El Nino’s effect on CO2 causes confusion about CO2’s role for climate change

Are the rising atmospheric CO2-levels a result of oceans warming up? And does that mean that CO2 has little role in the global warming? Moreover, are the rising levels of CO2 at all related to human activity?

These are claims made in a fresh publication by Humlum et al. (2012). However, when seeing them in the context of their analysis, they seem to be on par with the misguided notion that the rain from clouds cannot come from the oceans because the clouds are intermittent and highly variable whereas the oceans are just there all the time. I think that the analysis presented in Humlum et al. (2012) is weak on four important accounts: the analysis, the physics, reviewing past literature, and logic.

This time Humlum et al. did not directly remove part of the data which didn’t fit their conclusions, however, they chose to use a short record of global mean CO2 from NOAA Earth System Research Laboratory (ESRL), starting from 1980, rather than the longer Keeling curve from Mauna Loa starting in 1958.

The two CO2 records, however, are almost identical over 1980-2012 (green curves in Fig. 1), and hence it would be more appropriate to use the longer record because CO2 is expected to play a role for long timescales. Hence, the Humlum et al. paper highlights the need for sorting out some classic misunderstandings, namely the mix-up between time scales. We have already discussed the absurdly misguided claims of a “halted global warming” based on a brief period after 1998 (here and here and ….)

Fig. 1: Reproduction of Figure 1 in Humlum et al (2012). Also shown in light green is the Keeling curve. Some of the strongest El Ninos are shown with grey hatching.

In order to assess the claims made in Humlum et al. (2012) (in italics above), I have repeated part of their analysis and got very similar results (all reproduced with the on-line R-script). Fig 1 here is a replication of figure 1 in Humlum et al. (2012) and I got almost identical results using the Keeling curve from Mauna Loa starting in 1958 rather than the global curve starting in 1980.

Fig. 2 corresponds to the lower panel in their figure 2, and shows the results of my attempt to reproduce the quantities making up the basis for their claims: their ‘DIFF12’ quantities (a type of differentiation operator) which really is meant to describe the rate of changes in the original curves.

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  1. O. Humlum, K. Stordahl, and J. Solheim, "The phase relation between atmospheric carbon dioxide and global temperature", Global and Planetary Change, vol. 100, pp. 51-69, 2013. http://dx.doi.org/10.1016/j.gloplacha.2012.08.008