Those skeptical of the data on global climate change point out that there is a lot we still don’t know. But there are some things we do know: By 2020, there will be another 700 million additional vehicles on the roads—many in China. Ensuring that these new vehicles incorporate the latest clean technology will be one of the most critical public policy challenges of our time. The absence of total certainty or consensus on the dangers of climate change must not impede constructive action. Fortunately, scientists and engineers haven’t let it. And because of the advances they are making, I am convinced that one of today’s most pressing environmental problems will soon disappear.

By 2040, harmful vehicle emissions will be a thing of the past. Those who can remember the dark fumes pumped out of cars and trucks know that we’ve already come a long way. Lead, sulphur, and benzene have been progressively reduced or removed from new vehicles. In the United States, lead emissions have dropped by about 95 percent. If only a third of the cars in 2050 run at 60 miles per gallon rather than 30 miles per gallon, carbon dioxide emissions will decline by 1 million tons a year.

But the progress won’t stop there. New refinery technology is producing ever cleaner fuels. The quality of lubricants—which allow engines to operate efficiently—is improving. And engines themselves, whether hybrids or upgraded internal combustion machines, are becoming cleaner fuel burners. The combination of these trends will have a tremendous impact as the world’s capital stock of vehicles turns over during the next 35 years.

Vehicles, of course, are only one source of potentially harmful emissions. The static uses of energy—factories, schools, and homes—account for the bulk. There, the challenge is to...