The Pace—and Problems—of Climate Change Accelerate

One of the mightiest El Niño patterns in memory brought unprecedented drought and flooding in 2016, the hottest year on record. The planet also passed a grim milestone: an atmospheric carbon dioxide concentration of 400 parts per million, including remote Antarctica, which hasn’t seen that much CO2 for 4 million years. Climatologists target 350 ppm as the uppermost threshold before we see dire consequences, like catastrophic sea level rise. Some locations previously had topped 400 ppm on a seasonal cycle, but scientists say this time it’s permanent — and global.