Urban surfaces generally are made from asphalt or concrete, which soak up a lot of solar energy during the day, holding it until night, and causing cities to be much hotter than the surrounding areas. For a long time, we've thought of cities and nature as two very different things: cities are monuments to human industry, and nature is a place where wild things grow. Illustration by The Geostrata But this separation is proving deadly as the world's cities grow and the "Urban H