Buried treasure

ReportageOver the entire 800,000-­year record, atmospheric carbon dioxide has never peaked over 300 ppm. For all of human history, it sat around 275 ppm until about 200 years ago, when we began to dig up and burn coal to fuel the Industrial Age. In 1950, it punched through the 300-­ppm historic ceiling. In mid-May, as the forests of the Northern Hemisphere dropped their leaves, the planet exhaled atmospheric carbon dioxide at a new daily record of 421 ppm.