A beetle about the length of a well-trimmed fingernail may be challenging scientists' projections for global warming.
Forests store large amounts of carbon drawn from the atmosphere, helping Earth keep cool. But an infestation of mountain pine beetles is turning more than 144,000 square miles of woods in British Columbia from a slight carbon absorber - or sink - to a net CO2 emitter. Canadian scientists unveiled projections Wednesday that between 2000 and 2020, the forest will have lost 270 million tons of carbon into the atmosphere.
The process has the potential to become a vicious cycle: As the climate warms, it favors more severe outbreaks, and if severe outbreaks increase, that leaves fewer trees to absorb carbon and more emissions as dead trees decompose. Researchers say British Columbia's problem highlights a growing threat that North American forests, too, face from climate change.
"This is very important," acknowledges Tom Veblen, a geographer at the University of Colorado at Boulder who is looking at the interplay of climate change, insect infestations, and wildfires in forests in the western United States. He notes that climate models do not take this type of feedback into account when they gauge temperature trajectories as human-related greenhouse-gas emissions rise.
"It's been known for some time that insects are an important part of the boreal-forest carbon cycle," says Werner Kruz, a scientist at the National Resources Canada's Pacific Forestry Centre in Victoria, British Columbia, who headed the modeling effort. But, he adds, the failure to include bugs' cumulative effect in climate models could be leading researchers to overestimate the amount of human- generated CO2 forests can absorb.
British Columbia is deep into its worst infestation of mountain pine beetles on record. Annual emissions from the worst year of infestation come close to matching the average annual emissions from all the forest fires the country experienced between 1959 and 1999, researchers say. Over the 21-year period the projections cover, emissions from the affected forests appear comparable to five years' worth of emissions from Canada's entire transportation sector.
Canada's beetle problem highlights a threat North American forests face from climate change, in addition to wildfires, logging, mining, and other development activities, say researchers. By some estimates, mountain pine beetles and their bark-burrowing cousins infest some 50 million acres of forest, stretching from Alaska to the southwestern US.
And the outbreak highlights the challenges resource managers face as they try to preserve forest resilience in the face of a changing climate and pressure to exploit timber and mineral resources. Because the beetles stay burrowed underneath the bark, the only known method to control infestations before they get out of hand is to cut down the trees they've killed or the live trees they've infected. It's an approach that raises the hackles of some environmentalists and ecologists alike. …