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Warming Climate Fueling Wildfires, Study Says

Ben Harder
for National Geographic News
July 6, 2006
 
Fires now raging in the U.S. West may be stoked in part by
climate change.

Major forest fires are both more numerous and more devastating than they were a generation ago in the region. The culprit, according to a new report, is warmer temperatures.

(Related: "Explosive Wildfire Season Predicted for U.S. West, South" [April 28, 2006].)

Spring is arriving sooner than before, and snowpack is melting as much as a month earlier. One result: Snow-fed rivers that used to quench parched earth tend to run low as the summer wears on.

That makes the land vulnerable, says fire ecologist Thomas Swetnam of the University of Arizona in Tucson.

"An earlier spring," he said, means "a longer time for the fuels [trees, brush, grasses] to dry out."

Since 1987 average temperatures in the West have been nearly 2F (1C) warmer than they were from 1970 to 1986, he and his colleagues found.

During that same 1987-2003 period, "we had more large fires," said climate scientist and study leader Anthony Westerling.

The later period had four times as many major fires as the slightly cooler 1970-to-1986 period. In addition, the average amount of land burned annually during the 1987-to-2003 period was 6.5 times greater than during the earlier period.

The years with the hottest temperatures also saw the most major forest fires and the largest tracts of burned land.

The findings fit with other recent studies.

"In Canada our area burned has almost tripled in the past 30 years," said Mike Flannigan of the Canadian Forest Service in Sault Ste. Marie, Ontario.

In an average year 6.4 million Canadian acres (2.6 million hectares)roughly the area of New Hampshireyield to infernos.

"The warmer we get, the more area burned we get," Flannigan said.

The new study doesn't indicate whether human-made global warming or natural climate fluctuations are to blame for the recent upswing in wildfires.

Either way, study leader Westerling says, the recent rash of forest fires could be just a taste of things to come.

"If we get climate change in the future—or more climate change—you would expect to see more frequent occurrences of these really severe years," he said.

The study will appear tomorrow in the journal Science. Westerling, who conducted the research while at the Scripps Institution of Oceanography in La Jolla, California, recently moved to the University of California, Merced.

(Related: a wildland firefighter's story of danger and dedication [narrated slide show].)

A Degree of Prevention

The new finding, experts say, bursts a bubble that's been central to fire-control efforts: the notion that fire prevention is a local matter.

"It's always presumed that the reason" for the recent upswing in western wildfires "was there was a big buildup of fuels from decades of fire suppression," said ecologist Steven Running of the University of Montana in Missoula.

He calls it the "Smokey Bear effect."

Some policy directivessuch as the one President George W. Bush calls the Healthy Forests Initiativeemphasize removal of combustible material from vulnerable areas, in some cases by logging.

Thinning is important in some areas where local environment has been disturbed, such as the ponderosa pine forests of the Southwest, says the University of Arizona's Swetnam. But it's unlikely to help in the northern Rockies and other areas mid- and high-elevation areas, he says.

"The temperature effect on wildfires seems to be magnified at higher elevations and latitudes," he noted.

Thinning out forests around vulnerable towns "is the most immediate thing you can do to protect these communities," the University of Montana's Running said. "But it's not the whole story."

"Climate is a major factor also. It's been discounted up till now." The new study suggests that larger environmental shifts are afoot in the recent upswing of western wildfires, he says.

Federal agencies that fight fires need to adapt, says Connie Millar of the U.S. Forest Service's Pacific Southwest Research Station in Albany, California. She counts her own agency among those that must revise their firefighting approach.

"We're still treating it as if we can get this problem under control [locally]," she said. But the only way to reverse the trend in forest fires is to reduce temperature on a broad scale, she suggests.

Like an Earthquake

Millar notes that other agencies prepare for inevitabilities such as earthquakes by recognizing that people have little control over where and when disaster strikes.

"This is the way we need to treat fire," she said. "We won't be able to conquer it everywhere, just as we can't deflect an 8.0 earthquake coming through San Francisco at some point."

Most fires can be contained, says the Canadian Forest Service's Flannigan. "Just a few get away."

In the U.S. "one percent of the fires are responsible for 99 percent of the area burned. The one in a hundred that gets away burns a large chunk of real estate."

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