Wednesday, October 31, 2007

Trees contribute to global warming

What doesn't contribute to global warming? You do, I do, the boreal forest in Manitoba does too. (Boreal forest means northern forest; it applies Canada (farther north in the west) and Alaska plus northern Minnesota and Maine.) Canada's Globe and Mail:
Forests have long been thought of as an ally in the fight against global warming, but a new study suggests that Canada's boreal forest may in fact be releasing more greenhouse gases than it absorbs. “The boreal forest, at least in the north-central part of Manitoba, has gone from a weak carbon sink to a weak carbon source,” said Dr. Tom Gower of the University of Wisconsin, whose paper is being published Thursday in the journal Nature. “It is now contributing to atmospheric (carbon dioxide) concentration.” Dr. Gower and his fellow researchers studied a million-square-kilometre stretch of forest around Thompson, Man. The team took field measurements of how carbon moved between the forest and the atmosphere and then used computer modelling and forestry records to suggest how that cycle has changed since the 1950s. Trees absorb carbon dioxide as they grow and release it when they burn or decompose. Although results varied for individual years depending on the severity of the forest fire season, Dr. Gower found that the forest once absorbed, on average, slightly more carbon than it emitted — about five or 10 grams per square metre of forest per year. Now, however, the direction of that flow has reversed. On average, the forest actually emits about two grams per square metre per year. “(The forest) is actually contributing to rising carbon emissions,” Dr. Gower said.