[cbkeller]

Switching to any sort of commercial grid or cloud computing setup would be rather complicated by the fact that climate models are critically dependent on the fast, low-latency interconnects (e.g., infiniband) of a proper HPC system to achieve good performance at scale. This is usually coordinated with hand-written message passing via MPI directly in the relevant top-level Fortran (or C/++) program.

There are some other (i.e, “embarrassingly parallel”) scientific computing problems where a higher-latency distributed setup would be fine, but in climate models, as in any finite-element model, each grid cell needs to be able to “talk to” its neighbors at each timestep, leading to quite a lot of inter-process communication.