Global warming ignites wildfires.

• Position: Your Life

Over the last 20 years, global warming has caused a 300% increase in the number of large wildfires and a 600% jump in the area burned in the U.S., according to fire and climate scientists gathering at the Association for Fire Ecology Conference in Tucson, Ariz. Wildfire season has lengthened more than two months, and wildfires now are burning an average of five weeks, up from an average one week duration a decade ago. Further temperature increases and more frequent storms could result in even more active wildfire seasons in the years and decades ahead.

In the previous five years, nearly half of the Western states have experienced the largest wildfires in the last 50 to 100 years: Arizona, Colorado, and Oregon in 2002, Texas in 2006, and Idaho and Utah in 2007. Climate and weather factors have been among the principal drivers of large wildfire events.

"The changes we see in some Western ecosystems are a consequence of past land management uses, the spread of invasive species, the expansion of housing developments in fire-prone areas, and a warming climate with prolonged droughts," contends Tony Westerling of the Sierra Nevada Research Institute at the University of California, Merced. "These are creating conditions for a perfect firestorm of megafires that may cause extreme, irreversible...