If in mid-summer you went onto the top of the Grocery Outlet supermarket in Stockton, California, and placed your hand on the strange, glossy black panels you found there, you’d be shocked to find they were as cold to the touch as a basement fuse box. Installed by a company called SkyCool Systems, they are the first of a new breed of cooling technologies that radiate heat out through the atmosphere, lowering nearby air temperatures by about 10°F. Radiative cooling is what happens when the electromagnetic waves we call heat leave an object. It’s the phenomenon that puts you at risk for heat stroke in the desert during the day, and hypothermia at night; the absorbed heat evacuates the landscape at sundown, and without any moisture to trap it, leaves through Earth’s atmosphere into outer space. A UCLA scientist reasoned that if a certain spectrum of warming rays is radiated out to the atmosphere during the day, it would cool whatever it left, potentially offering an alternative to traditional air conditioning. The idea was that if something could radiate heat even in broad daylight, it could save thousands in refrigeration costs.