Wang Yuetang’s sneakers sink into the mud of what was once his thriving corn and peanut farm as he surveys the damage done by an unstable climate. Three months after torrential rains flooded much of central China’s Henan province, stretches of the country’s flat agricultural heartland are still submerged in several inches of water. It’s one of the many calamities around the world that are giving urgency to the U.N. climate summit underway in Glasgow, Scotland.