Grist: Over the last couple weeks, scientists and environmentalists have been keeping a particularly close eye on the Hawaii-based monitoring station that tracks how much carbon dioxide is in the atmosphere, as the count tiptoed closer to a record-smashing 400 parts per million. Thursday, we finally got there: The daily mean concentration was higher than at any time in human history, NOAA reported.
Don`t worry: The earth is not about to go up in a ball of flame. The 400 ppm mark is only a milestone,...