The world is warming. Near surface air temperatures in the first two decades of the twenty first century were 0.75°C warmer than they were over the thirty year period between 1951 and 1980 and about 1°C warmer than during the last two decades of the nineteenth Century. Much less clear, than our planet’s warming and its cause, is the detailed trajectory of this warming – even when conditioned on the carbon emission scenarios – and the quantitative implications of this warming for human and natural systems. High-performance computing is reaching a crescendo with the promise of Exascale machines just beyond the horizon. Within five years, computing systems capable of computing ensembles of trajectories of the climate systems over several decades and on spatial scales of 1 km, will become operational. The German national project WarmWorld by harnessing advances in information technology will compute and evaluate climate warming trajectories, make the information contained within them transparent to application communities, and help harmonize national efforts to provide, disseminate, and use the highest possible quality of climate information.

The first phase of the WarmWorld project comprises four modules, with JSC contributing to Modules 2 and 3. Module 2 is responsible for transforming the numerical weather prediction and climate model ICON into an open, scalable, modularized and flexible code named ICON-C (“ICON-consolidated”). Specific objectives of Module 2 are to refactor ICON with the goal of scalable development to enable portable performance improvements – ultimately making ICON faster. Module 2 activities will progressively redefine the ICON code structure to expose areas of performance improvement for targeted exploration of new programming concepts. To achieve those goals, the work exploits the analogy of space exploration, with three structured themes dubbed “Ignition”, “Lift-Off”, and “Stage Separation”. Work in the “Ignition” theme will transform the existing ICON code base into a modular design. In “Lift-Off”, separate granules will be connected by an event-driven control flow. These two themes will largely be based on the current Fortran version of ICON and will take advantage of groundwork in the preparatory project preWarmWorld. At the same time, fundamental rewrite of individual granules, using other programming languages than Fortran, domain-specific languages, or even approaches based on machine learning is organized in the “Stage Separation” theme.

Module 3 will develop novel methods to make information visible, accessible, and interoperable. Specific of objectives are to prepare a data-centric ICON workflow to manage the exascale data streams envisioned in WarmWorld, our `Mission to MARS’ which will establish harmonized access to simulation systems and their output at DKRZ, JSC, and ECMWF through the use of common interfaces and analysis back-ends, as well as prototype exascale analysis workflows that abstract the analysis from the information source, including observational ESA/EUMETSAT and measurement networks such as ACTRIS and IAGOS. Module 3 activities will develop the federated data system, and the tools to exploit it around the highly successful and efficient Field Database (FDB) system developed at ECMWF. This will provide access to data and output hosted by ECMWF without interfering with their operations, and benefit from external projects, such as ACROSS, funded to further develop this system. Exploitation will focus on developing software systems and standards that allow users to explore and analyze information hosted by FDB instances or produced by in-situ analysis in dedicated simulations. From the user point of view the eventual aim of the WarmWorld’s workflow concept is to have a common interface for ICON simulations and data stored in an FDB instance. These are advanced and developing concepts, hence this activity group also contains considerable prototyping designed to guide developments in the second phase of the WarmWorld project.