Will Climate Change Whip Up Global Wildfires?

Mixed message. A new fire model predicts that, between 2010 and 2039, climate change will make wildfires more likely in some places (orange) but less so elsewhere (blue).

Krawchuk et al., Global Pyrogeography, 4 (April 2009); PLoS ONE

Climate change--and the searing temperatures it will bring--can conjure up images of expansive forest fires forcing people to flee their homes. But the first global model to rely on actual fire data shows a more nuanced picture. In fact, just as much land will have a lower fire risk in the next 3 decades than will face heightened prospects of wildfires. Experts emphasize that less flame isn't always good news: Many of the world's shrublands require periodic fires to survive.

It only takes a couple of ingredients to prime an area for a forest fire: dry vegetation and hot, windy summers. But even with this simple equation, researchers have struggled to predict fire incidence worldwide. When they've tried, it has been based on rough assumptions, for example supposing that fires are likely to occur above certain temperature and below specific moisture levels.

For the new research, Max Moritz, a fire ecologist at the University of California, Berkeley, and his colleagues analyzed 10 years of satellite data on global fire activity. They divided the world into two categories: those that are fire-free and those that are fire-prone. Then they looked at the relationships between fire-prone areas and the amount of vegetation, climate patterns, and the opportunity for ignition, either from human activity or lightning. Finally, the researchers plugged these data into a climate-projection model that assumed that little will be done to curtail current greenhouse gas emissions.

Within the next 30 years, more than a quarter of the terrestrial world is likely to see relatively sharp changes in fire patterns, the team reports in this week's issue of PLoS ONE. About 9% of land, including places such as Scandinavia, the western United States, and the Tibetan Plateau, will see an increase in wildfires. Meanwhile, about 19% of land, including the southern United States, central Africa, and much of Canada, will see fewer fires. But this reduction in wildfires could also be troublesome. "In California, we have the chaparral shrublands. ... Some of the seeds of these shrubs only germinate after a fire," says Moritz.

"It's great that someone has done the first step" in quantifying the environmental drivers of fire patterns on a global scale, says Andrea Meyn, a geoecologist at the Potsdam Institute for Climate Impact Research in Germany. Understanding the changes in global wildfire activity adds "a missing piece" to modeling future wildfire events, adds Mike Balshi, who has studied the fire-climate change link and who is currently an ecologist at Neptune and Co., Inc., a private environmental consulting firm in Lakewood, Colorado.