Atmospheric CO2 and Global Temperature: Which Leads Which When Change Occurs?
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.
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.
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