TREES have always been our best friends. Now, researchers have found how these silent friends can help tackle one of this century's biggest problems: increasing levels of greenhouse gases (GHG) that subsequently lead to global warming. According to latest reports, Europe's forests are absorbing up to a third of the carbon dioxide (CO₂) spewed by the continent's cars, factories and power stations. The calculation comes from an investigation into the flow of air above 17 forests, from Iceland to Italy. It is the most xhaustive attempt yet to monitor how forests absorb CO₂ - a question that has acquired impressive proportions after the Kyoto Protocol, which allows nations to counter GHG emissions by planting carbon "sinks" such as forests.

Forests are the largest terrestrial sink for CO₂' the most important of the GHGS that cause global warming. Trees absorb the gas during photosynthesis and convert it into plant tissue. It is released again when trees die and decay. Left alone, a mature forest will generally be in equilibrium with the atmosphere, releasing as much CO₂ as it absorbs.

The clearance of tropical forest is causing an overall release of CO₂ into the air. But in the temperate regions, including Europe, where commercial foresters are increasing tree cover, forests are net absorbers of the gas. The European Commission's (EC'S) Euroflux project has accurately measured these gas exchanges using a technique called " eddy covariance". Sensors placed on towers in the forests measure both vertical wind speeds and the CO₂ content of the air some 10 times every second. Together, these measurements reveal how much of the gas the forest is absorbing or releasing.

For the past three years, Euroflux's scientists have measured this fluctuation in 17 typical types of forests in Europe. They range from commercial pine plantations to ancient beech forests. Along with satellite images of the extent of forest cover, the data reveal that the European Union's trees absorb between 120 and 280 million tonnes of carbon than they release. This compares with current European annual industrial emissions of around 800 million tonnes.