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Science Says: Hotter Weather Turbocharges US West Wildfires

A flag flies in the charred rubble of a home burned in the Carr Fire, Saturday, Aug. 11, 2018, in Redding, Calif.
Associated Press
A flag flies in the charred rubble of a home burned in the Carr Fire, Saturday, Aug. 11, 2018, in Redding, Calif.
Science Says: Hotter Weather Turbocharges US West Wildfires
Science Says: Hotter Weather Turbocharges US West Wildfires GUEST: Seth Borenstein, science writer, the Associated Press

Our top story on Midday edition. New evacuations have been ordered for the still expanding Mendocino complex fire. The new evacuations ordered in Glenn County follow previous orders in Lake Mendocino and Calusa counties. The largest fire in California history grew by an additional 9000 acres overnight. In total 349 942 acres have burned. A new analysis of Western fires by the Associated Press finds links between hotter than average temperatures and wildfires that have burned the most acres. One fire scientist offers a disturbing prediction that the West will soon see wildfires of a million acres. Joining me is Seth Borenstein science writer for The Associated Press and Seth welcome to the program. Thank you for having me. The headline of this AP story says that hotter weather turbo charges Western wildfires. What does that word turbocharging mean. It means that the hotter weather and the drier weather and they work together makes the fires burn hotter and makes the fires burn faster. And so that in turn makes these fires grow larger. So that's one that's what we saw in the data from the National Interagency Fire Center. When you compare that data with National Weather Service data no data that the hotter years tend to have. Much more acreage burned in fires out west and are scientists saying the hotter temperatures we're seeing are attributable to human caused climate change for scientists to attribute single events to human caused climate change they have to go through an elaborate and extensive analysis which involves a lot of computer simulations. They have not done that for this single year's fire seasons. What they have done is studies on past fire seasons and in peer reviewed studies they have shown a link between anthropogenic human caused warming and larger fires in the West and globally to specifically also looked at Alaska. Twenty five fifteen fire season in Alaska was devastating. They were able to find a connection to climate change in that. Now your story includes a formula for how much additional rainfall we need as the temperature rises. Would you share that with us. Sure. That's from Mike Flanagan at the University of Alberta Alberta in Canada. His research shows that for every degree Celsius which is one point eight degrees Fahrenheit for most of us that the temperature warms you need another 15 percent more rainfall to compensate for the drying. So as you know as it gets hotter and as the humidity is low what happens is the fuel that we need for fires dries out and the heat makes it dry. They're having a drought makes it even worse. So dry your fuel is more combustible. Now we have a clip from that scientist at the University of Alberta. Mike Flanagan let's hear what he has to say. If you looked at the climate models of the future and yes the our models are they're not even as good as the weather forecast for tomorrow or the next day but they're close to reality. You know many places in North America are going warm to 3 degrees Celsius and this would require thirty two point five percent increase in precipitation during the fire season and almost none of the models are snared or suggest this is going happen. So the bottom line is a warmer world will have drier fuels drier fuels made it easier for fires to start to spread and to burn more intensely. Now you spoke with firefighters themselves about the wildfires we're seeing now what did they have to say. This was earlier this year speaking to a veteran hotspot. Firefighters have been doing this for more than 30 years. And he said when he started he used to see 10000 acre fires and they thought that was really their hard won their big ones. And now you get hundred thousand acre fires frequently like the Mendocino fire. Mike Murphy complex last year the Northwest Oklahoma last year those were 607 100000 acre wildfires. So what used to be big is now nothing compared to what we're seeing now. And it takes a toll on them Marvin. Obviously there are unfortunately some deaths and that's that's the worst thing but there's only so much you can do. So right now when I talk to the National Interagency Fire Center as of last week the firefighters out west were getting help from the military and from firefighters from Australia and New Zealand who came over here to help the US fight fires here. Now people who are skeptical about the influence of climate change point to huge fires recorded in the West back in the 1930s and 40s. What about those claims. Well there were huge fires in the 30s and 40s but unfortunately we really don't know how huge the National Interagency Fire Center on their website where they list past fire years says that anything before 1983 is unreliable. When I talk to them they said back then you would have different agencies reporting fires in different ways and fires would be double counted Triple Crown and maybe even more. Plus they counted fires that are prescribed burns now which we don't count. And also there is a lot more wild land and fighting fires was a whole different matter then than now. So you can't compare data pre 1983 to now because when you want to compare stuff you need to compare apples to apples and oranges to oranges. We're talking apples. What happened before given the problem with data is oranges and I've been speaking with Seth Borenstein science writer for The Associated Press and Seth thank you very much. My pleasure.

As temperatures rise in the U.S. West, so do the flames.

The years with the most acres burned by wildfires have some of the hottest temperatures, an Associated Press analysis of fire and weather data found. As human-caused climate change has warmed the world over the past 35 years, the land consumed by flames has more than doubled.

Experts say the way global warming worsens wildfires comes down to the basic dynamics of fire. Fires need ignition, oxygen and fuel. And what's really changed is fuel — the trees, brush and other plants that go up in flames.


"Hotter, drier weather means our fuels are drier, so it's easier for fires to start and spread and burn more intensely," said University of Alberta fire scientist Mike Flannigan.

RELATED: Politics Of Wildfires: Biggest Battle Is In California's Capital

It's simple, he said: "The warmer it is, the more fire we see."

Federal fire and weather data show higher air temperatures are turbocharging fire season.

The five hottest Aprils to Septembers out West produced years that on average burned more than 13,500 square miles (35,000 square kilometers), according to data at the National Interagency Fire Center and the National Oceanic and Atmospheric Administration .


That's triple the average for the five coldest Aprils to Septembers.

The Western summer so far is more than 3 degrees Fahrenheit (1.7 degrees Celsius) warmer than the 20th century average. California in July logged its hottest month in 124 years of record-keeping.

The five years with the most acres burned since 1983 averaged 63.4 degrees from April to September. That's 1.2 degrees warmer than average and 2.4 degrees hotter than the years with the least acres burned, AP's data analysis shows.

In California, the five years with the most acres burned (not including this year) average 2.1 degrees warmer than the five years with the least acres burned.

A degree or two may seem like not much, but it is crucial for fuel. The hotter it is, the more water evaporates from plants. When fuel dries faster, fires spread more and burn more intensely, experts said.

For every 1.8 degrees Fahrenheit that the air warms, it needs 15 percent more rain to make up for the drying of the fuel, Flannigan said.

Fuel moisture levels in California and Oregon are flirting with record dry levels, NOAA western regional climate center director Tim Brown said.

And low humidity is "the key driver of wildfire spread," according to University of Colorado fire scientist Jennifer Balch who says the Western U.S. soon will start to see wildfires of 1 million acres (1,562 square miles).

Veteran Colorado hotshot firefighter Mike Sugaski used to consider 10,000-acre (16-square-mile) fires big, now he fights ones 10 times that or more.

"You kind of keep saying, 'How can they get much worse?' But they do," Sugaski said.

The number of U.S. wildfires hasn't changed much over the last few decades, but the area consumed has soared.

"The year 2000 seemed to be some kind of turning point," said Randy Eardley, the fire center's chief spokesman.

From 1983 to 1999, the United States didn't reach 10,000 square miles burned annually. Since then, 10 years have had more than 10,000 square miles burned, including 2017, 2015 and 2006 when more than 15,000 square miles burned.

Some people who reject mainstream climate science point to statistics that seem to show far more acres burned in the 1930s and 1940s. But Eardley said statistics before 1983 are not reliable because fires "may be double-counted, tripled-counted or more."

Nationally, more than 8,900 square miles (23,050 kilometers) have burned this year, about 28 percent more than the 10-year average as of mid-August. California is having one of its worst years.

Scientists generally avoid blaming global warming for specific extreme events without extensive analysis, but scientists have done those extensive examinations on wildfire.

John Abatzgolou of the University of Idaho looked at forest fires and dry conditions in the Western United States from 1979 to 2015 and compared that to computer simulations of what would be expected with no human-caused climate change. He concluded that global warming had a role in an extra 16,200 square miles (42,000 square kilometers) of forests burning since 1984.

A study of the 2015 Alaska fire season — the second biggest on record — did a similar simulation analysis, concluding that climate change from the burning of coal, oil and gas increased the risk of the fire season being that severe by 34 to 60 percent.

One 2015 study said globally fire seasons are about 18.7 percent longer since 1979. Another study that year says climate change is increasing extreme wildfire risk in California where wildfires already are year-round.

Also, drought and bark beetles have killed 129 million trees in California since 2016, creating more fuel.

Contrary to fire scientists, Interior Secretary Ryan Zinke this week told Breitbart radio that "what's driving" increased wildfires is an increase in fuel. He said the government has "been held hostage by environmental terrorist groups" that oppose clearing dead trees that they say provide wildlife habitat. Zinke, however, has acknowledged that climate change was a factor in worsening wildfires.

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