The extreme El Niño of 2015–2016 occurred at a time of record global warming and unprecedented strength of the Hadley circulation, with major implications for the interhemispheric carbon dioxide concentration difference. The roles of the mean transport by the Hadley circulation and by atmospheric waves and turbulent eddies in the seasonal and inter-annual carbon dioxide hemispheric differences are established during the period 1992–2016, including during the significant 2009–2010 step.