claim: the temperature increase in the second half of the 20th century could have taken place in steps driven by major ENSO events ( Jens Raunsø Jensen )
evidence: IPCC AR4 WG1 Ch9 2007, p. 690 : Recent estimates indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the second half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings.