Indications of Distinctive Efficacies of Transport Related Ozone Perturbations

Two series of equilibrium climate change simulations forced by ozone change patterns from transport emissions have been performed with two climate models. It is investigated whether radiative forcings like this lead to climate sensitivity and efficacy parameters that are significantly different among each other and from a reference forcing caused by a homogeneous CO2 increase. Identification of such differences is complicated by an unexpectedly strong dependence of the climate sensitivity on the strength of certain forcing patterns. Efficacy parameters calculated for the radiative forcings due to ozone increases resulting from aviation, shipping, and land transport emissions vary from unity by no more than 10%. Our results confirm earlier studies that hinted at the necessity to weight radiative forcings from different mechanisms individually in assessment studies, according to their efficacy, but more work is necessary before reliable efficacy parameters can be attributed to such forcings