Estimates of annual‐mean stratospheric temperature trends over the past twenty years, from a wide variety of models, are compared both with each other and with the observed cooling seen in trend analyses using radiosonde and satellite observations. The modelled temperature trends are driven by changes in ozone (either imposed from observations or calculated by the model), carbon dioxide and other relatively well‐mixed greenhouse gases, and stratospheric water vapour.The comparison shows that whilst models generally simulate similar patterns in the vertical profile of annual‐and global‐mean temperature trends, there is a significant divergence in the size of the modelled trends, even when similar trace gas perturbations are imposed. Coupled‐chemistry models are in as good agreement as models using imposed observed ozone trends, despite the extra degree of freedom that the coupled models possess.The modelled annual‐ and global‐mean cooling of the upper stratosphere (near 1 hPa) is dominated by ozone and carbon dioxide changes, and is in reasonable agreement with observations. At about 5 hPa, the mean cooling from the models is systematically greater than that seen in the satellite data; however, for some models, depending on the size of the temperature trend due to stratospheric water vapour changes, the uncertainty estimates of the model and observations just overlap. Near 10 hPa there is good agreement with observations. In the lower stratosphere (20–70 hPa), ozone appears to be the dominant contributor to the observed cooling, although it does not, on its own, seem to explain the entire cooling.Annual‐ and zonal‐mean temperature trends at 100 hPa and 50 hPa are also examined. At 100 hPa, the modelled cooling due to ozone depletion alone is in reasonable agreement with the observed cooling at all latitudes. At 50 hPa, however, the observed cooling at midlatitudes of the northern hemisphere significantly exceeds the modelled cooling due to ozone depletion alone. There is an indication of a similar effect in high northern latitudes, but the greater variability in both models and observations precludes a firm conclusion.The discrepancies between modelled and observed temperature trends in the lower stratosphere are reduced if the cooling effects of increased stratospheric water vapour concentration are included, and could be largely removed if certain assumptions were made regarding the size and distribution of the water vapour increase. However, given the uncertainties in the geographical extent of water vapour changes in the lower stratosphere, and the time period over which such changes have been sustained, other reasons for the discrepancy between modelled and observed temperature trends cannot be ruled out. Copyright © 2003 Royal Meteorological Society

The Modular Earth Submodel System (MESSy) provides an interface to couple submodels to a base model via a highly flexible data management facility (Jöckel et al., 2010). In the present paper we present the four new radiation related submodels RAD, AEROPT, CLOUDOPT, and ORBIT. The submodel RAD (including the shortwave radiation scheme RAD_FUBRAD) simulates the radiative transfer, the submodel AEROPT calculates the aerosol optical properties, the submodel CLOUDOPT calculates the cloud optical properties, and the submodel ORBIT is responsible for Earth orbit calculations. These submodels are coupled via the standard MESSy infrastructure and are largely based on the original radiation scheme of the general circulation model ECHAM5, however, expanded with additional features. These features comprise, among others, user-friendly and flexibly controllable (by namelists) online radiative forcing calculations by multiple diagnostic calls of the radiation routines. With this, it is now possible to calculate radiative forcing (instantaneous as well as stratosphere adjusted) of various greenhouse gases simultaneously in only one simulation, as well as the radiative forcing of cloud perturbations. Examples of online radiative forcing calculations in the ECHAM/MESSy Atmospheric Chemistry (EMAC) model are presented.

A parameterization of contrails for use in comprehensive global climate models is introduced. It is based on the thermodynamic theory of contrail formation, which has been applied in a consistent way with the cloud parameterization scheme of the version 4 European Center/Hamburg General Circulation Model. Both the coverage and the optical properties of contrails are calculated as functions of instantaneous values of atmospheric variables as they are provided by the climate model. The resulting spatial distributions of contrail parameters prove to be useful for explaining observed differences between contrails in different geographical regions. The time mean properties of the simulated contrails are in fair agreement with observations, though the values of ice water path and optical depth tend to be somewhat lower than those reported from in situ measurements. The radiative forcing of contrails resulting from the climate model experiments is substantially lower than estimated in a previous study, where mean parameters for contrails and the ambient atmosphere were prescribed in a radiative transfer model. One contribution to this disagreement arises from the smaller mean ice water content in the climate model simulations. However, the largest part must be related to a different treatment of the interference of contrails with natural high clouds. The sensitivity of the contrail radiative forcing to systematic errors in simulated ambient atmospheric variables (like temperature, humidity, and natural clouds) as well as to the parameterization of cloud and contrail overlap needs to be investigated further.