Comment on “The phase relation between atmospheric carbon dioxide and global temperature” by Humlum, Stordahl and Solheim

Humlum et al., 2013 conclude that the change in atmospheric CO2 from January 1980 is natural, rather than human induced. However, their use of differentiated time series removes long term trends such that the presented results cannot support this conclusion. Using the same data sources it is shown that this conclusion violates conservation of mass. Furthermore it is determined that human emissions explain the entire observed long term trend with a residual that is indistinguishable from zero, and that the natural temperature-dependent effect identified by Humlum et al. is an important contributor to the variability, but does not explain any of the observed long term trend of + 1.62 ppm yr− 1.