Marcus O. Köhler

Aviation radiative forcing in 2000: An update on IPCC (1999)

New estimates of the various contributions to the radiative forcing (RF) from aviation are presented, mainly based on results from the TRADEOFF project that update those of the Intergovernmental Panel on Climate Change (IPCC, 1999). The new estimate of the total RF from aviation for 2000 is approximately the same as that of the IPCC’s estimate for 1992. This is mainly a consequence of the strongly reduced RF from contrails, which compensates the increase due to increased traffic from 1992 to 2000. The RF from other aviationinduced cirrus clouds might be as large as the present estimate of the total RF (without cirrus). However, our present knowledge on these aircraft-induced cirrus clouds is too poor to provide a reliable estimate of the associated RF. Zusammenfassung Neue Abschatzungen der einzelnen Beitrage zum Strahlungsantrieb des Luftverkehrs werden vorgestellt, die im Wesentlichen auf Ergebnissen des TRADEOFF-Projektes beruhen und die die IPCC-Abschatzungen (1999) aktualisieren. Der neue Wert fur den gesamten Strahlungsantrieb des Luftverkehrs im Jahr 2000 ist in etwa gleich gros wie die IPCC-Abschatzung fur das Jahr 1992. Das ist im Wesentlichen eine Folge des stark reduzierten Strahlungsantriebes durch Kondensstreifen, wodurch der Anstieg aufgrund der Zunahme des Verkehrs von 1992 bis 2000 kompensiert wird. Der Antrieb durch andere luftverkehrsinduzierte Wolken konnte ebenso gros sein wie die neue Abschatzung fur den gesamten Strahlungsantrieb (ohne Zirren). Jedoch ist unser heutiges Wissen uber diese luftverkehrsinduzierten Wolken nicht gut genug, um belastbare Aussagen uber den damit verbundenen Strahlungsantrieb zu machen.

Impact of perturbations to nitrogen oxide emissions from global aviation

The atmospheric response to perturbations in NO x emissions from global air traffic is investigated by performing a coherent set of sensitivity experiments. The importance of cruise altitude, size of the emission perturbation and geographical distribution of emissions is systematically analyzed using two global chemistry transport models and an off-line radiative transfer model. NO x emissions from a contemporary aircraft inventory have been used to assess the impact of global air traffic on ozone and methane. In further experiments the NO x emissions are perturbed, in turn, in 16 cruise altitude bands between 5 and 15 km altitude. In the p-TOMCAT model we diagnose an annual mean ozone increase of up to 6 ppbv and a decrease in the methane lifetime of 3% due to global air traffic in 2002. Associated radiative forcings of 30 mWm−2 for ozone and −19 mWm−2 for methane are diagnosed; a simple method is used to estimate the forcing due to the methane-induced ozone change and this yields an additional −11 mWm−2. Results show that up to the tropopause, ozone production efficiency and resulting impacts increase per emitted mass of NO x with the altitude of the perturbation. Between 11 and 15 km we find that the geographical location of the NO x emissions plays a crucial role in the potential O3 impact and lifetime change of CH4. We show that changes in flight routing in this altitude range can have significant consequences for O3 and CH4 concentrations. Overall, we demonstrate a linear relationship in the atmospheric response to small emission changes which can be used to predict the importance of perturbations about the reference aircraft emissions profile, provided the geographical distribution of the emissions is not altered significantly.

Modelling Environmental and Economic Impacts of Aviation: Introducing the Aviation Integrated Modelling Project

The Aviation Integrated Modelling project is developing a policy assessment capability to enable comprehensive analyses of aviation, environment and economic interactions at local and global levels. It contains a set of inter-linked modules of the key elements relevant to this goal. These include models for aircraft/engine technologies, air transport demand, airport activity and airspace operations, all coupled to global climate, local environment and economic impact blocks. A major benefit of the integrated system architecture is the ability to model data flow and feedback between the modules. Policy assessment can be conducted by imposing policy effects on the upstream modules and following implications through the downstream modules to the output metrics, which can then be compared to a baseline case. A case study involving different evolution scenarios of the US air transportation system from 2000 to 2030 is used to show the importance of feedback and to model a sample policy scenario in order to illustrate current capabilities.

Global Atmospheric Chemistry and Impacts from Aviation

The atmosphere contains a large number of chemical trace compounds among which complex chemical processes take place. These processes form an important part of the natural global biogeochemical cycles. Anthropogenic emissions of chemically active pollutants can interfere in the natural chemical processes and result in impacts on the climate system or lead to the accumulation of substances hazardous to ecosystems. This chapter outlines the most important chemical processes taking place in the atmosphere with a view to the global scale and to an extent as they are of relevance to chemical interference caused by aircraft engine emissions. The effects caused by emissions of nitrogen oxides, sulfur compounds, and water vapor from subsonic aviation are discussed and placed into context with global atmospheric chemistry.