BBC NEWS | Special Report | 1998 | 10/98 | Global warming | Climate 'threatens third of forests'

By Environment Correspondent Alex Kirby

The World Wide Fund for Nature (WWF) says the world's changing climate poses a grave risk to one third of its forests.

WWF says this has serious implications for many plant and animal species, three-quarters of which depend on the forests for their survival. The warning comes days ahead of an international meeting in Buenos Aires to discuss the impact of climate change.

Most scientists believe climate change is being caused by human activity, especially the burning of fossil fuels like coal, oil and gas.

Carbon dioxide given off as the fuels burn is trapping more and more of the sun's heat close to the earth, instead of letting it radiate safely back into space.

Multiple effects

The inexorable rise in temperature is affecting forests in several ways, says WWF.

Latitudes nearer the poles are becoming warmer -- in fifty years or less, southern Britain may have a climate like central France today. Yet some tree species may not be able to keep up with the advancing heat front.

The climate is likely to become stormier. That may mean an increased risk of fire for tropical forests already dried out by drought.

Sea levels will continue to rise. Mangrove swamps, home to a wealth of species, may be at risk.

And in some places, trees will respond to climate change by encroaching on new areas, taking over African savannahs and Alpine meadows.

Burning forest
Fire risk set to increase
But forests will not only suffer from climate change. Increasingly, they will contribute to it.

As a tree grows, it absorbs carbon dioxide from the atmosphere to help it to maturity.

Once it is full-grown, the tree "locks up" the carbon dioxide it contains, and prevents it from re-entering the atmosphere.

But when the tree decays, or is burnt, all the carbon dioxide it contains is released, adding to the greenhouse effect.

Scientists estimate that up to one fifth of all greenhouse gases come from the burning, not of fossil fuels, but of "biomass" -- trees and other plants.

Some of the burning is accidental. But an increasing number of fires are started deliberately, to clear land for farming or other human purposes.

A problem or an opportunity ?

The world's forests are key players in the Buenos Aires climate conference, running from 2 to 13 November.

Because the forests can lock up such immense quantities of carbon dioxide, some countries are arguing that it makes more sense to plant trees than to reduce their own greenhouse emissions.

Smoke
Trees cannot cope with all our pollution
The argument comes mainly from countries in the superleague of polluters, like the USA.

There is some evidence to support them. A team of American researchers says the nation's trees could be sucking up just about all the 1.6 billion tonnes of carbon dioxide that the US emits every year.

But other climatologists say the researchers, the Carbon Modeling Consortium, had to rely on sparse data, and on models whose assumptions have not been thoroughly tested.

The members of the Consortium are all respected scientists. But, in the words of the weekly New Scientist magazine, "much more research is needed before these findings are nearly strong enough to inform policy".

And there is a warning from WWF to the delegates in Buenos Aires.

"Forests are threatened by climate change, so countries should not rely on them to soak up carbon dioxide", it says. "There is no substitute for cutting emissions at source".