Hofmann et al. (2009) figured that the growth of anthropogenic CO2 levels in the atmosphere might track the growth of the human population, so they assumed CO2 levels of zero for 1958 when measurements of CO2 at Mauna Loa Observatory commenced and got a nearly perfect fit between the ensuing exponential growth of population and that of CO2. They then extended CO2 levels back to before 1900 using data from Antarctic Ice Cores, which followed the same trend, though the fit wasn’t quite as good before 1950, perhaps because fossil fuel use had not yet begun to grow exponentially along with population. This result causes them to conclude that if the population growth levels off as it is generally expected to around 2050, the CO2 growth rates might do so as well, resulting in much lower atmospheric CO2 levels in 2050 than expected in the IPCC scenarios, maybe leveling out at around 430 ppm instead of the 475–525 ppm anticipated by the IPCC, and never getting to the values the IPCC projects for 2100 or 550–750 ppm. —Emil Morhardt
Hofmann, D., Butler, J., Tans, P., 2009. A new look at atmospheric carbon dioxide. Atmospheric Environment 43, 2084-2086.
David Hofmann, James Butler, and Pieter Tans at the NOAA Earth System Research Laboratory Global Monitoring Division suggest furthermore, that by tracking any decrease of CO2 from this steady exponential growth rate might be an interesting signal of any progress “…in the inevitable need to limit atmospheric CO2.” They also note that a if CO2 growth ceased to track population growth in the same way it might signal a change in business as usual. The don’t go any further in this speculation, but might be thinking about a potential per capita increase of fossil fuel use by newly industrialized populations in India and China.