On Nov. 5, 2015, we made an adjustment to the Scripps Mauna Loa CO 2 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