Climate change has doubled western US forest fires

Climate change has doubled western US forest fires
In July and August, the Roaring Lion fire devoured more than 8,000 acres of forest, along with over 60 homes and outbuildings in eastern Montana's Bitterroot Range. Here, the fire burns through dense conifers, July 31, 2016. Credit: Mike Daniels

A new study says that human-induced climate change has doubled the area affected by forest fires in the U.S. West over the last 30 years. According to the study, since 1984 heightened temperatures and resulting aridity have caused fires to spread across an additional 16,000 square miles than they otherwise would have—an area larger than the states of Massachusetts and Connecticut combined. The authors warn that further warming will increase fire exponentially in coming decades. The study appears today in the journal Proceedings of the National Academy of Sciences.

"No matter how hard we try, the fires are going to keep getting bigger, and the reason is really clear," said study coauthor Park Williams, a bioclimatologist at Columbia University's Lamont-Doherty Earth Observatory. "Climate is really running the show in terms of what burns. We should be getting ready for bigger years than those familiar to previous generations."

Fires in western forests began increasing abruptly in the 1980s, as measured by area burned, the number of large fires, and length of the fire season. The increases have continued, and recently scientists and public officials have in part blamed human-influenced . The new study is perhaps the first to quantify that assertion. "A lot of people are throwing around the words climate change and fire—specifically, last year fire chiefs and the governor of California started calling this the 'new normal,' " said lead author John Abatzoglou, a professor of geography at the University of Idaho. "We wanted to put some numbers on it."

Warmth drives fire by drying out the land. Warmer air can hold more moisture, and the air ends up sucking it out of plants, trees, dead vegetation on the ground, and soil. Average temperatures in forested parts of the U.S. West have gone up about 2.5 degrees F since 1970, and are expected to keep rising. The resulting drying effect is evident in the rise of more fires. Williams published a study last year showing how climate-driven removal of moisture from land worsened the recent California drought, which was accompanied by .

The overall increase in fire since the 1980s is about twice what the researchers attribute to climate change; the rest is due to other factors, they say. One has been a long-term natural climate oscillation over the Pacific Ocean that has steered storms away from the western United States. Another: firefighting itself. By constantly putting out fires, authorities have allowed areas they "saved" to build up more dry fuel, which later ignites, causing ever more catastrophic blazes, the researchers say. The costs of fire fighting have risen sharply in step; last year the federal government alone spent more than $2.1 billion. "We're seeing the consequence of very successful fire suppression, except now it's not that successful anymore," said Abatzoglou.

The authors teased out the effects of climate warming from other factors by looking at eight different systems for rating forest aridity; these included the Palmer Drought Severity Index, the MacArthur Forest Fire Danger Index and the Canadian Forest Fire Danger Rating System. They then compared such measurements with observations of actual fires and large-scale climate models that estimate manmade warming. The crunched data showed that 55 percent of the increase in fuel aridity expected to lead to fires could be attributed to human-influenced climate change. Climate's role in increasing such aridity has grown since 2000, the researchers say, and will continue to do so.

Williams and Abatzoglou say they do not account for some factors that could be offshoots of , and thus they may be understating the effect. These include millions of trees killed in recent years by beetles that prefer warmer weather, and declines in spring soil moisture brought on by earlier snowmelt. There is also evidence that lighting—the usual initial spark—may increase with warming.

The study does not cover western grasslands. These have seen more fires too, but there is little evidence that climate plays a role there, said Abatzoglou; rather, the spread of highly flammable invasive grasses appears to be the main driver.

Mike Flannigan, a fire researcher at the University of Alberta, said that previous studies have tried to understand the effects of climate on fires in parts of Canada, but that nothing had been done for the United States on this scale. "What's great about this paper is that it quantifies this effect, and it does it on a national scale," he said.

Worldwide, wildfires of all kinds have been increasing, often with a suspected climate connection. Many see a huge fire that leveled part of the northern city of Fort McMurray, Alberta, this May as the result of a warming trend that is drying out northern forests. Fires have even been spreading beyond, into the tundra, in places where blazes have not been seen for thousands of years. That said, fires are not expected to increase everywhere. "Increased fire in a lot of places agrees with the projections," said Jeremy Littell, a research ecologist with the U.S. Geological Survey in Anchorage, Alaska. "But in many woodlands, the relationship between climate and fire is not as tidy."

So far, this year has seen huge, though not record, fires. Over the summer, some 3 million acres burned across the United States, mostly in the West, from Washington state across to the Dakotas and down into Texas. Some scientists say the worst could be yet to come; in some places, the most dangerous conditions often occur from September to December, when desert winds interact with fuels that have been drying for five or six months.

The effects go beyond loss of trees and other vegetation. A 2012 study estimates that smoke from fires worldwide causes long-term health effects that kill some 340,000 people each year, mainly in sub-Saharan Africa and southeast Asia. Carbon released to the air adds to the burden of greenhouse gases already there, thus producing even more warming. Soot settling on snow and ice causes them to absorb more heat and melt faster.

Many scientists studying the issue believe the growth in U.S. western fires will continue for many years. Williams and others say that eventually, so many western forests will burn, they will become too fragmented for fires to spread easily, and the growth in fire will cease. But, he says, "there's no hint we're even getting close to that yet. I'd expect increases to proceed exponentially for at least the next few decades." In the meantime, he said, "It means getting out of fire's way. I'd definitely be worried about living in a forested area with only one road in and one road out."

Explore further

It's not just Alberta: Warming-fueled fires are increasing

More information: "The impact of anthropogenic climate change on wildfire across western US forests," PNAS, 2016.
Citation: Climate change has doubled western US forest fires (2016, October 10) retrieved 22 October 2019 from
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User comments

Oct 10, 2016
Six fires in California in the last year were arson. Does that factor in?

Oct 11, 2016
Six fires in California in the last year were arson. Does that factor in?

Why not?

Oct 11, 2016
The science says that more logging does not stop wildfires - http://www.nytime...tml?_r=0
-- onion donkey brays again.
How about going on a 1200 mile, CO2 spewing jaunt, in which you emit over a tenth of the US annual average, in JUST 2 DAYS. Would that stop wildfires?

Oct 11, 2016
So, the indiscriminate and perhaps ignorant attempts to put these fires out, over the decades, has left a lot of forests thats excellent tinder. Of course to the AGW Cult and their pathological lies with their pathological science, would ignore/conceal that fact.

Oct 11, 2016
Instead - deniers make sarcastic comments - thinking they have contributed to science.
-- The onion jackass hee haws again.
This jackass brays he knows all the science, yet he boasted about his 1200 mile, CO2 spewing jaunt, during which he emitted over a tenth of the US annual average. Now he thinks that by braying at the heretics he's saving the world.

Oct 11, 2016
Your understanding of science is clearly lacking - no one could deny the evidence of evolution seriously....
-- onion jackass hee haws yet again.
This jackass understands all the science, yet he went on a 1200 mile, CO2 spewing jaunt, during which he emitted over a tenth of the US annual average in JUST 2 DAYS.

Oct 11, 2016
Please think a little deeper into my comments, and respond with something more serious. And take the whole evolution framework into mind
-which you conveniently sum up in one word - god. Now thats not very deep at all is it?

When YOUR ideas dont make sense you just say 'gods will'. When YOUR ideas conflict with evidence you just say 'well no one can know the mind of god'. Etc.

And because you dont find scientists doing the same thing with their incomplete or imperfect theories (because theyre not idiots after all) then you think yours are superior.

Because, well, god.

Oct 11, 2016
Six fires in California in the last year were arson. Does that factor in?

Why not?

Well I doesn't matter what the cause of the wildfire is. What matters is that it's dry enough to cause a wildfire in the first place. That depends on drought conditions and with the excessive amounts of drought, wildfires are simply more common.

Oct 12, 2016
More pathological lies from the AGW Cult just to sustain their dogma and feed the Chicken Little idiot's hunger.
Take a gander at what was happening in the the 1930s, the hottest period in the US since 1900.

Oct 15, 2016
Wildfires scorched 40-50 million acres a year during the 1930s, making fire control a national priority. By 1960, the area burned annually had been reduced by 90 percent. But wildfires are again gaining ground on federal lands. [Source: USFS Wildland Fire Statistics] Congressional failure to attack the two primary underlying causes--disease and stand density--is making a bad situation worse. This 1996 Nevada fire burned to bedrock killing everything in sight.

Oct 16, 2016
But I am sure that Breitbart - Fox New - always print the truth for you. And here you are - claiming that evolution has never been observed - and involves "the spontaneous presentation of life from non-life."
Why are you inserting your irrelevant assumptions and beliefs into this thread and what does any of this have to do with forest fires?

Oct 19, 2016
Antirational can't understand a simple graphic.


And what does that graphic mean to YOU, out of curiosity?

Oct 19, 2016
It means we may have already set in motion the cause of our own demise.

Oct 19, 2016
It means we may have already set in motion the cause of our own demise.

That wasn't a very scientific analysis :)

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