When nextGEMS began in 2021, it set out with an ambitious goal: to bring global, kilometre-scale Earth system modelling from dream to reality. Four years later, as the project closes at the end of August 2025, the results speak for themselves — and for the hundreds of scientists, engineers, and collaborators who made it possible.

A Vision Realised

For the first time, multi-decadal global simulations at the kilometre scale — coupling atmosphere, ocean, and land — have been run with two different models: ICON and IFS-FESOM. Both now achieve an energetically consistent climate, a challenge that has plagued even long-established climate models, and can simulate decades in a matter of weeks, thanks to throughputs of up to 600 simulated days per day.

These breakthroughs lay the groundwork for the Climate Change Adaptation Digital Twin in the European Commission’s Destination Earth initiative and set a benchmark for future climate research.

The Power of Community

From the start, nextGEMS set out to break down silos between climate science, high-performance computing, and model development. Over 25 institutions from Africa, Asia, Europe, and North America joined forces, meeting online and — critically — in person at six hackathons.

Participant numbers grew from around 80 in the first cycle to over 130 in the third and fourth, with each meeting strengthening inter-institutional cooperation and cross-disciplinary exchange. The project’s open-data ethos, supported by tools like easy.gems, unified Intake catalogues, and example notebooks, made it easier than ever for participants to analyse terabytes of simulation output directly on the Levante supercomputer.

Hackathons: Where the Magic Happened

The six hackathons — in Berlin, Vienna, Madrid, Hamburg, Wageningen, and Stockholm — were much more than coding sprints. They were week-long collaborative laboratories where model developers, climate scientists, HPC specialists, and sectoral users sat side by side.

Working directly on Levante meant no need to transfer enormous datasets; ideas could be tested in real time. Feedback from these sessions fed directly into the next model cycle, making the hackathons the heartbeat of nextGEMS.

Nurturing the Next Generation

Early-career scientists (ECSs) played a central role—not only as observers, but also as coders, analysts, and co-authors. For many, nextGEMS offered their first opportunity to contribute to a major international modelling initiative.

Hackathons, in particular, created a unique environment where ECSs could learn directly from senior scientists. They received guidance on project design and research methods that helped them avoid wasted effort while fostering creativity and innovation. These events also provided valuable opportunities to build personal networks. Meeting hundreds of international researchers laid the foundation for long-term collaborations and partnerships, while also helping young scientists advance their ongoing projects. One hackathon participant, for example, used the event to distribute surveys and recruit interview partners for research on the human factor in developing the nextGEMS Earth system model.

Beyond hackathons, nextGEMS enabled ECSs to strengthen both scientific and technical skills. These included recognizing the limitations of models in representing the climate system, managing complex data, and analyzing results from multiple high-resolution global simulations. As one early-career scientist from the University of Hamburg reflected:

“Engaging with a large community and diverse model applications encouraged me to think creatively and broaden my perspective. These experiences were essential in shaping my understanding of the field.”

By providing space for learning, mentoring, and collaboration, nextGEMS has ensured that its legacy lies not only in the data and models it produced but also in the new generation of scientists it has prepared to lead the field forward.

Science Meets Society

However, nextGEMS didn’t only speak to scientists. Industry stakeholders from energy providers and fisheries joined hackathons to explore how kilometre-scale simulations could inform their planning. For example:

• Renewable energy operators examined high-resolution wind and solar data for better resource forecasting.
• Fisheries managers explored ocean currents and temperature changes that affect ecosystems.

At the 2025 Final Countdown Hackathon in Stockholm, a participant from the renewable energy company Statkraft described the experience as especially valuable. The informal setting allowed direct conversations with climate scientists and other participants about the challenges encountered when working with climate data and their opinions on its quality and usability. Additionally, the close collaboration with nextGEMS’ technical experts offered guidance on navigating specific technical aspects of the datasets, such as zoom levels and the Xarray grid.

Technical Milestones

Among the most notable achievements:

• Multi-decadal, energetically consistent km-scale simulations for 2020–2050 under the SSP3-7.0 scenario.
• Throughput leaps — from 17 simulated days per day in early ICON runs to over 400, and from 40 to 600 in IFS-FESOM.
• HEALPix output grids for direct model-to-model comparison.
• Harmonised data formats and common variable sets, enabling faster, more transparent analysis.

Scientific Insights

Working at kilometre scale allowed nextGEMS to explore climate processes in unprecedented detail:

• Tropical rainbelt dynamics and their connection to sea-surface temperature patterns, as studied by Segura et al., 2024, Bao et al., 2024, and Hohenegger et al., 2023.
• Soil moisture–precipitation feedbacks, which are key for drought prediction and were investigated by Lee & Hohenegger, 2024 and Hohenegger et al., 2023, among others.
• Stratocumulus cloud fields play a crucial role in the Earth’s radiation balance and are discussed in publications, such as those by Nowak et al., 2025 and Waclawczyk et al., 2022.

These insights are not only scientifically exciting — they have direct relevance for climate-sensitive sectors and adaptation strategies worldwide.

Looking Ahead

While the Horizon 2020 funding chapter closes, nextGEMS’ legacy is just beginning. The data, tools, and community it built will feed into Destination Earth’s digital twins, inform policy-relevant research, and continue to train the next generation of climate modellers.

The km-scale era has arrived — and the people who made nextGEMS possible have ensured it’s here to stay.

For those who want to dive deeper, we invite you to visit our multimedia library, where you can watch videos exploring the project’s key outcomes in more detail — from behind-the-scenes insights at our hackathons to explanations of what kilometre-scale modelling means for science and society. You can also explore the full breadth of our scientific output in our Zenodo community. Among these, we especially recommend the newly released paper by Segura et al. (2025), “nextGEMS: entering the era of kilometre-scale Earth system modelling”, which captures the technical breakthroughs, collaborative spirit, and scientific discoveries that define the project.

Km-scale models, such as ECMWF’s Integrated Forecasting System (IFS), play a vital role in the understanding and prediction of weather patterns and long-term climate trends. They can resolve smaller features, such as mesoscale eddies in the ocean, urban areas over land, and convective cloud structures in the atmosphere. These smaller processes are crucial for simulating a realistic uptake of heat by the ocean, or for extreme weather events and regional climate dynamics. However, while high-resolution models offer greater spatial accuracy, they come with the trade-off of significantly higher computational demands, making them more resource-intensive, and often require longer run times for simulations than low-resolution models. Although low-resolution models are computationally less expensive, they may overlook important small-scale processes, leading to less precise predictions in certain regions and different transient behaviour. Additionally, they may misrepresent extreme weather conditions. Balancing these trade-offs and developing improvements for high-resolution simulations are key for advancing climate models and are the focus of the nextGEMS project.

In the paper „Multi-year simulations at kilometre scale with the Integrated Forecasting System coupled to FESOM2.5 and NEMOv3.4“ by Rackow et al., a group of scientists, from several modeling centers, academia, and the wider nextGEMS community, present and evaluate the first multi-year-long km-scale model simulations, developed within the nextGEMS project, that connect the IFS to the ocean models NEMO and FESOM. The goal of the study was to present the different nextGEMS simulations and the scientific and technical progress that was made over the first three model development cycles. The authors present the data that emerged from the multi-year simulations, explain how to adjust the code of the ocean, atmosphere, and land models, and detail how to set up km-scale simulations that more accurately represent real-world processes. A particular focus was set on sea ice leads, the urban diurnal temperature cycle, and other phenomena, including variability patterns such as the Madden-Julian Oscillation (MJO) and the Quasi-Biennial Oscillation (QBO).

The IFS-FESOM model that emerged as a result of the nextGEMS research better incorporates connections between the atmosphere, land areas, urban areas (e.g., cities), the oceans, and sea ice in the polar regions. These components are important parts of the climate system as their interactions regulate the Earth’s climate, drive weather patterns, and impact the environmental conditions on our planet.

This blog post discusses the five main technical changes that led to the improvement of the simulations:

1. Tackling the issue of water non-conservation

Processes like evaporation, condensation, and precipitation enable the distribution of water across the globe and between the land surface, the atmosphere, and oceans. They also change the phase in which water is present on Earth. However, the total amount of water remains nearly constant in the Earth system and should also be conserved in climate models, without artificial sources or sinks of water. This is especially important as the amount of water present in the system influences the representation of other key processes, such as extreme weather events, temperature rise, or the conditions for vegetation activity in different regions.

In their 2025 study, Rackow et al. found that in the IFS, the total amount of water does not remain constant over time. Instead, the model accumulates an increasing amount of water as simulations progress. The researchers traced back this issue of water non-conservation to the use of Semi-Lagrangian advection schemes. These schemes are implemented in the IFS to reduce computational costs when simulating atmospheric transport processes. However, they only approximate how air—and with it, water—is moved in the real world. As a result, the amount of water in the model after advection tends to be overestimated. This overestimation becomes more pronounced at higher spatial resolutions and when deep convective processes are not parameterized—that is, when they are resolved explicitly rather than represented through simplified equations based on numerous assumptions.

Rackow et al. (2025) addressed this problem of water non-conservation in high-resolution climate models by introducing a tool called global mass fixer. This tool corrects errors in the distribution of water and ensures that the total amount of water in the model is more realistically maintained at each time step. However, this approach also increases computational costs, and although it drastically improves water conservation on a global scale, some other imbalances still remain. To fully resolve these issues, the authors suggest the addition of a total energy fixer to address remaining inconsistencies in the model’s energy balance.

A more detailed explanation of the water non-conservation challenge is given by Tobias Becker and other members of the ECMWF in their 2022 newsletter article, available here.

2. Representing the top-of-the-atmosphere (TOA) radiation balance more realistically

The radiation balance refers to the difference between the energy the Earth receives from the sun and the energy it radiates back into space. This balance is crucial in climate modeling because it determines whether the Earth’s overall temperature is stable, warming, or cooling. In previous configurations, this balance was not accurately represented, leading to model drift and impacting the estimates of global warming from increased greenhouse gas concentrations in multi-year simulations.

To address this issue, the researchers made several adjustments focused on how clouds are represented and formed in the models:

1. Alteration of cloud edge erosion rates to slow down the clouds’ process of breaking down and to make them persist in the model over a longer period
2. Reduction of subgrid-scale cloud heterogeneity to slow down the process of accretion and therefore slightly increase cloud cover. 
3. Adjustment of processes connected to mid-level convection to detrain in the liquid form and not in the ice form, which reflects the real-world behavior more accurately. 
4. Simplification of how the model calculates the movement of moisture (semi-Lagrangian advection scheme) by switching from the complex method of cubic interpolation to a simpler one, namely linear interpolation. This change was applied to all forms of water except for water vapor, i.e., rain, snow, and ice. The linear interpolation is faster and uses less computing power while still being accurate enough for these calculations. Additionally, linear interpolation reduces the issue of water non-conservation before the global mass fixers are applied and increases the diffusion around updrafts.
5. Enhancement of high cloud representation by reducing the size of ice particles to better align it with observational data. High clouds are clouds that form at high altitudes in the atmosphere, typically above 6,000 meters (20,000 feet) and are made up of tiny ice crystals rather than water droplets. These types of clouds are likely to occur more often in storm-prone regions, which underscores the importance of this model change for future predictions.

3. Simulation of intense precipitation

Deep convection is a process by which clouds can form in the atmosphere and build up high enough to reach an altitude where temperatures are below 0°C. Previous km-scale model simulations at 4 and 9 km without parametrizing this process  (Deep OFF) led to unrealistically intense and disorganized convective systems. To fix these issues, the researchers of this study refrained from turning off the parametrized deep convection processes completely and instead reduced the amount of mass transported at the base of clouds by a factor of six compared to the default configuration at a 9 km resolution. This approach provides a more realistic transition between parametrized and explicitly resolved convection at the km-scale. Following this, the updated model can more accurately predict extreme weather events and how they change in a warming climate.

4. Enhancing the eddy-resolving features in the mid- and high-latitude oceans

Eddies are small, swirling currents in the ocean that can significantly impact weather and climate. To capture these features more accurately, the model was refined with a resolution finer than 5 km in large parts of the global ocean, which allowed it to represent mesoscale eddies and sea ice leads. In combination with the high atmospheric resolution, this higher resolution of the ocean processes led to a better understanding of the complex air-ice-ocean interactions, revealing new aspects of how these three components work together. One important difference was to have the model explicitly represent the shape and make-up of sea ice leads and to represent the resulting heating of the atmosphere. By including these interactions, the model now simulates novel energy exchange and climate processes, with potentially significant implications for understanding extreme weather events in polar regions and the effects of climate change on sea ice and ocean circulation.

5. Improving the representation of cities and urban areas

The urban scheme, developed at ECMWF, provides a simplified method to improve the simulation of weather conditions in cities. Tested over multiple years, the scheme has demonstrated its ability to enhance the simulation of near-ground temperatures, particularly in urban areas. When combined with higher-resolution land static information and integrated into the IFS model, it significantly increased the model’s accuracy in representing land surface temperatures over urban areas, capturing both temporal variability (changes over time) and spatial variability (differences between urban areas and their rural surroundings). The IFS-based nextGEMS simulations are the first coupled climate simulations including explicitly the effect of urban areas. However, some limitations persist, such as discrepancies in nighttime temperatures, which may result, among other causes, from an inaccurate representation of heat emissions resulting from human activities, such as the heating of buildings or the operation of vehicles at night.

In addition to these five technical improvements, the study has also shown that km-scale models can improve the representation of atmospheric circulation and extreme precipitation events, and revealed previously unknown interactions between the climate components, which will be the focus of future research projects.

Source: Rackow, T., Pedruzo-Bagazgoitia, X., Becker, T., Milinski, S., Sandu, I., Aguridan, R., Bechtold, P., Beyer, S., Bidlot, J., Boussetta, S., Deconinck, W., Diamantakis, M., Dueben, P., Dutra, E., Forbes, R., Ghosh, R., Goessling, H. F., Hadade, I., Hegewald, J., Jung, T., Keeley, S., Kluft, L., Koldunov, N., Koldunov, A., Kölling, T., Kousal, J., Kühnlein, C., Maciel, P., Mogensen, K., Quintino, T., Polichtchouk, I., Reuter, B., Sármány, D., Scholz, P., Sidorenko, D., Streffing, J., Sützl, B., Takasuka, D., Tietsche, S., Valentini, M., Vannière, B., Wedi, N., Zampieri, L., and Ziemen, F. (2025).Multi-year simulations at kilometre scale with the Integrated Forecasting System coupled to FESOM2.5 and NEMOv3.4, Geosci. Model Dev., 18, 33–69, DOI: 10.5194/gmd-18-33-2025.

After four days of hacking and collaborating together, March 28th, 2025, marked the final session of „The Final Countdown“ hackathon in Stockholm. Focused on the possible applications of Storm-Resolving Earth System Models (SR-ESM) in the renewable energy sector, this was also the last hackathon of the nextGEMS project. Some extraordinary accomplishments were made during the past 5 years since the start of this visionary project. The group was, for example, able to create 10, 5, and 2 kilometer-scale runs, and are close to release runs with a resolution of 1 kilometer. However, nothing stands out more than the solid and compromised community nextGEMS has built up through the years: talented and curious people working together to push forward high-resolution climate modeling and understanding the possibilities it comprises for a warming and changing planet.

The last hackathon day involved a small plot contest, won by scientist Matthias Aengenheyster from the European Center for Medium-Range Weather Forecasts (ECMWF). His visual shows wind gust speed and 2-minute averaged precipitation in an area around Japan for the coupled IFS-FESOM model simulation at 2.8 km resolution. Near the bottom, a tropical cyclone is approaching Japan, while another one near the top is transitioning from inter-tropical to an extra-tropical cyclone as it moves to cooler latitudes.

During the closing session, the five thematic groups were able to share their advancements with the audience. For instance, the Renewable Energy group talked about their efforts to monitor wind speed shifts in the central Sweden region with nextGEMS’ climate models, where some of the stakeholder companies had placed wind turbines. In parallel, the Storms & Radiation team shared their intentions to prepare 3 thematic research papers on diverse topics, such as climate sensitivity, feedback decomposition and tropical cloud organization—the last one with a special focus on deep convective clouds.

In an engaging presentation, some of the early-career scientists and first-time hackathon attendees who participated in the Storms & Land group, provided interesting insights of the snow coverage observations in the Iberian mountain range. Similarly, the Storms & Ocean team share their observations of mesoscale ocean circulation patterns (typically between 10 to 500 km in diameter) occurring at shallow depths, as well as their interest of observing the historical future of “El Niño” phenomenon. The Storms & Society thematic group conducted several interviews during the event and disseminated a final survey with the participants to finish their work on Climate Science storylines and the impact of hackathons in knowledge co-production. 

Finally, Climate Physics Director at the Max Planck Institute for Meteorology, Bjorn Stevens, closed the event remarking some of the useful applications nextGEMS’ models have enabled, such as testing hypotheses underpinning climate change, studying changes at the mesoscale or blocking statistics, and the representation of hydrological extremes worldwide. Furthermore, he mentioned some of the forthcoming activities for the community, spearheaded by nextGEMS, such as the upcoming Global Hackathon taking place in May, 2025.

The nextGEMS project has entered its final phase and will come to an end in August, 2025. But before going separate ways, our project  members and partners gather one last time for the sixth nextGEMS hackathon from March 24th to 28th. In the stylish surroundings of Stockholm city, the Swedish Museum of Natural History, the largest museum of the Nordic country, hosts “The Final Countdown”. This time, the participants´ challenge is centered around how the high-resolution capabilities enabled by nextGEMS simulations can support and enhance renewable energy applications in a changing climate.

The first day kicked off with the arrival of a diverse group of scientists, stakeholders, students, and climate enthusiasts that totaled 73 registered participants. Within the museum´s classic setting, the introductory session evolved into an active and engaging conversation. Representatives from the Max Planck Institute for Meteorology (MPI-M) and the European Center for Medium-Range Weather Forecasts (ECMWF), updated the audience on the progress being made with the simulations of the ICON and IFS-FESOM Earth System models. 

Tobias Becker, researcher from the ECMWF, presented insights on two simulations at 2.8 km resolution, produced with 14 months of new data using the IFS-FESOM model. These recent advancements add local granularity and allow to check if atmospheric phenomena previously analyzed at coarser or less detailed resolutions also show up at this higher resolution. Additionally, he reported on two 30-year simulations – historical and scenario-based – at 9 km resolution that should provide valuable information on how extreme events change in warming climate, such as tropical cyclones.

The different thematic groups—Storms & Land, Storms & Ocean, Storms & Radiation, and Storms & Society— discussed their newest achievements and upcoming challenges. Dragana Bojovic, from the Storms & Society group, for example, talked about the survey analysis from the past five hackathons, as well as of the work on renewable energy and fisheries storylines. This time, a new group joined the Stockholm hackathon: the renewable energy group. This group includes not only researchers, but also different industry stakeholders, such as people working at Vestas, Satkraft, Anemos, and local participants, addressing future energy scenarios for 2050.

To conclude the day, participants took part in an ice-breaker session, which included a micro-poster activity designed to enrich conversations and connections through the use of visualizations. Some of the first-time participants in the event, like Diego Garcia and Antonio Robles from Universidad Complutense de Madrid in Spain, shared posters illustrating their observations on historical data regarding snow coverage along the Spanish highlands and future changes in Tropical Basin interactions, created with the IFS-FESOM model.

Easy Gems is an online platform that consolidates information on high-resolution climate simulations produced by the nextGEMS project and other European initiatives, such as European Eddy-Rich ESMs (EERIE), WarmWorld, and the DYAMOND initiative. Developed by the German Climate Computing Center (DKRZ), this platform serves as a repository of best practices and a comprehensive guide to create climate models. According to DKRZ Senior Scientist Florian Ziemen, one of the key aspects behind the creation of Easy Gems was “the idea was to have one place where you can find everything you need when you want to analyze high-resolution simulations.”

At the same time, the goal was to build something that was not tied strictly to a single project, thereby ensuring the sustainability of the platform and its data even after individual projects conclude. This approach prevents the platform from ending up in the „website dumpster,“ Ziemen explained. As a result, Easy Gems is designed to extend beyond individual projects by offering access to all simulation data—or „simulation gems“—hosted at DKRZ, while also functioning as a how-to resource or e-book.

Since nextGEMS drives the development of two European storm-resolving Earth-system models — the ECMWF Integrated Forecasting System (IFS) and the Icosahedral Nonhydrostatic Weather and Climate Model (ICON) — Easy Gems includes details on three development cycles of these Earth System Models, as well as some pre-final simulations. This encompasses simulations at various horizontal resolutions and evolving model configurations.

Additionally, the platform offers guidance on logging data, plotting data, and applying a variety of best practices in data processing. It is entirely user-driven, meaning that the Easy Gems community actively contributes and keeps the content up-to-date. Beyond serving as a guide, the platform acts as a comprehensive documentation tool for the project, providing access to project outputs that are further illustrated and explained.

The platform is organized into three main sections: Simulations, Processing, and Contribute. The Simulations section provides detailed information on the simulations currently available, while the Processing section offers tips and example scripts for data handling. Finally, the Contribute section explains how users can collaborate and become part of this community-driven effort.

Easy Gems encourages contributions from anyone, regardless of their background. Contributions can range from reporting errors and requesting additional articles to suggesting clearer descriptions or improved illustrations. To contribute and interact with Easy Gems, users need a DKRZ account. Additionally, additions require approval from other members of the community to ensure that the input is correct and avoid redundancies. Currently, there are 3,260 registered accounts, with approximately 490 users granted access to all the data hosted on the platform.

If you’re interested, feel free to check out Easy Gems here!