Wildfires and climate change

While no single wildfire can be said to have been caused by climate change, climate change has been making the fire season in the United States longer, and, on average, more intense. President’s Science Adviser talked recently about climate change and wildfires, a topic that’s on the mind of many who are grappling with tragic losses from the recent spate of uncontrolled fires in the northwestern United States and Canada. The influence of climate change on the wildfire regime comes not just from the higher summer temperatures and reduced summer soil moisture that go with global warming.

Climate change is also bringing us more dead trees kindling, in effect, killed by a combination of heat stress, water stress, and attacks by pests and pathogens that multiply faster in a warmer world. The National Climate Assessment, released in May, tells us consistent with earlier studies that longer, hotter, drier summers are projected to continue to increase the frequency and the intensity of large wildfires in the United States. In the western United States, the average annual area burned by large wildfires has increased severalfold in recent decades.

The evidence is strong that climate change is responsible at least in part for this increase. And the west is not the only U.S. region affected by wildfire. Today, the southeastern United States leads the nation in number of wildfires, averaging 45,000 fires per year, and this number continues to increase. And nationwide, the eight worst years on record in terms of area burned have all occurred since the year 2000. Wildfires, of course, are dangerous to human life and health, costly in terms of property loss, and generally harmful to ecosystems.

They destroy valued timber and wildlife, as well as homes and other built infrastructure. They promote soil erosion. They increase the risk from floods and landslides, and the damage can extend far beyond the location of the fire itself, through the impact of the smoke plume on air quality far downwind, and the destruction of downstream fisheries choked with silt eroded from slopes denuded by fire. In short, wildfires accentuated by climate change are putting communities, lives, health, jobs, and valuable natural resources at risk.