This one is a little more controversial.
Some cities have experimented with painting rooftops white to reflect sunlight and keep buildings cool, but Los Angeles went a step further and is painting entire roads white. Dark things like asphalt absorbs sunlight and emits that energy back into the air as heat. Painting the asphalt white would theoretically nip that process in the bud, and lead to cooler air temperatures.
The idea has some merit. Researchers Ariane Middel and V. Kelly Turner found that technique did cool the streets themselves by around 10 degrees. But there was a major knock-on effect. The same researchers also said it was likely the extra heat reflecting off the roads was being absorbed by ... people.
That means if you're a few blocks away, the white streets may help you feel cooler, but if you're on the street, you could actually feel hotter.
Nonetheless, LA is continuing with 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 that another type of paint could yield different results.
Painting rooftops has had greater success.
Results vary depending on the level of heat and materials a roof is made of, but in places like Ahmedabad in India, which gets seriously hot, cool roofs have shaved 3-8 degrees Fahrenheit of the heat in homes. According to Berkeley Lab's Heat Island Group, a black roof could be as much at 54 degrees (around 30 Celsius) hotter than a white roof.
Another option is the green roof. Cities all around the world have created "gardens in the sky" to cool down buildings.