Climate sensitivity of radiative impacts from transport systems

Comparing individual components of a total climate impact is traditionally done in terms of radiative forcing. However, the climate impact of transport systems includes contributions that are likely to imply climate sensitivity parameters distinctly different from the “reference value” for a homogeneous CO2 perturbation. We propose to introduce efficacy factors for each component into the assessment. The way of proceeding is illustrated using aviation as an example, and prospects for evaluating the other transport system in the EU project QUANTIFY are given

Implication of strongly increased atmospheric methane concentrations for chemistry–climate connections

Methane (CH4) is the second-most important directly emitted greenhouse gas, the atmospheric concentration of which is influenced by human activities. In this study, numerical simulations with the chemistry–climate model (CCM) EMAC are performed, aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth's atmosphere for the climate. We analyse experiments with 2×CH4 and 5×CH4 present-day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the OH abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical substances. The region above the tropopause is impacted by a substantial rise in stratospheric water vapour (SWV). The stratospheric ozone (O3) column increases overall, but SWV-induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical upwelling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2×CH4 experiment to be 0.69&thinsp;W&thinsp;m−2, and for the 5×CH4 experiment to be 1.79&thinsp;W&thinsp;m−2. A substantial part of the RH is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates. To our knowledge this is the first numerical study using a CCM with respect to 2- and 5-fold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.</p

Distinctive efficacies of the components contributing to total aviation climate impact

Separate climate sensitivity simulations were run for all important non-CO2 radiative forcing contributions from aviation (except for contrail cirrus), aiming at the quantification of an individual efficacy parameter for each component. All simulations were performed with the same climate model, E39A. The necessity to scale the original perturbations complicates a straightforward determination of efficacy values, particularly for aviation ozone. The results presented here indicate that a radiative forcing from water vapour increase caused by supersonic aviation would have a similar efficacy than CO2. Ozone changes induced by subsonic aviation and methane changes appear to have an efficacy larger than CO2, but the enhancement is moderate (~1.05). For line-shaped contrails we find an efficacy substantially smaller (~0.6) than CO2 in agreement with previous results. The (small) water vapour increase expected from subsonic aviation shows reduced efficacy (~0.7), too. Similar studies with other climate models are desirable in view of probable model dependency

Raeumlich-zeitliche Entwicklung energetischer Parameter waehrend blockierender Wetterlagen

TIB: RA 1818 (46) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman