How, in the days before refrigeration, before electric fans, before air-conditioning — did people make it through summer in New York?

The short answer is: A lot of them didn’t. Nearly 1,500 New Yorkers died during a heat wave in 1896, and nearly 700 fell victim to another one in 1901.

There were roughly 600 heat deaths in the city each year between 2000 and 2006, and experts predict climate change will cause that number to soar in the coming decades — but the conveniences of modern life mean they’re not as dangerous as they used to be.

Air conditioners became fixtures in public spaces in the 1930s and spread to private homes throughout the middle part of the 20th century. The risk of heat death has steadily dropped in conjunction with AC’s rise.

But the lack of AC also gave our recent ancestors an advantage: it made it easier for them to tolerate the heat.

Our reliance on air-conditioning is actually making the world hotter; residential cooling uses such a massive amount of energy, that AC use has climate researchers worried.

But on a psychological level, it’s also making the air outside feel hotter: The more air-conditioning you have, the more you need it to feel good.

Scientists call this the “adaptive comfort model”: the idea that our ideal temperature depends in part on whatever temperature we’ve recently been exposed to.