In Earth system modelling, the interacting domains (atmosphere, hydrosphere, cryosphere, ...) of the environment are simulated in conjunction to study the nature of feedbacks between the different domains and processes and how they influence the properties of the whole system.
I am coordinating the multi-institutional development and evaluation of the Modular Earth Submodel System (MESSy). For the development of MESSy we received the Heinz Billing Award for the Advancement of Scientific Computation 2005. MESSy is especially suitable for Earth system studies, because it allows the coupling of different processes through a generalised interface structure to a base model and to switch them on and off independent of each other. The generalised interface allows coupling the same submodels to different base models, from three-dimensional atmospheric general circulation models to box models. As a first application with a strong focus on atmospheric chemistry, we built and evaluated the ECHAM/MESSy Atmospheric Chemistry (EMAC) model, which is a numerical chemistry and climate simulation system that includes submodels describing tropospheric and middle atmosphere processes and their interactions with oceans, land and human influences. It uses the first version of the Modular Earth Submodel System to link multi-institutional computer codes.