Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM

[摘要] Improved estimates of the radiative forcing from tropospheric ozone increasessince the preindustrial have been calculated with the tropospheric chemistrymodel used at the Goddard Institute for Space Studies (GISS) within the GISSgeneral circulation model (GCM). The chemistry in this model has been expandedto include simplified representations of peroxyacetylnitrates and non-methanehydrocarbons in addition to background NO_x-HO_x-O_x-CO-CH₄chemistry. The GCM has improved resolution and physics in the boundary layer, improvedresolution near the tropopause, and now contains a full representation of stratosphericdynamics. Simulations of present-day conditions show that this coupled chemistry-climatemodel is better able to reproduce observed tropospheric ozone, especially in thetropopause region, which is critical to climate forcing. Comparison with preindustrialsimulations gives a global annual average radiative forcing due to tropospheric ozoneincreases 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 subtropicsduring spring and summer, and is more than 0.6 W/m² through nearly all theNorthern subtropics and mid-latitudes during summer. An alternative preindustrialsimulation with soil NO_x emissions reduced by two-thirds and emissions ofisoprene, paraffins and alkenes from vegetation increased by 50% gives a forcingof 0.33 W/m². Given the large uncertainties in preindustrial ozone amounts, thetrue value may lie well outside this range.

[学科分类] 大气科学