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Atmospheric CO2 and Global Temperature: Which Leads Which When Change Occurs?
Volume 16, Number 28: 10 July 2013

In a study recently published in Global and Planetary Change, Humlum et al. (2013) introduce their analysis of the phase relation between atmospheric carbon dioxide concentration and mean global air temperature by noting that over the last 420 thousand years, "variations in atmospheric CO2 broadly followed temperature according to ice cores, with a typical delay of several centuries to more than a millennium," citing Lorius et al. (1990), Mudelsee (2001) and Caillon et al. (2003). And they explain this relationship by stating it "is thought to be caused by the slow vertical mixing that occurs in the oceans, in association with the decrease in the solubility of CO2 in ocean water, as its temperature slowly increases at the end of glacial periods (Martin et al., 2005), leading to subsequent net out-gassing of CO2 from the oceans (Togweiler, 1999)."

So if this be true for glacial cycles, should it not also be true for seasonal cycles?

Feeling that such might indeed be the case, the three Norwegian researchers intensively studied the phase relations (leads/lags) between atmospheric CO2 concentration data and several global temperature data series - including HadCRUT, GISS and NCDC surface air data, as well as UAH lower troposphere data and HadSST2 sea surface data - for the period January 1980 to December 2011. And what did they find?

Humlum et al. report that annual cycles were present in all of the several data sets they studied and that there was "a high degree of co-variation between all data series ... but with changes in CO2 always lagging changes in temperature." More specifically, they state that "the maximum positive correlation between CO2 and temperature is found for CO2 lagging 11-12 months in relation to global sea surface temperature, 9.5-10 months [in relation] to global surface air temperature, and about 9 months [in relation] to global lower troposphere temperature," so that "the overall global temperature change sequence of events appears to be from the ocean surface to the land surface to the lower troposphere."

In discussing the subject further, Humlum et al. note it has sometimes been suggested that in certain periods of the past, increases in atmospheric CO2 concentration may have preceded the global temperature increases initiated by Milankovitch cycles. But they go on to say it has been shown that that interpretation of the proxy data "is ambiguous with regard to this," citing Alley and Clarck (1999), Shackleton (2000), Toggweiler and Lea (2010) and Shakun et al. (2012).

More recently still, Parrenin et al. (2013) conducted a new-and-improved analysis of the temporal phasing between atmospheric CO2 concentration and Antarctic temperature data obtained from ice cores at four different times when their trends changed abruptly, finding "no significant asynchrony between them," which is precisely what would be expected for a phenomenon occurring over a time frame of months, when error bars of potentially hundreds of years have previously been characteristic of the data involved.

And so it would appear that the climate-alarmist case for changes in earth's atmospheric CO2 concentration causing changes in global air temperature still remains as weak as ever, as just the opposite appears to be the case in situations where there is absolutely no question about the timing of the two phenomena in terms of their temporal relationship to each other.

Sherwood, Keith and Craig Idso

Alley, R.B. and Clarck, P.U. 1999. The deglaciation of the northern hemisphere: a global perspective. Annual Reviews of Earth and Planetary Sciences 27: 149-182.

Caillon, N., Severinghaus, J.P., Jouzel, J., Barnola, J.-M., Kang, J. and Lipenkov, V.Y. 2003. Timing of atmospheric CO2 and Antarctic temperature changes across Termination III. Science 299: 1728-1731.

Humlum, O., Stordahl, K. and Solheim, J.-E. 2013. The phase relation between atmospheric carbon dioxide and global temperature. Global and Planetary Change 100: 51-69.

Lorius, C., Raynaud, D., Jouzel, J., Hansen, J. and Le Treut, H. 1990. The ice-core record - climate sensitivity and future greenhouse warming. Nature 347: 139-145.

Martin, P., Archer, D. and Lea, D.W. 2005. Role of deep sea temperature in the carbon cycle during the last glacial. Paleoceanography 20: 1-10.

Mudelsee, M. 2001. The phase relations among atmospheric CO2 content, temperature and global ice volume over the past 420 ka. Quaternary Science Reviews 20: 583-589.

Parrenin, F., Masson-Delmotte, V., Kohler, P., Raynaud, D., Paillard, D., Schwander, J., Barbante, C., Landais, A., Wegner, A. and Jouzel, J. 2013. Synchronous change of atmospheric CO2 and Antarctic temperature during the last deglacial warming. Science 339: 1060-1063.

Shackleton, N.J. 2000. The 100,000 year ice-age cycle identified and found to lag temperature, carbon dioxide and orbital eccentricity. Science 289: 1897-1902.

Shakun, J.D., Clark, P.U., He, F., Marcott, S.A., Mix, A.C., Liu, Z., Otto-Bliesner, B., Schmittner, A. and Bard, E. 2012. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature 484: 49-55.

Toggweiler, J.R. 1999. Variation of atmospheric CO2 by ventilation of the ocean's deepest water. Paleoceanography 14: 571-588.

Toggweiler, J. R. and Lea, D.W. 2010. Temperature differences between the hemispheres and ice age climate variability. Palaeoceanography 25: 10.1029/2009PA001758.