Climate response to regional emissions of tropospheric ozone precursors

Climate change mitigation measures are likely to affect the distribution of emissions of ozone precursors. While the gases regulated in the Kyoto Protocol are long-lived and thus independent of the location of the emissions, the climate impact of emissions of NOx through ozone production is very variable due to non-linear chemical effects. At high ambient NOx concentrations additional NOx emissions produce less ozone (and OH) than at lower background NOx concentrations. If flexible mechanisms (e.g. emission trading and CDM) lead to changes in location of the emissions, the secondary effects through changes in the distribution of emissions of NOx and CO could be significant. In this study we have used two global chemical transport models (The University of Oslo-CTM2 model and the IPSL LMDz GCM/chemistry model) to calculate the effect of increasing NOx emissions in Europe or in SE Asia on ozone and methane. A subset of the ozone perturbations (scaled up to give a global forcing of 1W/m^2) were then used as input to two advanced GCMs (ECHAM4, run at DLR and LMDz) as well as the simpler Reading Intermediate GCM, to calculate the temperature response. The CTMs show that emissions in South-East Asia, where the ambient NOx concentrations are much lower than in Europe, have a much higher impact on ozone and radiative forcing. The value of climate sensitivity parameter is found to deviate significantly (-32% - +48%) from the corresponding value for a CO_2 experiment, however, with no systematic differences. Spatial variability in the temperature response, which might have significant impact on damages will be discussed.