Historical Atmospheric Carbon Dioxide Concentrations
“A major issue regarding the IPCC approach to linking climate and CO2 is the assumption that prior to the industrial revolution the level of atmospheric CO2 was in an equilibrium state of about 280 ppm, around which little or no variation occurred. This presumption of constancy and equilibrium is based upon a critical review of the older literature on atmospheric CO2 content by Callendar and Keeling.
“The data accepted by Callendar and Keeling had to be sufficiently low to be consistent with the greenhouse hypothesis of climate change controlled by rising CO2 emissions from fossil fuel burning.
“Natural concentrations are assumed to have been in equilibrium until mankind disturbed the natural situation. In this way, any long term observations that might display decadal to centennial natural variations in atmospheric CO2 are ruled out a priori by Callendar and Keeling. Their most egregious error was perhaps the dismissal of all data which showed variations from their presupposed average.”