CO2 variability in the pre-Keeling era
The Consensus View
Before the industrial era, circa 1800, atmospheric CO2 concentration was between 275 and 280 ppmv for several thousand years (that is, between 275 and 280 molecules of CO2 for every one million molecules in the air). This we know from the composition of ancient air trapped in polar ice.
A role for atmospheric CO2 in preindustrial climate forcing — PNAS
CO2 trends based on leaf remains of Quercus robur (English oak) from the Netherlands support the presence of significant CO2 variability during the first half of the last millennium. The amplitude of the reconstructed multidecadal fluctuations, up to 34 parts per million by volume, considerably exceeds maximum shifts measured in Antarctic ice. Inferred changes in CO2 radiative forcing are of a magnitude similar to variations ascribed to other mechanisms, particularly solar irradiance and volcanic activity, and may therefore call into question the concept of the Intergovernmental Panel on Climate Change, which assumes an insignificant role of CO2 as a preindustrial climate-forcing factor. The stomata-based CO2 trends correlate with coeval sea-surface temperature trends in the North Atlantic Ocean, suggesting the possibility of an oceanic source/sink mechanism for the recorded CO2 changes.
Hat tip to Ernst-Georg Beck who has been beating the drum for CO2 variability in the pre-Keeling era for some time.
Of course if CO2 and temperatures jump up and down without man's help (though maybe not as much as they have recently) then..., well work it out for yourself.....