  Power spectra of global surface temperature (GST) records reveal major
periodicities at about 9.1, 10-11, 19-22 and 59-62 years. The Coupled Model
Intercomparison Project 5 (CMIP5) general circulation models (GCMs), to be used
in the IPCC (2013), are analyzed and found not able to reconstruct this
variability. From 2000 to 2013.5 a GST plateau is observed while the GCMs
predicted a warming rate of about 2 K/century. In contrast, the hypothesis that
the climate is regulated by specific natural oscillations more accurately fits
the GST records at multiple time scales. The climate sensitivity to CO2
doubling should be reduced by half, e.g. from the IPCC-2007 2.0-4.5 K range to
1.0-2.3 K with 1.5 C median. Also modern paleoclimatic temperature
reconstructions yield the same conclusion. The observed natural oscillations
could be driven by astronomical forcings. Herein I propose a semi empirical
climate model made of six specific astronomical oscillations as constructors of
the natural climate variability spanning from the decadal to the millennial
scales plus a 50% attenuated radiative warming component deduced from the GCM
mean simulation as a measure of the anthropogenic and volcano contributions to
climatic changes. The semi empirical model reconstructs the 1850-2013 GST
patterns significantly better than any CMIP5 GCM simulation. The model projects
a possible 2000-2100 average warming ranging from about 0.3 C to 1.8 C that is
significantly below the original CMIP5 GCM ensemble mean range (1 K to 4 K).
