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Modelling Approach





Global Climate Module

The Global Climate Module determines the impact on the global climate system of the aircraft emissions identified by the Aircraft Movement Module. It considers the effects of carbon dioxide, nitrogen and sulphur oxides and water vapour emissions, together with the inclusion of contrails. The module can be used in three different configurations by employing various atmospheric models, depending on the application being studied.

These models aim to represent atmospheric processes at an appropriate resolution level, based on established and validated model versions that are specifically adapted for use in the integrated context of AIM.

Configuration 1:  The Module consists of an atmospheric general circulation model (GCM) with coupled modules for chemistry and radiation. This model calculates its own meteorological data and allows for the additional consideration of feedback mechanisms between atmospheric transport, chemistry, and radiation. A further advantage of this configuration is the general circulation model’s ability to simulate future meteorological conditions thereby allowing a more realistic prediction of the environmental impact of air traffic in future decades.

Configuration 2:  The Module consists of a global three-dimensional atmospheric chemistry transport model (CTM). This model uses external meteorological data to calculate the transport of chemical species, such as greenhouse gases and their precursors, and their chemical interactions. The calculated changes in the atmospheric composition will be fed into an off-line radiative module which calculates the radiative forcing impact. The advantage of this configuration is the use of actual meteorological data which, together with actual aircraft movements, will permit the realistic reproduction of the atmospheric impact due to global air traffic in the recent past or present.

Configuration 3:  The Module consists of a simplified parametric version of the chemistry transport model used in the second configuration and the off-line radiative module. This model is based upon recent scientific findings that under certain conditions the impact of small perturbations applied to the present-day aircraft emissions can result in a linear response in the impact on greenhouse gas concentrations. The advantage of this configuration is the ability to quickly perform a large number of sensitivity studies, strictly within the valid parametric range, at comparatively low computational cost.

All three of these configurations consider the processes shown below at varying degrees of detail and complexity. The Global Climate Module receives data from the Aircraft Movement Module on the global distribution of airborne emissions from aviation. Further inputs consist of actual meteorological data, obtained from the European Centre for Medium Range Weather Forecast (ECMWF), and surface based emissions appropriate for the present day or alternatively emission scenarios for the future atmosphere. The module can also provide boundary condition data for the Local Air Quality & Noise Module.

The results from the Module’s radiative calculations are primarily used to evaluate the atmospheric impact caused by global air traffic within the context of climate change. The obtained climate impact results provide the ability to assess the global impacts of a variety of policy options applied to the preceding AIM modules, but can also serve as input for economic costing (“monetisation”) calculations.