Global warming linked with wildfires
By Mike Taugher
CONTRA COSTA TIMES
The number and spread of major wildfires has exploded in western states since the late 1980s and is largely due to a warming climate, says a study to be published in Friday's edition of the journal Science.
Researchers found that wildfires in national forests burned four times as often and charred more than six times the number of acres since 1987 than they did during the period between 1970 and 1986.
And the conventional wisdom that the increasing fury of those forest fires was caused mostly by fire suppression and other forest management practices is mostly wrong, the study says.
Rather, a temperature increase of 1.5 degrees Fahrenheit led to earlier snowmelts, which caused forests to dry out earlier in the year. The result: a longer fire season that has more opportunities for fires to start and more time for fuel to dry out.
"I see this as one of the first big indicators of climate change impact in the continental United States," said one of the paper's authors, Thomas Swetnam of the University of Arizona's Laboratory of Tree-Ring Research.
"We're showing warming and earlier springs tying in with large forest fire frequencies," he added in a statement. "Lots of people think climate change and the ecological responses are 50 to 100 years away. But it's not 50 to 100 years away -- it's happening now in forest ecosystems through fire."
The paper allows that it is still uncertain whether the recent warming is due to the buildup of greenhouse gases in the atmosphere or an "unusual natural fluctuation."
But it adds that there is scientific consensus that global warming will increase spring and summer temperatures in the region in the coming decades -- and that ensures that wildfires will continue to worsen.
The study was led by scientists at Scripps Institution of Oceanography in La Jolla.
The researchers looked at 1,166 large fires in western forests between 1970 and 2003, and compared them to temperature and streamflow data that can be used to determine when the spring snowmelt occurs.
They found that average length of the fire season increased by 64 percent since 1987 and said that the period from 1987 to 2003 was the warmest such period since record-keeping began in 1895.
Forestry experts for years have attributed the increasing size, frequency and fury of forest fires on forest management practices.
Decades of fire suppression, for example, has altered forest structures, causing denser thickets of fuels and ladders of fire fuel that can reach the crowns of trees that otherwise could have escaped burning.
The study says that is only partially correct. Much of the increase in forest fires has been in the Northern Rockies, which have been largely untouched by intense forest management. And many of those forests are not so fire dependent that fire suppression should have much effect.
Nevertheless, forest management has been the focus of forestry officials and federal policy, especially the 2002 Healthy Forests law that was largely crafted by Democratic Sen. Dianne Feinstein and Rep. Richard Pombo, R-Tracy.
"This initiative blames increasing wildfire activity in the western United States solely on increasing stand density and the buildup of dead fuel as a result of fire exclusion policies," says a commentary accompanying the study in Science by Steven W. Running of the University of Montana.
"It does not acknowledge any role of changing climate in recent wildfire trends."
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