Neglected climate-change threat: wildfire smoke

Loretta Mickley began contemplating smoke during the summer of 2002.

“I was on vacation in Western Massachusetts, and that day, the air seemed rather sparkly,” Mickley reminisced. “I had never observed anything like it, and I asked my husband, ‘What’s happening?’ As an atmospheric chemist, I should know, right?”

The shimmering substance was soot, raised by a wildfire in Quebec and carried hundreds of miles along the eastern coastline.

Twenty-three years later, smoke has become the primary focus for Mickley, a senior research fellow at the John A. Paulson School of Engineering and Applied Sciences. Yet, it took years for the efforts of Mickley and colleagues to genuinely commence and expand across disciplines as the issue intensified with a warming planet.

While wildfires have existed for as long as our planet, their repercussions were poorly understood — often disregarded.

“For an extended period, smoke was deemed unimportant,” Mickley remarked. “Individuals considered climate change through the lenses of temperature and sea-level rise; that was all. They overlooked the fact that there could be this other aspect of climate change that might be extremely alarming, significantly detrimental to human health — not only near the fire, but hundreds of miles downwind.”

A surge of recent studies has altered that narrative. Chemists analyze the components of wildfire smoke. Engineers innovate and deploy new tools into the plumes. Medical researchers simulate its impacts on public health and trace its path into human bloodstreams. Environmental scientists and data analysts predict how much more fire activity we can anticipate as global temperatures continue to climb.

With numerous publications on smoke since 2015, Mickley is a pivotal member of a global research community — reaching out to regions where fires are ablaze.

“I examine agricultural fires in India and their corresponding smoke, which impacts millions,” Mickley stated. “I don’t travel to these locations, but we have conducted research in the Amazon, work in Australia … collaborating with local communities as much as possible.”

Preliminary findings indicate that wildfire smoke is extensively and particularly harmful. Burning trees, soil, and vehicles can release heavy metals as well as volatile organic compounds, Mickley noted, which “attach to and interact with human cells.”

Smoke from fires that extend to structures — such as those that devastated Southern California earlier this year — can contain perfluoroalkyl and polyfluoroalkyl substances, known as PFAS, which are associated with cancer and endocrine disruption, and which take decades to break down.

Our understanding of the smoke reveals that a large portion of its particle makeup comprises the minuscule particles referred to as PM_2.5.

By definition, these particles measure a maximum of 2.5 microns across — approximately 20 times finer than a human hair.

This characteristic renders them uniquely hazardous to human health, asserted Nicholas Nassikas, assistant professor of medicine at Harvard Medical School.

“Pollen [which is roughly four times larger] — that tends to get stuck in your nose,” remarked Nassikas, who also practices in pulmonology and asthma at Beth Israel Deaconess Medical Center. In contrast, PM_2.5 particles are “so minuscule that they can penetrate deep into the lungs and enter your bloodstream. This triggers a chain reaction of inflammation, potentially leading to severe health issues.”

This reaction can impair immune responses and — in the context of smoke — result in a dizzying array of negative health outcomes.

It’s not limited to heart or lung health: Mickley’s research in Australia discovered that after extended exposure to wildfire smoke, pregnant women were more likely to deliver prematurely, need neonatal intensive care intervention, or experience pregnancy loss.

The symptoms of COVID-19 seem to worsen in the smoke. NIH-funded studies have established an early but uncertain connection between inhaling wildfire smoke and dementia risk. Emergency hospital admissions increase for various ailments following periods in dense smoke — particularly among older adults.

In another area of the University, researchers have begun exploring the health impacts of smoke exposure along the fire line in Southern California.

Kari Nadeau — head of the Department of Environmental Health at the T.H. Chan School of Public Health — and her team are part of the LA Fire HEALTH Study consortium, investigating the mechanisms of adverse health impacts from smoke.

For a June publication, they examined the blood of 31 residents of California — both firefighters and civilians — who were exposed to smoke.

This blood was compared against that of a demographically matched, non-exposed group, focusing on billions of genetic and biological markers, stated Abhinav Kaushik, a co-author and research scientist at the T.H. Chan School of Public Health.

The findings revealed that California’s urban wildfire smoke — a complicated mix of heavy metals, PFAS, and organic compounds — disrupts the immune system. “Typically, immune cells are finely regulated, but following smoke exposure, some of those cells began to act abnormally — becoming hyperactivated,” Kaushik explained.

In contrast, other immune cells — burdened with cadmium and mercury isotopes — simply perished.

Heavy-metal toxicity was particularly stark in long-serving firefighters, Kaushik noted, “which may clarify the persistent illnesses firefighters face [disproportionately], ranging from cancer to asthma.”

Kaushik stated that smoke has emerged as “a public health crisis — there’s no doubt about it.”

The forthcoming phase for the LA Fire HEALTH Study, he continued, is to broaden its collection of blood samples in pursuit of a dependable biomarker for individual smoke exposure.

Even at this early phase, that effort serves a vital explanatory function to align with the concerning epidemiological models.

In a June study in Environmental Science & Technology, Mickley and co-authors from Harvard and British Columbia project that in 2020 — a year marked by extensive fires — smoke contributed to nearly 37,000 additional fatalities.

She observes that the confidence interval is broad: ranging from 25,000 to 47,000.

“In my perspective, the specific number isn’t crucial, just that we acknowledge it’s a significant figure,” Mickley explained. “Our intent in sharing these numbers is to underscore the urgency and potential human dangers stemming from wildfire smoke, which in turn is driven by climate change.”

It’s reasonable to assume that the hazards of wildfires, which thrive on drought, electrical storms, and elevated temperatures, may escalate as climate shifts occur.

Indeed, in 2014, Mickley and lead author Xu Yue — then a postdoctoral researcher at SEAS — projected that California’s burned area could roughly double by midcentury under one warming scenario proposed by the Intergovernmental Panel on Climate Change.

According to that model, what has historically been termed an “extreme fire year” in Southern California — with at least 25,000 acres ablaze — would likely become the norm rather than the exception. (Already, this year the region has experienced more than twice that area consumed by fire.)

During her presentations at alumni gatherings and events, Mickley promotes reasonable actions individuals can take: wearing N95 masks on days with heavy smoke, incorporating HEPA filtration systems in homes.

Instead of the zero-tolerance fire management approach employed for many years, she has supported the implementation of controlled burns to avert the catastrophic wildfires that can occur after a prolonged “fire deficit,” where fuel accumulation occurs.

However, those are local modifications, Mickley asserts, where the primary factor influencing health and safety is global: a changing climate already inflicting fire-related casualties, displacement, and ill health at an unprecedented scale.

Wildfire is a natural phenomenon, Mickley remarks. But, “We’re entering a new climate era that is not — and is largely driven by the greenhouse gases we’re releasing into the atmosphere. This is a formula for catastrophe.”