This chattering-class environmental picture is not necessarily wrong, but it does include many assumptions. One of them, that planting trees will make the world cooler than it would otherwise be, is the subject of a newly published study by Govindasamy Bala, of the Lawrence Livermore National Laboratory, in California, and his colleagues. Dr Bala has found, rather counter-intuitively, that removing all of the world's trees might actually cool the planet down. Conversely, adding trees everywhere might warm it up.
Now the scientists behind this study are not recommending that we cut down all the trees. Their point was merely that the environment and what affects it is a very complicated subject with few pat answers:
The reason for this is that trees affect the world's temperature by means other than the carbon they sequester. For instance forests, being generally green and bristly things, remain quite a dark shade even after a blizzard. They are certainly darker than grasslands smothered in snow, and thus they can absorb more of the sun's heat than vegetation which might otherwise cover the same stretch of land. That warms things up.
Transpiration—the process by which plants suck up groundwater and evaporate it into the atmosphere—is another and opposite matter. Woodlands are usually better than other ecosystems at getting water vapour into the air. In warm places this tends to make things cloudier, and those clouds, in turn, reflect the sun's heat back into space. That cools things down.
There is still a lot to learn about the climate on this planet. Until we have a better grasp on things, it makes no sense to allow politicians like Al Gore to decide how to address a problem that may not even exist.