Comment on “The phase relation between atmospheric carbon dioxide and global temperature”

The paper by Humlum et al. (2013) suggests that much of the increase in atmospheric CO2 concentration since 1980 results from changes in ocean temperatures, rather than from the burning of fossil fuels. We show that these conclusions stem from methodological errors and from not recognizing the impact of the El Niño–Southern Oscillation on inter-annual variations in atmospheric CO2.