There are many reasons why planting trees is a good idea, but don't be deluded by the proposition that it will help address the challenge of global warming. Apart from the fact that it takes about 20 years before trees become effective at capturing atmospheric carbon, a bit of basic research shows that there is insufficient land available to plant the number of trees required to counteract CO2 emissions. (We run out of land after 187 days). This episode explains why we need to rethink assumptions that planting trees will offset human carbon emissions.