Trend Technology 3: surfaces that cool below ambient temperature without electricity

Summary

Passive radiative cooling materials are the third emerging technology in the report, allowing surfaces to drop below the surrounding air temperature without electricity. The atmosphere traps most infrared radiation but lets a narrow band escape into deep space. These materials are engineered to release heat in exactly that band. They also scatter over 95% of incoming sunlight using microscopic air bubbles that act as tiny mirrors, so a treated surface loses more energy than it absorbs. The properties can be built into paint, roof tiles, window films and heavy fabrics, for new buildings or retrofits. The chapter frames this against urban heat islands in US cities that run 0.5–4.0°C warmer than surrounding rural areas and cooling systems that add to both heat and electricity demand.