The CO2 level in our atmosphere was only about 280 ppm before human-induced changes (industrialization) began occurring about 150 years ago. In 1958, the CO2 level in the atmosphere (as measured at the Mauna Loa Observatory in Hawaii) was ~315 ppm. By 2008, it has reached the level of ~388 ppm. The most recent measurement in June 2009 shows CO2 atm conc at 389.42 ppm. The upper safety limit for atmospheric CO2 is 350 parts per million (ppm)
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