Western firefighting veterans lamenting a "new normal" amid surging forest fires have received an explanation for the destructiveness they've been unable to quell. Rising temperatures are flatly to blame for recent fearsome fire seasons, leading scientists reported Monday.
The number of acres of forest burning yearly in large Western fires ballooned nine-fold from 1984 to 2015, with climate pollution and natural changes in the weather playing roughly equal roles in driving the deadly trend, research published in Proceedings of the National Academy of Sciences concluded.
The study showed that more than a century of fossil fuel burning, deforestation and farming has helped push the American West into an explosive new wildfire regime, and the findings suggest far worse could be ahead.
"The authors clearly demonstrate that a human influence on wildland fire as a consequence of global warming isn't just a prediction for the future - it's happening now," said Kevin Anchukaitis, a University of Arizona scientist who was not involved with the study.
Previous efforts to link Western wildfires with climate change have hinted at a profound relationship but led to unconvincing results, largely because long lists of factors influence ignition and wildfire properties.
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Monday's study focused on forest dryness, identifying the commanding role it has been playing in driving fires. The researchers relied on climate data and modeling to present a sweeping regional view of 30 years of worsening forest fires.
"The exact percentage of human contribution remains uncertain, but the overall relationship - an increase in fuel aridity, fire days, and fire extent - is clear and significant," Anchukaitis said. "The statistical analysis is very convincing and elegantly done."
Western wildfires have been devouring forests parched by higher temperatures in recent years, draining federal and local firefighting funds, killing residents unable to flee fast-moving flames and filling skies with sometimes-crippling levels of air pollution.
The new analysis showed temperature increases caused by rising levels of greenhouse gas pollution have had a drying effect on Western forests that caused 10.4 million acres to char in large fires during the three decades.
That suggests 44 percent of the forest area that burned during the three decades analyzed burned because of the effects of global warming. The finding was an estimate, with the researchers concluding global warming likely drove between 6 million acres and 16 million acres of forest fire.