This story was originally published by High Country News and is reproduced here as part of the Climate Desk Collaboration.

At a specialized cold lab in Boulder, Colorado, where indoor temperatures hover around minus 4 degrees Fahrenheit (minus 20 degrees Celsius), atmospheric researcher Anthony Bernal Ayala slices hailstones with a band saw, revealing layers of icy growth like the rings of a tree. These frozen rings — clear or cloudy, thick or thin — indicate the conditions in which the hail formed: A clear layer signals the water froze slowly, while a cloudy layer means it happened quickly, trapping air bubbles. Bernal Ayala then analyzes the crystalline structures, particles, and isotopes preserved in these layers.

“All that information can tell you a wonderful story of how the hailstone was growing, but nobody — not until now — was able to tap into that history,” said Bernal Ayala, who works for Atmospheric and Environmental Research, part of the JANUS Research Group.

Bernal Ayala’s research, conducted at the National Center for Atmospheric Research (NCAR), is part of a historic effort to study one of the costliest weather hazards. Researchers hope their findings will help protect lives and property from the stones that careen to Earth, battering roofs, pummeling crops, and pockmarking cars.

From 2023 to 2025, annual severe thunderstorm losses exceeded $50 billion nationwide, according to the Insurance Institute for Business and Home Safety — more than double the losses seen just a decade earlier. Hail accounted for 60 percent to 80 percent of the damage.

In Colorado, one of the country’s most hail-prone states, hail — not wildfire — is the main factor driving up insurance premiums. And researchers expect larger, more damaging hailstones to become more common with climate change.

“It’s going to just keep getting costlier and costlier,” Bernal Ayala said.

Even basic questions about hail have been notoriously hard to study. But a long-awaited resurgence in research, including the first major US field campaign to study hail in more than 40 years, could help change that. 

ICECHIP — the “In-situ Collaborative Experiment for the Collection of Hail In the Plains” — aims to improve forecasts, make warnings more precise and help communities better prepare. It received $11 million in funding from the National Science Foundation in 2024, just before deep cuts hit the foundation in 2025. 

For six weeks in spring 2025, about 100 scientists and university students chased hailstorms across the Central Plains and Front Range, from the Canadian to the Mexican border, using radar trucks to track storms and drones to take aerial footage. Researchers photographed hail with high-speed cameras, measured its impact with a tool called a disdrometer, recorded hail’s distribution and size based on its imprints on foam pads, captured it in specialized funnels, and crushed it to test its strength. 

Scientists from the Australian Bureau of Meteorology also used balloons to release golf ball-sized sensors into storms. Once aloft, each hail-like probe collected data on how fast it was traveling and whether ice was growing on it; a microphone even recorded water droplets and hailstones hitting it.

“This has really been the first time where we’ve been able to do a real comprehensive look at hail on the ground, hail aloft, the storm itself, the environment around the storm — just everything all at once,” said Becky Adams-Selin, ICECHIP’s lead investigator and a principal scientist at Atmospheric and Environmental Research, JANUS Research Group. 

ICECHIP’s samples were packed into 26 cooler-sized boxes and brought to NCAR. This internationally renowned hub for weather and climate research has been used to study hail for decades. In one of its last major campaigns, in the 1970s, the US investigated Soviet claims that it could suppress hail. 

Researchers say there’s no other US lab like it; the backup plan to store ICECHIP’s samples involved using a walk-in freezer from a fast-food restaurant.

Now NCAR’s own future is uncertain: In late 2025, the Trump administration said it would dissolve the center and transfer its work out of state. The University Corporation for Atmospheric Research (UCAR), which manages NCAR, sued the administration in March, alleging that it’s targeting NCAR to punish Colorado for retaining its mail-in voting system and because Gov. Jared Polis initially refused to release former Mesa County clerk Tina Peters, a 2020 election denier imprisoned for breaching election security and undermining election integrity.

In June, a federal judge temporarily blocked the White House from dismantling NCAR. The government has until Sept. 30 to respond to the lawsuit.

“I can’t even quantify the impact that it would have to our community if we lost NCAR,” Victor Gensini, professor of meteorology at Northern Illinois University, told HCN. “They are the beating heart.”

Previous research has predicted climate change’s effects on hail, noting that warmer temperatures could melt smaller hailstones before they land but also fuel stronger updrafts, keeping hailstones airborne longer and allowing them to grow bigger, enabling the most damaging hail to become more common. 

A record-setting stone recovered in Yuma County, Colorado, in 2023 measured more than 5 inches across. That year, the state logged 176 reports of hail 2 inches or greater, surpassing the previous record of 91 reports in 2018, according to the Colorado Climate Center.

Scientists say it’s difficult to know how much of the rise in damage is due to the increase in large hail versus the increased development in hail hotspots. The connection between a rapidly growing human footprint and higher insured losses has been dubbed the “expanding bull’s-eye effect.”

Gensini, a principal ICECHIP investigator, cites the development boom east of the Front Range, along Colorado’s Interstate 25 corridor, which has grown explosively in recent decades. The population of the Fort Collins metro area alone has doubled since 1990 to around 375,000 residents, according to the US Census Bureau.

This is happening across the Western US, as previously rural or open areas become densely populated, increasingly expensive targets for hail.

“Colorado is the poster child for what I expect the next 25 years to look like for hail,” Gensini said.

In 2019, Fort Collins became one of the first cities to adopt hail-specific roofing requirements for new builds and remodels. Marcus Coldiron, the city’s chief building official, said it was partly in response to all the shingles and roofing materials taken to the landfill after a catastrophic hailstorm in 2018.

It’s still unclear how well the requirements are working: Coldiron said fewer permits were being issued for roof replacements and fewer shingles were going to the dump. However, Fort Collins also hasn’t experienced a hailstorm as devastating as the one that hit in 2018.

A growing number of Front Range communities now require impact-resistant shingles in their building codes, and Colorado legislators recently passed a law offering grants to residents who install more resilient roofing.

ICECHIP’s researchers are also investigating how they can improve building materials as billion-dollar losses from single storms become more common.

“The dollars are simply piling up so fast,” said Ian Giammanco, a lead research meteorologist at the Insurance Institute for Business and Home Safety, one of ICECHIP’s key partners. “We’re still trying to understand how do we get the best materials onto roofs, onto people’s homes, onto businesses to actually start shaving off these losses.”   

Wildfires are popularly considered wild — restricted to the remote wilderness or the edge of forests, and to most, a problem for the dry and hot states of the Western US. But over the past few years, and now across the country, these fires are getting less wild and far more urban. 

This summer, fires in Spokane, Washington, demolished over 800 homes in a suburban neighborhood, and earlier in the season, the northeast coast was engulfed in smog from fires in Ontario. The Hawk Fire in Nevada razed more than 15,000 acres near Reno, destroying 47 homes before it was extinguished. The Los Angeles fires of last year remain some of the most devastating in recent memory, with over 37,000 acres burned — much of it densely built residential neighborhoods — and displacing 205,000 people from their homes. In Boulder, Colorado, the 2021 Marshall Fire destroyed nearly 1,000 homes. 

This changing geography of fires is affecting the health risks they present, too. 

When vegetation burns, it releases particulate matter, or PM 2.5, and with over 46 million homes in the continental US — this is approximately one-third of all homes — on the edge of fire-prone wildland, many more of us are being exposed to air filled with that soot. This alone is a major health risk. According to the World Health Organization, PM 2.5, is associated with premature death, severe damage to respiratory health, and cognitive impairment. It is especially dangerous for aging populations: a study published in February found that accumulated exposure to wildland smoke was associated with greater hospitalization risk for various cardiovascular diseases in older Americans, including irregular heart rhythms and heart failure, even when they are only exposed to moderate levels of PM 2.5.   

But the urban landscape has also changed the very composition of the smoke that increasingly hangs over all of us. As human structures and vehicles burn, the fires expose us not just to particulate matter but also to the chemical toxins of urbanization itself, from plastic to metal oxides and vehicle fuel. The changing nature of this smoke, in fire zones but also in surrounding regions as it drifts outward, exposes us to a new class of health risks. 

While researchers are still learning what exactly those risks might entail, early research suggests long-term dangers that are deeply troubling, especially as exposed populations age.   

The changing fire frontier 

In 2020, the worst California fire year on record, ate up 4.2 million acres of land, most of it wild, spewing huge amounts of PM 2.5 into the air as the blazes raged. Emergency rooms, already short-staffed by the ongoing pandemic, buckled under the burden immediately. Northern California’s Stanford Health Care system saw a 12 percent jump in hospital admissions over the weeks following the fires, and a 43 percent increase in cardiovascular conditions. In Oregon that same year, 10 percent of emergency room visits were due to asthma-like conditions induced by smoke as fires migrated north.  

Unfortunately, in a world of warming temperatures and drying conditions, that story is becoming all too common. In 2025, a total of 5.2 million acres of land burned across the US, and this year that number has already climbed to 8.5 million, before we’ve even hit the winter dry seasons that plague parts of the Southwest. 

Despite this, the global footprint of human housing continues to expand, and with it the danger.  

For centuries, human development has breached wildfire territory. However, over the last three decades, the zone that links the wild to cities and towns, called the wildland-urban interface (WUI), has grown substantially due to suburban construction. The US Forest Service found a 46 percent increase in the number of houses in the risky WUI zone between 1990 and 2020. By 2020, a third of US homes had been built in this highly vulnerable landscape. The math is simple: As suburbia expands into wilder regions, the more houses are exposed to wildland, and the fire risk grows greater. And when houses and other human-made goods burn, different and potentially more toxic forms of smoke can be produced. 

The Los Angeles County fires in January 2025, which saw large urban regions devastated by flames, were an unfortunate case study for these risks. The Palisades and Eaton fires began on the northern edge of the LA foothills, where dense housing meets more wild, and more fire-prone, terrain. In a retrospective analysis, Underwriters Laboratories’ Fire Safety Research Institute detailed how the urban-wildland makeup of Los Angeles County has not only put more communities physically in fire-prone zones, but also has historically made the geographic region itself more vulnerable to fires. 

As those fires spread into LA’s more urban areas in 2025, the smoke they produced became more dangerous, largely because of what was burning: more than 16,000 buildings, household items, and electric vehicles. The resulting emissions were thus far more complex than typical vegetation-only fires. 

“What’s burning is now very different,” said Jackie Goodrich, an epidemiology professor at the University of Michigan. “So now modern homes have tons of plastic, metals, and all of our electronic appliances, and electric vehicles have these batteries that have a lot of rare metals and other toxic materials we don’t even know about.” 

As a result, these emissions contain higher concentrations of volatile organic compounds (VOCs), metals, and carbon monoxide. PFAS, commonly dubbed “forever chemicals,” are also released through fire extinguishing foam and damaged firefighting gear, which traditionally contains PFAS to protect the skin from fuel that may soak through. These chemicals are associated with adverse health effects, including higher risk of certain cancers and weakening of the immune system. Many of these compounds are dangerous carcinogens. 

These urban fires have a dangerous impact on indoor air quality, too, as chemicals and metals are absorbed into soft surfaces like pillows or textiles. Studies conducted in the aftermath of the LA fires found that post-wildfire VOC levels were elevated inside evacuated homes during the months following the fires. All of this goes to show that Americans can face the health risks of WUI smoke exposure, even when their homes emerge from the blaze relatively undamaged.

These dangers mount over time and across populations

Studies examining hospital admission rates or emergency room visits offer some perspective on the short-term health effects of wildfires. But work by Goodrich and University of Arizona public health professor Jeff Burgess is providing new insight into long-term harm by using a subset of the population repeatedly exposed to and vulnerable to fires: the people who fight them. 

In a study published last year, Goodrich and her fellow researchers examined blood samples from fire responders working in mixed urban and wild areas. They found that exposure to smoke limited the genetic expression of a tumor suppressor known to inhibit gastric cancer cell growth. It also affected regulatory expression similarly associated with tumor proliferation across cancer types, as well as neurodegenerative diseases. 

Burgess has run similar studies across 33 states with 9,000 participating firefighters, allowing the researchers to examine changes in microRNA levels, blood proteins, and DNA methylation (which controls whether genes are on or off). His research on a small cohort of new fire recruits found altered DNA methylation at various sites in the genome, many of which are similarly linked to cancers, neurological disease, and cardiovascular disease. 

It is still unclear whether these biological warning signs lead directly to cancer, Burgess said, largely due to the natural latency period between exposure to toxic substances and actual onset of disease. But as participants age, he expects to see a higher incidence of cancer, especially as exposure to big fires accumulates. 

Firefighters have more prolonged exposure to these toxins than most, of course. But the health effects of wildland-urban fires can extend beyond self-selecting groups, especially as more people move into regions exposed to fire. Residents in the WUI are exposed to the same particulate matter and chemical slurry as firefighters. Goodrich suggests that this could lead to a higher risk of asthma and respiratory problems for children, as well as cardiovascular health incidents in adults.  

Examining longer-term gene expression effects, however, is still more difficult in the general population than it is in the firefighters that her lab studies. While firefighters are often exposed to the same chemicals over and over again, it can be harder to get a clear sense of how toxins affect the average civilian who encounters them more sporadically. 

That said, researchers at UCLA have been keeping a close eye on background toxic chemicals in the aftermath of the LA fires. In a paper published in June, they identified high levels of chromium 6, a carcinogenic metal nanoparticle that can cross cell membranes easily, in wildfire cleanup zones for up to two months following the actual fire. Abnormal concentrations of these heavy metals were also found up to six to nine miles downwind from the zones themselves.

Even following the disaster and immediate recovery periods of urban destruction, the public health dangers can persist: Toxic compounds like VOCs can contaminate waterways, and damaged air filtration systems can make it harder to protect surviving homes against future incidents.

As wildfires become less confined to the chaparral and forests and more likely to rage through suburban streets, we’ll all have to prepare to face the orange haze of fire season. And as we do, we’ll have to confront new dangers that may persist long after the blaze dies down.