Ash falling on Seattle and Portland.

Air so thick with smoke it’s hazardous for everyone in Spokane, regardless of age or health.

Landmarks threatened by charging flames in the Columbia River Gorge, on Mount Rainier and in Yosemite and Glacier national parks.

The forest fires burning across the western United States were caused in part by climate change and made worse by a legacy of fire suppression. The hazardous air quality brought by the fires is in some ways worse than when Mount St. Helens erupted in 1980, sending plumes of volcanic ash around the world.

With wildfires in the west increasing in frequency and duration over the last 30 years, summers like this are predicted to become more common.

John Abatzoglou, a climate scientist at the University of Idaho, studies the link between human-caused climate change and wildfires. It’s a “challenging question” to figure out what exactly contributes to a fire region in one year, but Abatzoglou said it’s clear human activity is a major factor, both through increasing temperatures and suppressing fires in western forests.

“Yet again, we’re having another above normal fire season, which we’ve seen repeatedly since 2000,” he said. “In the future, we can expect more years like this.”

Climate change to blame

When the wet, cold winter was winding down, many predicted a quiet fire season. That is, until the two-plus month dry spell.

“The fire season outlooks that were coming out in May were calling for a pretty benign fire season,” said Abatzoglou. “The influence of all that additional moisture can actually enhance fire potential.”

Over the last 150 years, global temperatures have increased by two to three degrees Fahrenheit, Abatzoglou said, leading to longer, drier summers, much like this one. Tuesday was Day 68 in Spokane without rain. The record for most rainless days was set in 1917, at 73.

By fighting fires, fuel was left on the forest floor and made into tinder with the warm, dry temperatures.

“Wildfires burn when it’s warm and dry. It’s a fairly straightforward idea,” Abatzoglou said. “You need to have fuel, enough vegetation. And you need your fuel to be dry enough to carry that fire.”

In a study published last fall in the Proceedings of the National Academy of Sciences, Abatzoglou and Columbia University bioclimatologist Park Williams, concluded that there will come a point when there’s not much left to burn, but that’s decades off. Until then, the fires will be much larger and more destructive than any we’re seeing today.

“Going forward in the next three to four decades…I expect fires to continue to become unrecognizable to previous generations,” Williams told the Washington Post last October. “In the 2030s, it is a very high likelihood that fires [will be] dwarfing the fires that we see today.”

The two climate scientists aren’t alone. The Union of Concerned Scientists warned recently that wildfires will be “more intense and long-burning.”

“The costs of wildfires, in terms of risks to human life and health, property damage, and state and federal dollars, are devastating, and they are only likely to increase unless we better address the risks of wildfires and reduce our activities that lead to further climate change,” the group wrote in an article on its website.

The U.S. Forest Service gives a similar warning, noting that “climate warming associated with elevated greenhouse-gas concentrations may create an atmospheric and fuel environment that is more conducive to large severe fires.”

Worst since Mount St. Helens

As the fires burn, the air quality will degrade beyond the haze blanketing the region in recent days.

Ron Edgar, who worked with the Spokane County Air Pollution Control Authority for 35 years before he retired in 2012, said he believes this week’s air quality is worse than what he dealt with in 1980, during the volcanic eruption of Mount St. Helens.

“The air outside, the look of it, reminds me of Mount St. Helens. But it may be worse,” Edgar said. “Even though it looked like talcum powder [in 1980], this is combustion materials.”

The pollution caused by the fires is a finer particulate than the volcanic ash, and much more hazardous to human health.

In 1980, the air quality agency didn’t have as sophisticated or sensitive instruments as today, and only measured for “total suspended materials,” a general term that didn’t account for particulate size. Nowadays, particulate monitors measure for particles 10 microns in size or smaller, called PM10, and for particles 2.5 microns or smaller, referred to as PM2.5 and is the more hazardous of the two.

Stephanie May, a spokeswoman for the Spokane Regional Clean Air Agency, said it’s nearly impossible to compare this year’s fire pollution with the volcanic pollution of 37 years ago. Still, she said Mount St. Helens left behind particulate readings that were far higher than today’s measurements.

“The highest reading for the Mount St. Helen’s ash episode was 236 times higher than the air quality standard in 1980,” she said. “The highest reading for the 2017 wildfire smoke episode is four times higher than the current air quality standard.”

When ash was as deep as six inches in some parts of the state in 1980, the air quality standard was 260 micrograms per cubic meter of air. At its worst, Mount St. Helens left 35,613 micrograms in a cubic meter of air, on May 19 , 1980.

The air quality remained above healthy levels for about a week until May 25, when rain fell and helped clean the air.

This year, the county agency has recorded 14 days of unhealthy levels, including on Tuesday. Air quality forecasts predict the conditions will last several more days. In 2015, there were sixteen days when pollutants were at unhealthy levels.

The air quality agency only started measuring for the smaller particulates in 1999. Before 2015, the worst year was 2002, when seven days reached unhealthy levels due to stagnant air and wood smoke.