the ground it grows in.

The tropics receive more sunlight, so they have more energy to convert atmospheric carbon dioxide into biomass. That is why tropical forests are better at storing carbon than their counterparts at mid-to-high latitudes.

At these latitudes, the warming effect of their dark colour outweighs the cooling effect of the CO2 they store. Bala's team say trees there can actually contribute to warming the planet.

The climate warming due to the absorption of heat by leaves more than offsets the cooling effect from carbon uptake, says Bala. The team found that if they removed forests from the planet in 2000, global temperatures in 2100 were 0.2°C cooler than if forests were left intact.

Carbon offsetting: not such a quick fix after all

The Register (UK)

Tue Dec 19

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