Fire and climate change

What does a warming climate have to do with wildfires?

Smoke and wildfires overtaking a park.
A crown fire in Yellowstone National Park. | Photo by Mike Lewelling, National Park Service.

As our nation faces catastrophic wildfires in Oregon and other Western states, we are reminded once again of the power and devastation wildfires can bring. Does it seem that wildfires, both in the U.S. and around the world, are becoming more severe in recent years? What does climate change have to do with it?

Fire is a natural part of many landscapes around the world. Depending on the landform and type of vegetation, fire historically occurred naturally at regular intervals. Throughout history, humans have always had an impact on fire intervals. For example, Native Americans in Michigan would regularly burn parts of the landscape to promote the growth of blueberry plants. 

Naturally occurring fires, or those started purposely for subsistence, had two main differences from the catastrophic fires we are experiencing today: frequency and intensity. Naturally occurring fires, typically caused by lightning, were sporadic, and fell in line with the historic fire intervals for a particular landscape. Human subsistence-caused fires were initiated on a much more regular basis, but they were on a small scale and of a low intensity.

However, fire intervals today are shortening, and research shows that human-caused climate change is a huge catalyst for this. Many studies have shown that the changing climate is having a direct impact on the frequency and severity of wildfires in the U.S. The result is that we are experiencing more frequent and more severe wildfires in recent decades.

So, how exactly does climate have an effect on wildfires? First, a warmer climate means that more vegetation will become prime fuel sources. In a typical forest, not all of the trees and plants found there are likely to burn. But during prolonged periods of excessive drought—higher temperatures, lower rainfall—even these typically unburnable sources of fuel become dry enough to ignite. And when they do, large scale, intense fires can occur, as the landscape has now become a tinderbox of fuel. More volatile weather patterns, with accompanying high winds, can quickly whip up flames into a crown fire (when it reaches the tops, or crowns, of trees), making fast and extensive spreading more likely.

Second, climate change is bringing longer fire seasons. In fact, researchers have found in recent decades that global fire seasons have been lengthened by as much as 19%. Normally in the U.S., the prime fire season runs from mid-summer through fall. A longer fire season means that there will be more days into the fall that are ideal fire weather. The length of the fire season is further compounded by mild winters—less snow and fewer months of snow cover means more time for vegetation to dry out.

Third, a warmer climate means that forest pests, both native and non-native, are flourishing, resulting in longer life cycles and higher population densities of these pests. This means that the pests are causing more tree mortality, further adding to the build-up of fuel. In Western states, populations of the native mountain pine beetle have been expanding farther north and into higher elevations. In fact, they have been faring so well in recent years that for the first time ever researchers are finding the beetles completing two life cycles per year.

Scientists expect this trend of severe wildfires to continue in upcoming years, and even to increase, which underscores the importance of being vigilant when it comes to fire safety. While lightning does start fires every year, the vast majority of wildfires are caused by humans. An errant spark, an untended campfire, or a hot exhaust pipe driven through tall grass could be all it takes to ignite the next devastating wildfire. 

The Michigan DNR maintains a wildfire dashboard for the state. It’s always important to get a burn permit when burning yard waste—most wildfires in Michigan are caused by people burning leaf and yard debris under unfavorable conditions. Burn permits can be obtained by calling your local DNR office.

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