It’s that time of year again. The time when, in the Indian capital of New Delhi, we shutter doors and windows to the grey-orange gloom and switch on our air purifiers, resigned to the deathly annual smog hanging over us, just like it has for years.

Cars, coal-fired power plants, and cookstoves keep New Delhi reliably near the top of the list of the world’s most polluted cities. But the haze is especially bad each autumn, when a cloud of smoke blows in from the northwestern states of Punjab and Haryana. Beginning in late September, rice farmers there burn their fields to clear them for the next crop, wheat….