Anybody who has suffered through a painfully hot summer night can tell you the setting of the sun provides little relief from the heat. In fact, it can feel even hotter at night than it does during the day. Why? Air conditioning is actually making things hotter.
I don’t mean that in a “climate change” way, although you are probably burning a lot of fossil fuels. Nope, according to Popular Science, it’s a function of how ACs work in the first place.
An air conditioner’s job is essentially to transfer heat out of a building and into the outdoors. It also, in a fit of irony, gets very hot in order to actually do this. Have enough ACs going in a city and you’ve got enough heat to drive up temperatures.
During the day, believe it or not, this isn’t such an issue: the planetary boundary layer of our atmosphere (basically the part that touches the Earth’s surface) is thickest when the sun’s out. In turn, that lets the heat go upward. At night, though, it gets much thinner, so that heat has nowhere to go. Thus, summer nights are just that touch more uncomfortable.
The solution isn’t to turn off your AC and swelter in solidarity; most believe the heat should instead be routed through city wastewater systems. Water is much better at absorbing heat than air, and that should clear away much of the excess temperature. As for the record heat of summer, well, maybe stop driving so much?