Effect of trends of middle atmosphere gases on the mesosphere and thermosphere

We focused our model study on the impact of increases in carbon dioxide (CO₂), methane (CH₄), and water vapor (H₂O), and decreases in ozone (O₃) between 1983 and 2003. We used both the National Center for Atmospheric Research Whole Atmosphere Community Climate Model and the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model, global mean version, in this study.

The model simulations indicate that CO2 is the main forcing mechanism of long-term changes in the thermsophere, with minor influences from O₃, CH₄, and H₂O. At 400 km altitude, global mean thermospheric neutral density decreased by ~4.5% due to CO2 forcing alone, whereas it decreased by ~4.8% due to the combined forcing from all four gases. O₃ depletion caused cooling in the stratosphere and mesosphere (maximum decrease of 0.5 K) due to reduced absorption of solar ultraviolet radiation, but had nearly no cooling effect in the thermosphere.