Air pollution is much worse than we thought

In the late 1960s, the US saw regular, choking smog descend over New York City and Los Angeles, 100,000 barrels of oil spilled off the coast of Santa Barbara, California, and, perhaps most famously, fires burning on the surface of the Cuyahoga River in Ohio. These grim images sparked the modern environmental movement, the first Earth Day, and a decade of extraordinary environmental lawmaking and rulemaking (much of it under a Republican president, Richard Nixon).

From the ’70s through the beginning of the 21st century, the fight against fossil fuels...