What was done
The authors note that recent research findings in both palaeoecology and solar science "indicate a greater role for solar forcing in Holocene climate change than has previously been recognized," especially in the publications of the Intergovernmental Panel on Climate Change (IPCC).  In this paper they review that evidence.

What was learned
The authors find much evidence within the Holocene for solar-driven variations in earth-atmosphere processes over a range of timescales stretching from the 11-year solar cycle to century-scale events.  They acknowledge that absolute solar flux variations associated with these phenomena are rather small; but they identify a number of "multiplier effects" that can operate on solar rhythms in such a way that "minor variations in solar activity can be reflected in more significant variations within the Earth's atmosphere."  They also note that nonlinear responses to solar variability are inadequately represented (in fact, they are essentially ignored) in the global climate models used by the IPCC to predict future greenhouse gas-induced global warming, while at the same time other "amplifier effects" are used to model well-known glacial/interglacial cycles of temperature change of the past and even the hypothesized CO2-induced warming of the future, where CO2 is not the major direct cause of the predicted temperature increase but is instead an initial perturber of the climate system that, according to the IPCC, sets other more powerful forces in motion that produce the bulk of the warming.

What it means
There seems to be an inherent reluctance within the IPCC bureaucracy to deal even-handedly with different aspects of climate change theory.  When "multiplier effects" suit their purposes (yes, they must have preconceived ideas about what increasing CO2 levels will do to Earth's climate; for they have already stated that there is a discernible human influence on the climate of the past century that they attribute to the historical rise in atmospheric CO2 concentration) they use them; and when they don't suit their purposes, they don't use them.  This type of behavior does not engender confidence in their conclusions.  Indeed, it makes them (both the IPCC and their conclusions) suspect.