SCIENTISTS have now discovered that huge quantities of greenhouse gases, including carbon dioxide, produced when fossil fuels are burned, are mopped up by boreal forests -- coniferous forests in the northern hemisphere -- which are themselves coming under the loggers' axe (New Scientist, Vol 141, No 1907).

It is established that the carbon dioxide concentration in the atmosphere has increased from a fairly constant 280 parts per million in the 17th century pre-industrial period to 355 parts per million today.

What flummoxed scientists, however, is that the amount of carbon dioxide in the air and that absorbed by the sea and plants falls far short of the estimates of gas produced by burnt fossil fuels. Scientists posited an untraceable "missing sink", the identity and location of which was one of the most vexing mysteries of climate research.

Now, Allan Auclair, a plant ecologist working with the Washington DC-based environmental consultancy, Science and Policy Associates, claims that northern forests are the secret hosts.

Into the ocean Earlier, Jorge Sarmiento of Princeton University had apparently proved that between 1890 and 1940 and after 1980, the world's oceans had absorbed the excess carbon dioxide. But he was unable to explain where almost 35 billion tonnes of carbon dioxide disappeared between 1940 and 1980.

Most scientists thought that this missing carbon dioxide was hidden somewhere in the northern hemisphere, which produces about 95 per cent of the carbon dioxide from burning fossil fuels.

Auclair then took a look at the boreal conifer forests that cover over 1.2 billion ha in Alaska, Canada, Russia and the Scandinavian countries. He compared his estimates of changes in the measured volume of wood in the boreal and the temperate forests -- which lie to the south of boreal forests -- with changes in the "carbon sink" for each year between 1890 and 1990.

Faster growth
Auclair's analysis of tree ring data revealed that trees in the temperate and boreal forests had grown faster than normal for the better part of this century. He found that a rise in the concentration of carbon dioxide led to a corresponding faster rate of growth and increase in the wood quantity of these forests, an increase that matched the missing volume that had so foxed Sarmiento.

Auclair's analysis of data between 1890 and 1990 shows that these forests changed from a carbon source -- when they released more carbon dioxide than they absorbed -- to a carbon sink and, more recently, reverted to a carbon source. Massive increases in the timber logged after the late 1970s and the toll taken by forest fires and pests has once again converted these forests into giant carbon sources.

Unfortunately, despite hard evidence indicating sweeping deforestation in the boreal forests, Northern governments, particularly of Canada and Russia, are hell-bent on hacking down their forests to increase timber production and export. Instead of repairing themselves, they are putting pressure on developing countries to sell tropical timber produced only from sustainably managed forests. It's time, most experts agree, that they stopped barking up the wrong tree.