Painting your buildings’ roof white just seemed like such a no-brainer way to reduce global warming with its reflecting and not-heat absorbing properties. New York City bought into this amazingly simple idea and its city run NYC Cool Roofs painted over 2 million square feet of rooftops white while the non-profit White Roof Project painted its share of roofs. But then the hammer dropped and a study on the heat island effect concluded that white roofs may promote cooling for each individually painted building but globally, they are causing more warming. Here’s how the white roofs don’t work:
- Rooftops painted white.
- Sunlight is reflected and surface temperatures fall.
- As temps fall, less water is evaporated to form clouds.
- Fewer clouds means higher surface temperatures.
So the cooling and energy savings would be local but any gains from the white roof would be negated by the overall increase in temperatures due to the white roofs. I have a weird feeling there’s going to be another study soon that negates the negate and we’ll be back to painting our roofs white again. Or maybe grey? [Discover Magazine]
Read the full study (PDF): Effects of Urban Surfaces and White Roofs on Global and Regional Climate.