And because air-conditioners work in part by venting hot air outside, they also make the surrounding neighborhood warmer. By some estimates air-conditioning can raise overnight temperatures by about two degrees Fahrenheit (one degree Celsius) in some cities, the report said. Practically speaking, if enough of your neighbors buy an air-conditioner it may increase the temperature in your home enough to drive you to do the same.

And then, of course, there’s climate change. India is already one degree Fahrenheit warmer on average than it was a century ago. This has led to more “cooling degree days,” or days when average temperatures are warm enough to necessitate air-conditioning.

“If you look at cooling degree days for Chennai or Mumbai, these are places that have twice as many cooling degree days as the hottest city in the U.S., Miami,” said Lucas Davis, director of the Energy Institute at the Haas School of Business of the University of California, Berkeley. “It’s unbelievably hot — there’s nothing in the U.S. that compares in terms of heat to these cities in India.”

And when it gets hot, forgoing air-conditioning can be deadly. The heat wave that plagued Chicago in 1995 killed more than 700 people, while the 2003 European heat wave and 2010 Russian heat wave killed tens of thousands each. Researchers have found that climate change made the European heat wave deadlier and the Russian heat wave more likely.

The introduction of home air-conditioning in the United States has cut premature deaths on hot days by 75 percent since 1960, another study has shown. That is why both Dr. Davis and Dr. Birol say the solution lies not in convincing countries to forgo air-conditioners, but in making air-conditioning more energy efficient. That could cut by half the additional energy demand for cooling in the coming years.

Many air-conditioners on sale in India today use twice as much electricity to provide the same amount of cooling as more efficient units, Dr. Davis said.

On the other end of the spectrum, air-conditioners sold in Japan and the European Union tend to be 25 percent more efficient than units sold in the United States and China.