On Nov. 5, 2015, we made an adjustment to the Scripps Mauna Loa CO2 record that has the effect of increasing concentrations we have reported since April 2015 by 0.4 parts per million (ppm). We made the adjustment after comparing our short-term calibration gases with the long-term calibration gases, concentrations of which have been determined manometrically. Comparing short- and long-term calibration gases is a normal part of the strategy for maintaining reliable long-term measurements. The adjustment increases the likelihood that concentrations will remain above 400 ppm permanently after 2015.
– Ralph Keeling