Strong winds blew across mountain slopes after a record-setting warm, dry summer. Small fires began to blow up into huge conflagrations. Towns in crisis scrambled to escape as fires bore down.

This could describe any number of recent events, in places as disparate as Colorado, California, Canada and Hawaii. But this fire disaster happened over 110 years ago in the Northern Rocky Mountains of Idaho and Montana.

The “Big Burn” of 1910 still holds the record for the largest fire season in the Northern Rockies. Hundreds of fires burned over 3 million acres – roughly the size of Connecticut – most in just two days. The fires destroyed towns, killed 86 people and galvanized public policies committed to putting out every fire.

Today, as the climate warms, fire seasons like in 1910 are becoming more likely. The 2020 fire season was an example. But are extreme fire seasons like these really that unusual in the context of history? And, when fire activity begins to surpass anything experienced in thousands of years – as research suggests is happening in the Southern Rockies – what will happen to the forests?

As paleoecologists, we study how and why ecosystems changed in the past. In a multiyear project, highlighted in two new publications, we tracked how often forest fires occurred in high-elevation forests in the Rocky Mountains over the past 2,500 years, how those fires varied with the climate and how they affected ecosystems. This long view provides both hopeful and concerning lessons for making sense of today’s extreme fire events and impacts on forests.

Lakes record history going back millennia

When a high-elevation forest burns, fires consume tree needles and small branches, killing most trees and lofting charcoal in the air. Some of that charcoal lands on lakes and sinks to the bottom, where it is preserved in layers as sediment accumulates.

After the fire, trees regrow and also leave evidence of their existence in the form of pollen grains that fall on the lake and sink to the bottom.

By extracting a tube of those lake sediments, like a straw pushed into a layer cake from above, we were able to measure the amounts of charcoal and pollen in each layer and reconstruct the history of fire and forest recovery around a dozen lakes across the footprint of the 1910 fires.

Lessons from Rockies’ long history with fire

The lake sediments revealed that high-elevation, or subalpine, forests in the Northern Rockies in Montana and Idaho have consistently bounced back after fires, even during periods of drier climate and more frequent burning than we saw in the 20th century.

High-elevation forests only burn about once every 100 to 250 or more years on average. We found that the amount of burning in subalpine forests of the Northern Rockies over the 20th and 21st centuries remained within the bounds of what those forests experienced over the previous 2,500 years. Even today, the Northern Rockies show resilience to wildfires, including early signs of recovery after extensive fires in 2017.

But similar research in high-elevation forests of the Southern Rockies in Colorado and Wyoming tells a different story.

The record-setting 2020 fire season, with three of Colorado’s largest fires, helped push the rate of burning in high-elevation forests in Colorado and Wyoming into uncharted territory relative to the past 2,000 years.

Climate change is also having bigger impacts on whether and how forests recover after wildfires in warmer, drier regions of the West, including the Southern Rockies, the Southwest and California. When fires are followed by especially warm, dry summers, seedlings can’t establish and forests struggle to regenerate. In some places, shrubby or grassy vegetation replace trees altogether.

Changes happening now in the Southern Rockies could serve as an early warning for what to expect further down the road in the Northern Rockies.

Warmer climate, greater fire activity, higher risks

Looking back thousands of years, it’s hard to ignore the consistent links between the climate and the prevalence of wildfires.

Warmer, drier springs and summers load the dice to make extensive fire seasons more likely. This was the case in 1910 in the Northern Rockies and in 2020 in the Southern Rockies.

When, where and how climate change will push the rate of burning in the rest of the Rockies into uncharted territory is harder to anticipate. The difference between 1910 and 2020 was that 1910 was followed by decades with low fire activity, whereas 2020 was part of an overall trend of increasing fire activity linked with global warming. Just one fire like 1910’s Big Burn in the coming decades, in the context of 21st-century fire activity, would push the Northern Rockies beyond any known records.

Lessons from the long view

The clock is ticking.

Extreme wildfires will become more and more likely as the climate warms, and it will be harder for forests to recover. Human activity is also raising the risk of fires starting.

The Big Burn of 1910 left a lasting impression because of the devastating impacts on lives and homes and, as in the 2020 fire season and many other recent fire disasters, because of the role humans played in igniting them.

Accidental ignitions – from downed power lines, escaped campfires, dragging chains, railroads – expand when and where fires occur, and they lead to the majority of homes lost to fires. The fire that destroyed Lahaina, Hawaii, is the most recent example.

So what can we do?

Curbing greenhouse gas emissions from vehicles, power plants and other sources can help slow warming and the impacts of climate change on wildfires, ecosystems and communities. Forest thinning and prescribed burns can alter how forests burn, protecting humans and minimizing the most severe ecological impacts.

Reframing the challenge of living with wildfire – building with fire-resistant materials, reducing accidental ignitions and increasing preparedness for extreme events – can help minimize damage while maintaining the critical role that fires have played in forests across the Rocky Mountains for millennia.

Kyra Clark-Wolf has received funding from the National Science Foundation and the Joint Fire Science Program

Philip Higuera receives funding from the National Science Foundation, United States Geological Survey, and Joint Fire Science Program.

Director Martin Scorsese’s new movie, “Killers of the Flower Moon,” tells the true story of a string of murders on the Osage Nation’s land in Oklahoma in the 1920s. Based on David Grann’s meticulously researched 2017 book, the movie delves into racial and family dynamics that rocked Oklahoma to the core when oil was discovered on Osage lands.

White settlers targeted members of the Osage Nation to steal their land and the riches beneath it. But from a historical perspective, this crime is just the tip of the iceberg.

From the early 1800s through the 1930s, official U.S. policy displaced thousands of Native Americans from their ancestral homes through the policy known as Indian removal. And throughout the 20th century, the federal government collected billions of dollars from sales or leases of natural resources like timber, oil and gas on Indian lands, which it was supposed to disburse to the land’s owners. But it failed to account for these trust funds for decades, let alone pay Indians what they were due.

I am the manager of the University of Arizona’s Indigenous Governance Program and a law professor. My ancestry is Comanche, Kiowa and Cherokee on my father’s side and Taos Pueblo on my mother’s side. From my perspective, “Killers of the Flower Moon” is just one chapter in a much larger story: The U.S. was built on stolen lands and wealth.

Westward expansion and land theft

In the standard telling, the American West was populated by industrious settlers who eked out livings from the ground, formed cities and, in time, created states. In fact, hundreds of Native nations already lived on those lands, each with their own unique forms of government, culture and language.

In the early 1800s, eastern cities were growing and dense urban centers were becoming unwieldy. Indian lands in the west were an alluring target – but westward expansion ran up against what would become known was “the Indian problem.” This widely used phrase reflected a belief that the U.S. had a God-given mandate to settle North America, and Indians stood in the way.

Starting in the 1830s, Congress pressured Indian tribes in the east to sign treaties that required the tribes to move to reservations in the west. This took place over the objections of public figures such as Tennessee frontiersman and congressman Davy Crockett, humanitarian organizations and, of course, the tribes themselves.

Forced removal touched every tribe east of the Mississippi River and several tribes to the west of it. In total, about 100,000 American Indians were removed from their eastern homelands to western reservations.

But the most pernicious land grab was yet to come.

The General Allotment Act

Even after Indians were corralled on reservations, settlers pushed for more access to western lands. In 1871, Congress formally ended the policy of treaty-making with Indians. Then, in 1887, it passed the General Allotment Act, also known as the Dawes Act. With this law, U.S. policy toward Indians shifted from separation to assimilation – forcibly integrating Indians into the national population.

This required transitioning tribal structures of communal land ownership under a reservation system to a private property model that broke up reservations altogether. The General Allotment Act was designed to divvy up reservation lands into allotments for individual Indians and open any unallotted lands, which were deemed surplus, to non-Indian settlement. Lands could be allotted only to male heads of households.

Under the original statute, the U.S. government held Indian allotments, which measured roughly 160 acres per person, in trust for 25 years before each Indian allottee could receive clear title. During this period, Indian allottees were expected to embrace agriculture, convert to Christianity and assume U.S. citizenship.

In 1906, Congress amended the law to allow the secretary of the interior to issue land titles whenever an Indian allottee was deemed capable of managing his affairs. Once this happened, the allotment was subject to taxation and could immediately be sold.

Legal cultural genocide

Indian allottees often had little concept of farming and even less ability to manage their newly acquired lands.

Even after being confined to western reservations, many tribes had maintained their traditional governance structures and tried to preserve their cultural and religious practices, including communal ownership of property. When the U.S. government imposed a foreign system of ownership and management on them, many Indian landowners simply sold their lands to non-Indian buyers, or found themselves subject to taxes that they were unable to pay.

In total, allotment removed 90 million acres of land from Indian control before the policy ended in the mid-1930s. This led to the destruction of Indian culture; loss of language as the federal government implemented its board school policy; and imposition of a myriad of regulations, as shown in “Killers of the Flower Moon,” that affected inheritance, ownership and title disputes when an allottee passed away.

A measure of justice

Today, about 56 million acres remain under Indian control. The federal government owns title to the lands, but holds them in trust for Indian tribes and individuals.

These lands contain many valuable resources, including oil, gas, timber and minerals. But rather than acting as a steward of Indian interests in these resources, the U.S. government has repeatedly failed in its trust obligations.

As required under the General Allotment Act, money earned from oil and gas exploration, mining and other activities on allotted Indian lands was placed in individual accounts for the benefit of Indian allottees. But for over a century, rather than making payments to Indian landowners, the government routinely mismanaged those funds, failed to provide a court-ordered accounting of them and systematically destroyed disbursement records.

In 1996, Elouise Cobell, a member of the Blackfeet Nation in Montana, filed a class action lawsuit seeking to force the government to provide a historic accounting of these funds and fix its failed system for managing them. After 16 years of litigation, the suit was settled in 2009 for roughly US$3.4 billion.

The settlement provided $1.4 billion for direct payments of $1,000 to each member of the class, and $1.9 billion to consolidate complex ownership interests that had accrued as land was handed down through multiple generations, making it hard to track allottees and develop the land.

“We all know that the settlement is inadequate, but we must also find a way to heal the wounds and bring some measure of restitution,” said Jefferson Keel, president of the National Congress of American Indians, as the organization passed a resolution in 2010 endorsing the settlement.

Who are the wolves?

“Killers of the Flower Moon” offers a snapshot of American Indian land theft, but the full history is much broader. In one scene from the movie, Ernest Burkhart – an uneducated white man, played by Leonardo DiCaprio, who married an Osage woman and participated in the Osage murders – reads haltingly from a child’s picture book.

“There are many, so many, hungry wolves,” he reads. “Can you find the wolves in this picture?” It’s clear from the movie that the town’s citizens are the wolves. But the biggest wolf of all is the federal government itself – and Uncle Sam is nowhere to be seen.

Torivio Fodder is an enrolled member of the Taos Pueblo, and of Comanche, Kiowa and Cherokee descent.

When wildfire smoke turns the air brown and hazy, you might think about heading indoors with the windows closed, running an air purifier or even wearing a mask. These are all good strategies to reduce exposure to the particles in wildfire smoke, but smoky air is also filled with potentially harmful gases. Those gases can get into buildings and remain in the walls and floors for weeks.

Getting rid of these gases isn’t as simple as turning on an air purifier or opening a window on a clear day.

In a new study published in the journal Science Advances, colleagues and I tracked the life of these gases in a home exposed to wildfire smoke. We also found that the best way to get rid of the risk is among the simplest: start cleaning.

The challenge of smoke particles and gases

In December 2021, several of my friends and colleagues were affected by the Marshall Fire that burned about 1,000 homes in Boulder County, Colorado. The “lucky” ones, whose homes were still standing, asked me what they should do to clean their houses. I am an atmospheric and indoor chemist, so I started looking into the published research, but I found very few studies on what happens after a building is exposed to smoke.

What scientists did know was that smoke particles end up on indoor surfaces – floors, walls, ceilings. We knew that air filters could remove particles from the air. And colleagues and I were just beginning to understand that volatile organic compounds, which are traditionally thought to stay in the air, could actually stick to surfaces inside a home and build up reservoirs – invisible pools of organic molecules that can contribute to the air chemistry inside the house.

Volatile organic compounds, or VOCs, are compounds that easily become gases at room temperature. They include everything from limonene in lemons to benzene in gasoline. VOCs aren’t always hazardous to human health, but many VOCs in smoke are. I started to wonder whether the VOCs in wildfire smoke could also stick to the surfaces of a house.

Tracking lingering risks in a test house

I worked with researchers from across the U.S. and Canada to explore this problem during the Chemical Assessment of Surfaces and Air, or CASA, study in 2022. We built on HOMEChem, a previous study in which we looked at how cooking, cleaning and occupancy could change indoor air.

In CASA, we studied what happens when pollutants and chemicals get inside our homes – pesticides, smog and even wood smoke.

Using a cocktail smoker and wood chips, we created a surprisingly chemically accurate proxy for wildfire smoke and released small doses into a test house built by the National Institute of Standards and Technology. NIST’s house allowed us to conduct controlled chemistry experiments in a real-world setting.

We even aged the smoke in a large bag with ozone to simulate what happens when smoke travels long distances, like the smoke from Canadian wildfires that moved into the U.S. in the summer of 2023. Smoke chemistry changes as it travels: Particles become more oxidized and brown, while VOCs break down and the smoke loses its distinctive smell.

How VOCs behave in your home

What we found in CASA was intriguing. While smoke particles quickly settled on indoor surfaces, VOCs were more insidious.

At first, the house took up these smoke VOCs – on floors, walls and building surfaces. But once the initial smoke cleared, the house would slowly release those VOCs back out over the next hours, days or even months, depending on the type of VOC.

This release is what we call a partitioning process: During the smoke event, individual VOC molecules in the air attach to indoor surfaces with weak chemical bonds. The process is called adsorption. As smoke clears and the air cleans out, the bonds can break, and molecules “desorb” back out into the air.

We could watch this partitioning happen in the air by measuring smoke VOC concentrations. On surfaces, we could measure the weight of smoke VOCs that deposited on very sensitive balances and then were slowly released.

Overall, we concluded that this surface reservoir allows smoke VOCs to linger indoors, meaning that people are exposed to them not just during the major smoke event but also long after.

Why worry about VOCs?

Smoke VOCs include well-known carcinogens, and high levels of exposure can induce respiratory and health problems.

While smoke VOC concentrations in our test house decreased with time, they remained persistently elevated above normal levels.

Given that VOC concentrations from other sources, such as cooking and cleaning, can already be high enough in homes to harm health, this additional long-term exposure source from smoke could be important. Further toxicology studies will be needed to determine the significance of its health effects.

How to clean up when smoke gets in

So, what can you do to remove these lingering smoke gases?

We found that air purifiers can remove only some of the VOCs that are in the air – they can’t clean the VOCs on your floors or in your walls. They also work only when they’re running, and even then, air purifiers don’t work particularly well to reduce VOCs.

Opening windows to ventilate will clean the air, if it isn’t smoggy or smoky outside. But as soon as we closed windows and doors, smoke VOCs started to bleed off the surface reservoirs and into the air again, resulting in an elevated, near-constant concentration.

We realized that to permanently remove those smoke VOCs, we had to physically remove them from surfaces.

The good news is that cleaning surfaces by vacuuming, dusting and mopping with a commercial, nonbleach solution did the trick. While some remediation companies may do this surface cleaning for you after extreme exposures, surface cleaning after any smoke event – like Canadian wildfire smoke drifting into homes in 2023 – should effectively and permanently reduced smoke VOC levels indoors.

Of course, we could reach only a certain number of surfaces – it’s hard to vacuum the ceiling! That meant that surface cleaning improved but didn’t eliminate smoke VOC levels in the house. But our study at least provides a path forward for cleaning indoor spaces affected by air pollutants, whether from wildfires, chemical spills or other events.

With wildfires becoming more frequent, surface cleaning can be an easy, cheap and effective way to improve indoor air quality.

Delphine Farmer receives funding from the Alfred P. Sloan Foundation, W.M. Keck Foundation, National Science Foundation, Department of Energy, and the National Oceanic and Atmospheric Administration.