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…

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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.

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