Transient behaviour of tropospheric ozone precursors in a global 3-D CTM and their indirect greenhouse effects

The global three-dimensional Lagrangian chemistry-transport model STOCHEM h as been used to follow the changes in the tropospheric distributions of the two major radiatively-active trace gases, methane and tropospheric ozone, following the emission of pulses of the short-lived tropospheric ozone prec ursor species, methane, carbon monoxide, NOx and hydrogen. The radiative im pacts of NOx emissions were dependent on the location chosen for the emissi on pulse, whether at the surface or in the upper troposphere or whether in the northern or southern hemispheres. Global warming potentials were derive d for each of the short-lived tropospheric ozone precursor species by integ rating the methane and tropospheric ozone responses over a 100 year time ho rizon. Indirect radiative forcing due to methane and tropospheric ozone cha nges appear to be significant for all of the tropospheric ozone precursor s pecies studied. Whereas the radiative forcing from methane changes is likel y to be dominated by methane emissions, that from tropospheric ozone change s is controlled by all the tropospheric ozone precursor gases, particularly NOx emissions. The indirect radiative forcing impacts of tropospheric ozon e changes may be large enough such that ozone precursors should be consider ed in the basket of trace gases through which policy-makers aim to combat g lobal climate change.