Indian women walking as smog envelops the Jama Masjid mosque in the old quarters of New Delhi last November. India's air now rivals China's as the world's deadliest. (Dominique Faget/AGENCE FRANCE-PRESSE via Getty Images)

DESPITE CALLING for clean air and clean water in his first speech to a joint session of Congress on Tuesday, President Trump is reportedly aiming to cut the Environmental Protection Agency’s staff by a fifth. Maybe Mr. Trump really believes there are enough “superfluous” EPA programs — such as, apparently, those addressing climate change — that his administration will throw out only bathwater and no baby. In reality, focusing only on the pollution challenges of the past, not those of the present or the future, ignores vast volumes of evidence on the ecological and human damage various types of pollution still cause. Imagine what the country would be like now if politicians had folded years ago to industry complaints about environmental protections now considered rudimentary.

Actually, you may not have to imagine. A group of American and Canadian researchers recently released a global air pollution death toll, finding that two major types of air pollution were associated with 4.2 million deaths in 2015, which was a staggering 7.6 percent of all deaths.

“Studies of long-term exposure to air pollution demonstrate that people living in more polluted locations die prematurely, compared with those living in areas with lower levels of pollution,” the report explained. The other side of the coin is that “when air quality improves, so does population health.”

Fine particulates from fuel burning, among other things, penetrate the lungs and enter the bloodstream, encouraging heart disease, strokes, lung cancer, chronic lung disease and respiratory infections. The researchers concluded that exposure to particulate pollution was the fifth deadliest health risk of all 79 they studied, ranking behind high blood pressure, smoking and high blood sugar, and about matching high cholesterol — conditions many people upend their lives in order to mitigate. Air pollution exposure was deadlier than having high body mass index or alcohol use.

No wonder the EPA has cited reductions in particulate matter to justify many Obama-era clean air regulations. Decades of environmental rules have resulted in relatively low — though not necessarily comfortable — particulate pollution levels in the United States and other developed nations. American air could still be cleaner; the researchers found that the nation’s levels of ozone — which also contributes to respiratory disease — were about the same as Nigeria’s and higher than China’s.

Yet Americans do not know how good they have it. Fully 92 percent of the world’s population lives in areas where fine-particulate levels exceed World Health Organization guidelines. The misery is concentrated: Half of air pollution’s death toll was in China and India alone.

Some particulate pollution is natural. But humans burning things — such as coal — is also a principle driver. Some of the pollution, such as that from archaic cooking and heating stoves, might abate with economic development. Yet if that very development relies on ramping up coal burning, people’s health will still be threatened.

Beyond appreciation for effective environmental enforcement, there are at least two lessons. First, major developing nations such as China and India must find a way to grow their economies without substantially degrading their air quality. Second, if world governments continue to press major developing nations on cross-border pollution matters, they will be aided by popular internal demand for cleaner air.