If a Tree Farts in the Forest ...

A surprising new study published in Nature, reported by the Guardian on 12 January 2006, may help explain why Kyoto Protocol signatories Canada and New Zealand haven't managed to reduce their greenhouse gas emissions any more effectively than nonsignatory Australia. Too many plants, not enough desert?

According to a study published today, living plants may emit almost a third of the methane entering the Earth's atmosphere.

The result has come as a shock to climate scientists. "This is a genuinely remarkable result," said Richard Betts of the climate change monitoring organisation the Hadley Centre. "It adds an important new piece of understanding of how plants interact with the climate."

Methane is second only to carbon dioxide in contributing to the greenhouse effect. "For a given mass of methane, it is a stronger greenhouse gas, but the reason it is of less concern is that there's less of it in the atmosphere," said Dr Betts.

But the concentration of methane in the atmosphere has almost tripled in the last 150 years, mainly through human-influenced so-called biogenic sources such as the rise in rice cultivation or numbers of flatulent ruminating animals. According to previous estimates, these sources make up two-thirds of the 600m tonnes worldwide annual methane production.

Frank Keppler, of the Max Planck Institute for Nuclear Physics, who led the team behind the new research, estimated that living plants release between 60m and 240m tonnes of methane per year, based on experiments he carried out, with the largest part coming from tropical areas.

Other perplexing results:

Tree planting

Researchers in North Carolina found that planting trees to soak up carbon dioxide can suck water and nutrients from the ground, dry up streams and change the soil's mineral balance

Aerosols

A recent study in Nature found cutting air pollution could trigger a surge in global warming. Aerosols cool the Earth by reflecting radiation back into space. Scrapping them would have adverse consequences

Global dimming

In 2003 scientists noticed levels of sunlight reaching the Earth's surface had dropped by 20% in recent years because of air pollution and bigger, longer-lasting clouds