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September 04,2013
A warmer planet is helping to fuel more wildfires in the United States, according to a new study.
Environmental scientists at Harvard University predict that by 2050, wildfire seasons will be three weeks longer, up to twice as smoky, and will burn a wider area in the western part of the country.
Fires in the Western United States have gotten worse since the 1970s. Scientists at Harvard University School of Engineering and Applied Sciences looked at past weather conditions and wildfires to find out why.
“In some regions, like the Rocky Mountains, really temperature is the driving force, but elsewhere variables like relative humidity can play a role," said Loretta Mickley, an atmospheric chemist and co-author of the study. "If one year is particularly moist, for example, in the Great Basin, Nevada, Utah area, then that will foster a lot of vegetation growth and then the following year all that vegetation can feed wildfires and their spread.”
The scientists then turned to a suite of 15 climate models based on the conclusions of the Intergovernmental Panel on Climate Change, the leading international body for the assessment of climate change. On average, the models predicted increases between 2 and 2.5 degrees Celsius by 2050.
“The finding for rainfall, which can diminish fire activity, and for relative humidity, we found only small changes, with some models predicting small increases and some models predicting small decreases in those variables," Mickley said. "So we found as in the past, temperature is really driving the changes that we predict for the future.”
The calculations suggest the probability of large wildfires would increase by factors of two or three, and that by 2050, the more than four-month fire season would be three weeks longer.
“If we just look at one month in the future for example, the area burned in the very forested Rockies could quadruple," Mickley said. "If we look at the whole fire season, we see increases more on the order of say 20 or 30 percent to 100 percent.”
While air quality in the United States has greatly improved in recent decades in response to federal laws, Mickley says air pollution is an unexpected consequence of longer lasting, widespread wildfires.
“These increases in wildfires could totally disrupt our efforts to clean the air," she said. "Last weekend, there was an area the size of some states in the eastern U.S. blanketed with unhealthy air over California and Nevada. And we call this increase in smoke an important climate penalty on air quality.”
That penalty would be air that is twice as smoky as it is today. These findings, Mickley says, underscore the need for better forest management. But also she adds, they send a signal to policy makers and the public to reduce fossil fuel emissions that are warming the planet.
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