Studies towards assessing the effects of aviation on climate

This study evaluates the capabilities of the carbon cycle and energy balance treatments in several existing simplified climate models that are either being used or could be used for evaluating the effects of aviation on climate. Since these models are used in policy-related analyses, it is important that the capabilities of such models represent the state of understanding of the science. We compare the Aviation Environmental Portfolio Management Tool (APMT) Impacts climate model, two models used at the Center for International Climate and Environmental Research-Oslo (CICERO-1 and CICERO-2), the Integrated Science Assessment Model (ISAM) model as described in Jain et al. (1994), the simple Linear Climate response model (LinClim) and the Model for the Assessment of Greenhouse-gas Induced Climate Change version 6 (MAGICC6). In this paper we do select case studies to illustrate the behavior of carbon cycle and energy balance model in these models. The results are not intended to show the absolute and likely range of the expected climate response in these models. Our intercomparison points to specific features in model representations of the carbon cycle and the energy balance model that need to be carefully considered in studies of aviation effects on climate. These results suggest that carbon cycle models that use linear impulse-response-functions (IRF) in combination with separate equations describing air-sea and air-biosphere exchange of CO2 can account for the dominant nonlinearities in the climate system that would otherwise not have been captured with an IRF alone, and hence, produce a close representation of more complex carbon cycle models. Moreover, results suggest that an energy balance model with a 2-box ocean submodel, and IRF that is tuned to reproduce the dominant mode of a new generation of coupled Earth system models produce a close representation of the globally-averaged temperature response of more complex energy balance models. 1 This chapter appeared in its entirety in the Journal of Atmospheric Environment as Khodayari, A., D. Wuebbles, S. Olsen, J. Fuglestvedt, T. Berntsen, M. Lund, I. Waitz, P. Wolfe, P. Forster, M. Meinshausen, D. S. Lee and L. L. Lim, (2013),“Intercomparison and Evaluation of the Capabilities of Simplified Climate Models to Project the Effects of Aviation on Climate”, Atmospheric Environment, 75, 321-328.