Greenhouse gas levels pass symbolic 400ppm CO2 milestone | AP

The Arctic Ocean with leads and cracks in the ice cover of north of Alaska. Photograph: Courtesy Eric Kort/Jet Propulsion Laboratory/NASA

Monitoring stations in the Arctic detect record levels of carbon dioxide, higher than ever above 'safe' 350ppm mark

June 1, 2012 (AP) -- The world's air has reached what scientists call a troubling new milestone for carbon dioxide, the main global warming pollutant.

Monitoring stations across the Arctic this spring are measuring more than 400 parts per million of the heat-trapping gas in the atmosphere. The number isn't quite a surprise, because it's been rising at an accelerating pace.

Years ago, it passed the 350ppm mark that many scientists say is the highest safe level for carbon dioxide. It now stands globally at 395.

So far, only the Arctic has reached that 400 level, but the rest of the world will follow soon.

READ MORE: The Guardian