Having planted a fair few trees, I've always wondered what the data on tree planting as a solution to global warming looks like. Bill Gates provides this in his book on pages 128 and 129. He gives a rule of thumb that a tree absorbs 4 tons of carbon dioxide over 40 years. He points out that if the trees in the picture weren't planted but some just grew naturally, there will be no extra carbon absorption. It is extra trees that count. Also it matters where the trees are planted. The tropics is better! He then calculates that 50 acres of trees would be need to be planted extra in the tropics and maintained in perpetuity to offset the lifetime carbon emissions of the average American. This would mean half the world's land mass for just USA alone.
