As my plane was landing in Beijing in mid-December, I realized I had forgotten to bring my N95 respirator mask, and instantly regretted it. But that day turned out to be clear, if chilly. A Chinese public-health expert later told me that it was no exception: There were far fewer days of smog in 2017 than just a couple of years ago.

Terrific, I thought — until I came to understand the unintended costs of the dramatic improvement in the capital’s air quality.

To reduce the levels of hazardous particles known as PM2.5, the Chinese authorities started a major campaign in 2013 to convert coal-generated heating to gas or electric heating. But in the northern province of Hebei, for example, as overzealous local officials put the changes in place, exceeding government targets, demand for the new fuels suddenly surged — creating shortages that left millions without proper heating in freezing temperatures.

This is but one example of the ways in which China’s air-pollution policy may have been a bit too successful. The Chinese government deserves credit for its resolve in tackling the problem. Yet the rapid concentration of power under President Xi Jinping — helped along by the steady purging of officials suspected of corruption — has put apparatchiks and bureaucrats on edge. And their rush to please has unexpectedly distorted how environmental policy is made and implemented, sometimes with unwanted consequences.