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Climate change: Arctic passes 400 parts per million milestone

Arctic monitoring stations show carbon dioxide levels are now above 400 parts per million. Carbon dioxide is the chief climate-change gas and stays in the atmosphere for 100 years. Before the Industrial Age, carbon dioxide levels were 275 ppm.

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NOAA's Chris Carparelli adjusts a glass flask that line the walls of an air sample processing room at NOAA's Earth System Research Laboratory in Boulder, Colo.. Researchers at the lab measure the levels of carbon dioxide and other greenhouse gases in air sent in weekly from sites around the world.

(AP Photo/NOAA, Will von Dauster)

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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 350 ppm 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.

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"The fact that it's 400 is significant," said Jim Butler, global monitoring director at the National Oceanic and Atmospheric Administration's Earth System Research Lab in Boulder, Colo. "It's just a reminder to everybody that we haven't fixed this and we're still in trouble."

Carbon dioxide is the chief greenhouse gas and stays in the atmosphere for 100 years. Some carbon dioxide is natural, mainly from decomposing dead plants and animals. Before the Industrial Age, levels were around 275 parts per million.

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