CO2 levels reach 400 ppm

For the first time in hundreds of thousands of years, carbon dioxide levels in the Arctic atmosphere have exceeded the level of 400 parts per million, monitoring shows. Although the milestone for this heat-trapping gas had been anticipated, the global monitoring director of the National Oceanic and Atmospheric Administration's Earth System Research Lab says it's a reminder that "we're still in trouble." (Globally, the level is around 395 parts per million.) [The Christian Science Monitor]