Review of the global models used within phase 1 of the Chemistry-Climate Model Initiative (CCMI)

We present an overview of state-of-the-art chemistry–climate and chemistry transport models that are used within phase 1 of the Chemistry–Climate Model Initia- tive (CCMI-1). The CCMI aims to conduct a detailed evalua- tion of participating models using process-oriented diagnos- tics derived from observations in order to gain confidence in the models’ projections of the stratospheric ozone layer, tro- pospheric composition, air quality, where applicable global climate change, and the interactions between them. Interpre- tation of these diagnostics requires detailed knowledge of the radiative, chemical, dynamical, and physical processes incor- porated in the models. Also an understanding of the degree to which CCMI-1 recommendations for simulations have been followed is necessary to understand model responses to an- thropogenic and natural forcing and also to explain inter- model differences. This becomes even more important given the ongoing development and the ever-growing complexity of these models. This paper also provides an overview of the available CCMI-1 simulations with the aim of informing CCMI data users.