Air conditioners have become ubiquitous in American single family homes over the past 40 years.

In the 43 years since the U.S. census bureau has started tracking the use of home air conditioning, the amenity has seen an enormous jump in popularity – particularly in the Northeast. Fewer than 10% of new single family Northeastern homes had air conditioning in 1973, but by 2015 that share had jumped to 75%.

Air conditioning is better and cheaper now than ever before, and it’s become an expected feature for the American home buyer, according to Zillow’s Svenja Gudell. But the growing need for cool air has raised concerns about climate change.

According to the Department of Energy, air conditioners use 5% of all electricity produced in the U.S., and produce 100 million tons of carbon dioxide per year. These greenhouse gases will mean a greater demand for air conditioning in the future – a “self-reinforcing habit”, according to Bloomberg’s Patrick Clark.

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