The increasing need for higher resolution and greater accuracy in weather forecasts and climate simulations continues to drive software and hardware developments in high-performance computing (HPC) systems. To achieve increasingly faster simulations, the adoption of hardware accelerators has proven highly effective in recent years. However, these HPC codes exhibit, in parts, divergent memory access and computation patterns. Hence, their performance benefits strongly depend on how well the software's computational characteristics align with the underlying hardware architecture. While an accelerator may be well-suited for some code regions, other architectures may achieve better performance and energy efficiency elsewhere. We therefore propose a highly heterogeneous setup for a performant and energy-efficient execution of complex HPC codes such as those used in the weather and climate domain, incorporating a variety of processor and accelerator architectures.

We present the first-ever global simulation of the full Earth system at 1.25 km grid spacing, achieving highest time compression with an unseen number of degrees of freedom. Our model captures the flow of energy, water, and carbon through key components of the Earth system: atmosphere, ocean, and land. To achieve this landmark simulation, we harness the power of 8192 GPUs on Alps and 20480 GPUs on JUPITER, two of the world’s largest GH200 superchip installations. We use both the Grace CPUs and Hopper GPUs by carefully balancing Earth’s components in a heterogeneous setup and optimizing acceleration techniques available in ICON’s codebase. We show how separation of concerns can reduce the code complexity by half while increasing performance and portability. Our achieved time compression of 145.7 simulated days per day enables long studies including full interactions in the Earth system and even outperforms earlier atmosphere-only simulations at a similar resolution.

This paper is about increasing parallelism in climate models via additional component concurrency.