It’s only October, and 2021 has already been a horrendous year for wildfires in the American west. The Dixie fire leveled the town of Greenville. The Caldor fire forced the evacuation of tens of thousands in Lake Tahoe. Some fires sent plumes so high into the atmosphere that the toxic air reached the east coast thousands of miles away.

Fire is an important part of life in the American west and essential for the health of the landscape, but as the climate has changed so have wildfires in the region.

What the US Forest Service once characterized as a four-month-long fire season starting in late summer and early autumn now stretches into six to eight months of the year. Wildfires are starting earlier, burning more intensely and scorching swaths of land larger than ever before. Risks for large, catastrophic fires like the Camp fire that leveled the town of Paradise in 2018 are rising.

Firefighters can still recall a time when battling a so-called megafire – a blaze that torches more than 100,000 acres – was a once-in-a-lifetime experience. These days, it’s far more common for fires to stretch across enormous spans of land.

More than half of the 20 largest fires in California history burned in just the last four years. Eight of the top 20 fires in Oregon occurred in that time frame too. Last year, Arizona saw the most acres burned in its history. California’s August Complex fire, which consumed more than 1 million acres alone, became the first-ever giga-fire in 2020. The Dixie fire this year came close to becoming the second, burning through more than 963,200 acres.

It’s hard to know what the past few years of exceptional blazes will mean in the long term, said Neil Lareau, an atmospheric scientist and professor at the University of Nevada. But the changes point to the dominant role of heat and a warming climate, he said.

“It’s lengthening fire season. It’s giving us more days that are burning at higher intensity. And the result of that is massive fires. They’re more intense, and they’re producing more extreme fire weather,” Lareau said.

Why this is happening

The conditions that set the stage for a staggering escalation in wildfire activity in the American west are layered and complicated, but the climate emergency is a leading culprit.

The climate crisis has amplified drought and heat, two factors that have always been natural parts of western landscape, but play crucial roles in driving bigger blazes.

As early as spring this year, when the landscape is typically still lush from winter rains, there were signs of the historic drought settling in across the region. Hillsides had already started to brown, shrubbery was shriveling, and the dense layer of duff, the damp vegetation that collects and decomposes on the forest floor, was quickly drying. The landscape was prone to burn much earlier than in typical years, increasing the risks that small ignitions could quickly turn into infernos.

Then came the heat. With the landscape already drying rapidly, devastatingly hot temperatures baked even more moisture out of the environment and helped summer deliver on the dire warnings: thousands of fires burned hot and fast.

Fueled by the desiccation and heat, the blazes behaved erratically, shooting sparks and embers over miles of containment lines and crossing terrain once believed less burnable.

Firefighters experienced conditions they had never encountered before, making the fires harder to fight and in some cases nearly impossible to stop.

“We have crossed some thresholds where fire is increasingly hard to control,” said Eric Knapp, a research ecologist for the US Forest Service fires and fuels program. “It is kind of controlling us at this point.”

How fire is changing

Some of the biggest blazes that burned in the US so far this year are examples of just how significantly fire has changed, a trajectory that’s expected to continue.

In the first nine months of 2021, the US has already recorded 11 wildfires reaching more than 100,000 acres in size.

The combination of drought, ample fuel, and wind conditions have made these fires harder to control, leading them to burn longer and cover more ground.

Some of the fires performed never-before-seen feats. The Dixie and Caldor fires crossed the granite ridges in the Sierra Nevada, traveling over one side of the mountainous range to the other.

Some burned so hot they formed pyrocumulous clouds, enormous cloud formations visible from space. In the Bootleg fire, the volatile atmospheric conditions produced a “fire tornado” that reached as high as 30,000 to 40,000ft and was powerful enough to tear the pavement off roads, according to Lareau.

While global heating exacerbated the conditions that helped create the bigger blazes, it didn’t act alone. Decades of mismanagement, with limited prescribed burns and thinning of the overgrowth has also played a role. Forests are now littered with too many dead and dying trees, old stumps, and dried underbrush that acts as tinder to spark fires faster and farther.

Meanwhile, the early start of the fire season means the window for proven fire mitigation efforts is shorter and shorter. “The fall prescribed burning window doesn’t exist in some years,” said Knapp.

What’s ahead

The summer has already been brutal, but the highest danger for fire may not yet have passed.

More than 95% of the west remains mired in drought, with more than half of the region classified in extreme or exceptional. It’s the most “expansive and intense” drought seen in this century, according to the US Drought Monitor.

Higher than normal fire threats also remain in Oregon and Washington, in the Great Basin, and Rocky Mountain areas according to the National Interagency Fire Center. While the Pacific north-west could see some relief in the coming months, problems in California are sure to mount.

As southern California braces for hot, dry, gusty winds typical in autumn, researchers fear that the rains needed to replenish the parched landscapes won’t come. Moisture levels are so low, even a strong storm won’t be enough to quell the flames of tomorrow.

“We are really concerned about what the fall is going to look like,” said AccuWeather’s chief meteorologist, Johnathan Porter. “It is hard to imagine it being any drier than it is now in southern California – it is a real extreme.”

Strong dry winds are expected to continue episodically over the next three months. And the rains that once signalled the end of the season are more and more erratic.

“The precipitation that used to end the fire season is becoming more variable and less reliable,” said LeRoy Westerling, a professor at University of California Merced who studies how the climate crisis affects wildfires.

As fires continue to grow in size and severity and with the season stretching longer and longer, firefighting forces are increasingly spread thin. Even though suppression costs have skyrocketed in recent years, fire crews struggle to keep up.

Bigger blazes are increasing the burdens carried by firefighters, who are experiencing higher rates of suicide, depression, and fatigue. Firefighters are leaving the force in large numbers, adding to the crunch. At the start of this summer the USFS reported that 725 vacant firefighting positions went unfilled.

There are still solutions and mitigations that could slow the shift in intensity – but researchers say that window is closing.

“The trends that are driving this increase in fire risk, fire size, fire severity over time are continuing – that’s climate change.”