Is Global Warming Causing More, Larger Wildfires?

Higher spring and summer temperatures and earlier snowmelt are extending the wildfire season and increasing the intensity of wildfires in the western United States. On 3 April 2006, the U.S. weekly news magazine Time ran a report on global warming with the cover title “Be worried, be very worried. ” Similar coverage of global warming has emerged in other general-interest magazines in recent months, triggered by scientific studies that are finding evidence for adverse impacts of global warming occurring today, not merely projected for future decades. These adverse impacts— from higher probabilities of category 4 and 5 hurricanes (1, 2) to higher rates of sea-level rise (3)—are found not in some distant unpopulated region, but rather right in our own back yards. In this week’s Science Express, Westerling et al. (4) come to a similarly discomforting conclusion for wildfires. They show that warmer temperatures appear to be increasing the duration and intensity of the wildfire season in the western United States. Since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has