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Before the Industrial Revolution, carbon dioxide levels were around 280 ppm, and they were closer to 200 during the Ice Age, which is when sea levels shrank and polar places went from green to icy. There are natural ups and downs of this greenhouse gas, which comes from volcanoes and decomposing plants and animals. But that's not what has driven current levels so high, Tans said. He said the amount should be even higher, but the world's oceans are absorbing quite a bit, keeping it out of the air. "What we see today is 100 percent due to human activity," said Tans, a NOAA senior scientist. 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. The world pumps on average 2.4 million pounds of carbon dioxide into the air every second for a total of 38.2 billion tons in 2011, according international calculations published in a scientific journal in December. China spews 10 billion tons of carbon dioxide into the air per year, leading all countries, and its emissions are growing about 10 percent annually. The U.S. at No. 2 is slowly cutting emissions and is down to 5.9 billion tons per year. The speed of the change is the big worry, said Pennsylvania State University climate scientist Michael Mann. If carbon dioxide levels go up 100 parts per million over thousands or millions of years, plants and animals can adapt. But that can't be done at the speed it is now happening. Last year, regional monitors briefly hit 400 ppm in the Arctic. But those monitoring stations aren't seen as a world mark like the one at Mauna Loa, Hawaii. Generally carbon levels peak in May then fall slightly, so the yearly average is usually a few parts per million lower than May levels.
___ Online: NOAA monitoring at Mauna Loa:
http://www.esrl.noaa.gov/gmd/
ccgg/trends/weekly.html
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