Fossil Fuel Emissions and Fossil CO2 in the Atmosphere
Luciano Lepori S, Gian Carlo Bussolino, Andrea Spanedda and Enrico Matteoli C
IPCF-CNR, Pisa, Italy
The comparison of fossil fuel emissions (6.4 GtC/yr) with the growth rate of atmospheric CO2 (3.2 GtC/yr) suggests that about half of the anthropogenic CO2 has not remained in the atmosphere: it has dissolved in the ocean or has been taken up by the land. The isotope ratio C13/C12 of atmospheric CO2 has been measured over the last decades using mass spectrometry. From these data the fraction of fossil CO2 in atmospheric CO2 is straightforwardly calculated: 5.9 %(1981) and 8.5 %(2002). These results indicate that the amount of past fossil fuel and biogenic CO2 remaining in the atmosphere, though increasing with anthropogenic emissions, did not exceed in 2002 66 GtC, corresponding to a concentration of 31 ppm, that is 3 times less than the CO2 increase (88 ppm, 24 %) which occurred in the last century. This low concentration (31 ppm) of anthropogenic CO2 in the atmosphere is consistent with a lifetime of t(1/2) = 5.4 years, that is the most reliable value among other in the range 2-13 years, obtained with different measurements and methods. Contrary to the above findings on the concentration of fossil CO2 and its residence time in the atmosphere, in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change it is stated that almost 45 % of anthropogenic emissions, corresponding to 88 ppm or 24 % of the total CO2, have remained in the atmosphere with a mean lifetime of t(1/2) = 30.5 years. On these assumptions are based both the theory of Anthropogenic Global Warming and the climate models.
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