Reuters: The amount of climate-warming carbon dioxide in the atmosphere topped 400 parts per million at a key observing station in Hawaii for the first time since measurement began in 1958, the National Oceanic and Atmospheric Administration said on Friday.
To many scientists, crossing the 400 ppm threshold, which means that there are 400 molecules of carbon dioxide for every million molecules in the air, is a bit like the Dow Jones Industrial Average rising above 15,000 points.
"It's important mainly...