More than half of humanity is crowded together in cities. That’s about 4 billion people living on top of one another, working, commuting, polluting, and figuring out how to survive. And that proportion will only rise: By the end of the century, about 85% of the world’s population will be urban, according to the Organization for Economic Cooperation and Development. Cities are also incredibly vulnerable to climate change. High temperatures, sea level rise, and extreme weather are all felt more acutely in urban areas. Built on concrete, they absorb solar radiation but not water, making the effects of both heat waves and heavy rains more severe. If humans keep emitting planet-warming greenhouse gases at our current pace, Earth will warm by at least 3C and as much as 4C by the end of the century compared with preindustrial temperatures, causing much of the planet to become unlivable. Radical emissions […]