Ken Calderia, of the Carenegie Instition’s Department of Global Ecology has an op-ed in the NYT today, in which he cautions against willy-nilly tree-planting projects for carbon sequestration:

While preserving and restoring forests is unquestionably good for the natural environment, new scientific studies are concluding that preservation and restoration of forests outside the tropics will do little or nothing to help slow climate change. And some projects intended to slow the heating of the planet may be accelerating it instead.

Trees don’t just absorb carbon dioxide — they soak up the sun’s heating rays, too. Forests tend to be darker than farms and pastures and therefore tend to absorb more sunlight. This has a warming influence that appears to cancel, on average, the cooling influence of the forest’s carbon storage. This effect is most pronounced in snowy areas — snow on bare ground reflects far more sunlight back to space than does a snowed-in forest — so forests in areas with seasonal snow cover can be strongly warming.

In contrast, tropical forests appear to be doubly valuable to the earth’s climate system. Not only do they store copious amounts of carbon, the roots of tropical trees reach down deep, drawing up water that they evaporate through their leaves. In the atmosphere, this water may form clouds that reflect sunlight back to space, helping to cool the earth.

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He goes on to play out some reasonable concerns about the application of forest-planting schemes:

These findings have important policy implications. It has been suggested that agreements to limit climate change should consider carbon stored in forests. If so, they would need to consider the direct climate effects of forests so as to avoid perverse incentives to plant warming forests in places like the United States, Canada, Europe and the former Soviet Union. However, tropical forests, which are generally found in developing countries, may be due a double climate credit — one for their carbon storage and another for their cooling clouds.

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In the end he (IMHO) rightfully points the finger back at policy makers and leaders to take the hard road:

We cannot afford to indulge ourselves with well-intentioned activities that do little to solve the underlying problem. Instead, we must demand that our political leaders do more to revolutionize our energy system and preserve our environmental inheritance for future generations.