Increasing carbon dioxide concentration in the upper atmosphere observed by SABER

Carbon dioxide measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument between 2002 and 2014 were analyzed to reveal the rate of increase of CO2 in the mesosphere and lower thermosphere. The CO2 data show a trend of ~5% per decade at ~80 km and below, in good agreement with the tropospheric trend observed at Mauna Loa. Above 80 km, the SABER CO2 trend is larger than in the lower atmosphere, reaching ~12% per decade at 110 km. The large relative trend in the upper atmosphere is consistent with results from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS). On the other hand, the CO2 trend deduced from the Whole Atmosphere Community Climate Model remains close to 5% everywhere. The spatial coverage of the SABER instrument allows us to analyze the CO2 trend as a function of latitude for the first time. The trend is larger in the Northern Hemisphere than in the Southern Hemisphere mesopause above 80 km. The agreement between SABER and ACE‐FTS suggests that the rate of increase of CO2 in the upper atmosphere over the past 13 years is considerably larger than can be explained by chemistry‐climate models. Key Points The longest running upper atmospheric CO2 data set reported The relative CO2 trend in the lower thermosphere is much larger than predicted by models The CO2 trend is asymmetric between two hemispheres