President Trump’s rollback on Tuesday of stringent automobile mileage and emissions standards torpedoes the biggest single step any nation has taken to fight the climate crisis. In dispensing with Obama-era rules in the name of imaginary regulatory reform, he will damage the health of the planet, our pocketbooks and even the very auto industry he thinks will benefit.

The Obama administration set the standards in 2012 to cut emissions and improve gas mileage roughly 5 percent a year from 2021 to 2025. Thirteen automakers agreed to them.

Now Mr. Trump’s decision will slash required fuel-efficiency improvements to just 1.5 percent a year, beginning in 2021, but that won’t even be achieved because of various credits automakers can receive for making vehicles that run on natural gas or employ more efficient air-conditioning refrigerants — even if emissions aren’t reduced. The 2025 new-vehicle fleet would average 31.8 real-world m.p.g., compared with 37.5 m.p.g. under the rules Mr. Trump is eviscerating, according to Consumer Reports.

Under the Trump plan, which is almost certain to face a court challenge by states and environmental groups, including ours, by 2040, vehicles will burn 142 billion additional gallons of gasoline and emit as much as 1.5 billion more tons of pollutants that warm the planet, an Environmental Defense Fund analysis found. That’s the equivalent of the pollution of 68 coal plants operating for five years, according to the E.D.F.