Trees Do Cause Pollution

Everyone knows trees are "A Good Thing". They take in the carbon dioxide that threatens our planet with global warming and turn it into fresh, clean oxygen for us all to breathe.

But now it seems we need to think again. In a discovery that has left climate scientists gasping, researchers have found that the earth's vegetation is churning out vast quantities of methane, a greenhouse gas far more potent even than CO2. This is not a product of trees and plants rotting, which everyone already knew was a source of methane; it is an entirely natural side-effect of plant growth that scientists had somehow missed. Yet it is by no means trivial: preliminary estimates suggest that living trees and plants account for about 10 to 30 per cent of the methane entering the atmosphere.

The discovery, reported by an international team of scientists in the current issue of the journal Nature, is adding fresh fuel to the debate over the confidence we can put in global warming science. It does not affect claims that the earth is warming up, which centre on measured effects rather than their likely causes. It does, however, raise serious doubts over grand plans for combating the warming process - such as the Kyoto protocol. The protocol allows countries to offset their greenhouse gas emissions through reforestation programmes, with trees being thought to cancel out some of the warming effect by mopping up CO2. The discovery that these new forests would themselves generate another greenhouse gas raises, at the very least, doubts about the size of the net benefit.