You can’t see particles smaller than 2.5 microns. But they kill 3.4 million people a year.
Climate change is going to have profound consequences on human health and survival. Most obviously, a hotter world means more heat stroke and other heat-caused deaths.
A recent study on the mortality cost of climate change found that every 4,434 metric tons of carbon dioxide emitted — about the combined lifetime emissions of 3.5 Americans, the study estimates — will cause a heat-related death this century.
But the situation is even worse than that number suggests. Danny Bressler, the environmental economist who authored the paper, notes his estimate leaves out some other potential climate-related deaths, like those from flooding and reduced food supply. He’s just estimating what higher temperatures alone will do, writing that he “does not consider likely mortality co-benefits of stricter climate policies, such as decreases in particulate matter pollution.”
That’s a technical way of putting it. Here’s a simpler way: When we burn fossil fuels, not all the resulting pollution goes up high into the atmosphere. Some of it accumulates in the air that we breathe every day.
And it kills us. A lot of us. The Global Burden of Disease study, a common benchmark for public health work, estimates that 3.4 million people die prematurely every year due to air pollution. More recent research puts the total even higher, at 10 million a year. A recent paper suggested that 90 percent of the world’s population lives in areas with air pollution higher than World Health Organization guidelines (guidelines that the organization itself is toughening).
The particles in question here are invisible to the naked eye — but their effects are anything but.
The public health threat of particulate matter
This problem goes by a lot of different names — “air pollution,” “low air quality,” “PM 2.5 pollution” — but it is directly tied to our climate problem.
Burning fossil fuels, in a car or steel mill or power plant, produces carbon dioxide and methane, but it also produces other pollutants. The term “PM 2.5” refers to particles smaller than 2.5 microns (or 0.0025 millimeters — tinier than a grain of sand) suspended in the air. Sometimes colloquially called “soot,” PM 2.5 usually comes from burning stuff: wood in fireplaces, propane in generators, coal in power plants, and gasoline in cars.
But PM 2.5 pollution doesn’t just emanate from controlled combustion. Fossil fuels also contribute to PM 2.5 emissions indirectly: Global warming is increasing the frequency and severity of wildfires, which subject people to huge quantities of particulate matter. The largest wildfire in California’s history, the Camp Fire of 2018, led PM 2.5 levels in the nearby city of Chico to increase by about 12 times the EPA limit.
This all matters because PM 2.5 emissions are extremely deadly. Because PM 2.5 particles are so small, they can easily reach the lungs and even the bloodstream, and long-term exposure can cause a variety of serious health problems, like lung cancer, emphysema, strokes, heart attacks, and cognitive decline.
And we have very good causal evidence that high levels of exposure to PM 2.5 pollution lead to a decline in overall health and life expectancy. Some of the early convincing evidence came from the US, particularly an influential “Six Cities Study” released in 1993. That study found significant relationships between levels of air pollution and overall mortality, driven by higher rates of lung cancer and other lung diseases and heart disease.
A more recent and methodologically strong set of research has focused on China, specifically its “Huai River policy” instituted in the 1950s. The Chinese Communist government had promised free heating in wintertime as a new state-provided benefit, but lacked the resources to offer the benefit nationally. Instead, it only gave free or heavily subsidized coal for heating to households north of the Huai River. The Huai roughly bisects eastern China; Beijing is several hundred miles to its north, and Shanghai slightly to its south.
That meant communities north of the river were exposed to much more particulate pollution from burning coal than communities to the south. Retrospective work comparing lifespans above and below the Huai River suggested that these emissions were incredibly deadly, directly reducing life expectancy by five and a half years for people north of the river compared to those living south of it.
Air pollution is costing millions of lives — and more
Worldwide pollution isn’t quite as bad as it was north of the Huai, but it’s not great either. The University of Chicago’s Air Quality Life Index, which regularly estimates the human toll of particulate pollution, this fall issued a report estimating that the average person on Earth loses 2.2 years of life expectancy due to particulate pollution, compared to a scenario in which every country followed WHO guidelines.
“Alcohol use reduces life expectancy by 9 months; unsafe water and sanitation, 7 months; HIV/AIDS, 4 months; malaria, 3 months; and conflict and terrorism, just 7 days,” researchers Ken Lee and Michael Greenstone write in the report. “Thus, the impact of particulate pollution on life expectancy is comparable to that of smoking, almost three times that of alcohol and drug use and unsafe water, five times that of HIV/AIDS, and 114 times that of conflict and terrorism.” By their count, lowering air pollution levels below those specified in WHO guidelines would enable people currently alive to enjoy 17 billion more years on Earth, collectively.
And that’s a relatively conservative figure. Shortly after the report’s release, the World Health Organization set stricter guidelines for particulate pollution. Its prior standard, undergirding the UChicago analysis, was that particulate concentration in the air we breathe should be kept to under 10 micrograms (µg, or a millionth of a gram) per cubic meter of air. The new threshold, developed due to evidence that even lower concentrations can be harmful to human health, is half that: 5 µg/m³.
Cutting global air pollution down to that new, lower threshold would save even more millions of life-years.
And the harms of particulate pollution are not limited to life expectancy. Patrick Collison, the entrepreneur and cofounder of Stripe, has taken a research interest in this topic and has a useful compendium of recent work on air pollution harms. Among the studies he highlights:
- A very small increase in particulate pollution (specifically an increase in PM 2.5 concentration of 1µg/m³) causes, by one estimate, a 0.8 percent reduction in GDP that year, mostly because air pollution increases absenteeism and reduces productivity.
- Alzheimer’s diagnoses triple when long-term air pollution exposure is substantially increased (by 10 µg/m³). Parkinson’s and dementia diagnoses increase too.
- Air pollution reduces cognitive functioning in young people. Applying US air pollution standards to China would substantially raise test scores on both reading and math in the latter country, from the median to the 63rd and 58th percentiles respectively.
- Chess players, baseball umpires, and stock traders all perform worse at their jobs when exposed to more air pollution. Those jobs are unusually easy to quantify, but it stands to reason that people’s performance at other jobs suffers too.
Even if air pollution doesn’t kill you, it probably impedes your cognitive functioning, makes you poorer, and increases your susceptibility to brutal diseases like Alzheimer’s.
How combating climate change can extend life expectancy
Air pollution is a tough problem, but the good news is that we can help solve it by solving another tough problem. Actions to combat global warming can also dramatically cut air pollution deaths.
In 2018, a team of earth scientists at Duke and Columbia universities modeled what would happen to air pollution deaths if the world actually acted to confront climate change. They considered a scenario where 180 fewer gigatons of CO2 are emitted by 2100. That’s roughly the reductions needed to keep warming to 2ºC or below — the goal of the Paris climate agreement.
If we reduce emissions that much, we would prevent about 110 million to 196 million premature deaths by 2100. Averaged over the 80-year period the paper considers, that’s 1.4 million to 2.5 million deaths per year averted. (The improvements would need time to take effect, so more lives would be saved later in the century than in the next 10 years or so.)
The good news is that governments have regulatory levers for reducing air pollution deaths — and some are pulling them. The UChicago Air Quality Life Index report estimates that since 2013, China has reduced air pollution by 29 percent, for an average lifespan extension of 1.5 years for each of its citizens (assuming there’s no backsliding on pollution).
The passage of a stronger version of the Clean Air Act in the US, similarly, was followed by a 50 percent reduction in particulate pollution between 1970 and 1979, aided by a slow economy. Economists Kenneth Chay and Michael Greenstone have estimated that the Clean Air Act caused an immediate and sharp decline in infant mortality in the US. By their figures, some 1,300 fewer infants died in 1972 than would have if the Clean Air Act amendments of 1970 hadn’t passed. What’s more, research from economists Adam Isen, Maya Rossin-Slater, and W. Reed Walker suggests that the Clean Air Act amendments led children to have higher earnings as adults than they would have had if they’d been exposed to prior levels of pollution.
There are also things you can do at an individual level to mitigate your air pollution intake. My colleague Rebecca Leber wrote about a tool that lets you investigate air quality where you live, and you can help prevent emissions from harming yourself or your loved ones with an electric air purifier (I have two running in my apartment).
But air pollution is not an individual problem, any more than climate change is. The long-term solutions involve setting much stricter regulations or higher taxes targeting particulate emissions, and replacing common sources like coal plants with solar, nuclear, or wind power.
The Biden administration is moving in the right direction. The Environmental Protection Agency, under Biden’s appointee Michael Regan, is reviewing its air quality standards, last reevaluated in 2012, in response to “the strong body of scientific evidence [which] shows that long- and short-term exposures to fine particles (PM2.5) can harm people’s health, leading to heart attacks, asthma attacks, and premature death.” A scientific panel at the EPA has signaled support for lowering the amount of PM 2.5 allowed in the air by as much as a third.
But this is also a global problem that hits the developing world even harder. Spreading green tech to emerging economies like India and Brazil is not just a climate necessity. It’s a public health necessity too.
A version of this story was initially published in the Future Perfect newsletter. Sign up here to subscribe!