SOCTOC - Effects of anthropogenic stratospheric ozone changes on climate sensitivity and tropospheric oxidation capacity - Subproject: Tropospheric Chemistry (SOCTOC-CHEM)
Partners
Dr. Hauke Schmidt, Max Planck Institute for Meteorology (MPI-M), Bundesstr. 53, 20146 Hamburg
Dr. Roland Ruhnke, Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen
The project in a nutshell
Future stratospheric ozone will be influenced by both changes in the anthropogenic halogen loading and changes in the Brewer-Dobson Circulation, i.e. the large-scale stratospheric overturning circulation. In SOCTOC we are studying effects of these ozone changes on a) the tropical tropopause layer (TTL) and climate sensitivity (subproject SOCTOC-TTL, led by MPI-M), and on b) tropospheric oxidation capacity and hence the greenhouse gas (GHG) methane and climate (subproject SOCTOC-CHEM, led by KIT).
Increased upwelling in the tropical stratosphere, as simulated robustly by climate models for global warming, would reduce ozone in the lower tropical stratosphere. Recent publications have provided very different estimates of the impact of such an ozone change on climate sensitivity, ranging from a 25% reduction to zero net effect compared to models that don’t represent these ozone changes. First results with an idealized 1-dimensional model of the tropical atmosphere indicate that indeed vertical shifts of the ozone profile (as expected from anthropogenic circulation changes) would affect surface temperature, and that this effect is mediated by changes in water vapour (Fig. 1).
Globally, due to decreasing stratospheric halogen content, a recovery of the ozone layer is expected for the next decades. This would alter the UV radiation flux into the troposphere with consequences for the primary production of OH radicals and hence tropospheric chemistry, for instance in terms of the lifetime of CH4, which is responsible for about 20% of the GHG induced warming since preindustrial times. Whether changes in the emissions of methane or in tropospheric OH concentrations are the cause of the observed flattening in the CH4 trend in the early 2000s is under debate.
Using a hierarchy of numerical models from 1D radiative convective equilibrium to the global ICON model with interactive chemistry we try to narrow down the uncertainties related to these two effects of stratospheric ozone changes.
Besides the scientific goals, this project aims at a further development of the ICON atmospheric GCM and its coupling to chemistry packages. We implement and apply configurations of ICON coupled via the ART module to both a comprehensive chemistry code and computationally cheap linearized ozone chemistry. This will allow us to evaluate the usefulness of the latter approach for climate studies. First results (Meraner et al., 2020) indicate that ozone variations caused by circulation anomalies are qualitatively well represented by the Cariolle-scheme (one variant of existing linear schemes) but often underestimated quantitatively.