  We demonstrate an alternative correlation between the El Ni\~no Southern
Oscillation (ENSO) and global temperature variation to that shown by McLean et
al. [2009]. We show 50% of the variation in RATPAC-A tropospheric temperature
(and 54% of HadCRUT3) is explained by a novel cumulative Southern Oscillation
Index (cSOI) term in a simple linear regression. We review evidence from
physical and statistical research in support of the hypothesis that
accumulation of the effects of ENSO can produce natural multi-decadal warming
trends. Although it is not possible to reliably determine the relative
contribution of anthropogenic forcing and SOI accumulation from multiple
regression models due to collinearity, these analyses suggest that an
accumulation ratio cSOI/SOI of $4.8\pm1.5%$ and up to $9\pm2%$ is sufficient
for ENSO to play a large part in the global mean temperature trend since 1960.
