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This one is a bit more controversial.

Some cities experimented with painting roofs white to reflect sunlight and keep buildings cool, but Los Angeles went further and painted entire roads white. Dark things like asphalt absorb sunlight and radiate that energy into the air as heat. Painting the asphalt white would theoretically nip this process in the bud and lead to cooler air temperatures.

The idea has merit. Researchers Ariane Middel and V. Kelly Turner discovered that the technique cool the streets themselves by about 10 degrees. But there has been a major ripple effect. The same researchers also said it was likely that the extra heat reflected from the roads was absorbed by… people.

This means that if you’re a few blocks away, the white streets might help you feel cooler, but if you’re on the streets, you might actually feel warmer.

Nonetheless, LA is continuing this program to see what works and what doesn’t. It currently uses a grayish-white substance called CoolSeal, once used to help hide grounded aircraft from satellites, but it’s possible a different type of paint will give different results.

Painting the roofs was more successful.

Results vary depending on the level of heat and the materials the roof is made of, but in places like Ahmedabad, India, where it is very hot, cool roofs reduced the heat from homes by 3 to 8 degrees Fahrenheit. According to Berkeley Lab’s Heat Island Group, a black roof could be as much as 54 degrees (about 30 degrees Celsius) hotter than a white roof.

Another option is the green roof. Cities around the world have created “gardens in the sky” to cool buildings.