Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM
Résumé
The tropospheric chemistry model used at the Goddard Institute for Space Studies (GISS) within the GISS general circulation model (GCM) to study interactions between chemistry and climate change has been expanded and integrated into a version of the GCM with higher vertical resolution. The chemistry now includes peroxyacetylnitrates and non-methane hydrocarbons in addition to background NOx-HOx-Ox-CO-CH4 chemistry. The GCM has improved resolution and physics in the boundary layer, improved resolution near the tropopause, and contains a full representation of the stratosphere. Simulations of present-day conditions show that this coupled chemistry-climate model is better able to reproduce observed tropospheric ozone, especially in the tropopause region, which is critical to climate forcing. Comparison with simulations of preindustrial conditions gives a global annual average radiative forcing due to tropospheric ozone increases of 0.30 W/m2 with standard assumptions for preindustrial emissions. Locally, the forcing reaches more than 0.8 W/m2 in parts of the northern subtropics during spring and summer, and is more than 0.6 W/m2 through nearly all the Northern subtropics and mid-latitudes during summer. An alternative preindustrial simulation with soil NOx emissions reduced by two-thirds and emissions of isoprene, paraffins and alkenes from vegetation increased by 50% gives a forcing of 0.33 W/m2. Given the large uncertainties in preindustrial ozone amounts, the true value may lie well outside this range.
Domaines
Océan, Atmosphère
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