A milestone in weather and climate research

A team of researchers from Germany and Switzerland involving Empa is setting a milestone in weather and climate research: At the beginning of February, the renowned climate and weather model ICON has become available to all interested parties under an open source license. This is intended to make science and the scientific services behind it more transparent. At the same time, further scientific progress is made possible in an area from which society can particularly benefit in times of climate change.

Empa / Meteo Schweiz / CS2M 01.02.2024

ICON (ICOsahedral Non-hydrostatic modelling framework) is a numerical weather model and uses three-dimensional computer simulation to calculate changes in the atmosphere over the next few hours and days. Such weather models are mainly used by national weather services such as the Federal Office of Meteorology and Climatology (MeteoSwiss). The research institutions behind ICON and its current developers are the German Climate Computing Center (DKRZ), the German Meteorological Service (DWD), the Karlsruhe Institute of Technology (KIT), the Max Planck Institute for Meteorology (MPI-M), and the Swiss Center for Climate Systems Modeling (C2SM, with ETH Zürich, MeteoSwiss, Empa, WSL and Eawag as partners).

ICON shows how beneficial the collaboration between research and the national weather services is: The close cooperation results in very efficient weather forecasts and climate projections, which benefit not only the research community but also the public. The release of the code is an important step towards strengthening trust in science and research institutions. Oliver Fuhrer, Head of the Numerical Prediction Department at MeteoSwiss, underlines this: "The open source availability of the ICON model marks a decisive moment in meteorological research. The ICON model is currently in the test phase at MeteoSwiss with the goal of deploying it for daily weather forecasts this year."

ICON was initially developed jointly by the DWD and MPI-M as an atmospheric and weather forecasting model and is now used in Germany and Switzerland for operational weather forecasting. With regard to climate research, MPI-M has developed suitable models of other components of the Earth system that allow ICON to be used as a fully coupled climate and Earth system model. In addition to the model component for ocean circulation, there is one for marine biogeochemistry as well as for the land biosphere and hydrological processes.

The specially developed Community Interface (ComIn), for example, enables scientists to extend the ICON model with their own plug-ins without having to change the complex model code. This not only promotes flexibility in research, but also unleashes the power of innovation within the scientific community.

KIT has developed a model component – ICON-ART – that allows the prediction of aerosols and atmospheric chemistry and their interaction with the physical state of the atmosphere. Aerosols and the chemical composition of the atmosphere determine air quality and influence solar radiation, clouds and precipitation. Empa was also involved in the development of ICON-ART and has developed a module for the efficient integration of emission data and implemented a detailed scheme for chemical reactions, which is important for simulations of air quality. The YAC software component required for coupling the sub-models was developed jointly by DKRZ and MPI-M and published as open source from the outset.

All sub-models are included in the open source release, so that ICON can be used in a wide range of resolutions and configurations to enable a whole range of applications – from global and regional weather forecasts and climate projections to very high-resolution digital twins of the Earth system.

The release of the ICON model code under an open source license is a decisive step towards open, transparent, quality-assured and collaborative science. Researchers worldwide will have the opportunity to build on one of the leading models for weather forecasts and climate simulations and work together on pioneering projects. Commercial use is also possible under the license. The publication takes place against the backdrop of a changing research landscape that promotes increased collaboration and the exchange of knowledge.

The open source release facilitates the integration of ICON into international research collaborations and strengthens Europe's position in the field of climate and weather research. It also enables more efficient collaboration with supercomputer manufacturers, who can test and improve the performance of their hardware using weather and climate models.

Scientific benefits and broader applications

"Open source licensing will simplify the exchange with our partners in science and could support the creation of new innovative start-ups in the environmental sector", says Dominik Brunner, head of the Atmospheric Modeling and Remote Sensing group in Empa's Air Pollution / Environmental Technology lab. According to Brunner, ICON-ART, together with measurements on the ground and from satellites, also makes it possible to detect and quantify the sources of greenhouse gases and air pollutants even more reliably.

Brunner's team has just published an impressive example of this on the EGUsphere expert platform. The researchers used ICON-ART to estimate methane emissions across Europe and compared them with the quantities officially reported by the individual countries. According to the Empa researcher, this corresponds very well for many countries, with some countries even having lower emissions than reported – while some others have significantly higher emissions. The study will soon be published in the journal Atmospheric Chemistry and Physics.