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Are massive wildfires the new normal?

Tom Harbour of the U.S. Forest Service readily admits he doesn't know all that much about climate change.

But the folksy and plain-spoken Harbour knows plenty about fighting wildfires. And since he first joined the service in 1970 , Harbour, the agency's national director for fire and aviation management, has witnessed "longer seasons" and "bigger fires."

"When I started 45 years ago, the sense that we would have half-million acre fires in timber just was completely out of the question," Harbour told CBS News. He says fire season is now 78 days longer than when he started. "So, you know, I don't know all the climate change stuff. I know what I see. I know what I've lived ... I don't know exactly why it's happening but I know it's happening."

Harbour's observations are backed up by a study this month in Nature Communications that found fire seasons across the globe are about 20 percent longer than they were 35 years ago, and that the burnable areas affected by fire have doubled during that time.

The study comes as North America is enduring another active season, with thousands of wildfires in Canada and Alaska sending smoke as far as the Midwest. Many of the fires have been fueled by long-running droughts in California and other Western states, with thousands of acres in the Napa Valley catching fire over the weekend while winds also sent flames racing through part of Glacier National Park in Montana.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this natural-color view of the smoke plume from Canadian fires as it passed over Wisconsin, Michigan, Indiana, Ohio, and West Virginia on the morning of June 9. Smoke reached Mid-Atlantic states by that evening and persisted there on June 10. NOAA

The numbers of fires and acres burned this year is slightly above the 10-year average. A majority of that has been in Alaska, where 4.8 million of this season's 5.5 million acres have burned, according to the Forest Service. One factor there is that Alaska is so big and many areas are so remote.

"The fire season this year is driven mainly by drought along the West Coast, Northwest and the biggest impact has been Alaska," Robyn Heffernan, a national fire weather science and dissemination meteorologist at the National Oceanic and Atmospheric Administration.

"Alaska has had a really big fire season," she said. "That was to due with poor winter precipitation they have had up there and dry conditions throughout the spring."

Those fires and the choking haze they produce have prompted a debate in the fire community over what is behind the blazes and whether climate change could be to blame. Most often fires are helped along by higher temperatures, lower humidity, stronger winds or a combination of all three.

"We don't really know what role, per se, climate change is having but we can show that these changes are a result of things like increasing temperatures and more frequent rain-free days, so longer dry periods essentially," said the Forest Service's Matt Jolly, a co-author on the Nature Communications study. "Those things have direct links back to documented climatic changes."

Heffernan also was careful to downplay a direct link between increased fires and climate change, though she added that global warming is causing more extremes in the weather, "swings of extreme heat, extreme cold, more extreme severe weather seasons ... that we can tie to climate change."

Firefighters hurt in northern California wildfires 01:26

"But then making the link between that and fire gets a little bit fuzzy," she said, noting the Southwest had a mild fire season partly due to two tropical systems that dumped rain in places like Texas. "It's not like you can say a blanket statement that this year is a bad fire season. It's all dependent on where you are."

Still, recent decades have seem some of the biggest and most deadly fires worldwide, including 1997-98 blazes in Indonesia peat lands that blanked Southeast Asia in haze and released up to 40 percent of fossil fuel emissions at the time; the worst-ever fire season in Western Russia in 2010; and a marked increased in fires in Northern Rocky Mountains over the past several decades.

At the same time, factors contributing to big fires have all increased: the number of rain-free days has risen by 1.31 days per decade, and average temperature on vegetated land increased by 0.185 degrees per decade, while the annual relative humidity dropped by 0.127 percent per decade, according to the Nature study.

"Ecosystems are designed to withstand the normal climate situation, but we suspect that things aren't normal anymore," South Dakota State University's Mark Cochrane, another co-author on the paper, said.

And looking further out, bigger and badder fires are likely to become the normal as temperatures rise due to the continued burning of fossil fuels like oil and coal.

Drought fueling wildfires on West Coast 01:59

A study out earlier this month in the International Journal of Wildland Fire predicts that climate change will be responsible by mid-century for more mega-fires.

Using a model to accurately simulate locations and timing of the largest wildfires across the U.S. in the past 30 years, they saw an increase in fire potential in nearly all regions, but especially in the northwest, northern California, Florida and the northern Great Lakes.

"Our study paints a fairly grim picture," said co-author John Abatzoglou, associate professor of geography at University of Idaho. "Climate change will up the odds of conditions that have historically accompanied these large fires. While it may be challenging to slow the pace of climate change, our work highlights hot spots where land management might be able to focus adaptation efforts."

The trend for more fires is especially problematic in the United States, as more and more Americans are building homes in wildfire country, resulting in more structures potentially burning down and lives lost.

U.S. spending on fire suppression has increased from $239 million in 1985 to $1.5 billion last year, according to the National Interagency Fire Center. Currently, there are nearly 45 million homes considered at risk, with hundreds, if not several thousand, burning each year.

Global patterns of fire weather season length changes from 1979 to 2013. A shows areas with significant trends in fire weather season length from 1979 to 2013. B shows regions that have experienced changes in the frequency of long fire weather seasons . Nature Communications

Tom Harbour knows he can't control the climate so he is focused on what he can do: improve training of firefighters and work with local and state government to ensure homes are being built in a way that "provides those firefighters with a much better opportunity to not only protect the home but to protect themselves, ultimately keeping folks alive."

"I'm really concerned about this witches' brew of what scientists are telling us about what is going to happen with the fire season and certainly with what we are doing as a nation - more homes at risk and more private land being developed," Harbour said.

"I'm responsible for 10,000 firefighters. That is where rubber hits the road for me," he said. "I worry about the complexity that we're asking our young wildland firefighters - our smoker jumpers, hot shots and folks on engines - to face into the future with longer, more intense fire seasons, more ground at risk."

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