“For years, I had this figure in my head — 4.2 million deaths,” Karn Vohra says. That’s the annual number of fatalities attributed to air pollution — dust, wildfire smoke, fossil-fuel combustion — by a well-known study. It’s a large number, but calculations done by a team including Vohra, a Ph.D student at the University of Birmingham in the UK, indicate the actual death toll may be more than double that number he had in his head for so long.
The team of scientists estimates air pollution created by the burning of fossil fuels was responsible for a staggering one in five deaths globally — a total of 8.7 million lives lost — in 2018 alone.
The study was a collaboration between scientists at Harvard, the University of Birmingham, the University of Leicester, and University College London. Two developments, the researchers say, helped lead to the more precise figure: better mapping data and a new model for assessing the risks posed by air pollution, based on recent health studies. “This new statistical model with these new health studies shows that there’s far more sensitivity [to fossil-fuel pollution] than was previously assumed,” Dr. Eloise Marais, a geographer at University College London, and co-author on the study, tells Rolling Stone. “That new information plays quite a large role in the much higher estimates that we obtained.”
Previous studies used surface and satellite observations to calculate the total particulate matter from all sources combined — not just fossil fuels. In this case, Vohra says, “We break the whole globe into a grid of squares — these squares can be as small as 50 by 60 kilometers.” Researchers then were able to do a detailed analysis using a sophisticated 3D model that can distinguish the super fine particulate matter generated by burning fossil fuels, specifically.
Once they were able to see exactly where the pollution from fossil fuels is concentrated, scientists sought to understand the impact that pollution was having on the populations in those areas. Specifically, they focused on particulate matter known as PM2.5. When inhaled, these tiny particles — less than 2.5 micrometers in diameter, or 30 times smaller than a strand of human hair — can exacerbate existing health conditions or create new ones, leading to shorter lives. Exposure to PM2.5 has been associated with heart and lung disease, bronchitis, asthma and other conditions.
“It’s a bit tricky to explain premature mortality,” Vohra says. Generally speaking, scientists look at the average age at death in a given area — “any taking place sooner than that, earlier than that, would be defined as a premature mortality,” he says.
Researchers found that higher death rates were concentrated in countries and regions that burn more fossil fuels. India, China, Europe and the United States — particularly the northeastern U.S. — were hotspots. “It’s about density of population, so [areas in which there is] a lot of use of cars, but also a concentration of power plants are contributing in the Northeast,” Marais says. Concern about the type of air pollution that Marais, Vohra, and their collaborators looked at is particularly acute for two vulnerable groups: adults 65 years and older, and young kids whose lungs are still developing.