The CO2 in short gets depleted in ice core measurements and has not been corrected properly. (jennifermarohasy.com)
Combined with ice core measurements from Greenland and Antarctica, this tells us that atmospheric CO2 levels are the highest in over 15 million years (Tripati 2009). (skepticalscience.com)
A.D. 1700...» which are at variance with multiple direct CO2 ice core measurements from Greenland and Antarctica, and there wasn't significant anthropogenic industrial fossil fuel consumption and CO2 emissions at those dates. (realclimate.org)