During heat waves in Phoenix, while some people fry eggs on sidewalks, Matt Heath, a heating, ventilation, and air-conditioning (HVAC) service manager at AC by J, is on the front line, helping maintain air conditioners in people’s homes. Heath has great job security: Half of Phoenix residents are at risk of an emergency-room visit or worse if their electricity fails during a future heat wave, according to a recent study. Air-conditioning is what keeps people there comfortable—and alive—a growing fraction of the year. The extreme heat already kills hundreds of Phoenix-area residents every year, a number that went up by 25 percent from 2021 to 2022.

Phoenix is a harbinger of life in the many hot parts of the world that are getting richer, where people are demanding ever more air conditioners. This in turn exacerbates the extremes of climate change due to increased demand for fossil-fuel-intensive sources of electricity, as well as leakage of refrigerants, themselves noteworthy greenhouse gases. “Most of the growth of air-conditioning will be in other countries,” says mechanical engineer Vince Romanin, cofounder and CEO of the San Francisco–based Gradient Comfort, “and restricting access is not fair.” Instead, he and others are trying to invent new climate-control technology that doesn’t further increase the dangers facing the planet’s climate.