When temperatures stay high and there’s little wind, fans are the next-most-sustainable choice because they bring relief while using relatively little electricity.

“Ceiling fans are very effective because they help a room feel colder while using a lot less energy than a central air-conditioner,” said Lauren Urbanek, who works on energy policy at the Natural Resources Defense Council.

Box fans are a good option, too. They typically consume less energy than a 100-watt light bulb.

Air-conditioners are the most popular way to cool a house — nearly 90 percent of homes in the United States have them. But, they are also the most damaging to the environment because they consume a lot of power and discharge hot air that can raise outside temperatures, a phenomenon known as the heat-island effect. That’s especially a problem in cities.

“They exacerbate climate change by increasing carbon dioxide emissions from power plants as well as some direct leakage of HFCs,” said David Abel, a postdoctoral researcher at the University of Wisconsin-Madison. He was referring to hydrofluorocarbons, chemical coolants that are also powerful greenhouse gases.

The human and environmental impacts of air-conditioners are mixed. A study in 2016 that focused on the immediate cooling benefits found that air-conditioners had cut premature deaths on hot days in the United States by 75 percent since 1960. On the other hand, Dr. Abel was the lead author of separate study, in 2018, that looked at the air pollution aspect. That research concluded that air-conditioners could cause hundreds of deaths in the Eastern United States by midcentury because of air pollution.