Scientific American: Human activity results in the emission of some 30 billion metric tons of climate change–causing carbon dioxide (CO2) per year. About half of the greenhouse gas is absorbed by the world’s oceans and plants, among other natural processes, but the rest lingers in the atmosphere for a century or more, driving up annual CO2 concentrations by around two parts per million (ppm). Those atmospheric concentrations have climbed from roughly 280 ppm in the 18th century before the widespread …