The searing heat and roaring winds may be slowly giving way to calmer, slightly more temperate conditions in the West, but the toll from the wildfire crisis continues to grow, disrupting lives for tens of millions. Deaths in Washington, Oregon and California have increased to at least 17, and nearly 500,000 people in Oregon alone — or 10 percent of the entire state’s population — have either evacuated or have been told to be ready to leave.

Based on numbers released Thursday, California has seen 3.1 million acres burn so far this season, the most of any season, the vast majority of which has taken place since mid-August. Six of the state’s top 20 largest fires are currently burning, including the largest wildfire on record, known as the August Complex.

These wildfires are what is known as a compound disaster, in which more than one extreme event takes place at the same time, across a varied geography. While climate scientists have been warning that compound disasters are an inevitable result of human-caused climate change, a spate of simultaneously burning, rapidly expanding fires spanning the entire West Coast was not expected for several more decades if greenhouse gas emissions remain high.

Perhaps more ominously, there is no exact historical precedent for these blazes.

Oregon has seen more than 900,000 acres burn in just 72 hours, which is larger than the state of Rhode Island and compares with its 10-year average annual wildfire seasonal total of just 500,000 acres. A spate of destructive fires in the state of Washington, related to the same hot, dry and windy weather pattern, has also charred at least 587,000 acres.

Thick, stagnant smoke is creating some of the worst air quality conditions in the world in places like Portland, Ore., and San Francisco, beating out cities in India and China. On Friday, a NOAA satellite spotted a 1,500-mile-long trail of smoke, resembling an ash-colored extended arm, reaching to the west above the Pacific Ocean and ingested into a swirling storm system.

Even to climate scientists who study wildfires, whose key message is to get used to the unprecedented, this fire event has been shocking.

Studies have documented an increase in acres burned in large fires across the West due to global warming, and projections unanimously show that the region is trending hotter, drier and more susceptible to large blazes to come. For example, a study published in August shows California’s frequency of fall days with extreme fire-weather conditions has already more than doubled since the 1980s.

But the geographic scale of this disaster, including the way that so many of these fires behaved once they began, is an indicator to scientists that this disaster is unprecedented in modern times, and a dark precursor of a future without steep cuts in greenhouse gas emissions.

The Creek Fire was a warning

When the Creek Fire burned 100,000 acres of Sierra Nevada forest in a single day during Labor Day weekend’s record-breaking heat wave, it was a warning of what was to come later in the week.

In addition to the heat wave and extreme fire weather in place at the time, the Creek Fire has another connection to climate change. The blaze burned through stands of dead trees in the southern Sierra Nevada, an area hard-hit by the 2011-2017 drought and an epicenter of the tree mortality that occurred during that time. Studies have shown that human-caused global warming caused that drought itself to be more likely and severe.

“I can’t say it was unexpected what happened there, but the speed with which it went was mind-blowing to a lot of us,” said Eric Knapp, a research ecologist with the U.S. Forest Service in Redding, Calif.

Radar imagery shows the massive fire-induced thunderstorm composed of smoke and ash that towered above the fire grew to a height of 55,000 feet, which indicates that extreme fire behavior took place.

It was just after the heat wave had peaked that fierce and relentless dry winds moving from the land to the sea arrived along the West Coast, and wind-driven blazes tore a path of destruction through Washington, Oregon and Northern California.

“We never expected so many of these places to burn at the same time to the degree that they did,” said Dana Skelly, a fuels program manager for the U.S. Forest Service in Portland. “The systems that people rely on to help them get through these events are completely maxed out.”

The tragedy that is playing out exceeds the California fire disasters of 2017 and 2018, which at the time were worse than most people could have imagined was possible for wildfire.

“I do not have anything to compare with these current events where there are upward of seven fires greater than 100,000 acres, each burning in the Northwest, mainly Oregon, along with countless large fires in California that erupted in size,” John Abatzoglou, a climate scientist at the University of California at Merced, said in an email.

According to Knapp, most fire records date to 1910, so it is difficult to discuss fire size before that time.

“But I think it is fair to say that these fires are unprecedented for the speed at which they moved,” he said. “We’ve never seen so many fires cover so many acres in such little time.”

Nick Nauslar, a meteorologist at the National Interagency Fire Center in Boise, Idaho, said this event far surpasses anything in the modern record.

“Multiple fires made 20+ mile runs in 24-hours over the last few days in California, Oregon, and Washington,” he said in an email. “Most of these fires are making massive runs in timber and burning tens of thousands of acres and in some cases 100,000+ acres in one day. The shear amount of fire on the landscape is surreal, and no one I have talked to can remember anything like it.”

‘Remarkable’ setup

Wind is pressing the accelerator on fires that were already moving at alarming rates this summer, and this doesn’t typically happen so early in September.

“This wind event is extremely unusual in terms of its timing, extent and strength for the West Coast,” Abatzoglou said.

Typically, stronger land-to-sea wind patterns set up later in the fall season, when cold air descends into the interior Western states. But the cold not only arrived early this year, it was record cold with snow in the Rockies. The contrast with record heat on the West Coast amplified the air pressure gradient that drove the winds.

“Both the heat and dryness and the winds were unusual in isolation, but the combination of them at the apex of the fire season is even more remarkable,” Abatzoglou said.

According to Abatzoglou, human-caused climate change is accelerating the rate that vegetation dries, through increases in both temperature and the vapor pressure deficit, a measure of atmospheric dryness. Over the past 30 days, the West has seen its highest vapor pressure deficit readings in the last 40 years for this time of year.

“Dry fuels set the table for lands that are more receptive to igniting and carrying fire; this has been compounded by some regions with massive drought kill loading the number of dead fuels, and moreover the legacy of fire suppression leading to more fuels to burn,” he said.

The Big Blowup of 1910

This week’s firestorms have drawn comparisons to the Big Blowup of 1910, a wind-driven conflagration in the northern Rockies that also followed a very dry season. On Aug. 20, 1910, dry cold fronts passed through and unstable air helped blow up scores of fires in north Idaho and western Montana, along with parts of Washington and British Columbia.

These wildfires torched more than 3 million acres and killed 85 people, including 78 firefighters in six separate incidents.

“Because of the trauma of 1910 fires for the Forest Service, it wanted to double down to ensure that large fires would never happen again,” said Stephen Pyne, a fire historian and emeritus professor at Arizona State University.

It ushered in the modern era of American-style firefighting, or “fire suppression,” that continues today. The first fire weather forecasts for high winds were also a result of the 1910 fire.

Though it was a landmark event in American fire history, it did not have the scope of what is unfolding right now.

“The 1910 fires were very strongly clustered across the Idaho panhandle and into Montana and not nearly as widespread as what we’re seeing at the moment,” Abatzoglou said.

New era began in the 1980s

Due in part to a heavy investment in firefighting infrastructure, annual burned acreage plummeted in the 1950s, and a relatively quiet period ensued that lasted for several decades.

However, in the 1980s, things began to shift. The first of the modern fire sieges took place in 1987, when 11,000 lightning strikes helped torch 640,000 acres, many of them in California and Oregon.

In the last 30 to 35 years, the West has seen a steady rise in the intensity of wildfires as well as acreage burned, tied to human-caused climate change. The legacy of decades of fire suppression also looms large.

“Fires today are much more intense and putting up much more smoke per area burned because we’re consuming all the fuel accumulated during the years of suppressing almost all fires,” Knapp said.

A ‘phase change’ in 2017

In California, the 2017 season was an inflection point because it initiated a multiyear series of conflagrations in both the northern and southern parts of the state that has continued into 2020.

There used to be several years in between notable fire outbreaks, and they rarely occurred in both summer and fall of the same year.

“California has had big fires — it is built to burn,” Pyne said. “But I can’t think of any time over the last 100 years where we’ve had serial fire outbreaks, four years running.”

“That I can find no record of happening before,” he added. “That is the big switch; that is the phase change.”

An earlier version of this story contained a caption that incorrectly stated the U.S. Forest Service photo showed damage from the 1910 fires. This story has been updated.