The leading reason for the loss of average lifespan is air pollution. According to an analysis, it cuts 1.8 years from the average life expectancy of humans globally. It is currently the biggest threat to human lives.

The research studied the particulate matter (PM) caused by the burning of fossil fuels. These microscopic particles penetrate deep into the lungs, bypassing the body’s natural defenses and enter the bloodstream, causing lung disease, cancer, strokes, and heart attacks.

The Air Quality Life Index, or AQLI, represents a completely novel advancement in measuring and communicating the health risks posed by particulate matter air pollution. This is because the AQLI converts particulate air pollution into perhaps the most important metric that exists: its impact on life expectancy.

The report said that the AQLI reveals that, averaged across all women, men, and children globally, particulate matter air pollution cuts global life expectancy short by nearly 2 years relative to what they would be if particulate concentrations everywhere were at the level deemed safe by the World Health Organization (WHO). This life expectancy loss makes particulate pollution more devastating than communicable diseases like tuberculosis and HIV/AIDS, behavioral killers like cigarette smoking, and even war.

Some areas of the world are impacted more than others. For example, in the United States, where there is less pollution, life expectancy is cut short by just 0.1 years relative to the WHO guideline. In China and India, where there are much greater levels of pollution, bringing particulate concentrations down to the WHO guideline would increase average life expectancy by 2.9 and 4.3 years, respectively.

“While people can stop smoking and take steps to protect themselves from diseases, there is little they can individually do to protect themselves from the air they breathe,” Michael Greenstone, the director of the Energy Policy Institute at the University of Chicago told the Guardian.

“The [research] tells citizens and policymakers how particulate pollution is affecting them and their communities and reveals the benefits of policies to reduce particulate pollution.”

But if good measures are taken, this can be reversed. The AQLI’s data also show that, more recently, three years into a “War on Pollution,” China has achieved large reductions in air pollution. If these improvements are sustained, the average resident there would see their life expectancy increase by 0.5 years. Reductions in air pollution resulting in large part from the Clean Air Act have added more than 1.5 years to the life expectancy of the average American since 1970.