Forests will accelerate global warming crisis, say scientists
Copyright 2000, Agence France Presse
November 8, 2000
Tree loss caused by climate change, together with ageing forests, will disastrously speed up global warming over the next century, according to research published Thursday ahead of key negotiations next week.
The likely rise in the Earth's atmospheric temperature may be under-estimated by more than a third, because warming will accelerate in the last half of the century, the authors say.
Environmentalists hope that planting forests will stave off global warming because trees absorb carbon dioxide (CO2), the biggest cause of the problem, through photosynthesis.
But, say researchers at Britain's Hadley Centre for Climate Prediction and Research, the truth is more complex and gloomier.
In a paper published in the British science journal, they say climate change could cause existing forests in vulnerable areas, such as the Amazonian rainforest, to shrink, thus reducing the size of the "sink" that can soak up CO2.
At the same time, many forested areas will mature as part of the natural cycle of growth. As trees die, fall into the undergrowth and rot, they release as methane the CO2 they have stored, thus contributing to the global warming problem.
Coupled to this are likely changes in the way that the ocean absorbs CO2 because plankton and marine plants, which also feed on carbon dioxide, will be affected by climate change that could alter the sea's currents.
On current trends, "the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter," the experts warn.
This so-called feedback -- the way in which forests store carbon and then release it back into the atmosphere -- is an immensely important factor in calculating how bad global warming will be, they warn.
The Hadley Centre calculates that if the feedback is not taken into account, global mean temperature will rise by four deg. Celsius (8.4 deg. Fahrenheit) by 2100.
But if the feedback is taken into account, the rise will be more than a third higher, at 5.5 deg. Celsius (11.55 deg. F.).
That is a potentially catastrophic scenario.
By comparison, since 1860, the global mean surface air temperature has increased by between 0.4 and 0.8 deg. C. (0.85-1.7 Fahrenheit), according to the latest draft estimates by UN's Intergovernmental Panel on Climate Change (IPCC).
The IPCC also predicts a temperature rise of between 1.5 and six deg. C. (3.2 and 12.7 deg. F.) from 1990-2100, making sea levels rise by 14-80 centimetres (5.5-32 inches) -- enough to swamp low-lying states and delta regions and inflict destructive changes in weather patterns.
Forestry will be one of the most contentious issues at the UN talks on global warming, due to unfold in The Hague from November 13-24.
The negotiations are the final attempt to build the machinery of the 1997 Kyoto Protocol, the sole international treaty aimed at reducing emissions of CO2 and other "greenhouse" gases caused by burning oil, gas and coal.
The United States is in dispute with the European Union (EU) over how far to credit forests as a benefit to offset national quotas in gas emissions.
Washington wants a generous definition of how forests are valued, in what environmentalists charge is an attempt to reduce the economic and political cost of reducing US gas emissions by enforcement.
Commenting on the Hadley Centre model, Princeton University climatologist Jorge Sarmiento asked whether its calculations may have been too pessimistic.
There were "large uncertainties" about theories that increased dryness would trigger a dramatic collapse of the Amazonian rainforest and that more methane would be released from biomass because of warmer temperatures, he said.