Background
The author writes that "global surface temperature records (e.g. HadCRUT4) since 1850 are characterized by climatic oscillations synchronous with specific solar, planetary and lunar harmonics superimposed on a background warming modulation," which he says "is related to a long millennial solar oscillation and to changes in the chemical composition of the atmosphere (e.g. aerosol and greenhouse gases)." However, he notes that "current general circulation climate models, e.g. the CMIP5 GCMs, to be used in the AR5 IPCC Report in 2013, fail to reconstruct the observed climatic oscillations."

What was done
As an alternative to the IPCC's approach to the subject, Scafetta describes an empirical model that uses: "a specific set of decadal, multi-decadal, secular and millennial astronomic harmonics to simulate the observed climatic oscillations," plus "a 0.45 attenuation of the GCM ensemble mean simulation to model the anthropogenic and volcano forcing effects." And what are the results of this approach?

What was learned
Scafetta reports that his proposed empirical model "outperforms the GCMs by better hind-casting the observed 1850-2012 climatic patterns." More specifically, he notes that "about 50-60% of the warming observed since 1850 and since 1970 was induced by natural oscillations likely resulting from harmonic astronomical forcings that are not yet included in the GCMs."

What it means
The way Scafetta sees things, "the results of this analysis indicate that the GCMs do not yet include important physical mechanisms associated with natural oscillations of the climate system." And, therefore, he suggests that interpretations and predictions of climate change based on current GCMs, including the CMIP5 GCMs to be used in the IPCC AR5, are "questionable."