If you think you're hearing about more wildfires than in the past, you're right. Many regions around the globe have seen a sharp increase in the number and extent of these fires over the past several decades. Now, research links this upsurge in some areas to longer, hotter droughts—in other words, to climate change.
In many places, spring comes earlier and fall comes later, meaning that the fire season is longer. Annual variation in the number of fires is linked to spring and summer temperatures. In the American West, spring and summer temperatures averaged 0.87°C (1.6°F) higher between 1987 and 2003 than in the previous 15 years. That same span saw four times as many wildfires—many at higher elevations.
Satellites track forest fires by sensing heat emitted from Earth's surface. A nighttime reading of higher than 38.9°C (102°F) is classed as a burning fire. Each point on this map records a fire that burned in 2007. Because forest fires emit significant CO2, an increase in wildfires will make curbing greenhouse gas emissions even harder.
The Flowers that Bloom in the Spring
Warming temperatures can mean that spring comes earlier to some regions, resulting in a longer fire season. Fire scientists are learning that wild lilacs in the western United States are a good natural fire alarm: if they bloom before May 20, it will be a bad fire year.
Doomed by Drought
More than a thousand years ago, the Ancestral Pueblo peoples built a thriving culture in the American Southwest. Their towns, linked in a far-flung network of social ties and exchange, boasted impressive buildings of masonry and adobe. Pueblo Bonito, in Chaco Canyon, New Mexico, rose to several stories and had more than 800 rooms.
But naturally occurring climate cycles in the region exposed the Ancestral Puebloans to periodic spells of extreme drought. Eventually, a series of epic droughts scorched the Southwest—some lasting many decades. Regional drought in the mid-1100s drove many farms to failure, and by AD 1150 Pueblo Bonito was largely deserted. Today's Southwesterners haven't experienced droughts as harsh as those—but history tells us they will.
The Ancestral Puebloans relied on corn, which needs winter rain to germinate and summer rain to grow. In order to encourage that rainfall, people created images of creatures linked with water—frogs and tadpoles—sculpting them and painting them on water vessels.