Like all urban parks, Central Park cools New York City through evaporation. That is, its plant life and ponds give off moisture, which takes heat energy with it. It's as if the park sweats.

Until recently, though, we didn’t know whether green spaces cool the planet as a whole. It was thought that their local cooling effect could be part of a zero-sum game, leading to equivalent warming elsewhere when the water they give off condenses. They might even help increase the planet’s overall temperature, promoting the formation of the kind of clouds that hold in heat.

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But while evaporation from parks does cause clouds, they’re the other kind — the kind that helps cool the Earth. The clouds that green spaces give rise to are low-lying and white, and they reflect sunlight back into space, acting like a sun shade on a hot day. And, according to Ken Caldeira, the principle investigator on this study, the clouds reflect 3/4 as much heat as they remove from the city. In other words, parks help the planet almost as much as they help the city.

Parks: they are awesome. All the more reason to turn more of our cities into green space.

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