WASHINGTON (AP) â" The worldâs 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 isnât quite a surprise, because itâs 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.
âThe fact that itâs 400 is significant,â said Jim Butler, global monitoring director at the National Oceanic and Atmospheric Administrationâs Earth System Research Lab in Boulder, Colo. âItâs just a reminder to everybody that we havenât fixed this and weâre still in trouble.â
Carbon dioxide is the chief greenhouse gas and most of it lasts about 100 years in the air, but some of it stays in the atmosphere for thousands of years. Some carbon dioxide is natural, mainly from decomposing dead plants and animals. Before the Industrial Age, levels were around 275 parts per million.
For more than 60 years, readings have been in the 300s, except in urban areas, where levels are skewed. The burning of fossil fuels, such as coal for electricity and oil for gasoline, has caused the overwhelming bulk of the man-made increase in carbon in the air, scientists say.
Itâs been at least 800,000 years â" probably more â" since Earth saw carbon dioxide levels in the 400s, Butler and other climate scientists said.
Until now.
Readings are coming in at 400 and higher all over the Arctic. Theyâve been recorded in Alaska, Greenland, Norway, Iceland and even Mongolia. But levels change with the seasons and will drop a bit in the summer, when plants suck up carbon dioxide, NOAA scientists said.
So the yearly average for those northern stations likely will be lower and so will the global number.
Globally, the average carbon dioxide level is about 395 parts per million but will pass the 400 mark within a few years, scientists said.
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.
âThis is the first time the entire Arctic is that high,â he said.
Tans called reaching the 400 number âdepressing,â and Butler said it was âa troubling milestone.â
âItâs an important threshold,â said Carnegie Institution ecologist Chris Field, a scientist who helps lead the Nobel Prize-winning Intergovernmental Panel on Climate Change. âIt is an indication that weâre in a different world.â
Ronald Prinn, an atmospheric sciences professor at the Massachusetts Institute of Technology, said 400 is more a psychological milestone than a scientific one. We think in hundreds, and âweâre poking our heads above 400,â he said.
Tans said the readings show how much the Earthâs atmosphere and its climate are being affected by humans. Global carbon dioxide emissions from fossil fuels hit a record high of 34.8 billion tons in 2011, up 3.2 percent, the International Energy Agency announced last week.
The agency said itâs becoming unlikely that the world can achieve the European goal of limiting global warming to just 2 degrees based on increasing pollution and greenhouse gas levels.
âThe news today, that some stations have measured concentrations above 400 ppm in the atmosphere, is further evidence that the worldâs political leaders â" with a few honorable exceptions â" are failing catastrophically to address the climate crisis,â former Vice President Al Gore, the highest-profile campaigner against global warming, said in an e-mail. âHistory will not understand or forgive them.â
But political dynamics in the United States mean thereâs no possibility of significant restrictions on man-made greenhouse gases no matter what the levels are in the air, said Jerry Taylor, a senior fellow of the libertarian Cato Institute.
âThese milestones are always worth noting,â said economist Myron Ebell at the conservative Competitive Enterprise Institute. âAs carbon dioxide levels have continued to increase, global temperatures flattened out, contrary to the modelsâ used by climate scientists and the United Nations.
He contends temperatures have not risen since 1998, which was unusually hot.
Temperature records contradict that claim. Both 2005 and 2010 were warmer than 1998, and the entire decade of 2000 to 2009 was the warmest on record, according to NOAA.
On the Web
NOAAâs global monitoring lab: http://esrl.noaa.gov/gmd/
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