Upper Atmosphere Responses to IPCC's Worst Scenario of CO ₂ Increase in the 21st Century

Abstract Over centuries, the increasing CO 2 emission has intensified the upper atmospheric cooling and contraction effects. To predict the impacts of CO 2 long‐term increase on the upper atmosphere in the future, a 90‐year simulation with CESM2/WACCM‐X is performed. It reveals prominent dynamical responses in addition to density responses reported before. (a) Main thermospheric parameters such as thermosphere temperature, neutral mass density, and electron density almost keep the decreasing trends; (b) The meridional circulation is strengthened especially in June; (c) The diurnal tides have a reduction/enhancement response above/below the 200 km in the thermosphere, while the semi‐diurnal tides decrease throughout the thermosphere. These results are in line with those previously obtained from the GAIA model, thus confirming the acceleration of the upper atmosphere circulation accompanying the cooling effect. The agreement also implies consistency between the two models in predicting the CO 2 impacts on the dynamics of the background thermosphere and ionosphere.