Canada’s carbon sink has sprung a leak
Until recently, its vast forests vacuumed up carbon dioxide. Now that process has been thrown in reverse.
Billions of tiny mountain pine beetles are treating Canada’s boreal forest like a 3,000-mile-long salad bar, transforming a key absorber of carbon dioxide greenhouse gas into a CO2 emitter instead.Skip to next paragraph
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In just a decade, exploding beetle populations and a rise in wildfires have flipped Canada’s boreal forest from its longstanding role as a natural carbon vacuum – sucking up 55 million or more tons of CO2 annually – to that of a giant tailpipe emitting up to 245 million tons of CO2 each year, according to the Canadian Forest Service.
That sharp about-face is raising questions about the future of northern forests worldwide that are being hit hard by global warming – including Russia’s massive boreal expanse, where wildfires have risen dramatically.
The trend has grown clearer in the past decade and was one reason that Canada did not count its forests as a carbon sink as part of the Kyoto climate treaty process: It couldn’t be sure they were.
Debate over how best to respond is growing. Some forest experts argue for more logging to remove vulnerable trees before beetles or fire get to them. Other scientists and environmentalists say the solution lies in logging less and leaving more boreal in its natural state. In 2007, 1,500 highly respected scientists from more than 50 countries called for more protection of Canada’s 1.4 billion-acre boreal forest, calling it one of the largest intact forest and wetland ecosystems left on Earth and home to large populations of grizzly bear, caribou, and wolves.
“The debate is raging on both sides of the argument – and both are using the science for their own purposes,” says Werner Kurz, senior research scientist for the Canadian Forest Service. “Our analysis shows Canada’s boreal has been a sink [CO2 absorber] as recently as the late 1990s, but has now become a source of carbon dioxide.”
Central to the debate is how long trees will be around to absorb and store carbon. Old-growth forests 400 years old or older may store a lot more carbon than a young forest does – but a young forest absorbs it far faster. Since old forests are considered vulnerable to beetles and fires, the question becomes: What’s the right mix of old, slow-growing and young, fast-growing forests?
According to Dr. Kurz’s mathematical model, fires and beetles are projected to destroy a Montana-size swath (144,000 square miles) of boreal by the year 2020, if trends continue. CO2 releases from decaying wood due to the beetle alone are projected at 270 million tons over that period.
While the logging of tropical forests is under scrutiny for hastening global warming, some suggest that more logging of northern boreal makes sense in light of fires and insect devastation.
“If one is truly concerned about the risks to the environment from climate change, then the case can be made that logging of sustainably managed forests should be encouraged,” Ontario Forest Research Institute scientists concluded in a study published last year.
The provincial government study found that carbon may be stored longer in wood products like construction lumber (which has a half-life of 67 to 100 years) than as forest. Using wood in construction also reduces carbon emissions if it replaces steel or concrete. The report concluded that more, not less, timber harvesting is called for in the beetle- and fire-prone boreal.
Cutting more trees is “robbing the carbon bank.” Despite its shift from carbon sink to carbon source, Canada’s boreal forest remains today a repository to an estimated 186 billion tons of carbon, the equivalent of 27 years of global carbon emissions.
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“Such studies [as the Ontario Forest Research Institute’s] fit conveniently with the timber industry’s conclusion that these forests should be logged,” Ms. Smith says. “The idea that you’re going to reduce global warming by logging more is ridiculous. These forests are storing an enormous amount of carbon.”