Evolution of the Latitudinal Gradient of Atmospheric CO2 and Its Relationship to Anthropogenic and Natural Sources and Sinks
Stephen
Charles
Piper, UCSD/Scripps Institution of Oceanography, scpiper@popmail.ucsd.edu
(Presenting)
Ralph
Keeling, UCSD/Scripps Institution of Oceanography, rkeeling@ucsd.edu
The annual mean atmospheric CO2 concentration currently is higher in the northern hemisphere than in the southern hemisphere because 90% of fossil fuel is burned in the northern hemisphere, and the interhemispheric mixing time of fossil fuel CO2 in the atmosphere is on the order of 1 year. This latitudinal gradient of atmospheric CO2 varies somewhat unpredictably from year to year on the El Nino time scale, but over the longer term, since the late 1950s, when direct CO2 measurements began to be measured, the north-south gradient has varied in close proportion to the magnitude of global annual fossil fuel emissions.
By regressing the difference of CO2 at each station in the Scripps network, supplemented by snapshot surveys in 1962, 1968 and 1980, from the CO2 at the South Pole against fossil fuel emissions, we can identify the latitudinal gradient attributable to anthropogenic emissions, and sources and sinks that vary in proportion to fossil fuel emissions. By extrapolating the regressions to zero fossil fuel emissions, we obtain a latitudinal gradient that is lower in the northern hemisphere than the southern by about 1 ppm, and a well-pronounced equatorial peak in CO2. The north-south gradient produced by a similar treatment of 13C/12C observations agrees somewhat well with a model prediction of temperature-dependent equilibrium fractionation suggesting that the equatorial peak in CO2 is produced by an oceanic source, or a very strong source of CO2 from C4 plants, and that any underlying terrestrial biospheric CO2 flux not correlated with fossil fuel emissions is small.