What was done
The author briefly reviews what we know (and don't know!) about climate change throughout the Holocene, focusing on the period from 7000 to 5000 years ago.

What was learned
Between 7000 and 5000 years ago, in the words of the author, "land air temperatures appear to have declined across much of the globe," although sea surface temperatures in the North Atlantic may have warmed a bit, possibly in response to changes in the North Atlantic thermohaline circulation.  Simultaneously, atmospheric CO2 concentration increased by just over 10 ppm, at a time when, as the author restates for emphasis, "the evidence from ice cores suggests that both hemispheres cooled."

What it means
These data from the real world once again describe a situation where rising atmospheric CO2 concentrations do not produce global warming.  In fact, as the air's CO2 content rose throughout this 2000-year period - albeit at a very slow rate - earth's climate cooled.