Carbon dioxide has been steadily rising since the start of the Industrial Revolution, setting a new high year after year. There’s a notable new entry to the record books. The last station on Earth without a 400 parts per million (ppm) reading has reached it. In the remote reaches of Antarctica, the South Pole Observatory carbon dioxide observing station cleared 400 ppm on May 23, according to an announcement from the National Oceanic and Atmospheric Administration on Wednesday. That’s the first time it’s passed that level in 4 million years
— source climatecentral.org