California Democratic Senator Barbara Boxer, chair of the Senate Committee on Environment and Public Works, wrote in a recent essay for The Hill that this past summer’s devastating “Rim Fire” was one more sign of the consequences of climate change. Boxer wrote:

The prolonged periods of record-high temperatures and droughts associated with climate disruption have been devastating to my home state of California, most recently in the form of larger and more frequent wildfires.

…Those who choose to continue to claim that climate change does not exist are standing on the wrong side of science and history.

That may be the case, but the story of wildfire in the American West is complicated. Four distinct forest regions in the West — the Sierra in California, the Rockies, the Pacific Northwest forests of Oregon and Washington, and the Southwest forests of Arizona and New Mexico — all respond to climate change in different ways. Meanwhile, the US Forest Service’s 20th century legacy of suppressing every fire that ignites has resulted in overgrown forests thick with deadfall and primed to burn. Finally, as people have built homes and towns deeper into forested lands, firefighting resources devoted to saving them have ballooned — making fighting forest fires more expensive for government agencies already spread thin.

California’s Rim Fire, the 4th largest in the state’s history, burned 257,000 acres of Sierra wilderness, including parts of Stanislaus National Forest and Yosemite National Park. Discovered on August 17 when it had consumed only 40 acres, it grew to 10,000 acres 36 hours later and to more than 105,000 acres over the next two days. Ignited by a hunter whose illegal campfire got out of control, the conflagration grew rapidly, surprising even seasoned firefighters. Still, there’s no question the forest was ready to burn, and the statistics suggest the number and size of wildfires in California is increasing.

Cal Fire, the state’s firefighting arm, has compiled some pretty unsettling statistics, as reported September 4 by the San Francisco Bay Guardian. Among them:

  • There were 5,135 fires in California from January 1 through August 31 of this year.
  • Over the same time span last year, there were 3,731 fires recorded.
  • The average over the past five years is 3,638.
  • Seven out of the 10 largest wildfires in California history have occurred over the past decade.

More Summer-like Days = More Wildfires

“What we’ve been seeing here in this past decade is longer summers — seven to eight days longer than normal,” Daniel Berlant, an information officer with Cal Fire, told the SF Bay Guardian. “There’s a correlation between a longer summer and more wildfires.”

The grim statistics for California, of course, comprise only part of the national picture for wildfires. By late August, when the Rim Fire was rapidly growing, 31,900 fires had burned 3 million acres across the U.S. in 2013, according to a Washington Post story published by Climate Connections on Aug. 23. The 2013 numbers have actually been mild, compared with other fire seasons over the past decade. The Post story:

Last year produced the second-worst season on record: 67,700 fires burned 9.3 million acres, according to the National Interagency Fire Center. In 2006, more than 96,300 fires burned 9.8 million acres. A total burn of 5 million acres was once a rarity in fire seasons that ran from June to September before 2001. But since then, the season has expanded from May to October, as a changing climate has brought longer stretches of dryness and drought, providing fires more fuel to burn.

One result of all this? For the second consecutive year, the federal government has depleted its budget to fight fires before the end of the season. By August 19, the U.S. Forest Service had spent nearly $1 billion to fight fires, leaving only $50 million to fight some 40 fires burning throughout the West, as well as in Wyoming, Montana and other states, the Post reported.

Rim Fire as Seen by Media and Bloggers

Confronted with a massive wildfire in California, media across the nation uniformly connected the intensity and size of the Rim Fire to climate change, a broad review of reports in August and September suggests. Below are some news reports, blog posts, and other features with relevant passages cited.

Climate Central, August 26:

Parts of the West have been warming faster than the rest of the lower 48 states since the 1970s, a trend tied to climate change as well as natural climate variability. Anthony Westerling, a climate scientist at the University of California at Merced who studies how climate change effects wildfires, said that increasing temperatures promotes evaporation, which leads to more frequent instances of “extreme fire conditions.”

Time, August 28:

Climate change is expected to increase periods of intense heat and intense dryness, even as precipitation increases globally overall. That’s a formula for more fires.

Salon, August 28:

A perfect storm of conditions, many attributable to climate change and human activity, helped it explode.

(The story, by Lindsey Abrams, went on to list the key factors: record-breaking drought; abnormal seasons — “The dry winter melted into a premature spring”; aggressive firefighting in the past; a rapidly growing population; and crippling budget cuts.)

Onearth (published by the Natural Resources Defense Council), August 28:

The Rim Fire is exactly the kind of bigger, badder blaze that forest ecologists predict in an era of climate change-driven droughts, combined with overdevelopment in fire-prone areas and decades of poor forest management.

Dot Earth, August 29:

Assessing the drivers of wildfire trends in the American West these days can be akin to Hercule Poirot’s task on the Orient Express, on which there was one murder with 12 final suspects — all of whom were guilty.

For western [wild]fire (it’s hard to see how the wild part of that word applies any more, given how many human factors are involved), the suspects are a century of accumulated “fire debt” from fire suppression efforts, development and road construction, natural fluctuations in drought and heat on many time scales, spreading invasive tinder-like grasses and the building influence of greenhouse-driven global warming.

This Dot Earth post zeros in on past fire suppression policies as the prime culprit for the intensity and size of the 2013 Rim Fire. (More on this topic below)

Los Angeles Times, August 31:

In an interview with The Times, National Park Service Director Jon Jarvis said the massive Rim Fire is one example of what is to be expected across the West as climate change, drought and decades of fire suppression leave forests dried-out, overloaded with fuel and more vulnerable to catastrophic wildfires.

“It is a fire that’s demonstrating the challenges that we in the land-management business are facing with climate change,” he said. “A legacy of fire suppression in these forests and, recently, a reduction in our fire funding is all resulting in these huge fires that are incredibly difficult to control and very expensive.”

Mother Jones, September 3:

Though this season hasn’t been a particularly bad season for wildfires so far, there’s reason to be concerned that fires will only grow larger and more frequent as hot, dry weather becomes increasingly common in the West.

Check out this article on climate change and fire from Mother Jones.

San Francisco Chronicle, September 3:

Scientists have long predicted an increase in fire intensity and frequency in California as a result of climate change….”It is hard to point to any two or three years in a row and say, gosh, this is due to climate change, but the conditions now have a lot of characteristics of what we would expect from climate change,” [UC Berkeley Cooperative Extension fire scientist Max] Moritz said. “We are seeing some record-breaking fire years.”

Live Science, September 4:

Researchers predict that wildfires will tear through the western forests more often as a result of climate change: Drought and higher temperatures in the western United States will increase fire frequency by drying and warming landscapes.

Merced Sun-Star, September 8:

As the climate changes and more fires take place, there is a chance that big, fire-resistant trees might not recover.

Washington Post, September 26:

Climate change has heated up and dried out the region, making forests more flammable….A study in 2012 by a team of researchers at the University of California at Berkeley looked at 16 different climate models and concluded that wildfire activity was likely to become much more widespread in regions such as the Western United States if humans keep pumping carbon into the atmosphere and the world heats up.

Different Forests, Different Responses to Warming

Why the Rim Fire exploded into the disaster it was had a lot to do with the characteristics of the region that are distinct from other forests in the country, according to Anthony Westerling, a fire researcher at the University of California at Merced.

There is a lot of variability in wildfire occurrence in the Sierra in Northern California — on annual and decadal time scales, Westerling said. Years with a lot of forest area burned, such as 1987 and 2008, usually have a lot of fires ignited by lightning strikes.

The Rim Fire, by contrast, was ignited by a single person in a region where ignitions were fairly rare. But once it got going, it grew very big very fast.

Why? Westerling points to the warming climate as part of the answer. “It’s been warmer than average, throughout the year, for decades,” Westerling said in a recent telephone interview. It’s not clear that climate change is driving changes in precipitation in the Sierra — at least not yet — but it’s undisputed that it’s gotten warmer, he said.

“Every time you notch that temperature up, you’re increasing the evaporative demand,” Westerling said. “And, everything else held equal it’s going to be drier over the long term, because you’re sucking more moisture out of the soils and out of the fuels. And we’ve been doing that year in and year out for a long time now.

“So, when you ask, ‘Has the Rim Fire been affected by climate change?’ Of course it has. And so has every other fire that’s burned here for years. They’re all burning fuel that’s drier than it otherwise would have been, because it’s warmer.”

Conditions in the Sierra are very different from those seen in other forests — the Rockies, for example. Forests there are actually much more sensitive to a warming climate, Westerling said. On average they’re colder and wetter, and that makes the region much more sensitive to changes in temperature.

These differences in response to warming temperatures, along with differences in forest types and management histories, mean that a blanket fire suppression policy across the nation makes little sense, fire experts say. There are signs, however, that things are changing.

Fighting Fire with Fire

Played-up in numerous media reports about the Rim Fire was the issue of fire suppression — specifically the US Forest Service’s policy in the past to aggressively fight every wildfire that ignites — and the current shift in thinking.

An Associated Press story on September 27 framed the issue:

The conundrum facing forest ecologists is what to do now in an agency that is transitioning from one with a heavy focus on timber production to one whose actions now take into consideration the impacts of climate change, carbon sequestration and habitat.

Decades ago when the last fires swept through the Stanislaus, foresters replanted vast stands of conifers. Absent funding to manage those forests, and lacking a market for small trees that could be sold from thinning, they had stood relatively untouched. Inspections this week revealed that those were some of the most heavily devastated from a fire that has become a laboratory for forest management in an era of rapid environmental changes brought by climate warming.

“When they planted those plantations, the foresters wanted to grow forest for wood production,” said federal forest ecologist Hugh Safford a day after surveying the impact. “Now there are a lot of things that we are trying to do that we have to take into consideration: watershed protection, wildlife habitat restoration, climate change resilience. That’s a big switch in thinking.”

In the October 3 issue of the journal Science, a group of seven leading fire scientists warned against a blanket national policy supporting fire suppression. Among the researchers were Scott Stephens of the University of California at Berkeley, James Agee of the University of Washington, William Romme of Colorado State University, and Thomas Swetnam of the University of Arizona. In their words:

With projected climate change, we expect to face much more forest fire in the coming decades. Policymakers are challenged not to categorize all fires as destructive to ecosystems simply because they have long flame lengths and kill most of the trees within the fire boundary.

Ecological context matters: In some ecosystems, high-severity regimes are appropriate, but climate change may modify these fire regimes and ecosystems as well….Fire policy that focuses on suppression only delays the inevitable, promising more dangerous and destructive future forest fires.

On October 16, NPR’s “Morning Edition” reported on an ongoing controversy over whether to thin forests and burn the harvested wood for power at biomass power plants. NPR reporter Lauren Sommer wrote in an accompanying story:

For decades, the Forest Service tried to put out every fire by 10 a.m. the morning after it started. Small trees grew in, and during the Rim Fire they became ladders, carrying flames up to the treetops and leaving charred trunks. “You can call it thinning, but thinning is really logging,” Kevin Bundy of the Center for Biological Diversity told Sommer. “You have to build roads and skid trails and landings. There can be a fair amount of environmental damage associated with thinning operations.”

Bundy said biomass power plants would only add pressure to cut trees — trees that are storing carbon as they grow. “When you cut those trees down and burn them for bioenergy, you put all that carbon into the atmosphere, where it warms the climate.”

Wildfire a Worry for Insurers

As arguments over fire suppression continue, the insurance industry is taking notice of the increasing number of wildfires across the globe. Earlier this year, Lloyd’s of London released a report on the subject.

“The report notes that wildfires have occurred naturally for 400 million years, so why are they growing more intense now compared to the past?” The Washington Post reported in a story on October 17. “The experts at Lloyd’s say that the answer is twofold: human activity and climate change are both negatively affecting the development of these disasters.”

In California, the Rim Fire is a signpost toward a warmer and more threatening future. Scott Stephens, one of the researchers who penned the essay in Science calling for more prescribed burns in American forests, told San Francisco’s KALW radio on October 10 about a recent trip to forests scorched by the Rim Fire.

“Well, it just looks like tens of thousands, millions of big black sticks, and sticks are standing straight up,” Stephens said. “The change in habitat has been profound. Some people call California the Golden State, I call it the pyro state.”

NOTE: Journalists seeking more guidance on covering the Rim Fire’s aftermath and the intersection between climate change and future wildfires can check out a webpage prepared by the Joan Shorenstein Center on the Press, Politics and Public Policy at Harvard.

Several studies on the links between wildfires and climate change are to be highlighted at the upcoming American Geophysical Union fall meeting in San Francisco December 9-13. As it did last year, The Yale Forum again this year will be posting on these sessions and others from the AGU meeting.

Bruce Lieberman, a long-time journalist, has covered climate change science, policy, and politics for nearly two decades. A newspaper reporter for 20 years, Bruce worked for The San Diego Union-Tribune...