The Christian Scientist Monitor reports that 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 seen as a big 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.
"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.
The Arctic is the leading indicator in global warming, both in carbon dioxide in the air and effects, said Pieter Tans, a senior NOAA scientist.
"This is the first time the entire Arctic is that high," he said.
Tans called reaching the 400 number "depressing," and Butler said it was "a troubling milestone."