Cooling Cities with White Roofs

It is common knowledge that people wearing white clothes tend to feel more cool in the desert than wearing black clothes. This is because black is a non-color that attracts more photons, and lets fewer get reflected back from whence they came. The same line of reasoning holds true for global warming and incoming sunlight, experts say. If a city looks black from above, then it's more likely to hold in excessive heat, both causing the temperatures at street level to grow, and promoting global warming and climate change at the same time. The best defense against this is simply painting all roofs white.

Recent studies have indicated that such a practice, spread around the globe, could have a significant impact on the level of warming our planet currently experiences. This was also the conclusion of the first-ever computer simulation of how white cities would influence heat accumulation and dispersion. The investigation was led by scientists at the National Center for Atmospheric Research (NCAR), in Boulder, Colorado, and was funded by the US National Science Foundation (NSF). Full results of the work are to be published in an upcoming issue of the American Geophysical Union's esteemed scientific journal Geophysical Research Letters.

“Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat. It remains to be seen if it's actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation,” the leader of the new study, NCAR scientist Keith Oleson, explains. “Climate change mitigation research is an extremely important topic. Whether on white roofs or other climate change mitigation subjects, it's important to consider the many feedbacks and complicating considerations that make research in this area very complex,” the NSF Program Director for NCAR, Steve Nelson, adds.

When compared with adjacent rural areas, the world's cities are genuine “heat islands.” They feature black tarmac roads, dark rooftops, and generally more surfaces that can trap sunlight, and cause warming. This is one of the main reasons why most cities are two to five degrees Fahrenheit (about one to three degrees Celsius) warmer than their surrounding areas. But the issue of painting roofs white is double-faced, the researchers say. White roofs in cities at high latitudes would mean more energy expenses for cities, and this would offset the gains caused by painting the roofs in the first place.

“It's not as simple as just painting roofs white and cooling off a city,” Oleson says. “It's critical to understand how climate change will affect vulnerable urban areas, which are home to most of the world's population,” study coauthor and NCAR scientist Gordon Bonan shares.