On sweltering summer days, dark asphalt soaks up the sun and acts like a secondary heater under our feet.
That’s why Los Angeles is pushing a novel plan to cool down the city: Turn the streets a different color.
The idea of “cool pavements” has been kicking around City Hall for years, but only recently has it resulted in action on the ground.
Matt Peterson, Los Angeles’s chief sustainability officer, said test applications of a light gray coating known as CoolSeal had shown a 10-degree reduction in heat gain.
“It was pretty significant, particularly when you’re talking about asphalt that gets up to 130, 140 degrees,” he said.
Climate models suggest that parts of Los Angeles could see roughly three times as many extreme heat days — defined as more than 95 degrees — by midcentury.
Lighter-colored pavements won’t counteract the trend by themselves, but experts say a mix of measures that includes reflective roofs and more tree canopy could make a dent.
Mayor Eric Garcetti has predicted that the city could reduce its so-called urban heat island effect — caused by dark surfaces, lack of vegetation and discharges from traffic and industry — by three degrees over the next 20 years.
Proponents of cool pavements say that aside from providing greater physical comfort, even a small drop in temperatures would reduce energy use and mitigate the health risks associated with extreme heat.
Still, some environmental experts warn that more research is needed. What if, for example, the greenhouse gas emissions involved in the manufacture and deployment of cool pavements only worsen matters?
It is certain that lighter surfaces lower temperatures, said George Ban-Weiss, an assistant professor of civil and environmental engineering at U.S.C.
But he added, “The science is less settled on whether the benefits outweigh the penalties.”
For now, Los Angeles is testing how CoolSeal, made by Guard Top, based in Dana Point, performs over time on a handful of city streets.
In May, a work crew slathered it onto a street in the Canoga Park neighborhood. Weeks later, residents told The Los Angeles Daily News that they could already feel the difference.