Wildfires in the western half of the United States, including Oregon, have been burning hotter, faster and twice as large over the last 30 years and a good heap of the blame belongs to climate change brought on by humans.

That's according to researchers at the University of Idaho and Columbia University in New York, who released a study Monday showing that rising temperatures due to climate change have increased fire activity and burned an additional 16,000 square miles, an area larger than the state of Maryland, that otherwise would have gone unscorched.

Lead author John Abatzoglou, a professor of geography at the University of Idaho, said the study is likely the first to quantify what firefighters, scientists and public officials have been saying for years, that fires are burning hotter and bigger because of climate change caused by humans.

"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,'" Abatzoglou said in a statement. "We wanted to put some numbers on it."

And the numbers are striking. Average temperatures in western forests have gone up by about 2.5 degrees since 1970, researchers found. Warmer air holds more moisture and that water vapor is sucked from soil, plants, trees and dead vegetation. What is left is a veritable tinderbox and conditions in increasingly arid forests are likely to get worse before they get better.

"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 fire years than those familiar to previous generations."

You don't need to look to the future to find these massive conflagrations, either. In 2002, the Biscuit Fire, which scorched roughly 500,000 acres in southern Oregon and California, was the largest in the country for that year. In 2012, another half million acres of southeast Oregon rangeland was torched by the Long Draw Fire and, just last year, the Canyon Creek Complex Fire burned more than 110,000 acres and destroyed 43 homes.

The authors concede that the overall area that's burned since the 1980s is more than can be accounted for by climate change. Natural weather patterns have steered storms away from the west coast, plunging much of the west into a devastating drought in recent years. Some of the uptick in wildfires can be attributed to firefighting efforts themselves, the authors wrote, as fires that are quickly put out leave behind dry fuel, which can cause even more catastrophic conflagrations the next time it burns.

"We're seeing the consequence of very successful fire suppression, except now it's not that successful anymore," Abatzoglou said.

To exclude other factors and pin the blame on climate change, the authors examined eight forest aridity scales — including the Palmer Drought Severity Index, the MacArthur Forest Fire Danger Index and the Canadian Forest Fire Danger Rating System — and compared them with observations of actual fires and large-scale climate projections, which estimated the effects of manmade climate change.

Fuel aridity, the dryness that leads to these massive blazes, increased by 55 percent and was directly attributable to human-influenced climate change, the data showed.

The data showed that 55 percent of the increase in fuel aridity expected to lead to fires could be attributed to human-influenced climate change. The role climate change plays in the increase in aridity has grown since 2000, and experts predict it will continue to do so.

The continuing upward trend that scientists predict will lead to more massive fires for decades to come, has a bit of a silver lining, if you can call it that. Eventually, Williams said, western forests will become so fragmented that fires will have trouble spreading.

"There's no hint we're even getting close to that yet," he cautioned. "I'd expect increases to proceed exponentially for at least the next few decades."

For now, Williams said, people who live in fire-prone areas should expect to see bigger blazes and should plan accordingly.

"It means getting out of fire's way," he said. "I'd definitely be worried about living in a forested area with only one road in and one road out."

— Kale Williams

503-294-4048

-- Interactive map by Lynne Palombo