Send me a link to the original published paper by the blogger David Middleton and we can go from there.
I see. Are you saying the data in the chart is false The blogger post is references the following published papers among others:
Rapid atmospheric CO 2 changes associated with the 8,200-years-B.P. cooling event
It thus may be concluded that leaf-based CO 2 data support a much more dynamic evolution of the Holocene CO 2 regime than previously thought. In effect, there seems to be every indication that the occurrence of Holocene CO 2 fluctuations is more consistent with current observations and models of past global temperature changes than the common notion of a relatively stable CO 2 regime until the onset of the Industrial Revolution.
Another that shows more rapid and wider fluctiations:
Atmospheric CO 2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of Tsuga heterophylla needles
A stomatal frequency record based on buried Tsuga heterophylla needles reveals significant centennial-scale atmospheric CO 2 fluctuations during the last millennium. The record includes four CO 2 minima of 260–275 ppmv (ca. A.D. 860 and A.D. 1150, and less prominently, ca. A.D. 1600 and 1800). Alternating CO 2 maxima of 300–320 ppmv are present at A.D. 1000, A.D.1300, and ca. A.D. 1700. These CO 2 fluctuations parallel global terrestrial air temperature changes, as well as oceanic surface temperature fluctuations in the North Atlantic. The results obtained in this study corroborate the notion of a continuous coupling of the preindustrial atmospheric CO 2 regime and climate.
Care to comment on these? There are others.