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.