Comment on “Influence of the Southern Oscillation on tropospheric temperature” by J. D. McLean, C. R. de Freitas, and R. M. Carter

McLean et al. (2009) (henceforth MFC09) claim that the El Niño–Southern Oscillation (ENSO), as represented by the Southern Oscillation Index (SOI), accounts for as much as 72% of the global tropospheric temperature anomaly and an even higher 81% of this anomaly in the tropics. They conclude that the SOI is a “dominant and consistent influence on mean global temperatures,” “and perhaps recent trends in global temperatures.” However, their analysis is inappropriate in a number of ways and overstates the influence of ENSO on the climate system. This comment first briefly reviews what is understood about the influence of ENSO on global temperatures and then shows that the analysis of MFC09 greatly overestimates the correlation between temperature anomalies and the SOI by inflating the power in the 2–6 year time window while filtering out variability on longer and shorter time scales. The suggestion in their conclusions that ENSO may be a major contributor to recent trends in global temperature is not supported by their analysis or any physical theory presented in their paper, especially as the analysis method itself eliminates the influence of trends on the purported correlations.