To clear the way for planting wheat in November, a farmer in Punjab, India, sets aflame the leftover straw, or stubble, of a harvested rice paddy crop in October. The burning residue fills the air with carbon monoxide, ozone, and fine particulate matter (PM2.5) that will make it harder to breathe for days afterward and for miles around. It’s a scene that’s replicated on about 2 million farms in the Punjab and Haryana states of northwest India every autumn (and every spring after the wheat harvest), raising health risks —…