Background
The author - who is associated with the Active Cavity Radiometer Solar Irradiance Monitor Laboratory at Duke University in Durham, North Carolina (USA) - recently developed what he calls an "astronomical-based empirical harmonic climate model," which assumes that the earth's climate system is resonating with, or is synchronized to, a set of natural frequencies of the solar system (Scafetta, 2010, 2011). And he indicates that the major hypothesized mechanism upon which the model is based is that "the planets, in particular Jupiter and Saturn, induce solar or heliospheric oscillations that induce equivalent oscillations in the electromagnetic properties of the [earth's] upper atmosphere," which phenomenon in turn induces similar cycles in cloud cover and terrestrial albedo, "forcing the climate to oscillate in the same way."

What was done
Very simply, Scafetta tested the performance of his newest model "against all general circulation climate models (GCMs) adopted by the IPCC (2007) to interpret climate change during the last century," which exercise yielded a number of intriguing results.

What was learned
First of all, the solar scientist found that "the GCMs fail to reproduce the major decadal and multi-decadal oscillations found in the global surface temperature record from 1850 to 2011," but he notes, secondly, that his harmonic model (which uses cycles having periods of 9.1, 10-10.5, 20-21 and 60-62 years) "is found to well reconstruct the observed climate oscillations from 1850 to 2011". And he indicates, thirdly, that his own model "is able to forecast the climate oscillations from 1950 to 2011 using the data covering the period 1850-1950, and vice versa."

What it means
Scafetta concludes that the results he obtained "reinforce previous claims that the relevant physical mechanisms that explain the detected climatic cycles are still missing in the current GCMs and that climate variations at the multi-decadal scales are astronomically induced and, in first approximation, can be forecast," further noting that "the presence of these large natural cycles can be used to correct the IPCC projected anthropogenic warming trend for the 21st century." And in doing so, he finds that "the temperature may not significantly increase during the next 30 years, mostly because of the negative phase of the 60-year cycle," and that IPCC-projected anthropogenic CO2 emissions would imply a global warming of only 0.3-1.2°C by 2100, as opposed to the 1.0-3.6°C that is currently projected by that global body.

References
Scafetta, N. 2010. Empirical evidence for a celestial origin of the climate oscillations and its implications. Journal of Atmospheric and Solar-Terrestrial Physics 72: 951-970.

Scafetta, N. 2011. A shared frequency set between the historical mid-latitude aurora records and the global surface temperature. Journal of Atmospheric and Solar-Terrestrial Physics 74: 145-163.