The influence of different greenhouse gases to future stratospheric and mesospheric ozone in EMAC

To evaluate future climate change in the middle atmosphere and the chemistry-climate interaction of stratospheric ozone, we performed long-term simulations from 1960 to 2050/2100 with the model ECHAM/MESSy Atmospheric Chemistry (EMAC). In addition to these standard simulations we performed different sensitivity simulations. For these sensitivity simulations we used the same model setup as in the standard simulations but changed the boundary conditions for CO2, CH4, N2O, and ozone-depleting substances (ODS). For example we fixed the mixing ratios of CO2, CH4, and N2O in the boundary conditions to the amounts of 2000. In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO2 mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH4, which also forms additional H2O in the upper stratosphere and mesosphere. The simulated ozone recovery leads to warming of the middle atmosphere. In EMAC the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NOx and HOx mixing ratios due to increased N2O and CH4 lead to intensified ozone destruction. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NOx is of similar importance in some regions. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport.