Higher temperatures mean drier vegetation and more lightning. And in a combination of scenarios involving computer models of atmospheric circulation and carbon emissions through the end of the century, scientists from Canada’s government and the University of Alberta found that would mean large increases in the number of fires “where existing suppression resources become ineffective.”
“They’re extreme fires that are uncontrollable, at least for a period of time,” said Mike Flannigan, a professor of wildland fire at the University of Alberta and a co-author of the new study.
Think of the 1.5 million-acre blaze that ripped into the Alberta city of Fort MacMurray in 2016, sending tens of thousands of people fleeing through smoke so thick they could barely see the roads. Or the quarter-million acre Rim Fire in northern California three years earlier. Or the swift-moving fires that killed more than a dozen people in Gatlinburg, Tennessee, in November — and more than 60 in Portugal in June. Once a fire reaches a certain intensity, firefighters can’t work on the ground, and even aircraft are little help.
“For any particular region, I wouldn’t expect every year to be a bad fire year,” Flannigan said. “But on average, in our forests in Canada, the United States, and I would say Siberia as well, we’re going to expect a lot more fire in the future. We’re seeing it in places like Portugal and Chile as well.”
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The findings were released online this week by the scientific journal Environmental Research Letters.
Climate change is already producing longer fire seasons. The Canadian government says the area burned every year could double this century as temperature, moisture, rainfall, and lightning patterns shift, “with severe environmental and economic consequences.” And those longer seasons are burning through firefighting budgets: With fire seasons now averaging 78 days longer than in 1970, the US Forest Service has warned that two-thirds of its funding may be consumed by firefighting within a decade.
If planet-warming carbon emissions continue without restraint, the risk of those uncontrollable fires more than doubles in parts of northern and northeastern Canada by 2100, the new study concluded. And it’s not just a distant threat: The number of uncontrollable fires would grow by about 20 percent by 2040 in the worst-case scenario. Even in scenarios where warming is held down, the numbers go up.
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Flannigan said other studies have shown that for every degree Celsius (1.8 degrees Fahrenheit) of warming, lightning — the cause of many wildfires — jumps 10 to 12 percent. Warmer air also sucks more moisture out of the dead wood and plants on the forest floor — and every extra degree of heat requires 15 percent more precipitation to balance out that evaporation. And extreme conditions can lead not only to more intense but exponentially bigger fires.
“The more dried fuel you have, the more energy you have going into that fire,” he said. “The more energy you have in that fire, the more difficult it is to manage.”