DOES USING THE AC MAKE IT HOTTER OUTSIDE?
SHORT ANSWER: YES, BUT ONLY AT NIGHT
In 1975 Texas Monthly published an article that tried to explain why Houston had become “The Hottest Place in the Whole USA.” It read: “One heat-producing machine is the very device designed to eliminate heat–the good old air conditioner.” An AC unit transfers warmth from inside buildings to the air outside, and it guzzles electricity, which generates waste-heat that must be vented too.
Over the years, climatologists have tried to measure this effect. In 2007 Yukitaka Ohashi of the Okayama University of Science in Japan found that ACs can raise temperatures in downtown Tokyo by as much as 2°F. A 2013 study modeling temperatures on the streets of Paris found that the effect was most acute at night–surprising, given that we use the most air conditioning when the sun is up.
That’s because the planetary-boundary layer–the part of the atmosphere in contact with Earth’s surface–is thickest during the day, so the extra heat we generate gets dispersed upward. At night, however, the layer shrinks from 1 or 2 miles thick to as little as 330 feet, so the heat remains closer to the surface.