THE STUDY JUNE 14, 2011
The Wallow wildfire is still raging after more than two weeks, today becoming the largest wildfire in Arizona history. The Wallow wildfire has already burned over 733 square miles, but as of yesterday, only 18 percent had been contained, with more than 4,000 firefighters working to put it out. The monster fire has some people wondering—does climate change mean there will be more fires like this in the future?
Probably, scientists say. A study by A.L. Westerling and H.G. Hidalgo called “Warming and Earlier Spring Increase Western U.S. Forest Fire Activity” found that wildfire frequency in the western United State “increased suddenly and markedly in the mid-1980s.” The authors argue that climate change is a better explanation for the increase in wildfires than land-use change alone, although land-use changes have also had an effect. As temperatures rose, the average number of wildfires quadrupled between 1987 and 2003, compared to the average number from 1970 to 1986. The total area burned also increased by six and a half times. The average season length (time between first wildfire and last) increased 64 percent. Additionally, the authors found a correlation between wildfire frequency and the timing of the first snow melt.
Westerling and Hidalgo note that climate change will likely exacerbate these trends. “Virtually all climate-model projections indicate that warmer springs and summers will occur over the region in coming decades,” they note. “These trends will reinforce the tendency toward early spring snowmelt and longer fire seasons. This will accentuate conditions favorable to the occurrence of large wildfires, amplifying the vulnerability the region has experienced since the mid-1980s.” They also fear a feedback loop. Citing studies that estimate that western forests capture 20-40 percent of CO2 in the United States, Westerling and Hidalgo note that sparser forests cannot absorb as much carbon, further increasing atmospheric carbon dioxide and exacerbating the greenhouse effect. If current temperature trends continue, we could be putting out a lot more fires.