Contrary to the oft-repeated mantra that today’s CO2 concentration is unprecedentedly high, our current geologic period, the Quaternary, has seen the lowest average levels of carbon dioxide since the Precambrian. Though CO2 concentrations briefly peaked 320,000 years ago at 300 ppm, the average for the past 800,000 years was 230 ppm (Luthi 2008). The average CO2 concentration in the preceding 600 million years was more than 2,600 ppm, nearly seven times our current amount and 2.5 times the worst case predicted by the IPCC for 2100. Our current geologic period (Quaternary) has the lowest average CO2 concentration in more than 600 million years.