SCREAM is the DOE E3SM project's next generation global atmospheric model. It has a nonhydrostatic dynamical core and state-of-the-art parameterizations for microphysics, moist turbulence and radiation. It has been written from scratch in C++ with the Kokkos library used to abstract the on-node execution model for both CPUs and GPUs. SCREAM contains several algorithmic innovations including a highly efficient HEVI-IMEX timestepping and semi-Lagrangian tracer transport and separate physics/dynamics grids which exploits the effective resolution of the dynamics.

In this presentation we will show SCREAM's Exascale performance on the DOE OLCF Frontier system, as well as SCREAM's performance portability across a wide range of CPUS and multiple GPUs from AMD, NVIDIA and Intel. On Frontier, SCREAM obtains record setting performance. At global cloud permitting resolution (3.25 km grid spacing ) it runs well on 27,000 AMD MI250 GPUs, obtaining a throughput of 1.26 simulated-years-per-day.