Climate change endangers the northern forests.

From 50 to 90 percent of the boreal forests, the world's largest ecosystem, may disappear because of climate change, according to a recent report by the environmental group Greenpeace. "The Carbon Bomb" warns that a doubling of atmospheric carbon dioxide levels in the next 30 to 50 years could mean the end of the vast forests that surround the Arctic Circle. Other researchers disagree with some of the report's findings but support its recommendations.

Consisting largely of conifers, the boreal forests account for about a third of the world's total forest area. Canada, Alaska, and Scandinavia all contain tracts of boreal forest, but 73 percent of the forests are Russian. These forests play a crucial role in regulating global climate by absorbing large amounts of carbon dioxide that would otherwise contribute to global warming. More carbon may be locked up in the boreal forests than in any other terrestrial ecosystem.

Boreal forests are thought to be especially sensitive to climate change. Drier weather, for instance, could upset the hydrological balance of the widespread bogs, and increase the incidence of fires. Warmer temperatures could open up areas to southern pests or to expanding temperate forests, which could displace native plant communities. According to the report, the past two decades have already seen an increase in pest outbreaks and fires, as well as declines in some tree species. Increased logging is also taking a serious toll--and making a massive contribution to atmospheric carbon.

The report projects a vicious circle in which accumulating greenhouse gases warm the climate enough to boost the rate of burning and decay in the boreal forests. This in turn could release up to 225 billion more tons of carbon, increasing current atmospheric levels by one-third and provoking yet more climate change.

In Canada, the report has been criticized by some government and timber industry scientists. Henry Hengevald, senior advisor on climate change for the Canadian Ministry of the Environment, says that ecological disruption on the scale the report describes would take 300 to 400 years. Mike Apps of the Canadian Forest Service and Chris Lee of the Canadian Institute of Forestry think the report overestimates the amount of forest likely to be destroyed. But all three scientists support Greenpeace's call on the Canadian government to adopt a plan to reduce carbon dioxide emissions by 20 percent. That consensus offers hope that the boreal forests will win serious attention at the Berlin climate summit next March.