More evidence that using carbon offsets to plant trees is a bad idea has been presented by scientists from Stanford University and Lawrence Livermore Laboratory in a paper published in the Proceedings of the National Academy of Scientists. According to a report in the Guardian the scientists found that tree planting increases warming unless it occurs within a thin strip of tropical land at the equator. The problem with planting trees elsewhere is that whereas grassy areas and snow reflect a lot of sunlight back out of the atmosphere, trees, being dark in color, absorb most of the suns rays. This soaking up of the heat overwhelms the cooling effect of absorbing the greenhouse gas carbon dioxide. In areas near the equator trees promote the formation of convective clouds which produce cooling and the overall effect of adding trees in such tropical areas is cooling.
Although it appears that planting trees outside of the tropics increases global warming the scientists by no means advocate chopping down trees in nontropical regions to combat global warming since trees have many important functions such as providing habitat for various animals and plants, protecting watersheds, etc. It therefore appears that outside of the tropics that the main goal should be to preserve the forests that we already have.