Scientists have long known that cities tend to be hotter than rural areas, partly because of waste heat from cars and air-conditioners and partly because concrete buildings and asphalt roads absorb heat. The resulting urban heat island effect can raise local temperatures by two to five degrees Fahrenheit on average.

According to the U.S. Environmental Protection Agency, most of the roughly 2 percent of the earth’s land surface covered in urban development suffers from some level of urban heating. New York City averages 1-3 degrees C warmer than the surrounding countryside, 

To facilitate the cooling of its rooftops, New York City has coated more than 5 million square feet of its roofs with a light, reflective coating via the CoolRoofs Initiative, which reduces cooling costs, cuts energy usage, and lowers greenhouse gas emissions. Los Angeles is going even further and replacing some of its dark asphalt roads with lighter materials. Test applications of a light gray coating known as CoolSeal had shown a 10-degree reduction in heat gain.

Currently, most scientists don’t think that reflective surfaces are a substitute for cutting greenhouse gas emissions. At best, they might partially offset some of the effects of global warming locally. But severe heat waves have already killed more than 128,000 people worldwide since 2000. And with global temperatures still on the rise, every little bit helps.

Learn more @ Yale Environment 360