Global warming intensifying wildfires?

Utah and other western states are in the throes of more frequent, longer-burning and more intense wildfires caused by global warming, according to a research report published Thursday.

The report added that this human-influenced disaster may only worsen.

"To me, this is the equivalent of what hurricanes are for the southeast coast," said Steven W. Running, professor of ecology at the University of Montana in Missoula. "This is a natural disaster that we've always lived with periodically, and now we see for the first time evidence that global warming is accelerating the regularity and intensity of these wildfires."

The report, titled "Warming and Earlier Spring Increases Western U.S. Forest Wildfire Activity," was published in the latest edition of Science Express, the weekly journal of the American Association for the Advancement of Science. Its authors are Anthony L. Westerling, Hugo G. Hidalgo and Daniel R. Cayan of the Scripps Institution of Oceanography in La Jolla, Calif., and Thomas W. Swetnam of the University of Arizona in Tucson.

Running wrote an accompanying opinion piece, "Is Global Warming Causing More, Larger Wildfires?"

The research report noted that while increases in western forest wildfires have been observed in recent years, the extent of the changes hasn't been documented until now, and climate's role in the changes weren't previously established.

The researchers compiled a database of 1,166 large wildfires that have struck the West from 1970 through 2003, comparing them to climate and other data. They concluded that large wildfires "increased suddenly and dramatically in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations and longer wildfire seasons."

The greatest increases were in midelevation forests in the northern Rocky Mountains and are "strongly associated with increased spring and summer temperatures and an earlier snowmelt," the report said.

If summer droughts increase in western mountains, more large wildfires will reduce the trees, the report said. That means fewer trees will be available to absorb carbon dioxide, a pollutant many scientists blame for global warming. Meanwhile, if fires continue to worsen, they will release more carbon to the air, according to the report.

That suggests the forests in the West "may become a source of increased atmospheric carbon dioxide," the report added, "even under a relatively modest temperature-increase scenario."

Why is the West especially in danger from the changes?

The rest of the nation gets enough summer rainfall that "they just aren't as dry during the heat of the summer as we are," Running said in a telephone interview Thursday. "What little summer rainfall we get evaporates within hours to a few days."

That doesn't do much to "rehydrate the forest," Running said.

The best climate models he knows about say that in western North America, summer temperatures should increase between 2 degrees and 5 degrees in the next 50 or 60 years.

"What I find critical there is, the Westerling paper already shows this level of wildfire activity with only 0.9 degree increase," Running said. "If we have another 2- or 3-degree increase on top of that, we can imagine a doubling or more in the wildfire activity and burn area in the coming decades."

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