Attributing climate change to NOx emissions

Kurzfassung

Climate change is a challenge to society. Identifying promising mitigation measures requires a good understanding of the contribution from anthropogenic emissions, e.g. from transport (aviation, road, shipping) to climate change. Non-CO2 emissions, like NOx, perturb greenhouse gases like ozone highly non-linearly. Recent reviews have estimated the contribution from transport to climate change. Their approach uses state-of-the art numerical models and compares a base case with "all emissions" to a perturbation run with "changed emissions". But it was questioned whether this so-called "perturbation-approach" is appropriate and a "tagging approach" was instead suggested,which is an accounting system following emitted species and their chemical reaction pathways. In this study we indeed show that the contribution of road traffic to climate change via ozone formation, hence its potential mitigation gain, is systematically underestimated, when using the "perturbation approach", since the gain is partly compensated by a mitigation loss of other sectors due to increased ozone formation. Therefore, we argue that individual mitigation gains have to be regarded simultaneously with implications on other sectors.