CO2 levels increased 23% in 50 years
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)
Jansen, E., J. Overpeck, K.R. Briffa, J.-C. Duplessy, F. Joos, V. Masson-Delmotte, D. Olago, B. Otto-Bliesner, W.R. Peltier, S. Rahmstorf, R. Ramesh, D. Raynaud, D. Rind, O. Solomina, R. Villalba and D. Zhang, 2007: Palaeoclimate. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.