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S1: Diagnosis and Metrics in Climate Models

Principal investigators: Prof. Hans Burchard (Leibniz Institute for Baltic Sea Research Warnemünde), Prof. Veronika Eyring (MARUM, University of Bremen), Prof. Thomas Jung (Alfred Wegener Institute for Polar and Marine Research/MARUM, University of Bremen), Dr. Martin Losch (Alfred Wegener Institute for Polar and Marine Research), Prof. Jens Rademacher (University of Hamburg), Prof. Bjorn Stevens (Max Planck Institute for Meterology Hamburg)

The S1 project is dedicated to advancing climate model evaluation by developing innovative diagnostics, enabling technologies, and comprehensive assessment methods. The primary goal is to assess how improved model consistency influences biases and the response to external forcing in climate simulations. S1 plays a central role in evaluating model developments proposed by the CRC and its various project areas, with a specific focus on two key climate models used by the German and European climate research community:ICON and IFS-FESOM.  

In its third phase, S1 will expand its work on new diagnostics and metrics, including spectral analysis tools on unstructured meshes and water mass transformation diagnostics, to enhance model quality assessment. Given the strong mathematical foundation required for some of these developments, mathematicians will be an integral part of the team. 

S1 will focus on the following core themes:  

- Development of spectral analysis tools for different mesh types, improving model diagnostics on unstructured grids.  
- Advancing diagnostics and metrics tailored for kilometre-scale models and common HEALPix meshes to enable cross-model comparisons.  
- Evaluating subgrid-scale processes, particularly their role in numerical mixing, overflows, and dense gravity currents, and their influence on model energetics.  
- Developing diapycnal water mass transformation diagnostics and applying them to study the meridional overturning circulation.  
- Assessing the performance of FESOM, ICON-o, and their coupled counterparts (IFS-FESOM and ICON) to identify strengths and areas for improvement.  
- Enabling technologies for efficient analysis of high-resolution model data, ensuring that diagnostics are memory-efficient and scalable.  
- Enhancing diagnostic frameworks, such as ESMValTool and pyfesom2, to facilitate seamless integration of new methodologies into broader research efforts.  
- Ensuring documentation, code management, and data governance, securing the long-term usability and accessibility of the developed tools. 

 

A key legacy of S1 will be the dissemination of easy-to-use, high-performance, and portable diagnostic software, ensuring that the tools developed within the project remain accessible and impactful for the broader scientific and modeling community. Furthermore, S1 will analyze simulations conducted both within the CRC and in external projects (e.g., CMIP, nextGEMS, and Destination Earth), ensuring that the outcomes of S1’s work contribute directly to international climate research efforts. Ultimately, S1 aims to synthesize the CRC’s impact on model quality and effectively communicate key findings to the scientific and modeling communities, fostering improvements in climate modeling and simulation capabilities.

FESOM model

One of the two ocean models used in the TRR181 project is FESOM (Finite-Element/volumE Sea ice-Ocean Model), which is part of the AWI-CM climate model of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI).

FESOM is the only ocean model participating in CMIP6, that is formulated on an unstructured mesh. This allows scientists to flexibly increase horizontal resolution of the model in more energetically active areas of the ocean like the Gulf stream or Agulhas current. The resulting model resolves important details of ocean circulation, but is still computationally efficient.

FESOM ocean currents in Indian and Pacific oceans (100m)

Report - CMIP 2026 Community Workshop in Kyoto, Japan by Tina Gier (March 26)

From March 9 to 13, I had the pleasure of attending the CMIP 2026 Community Workshop in Kyoto, Japan. As a climate scientist, it was a privilege to have a conference on the Coupled Model Intercomparison Project (CMIP) in the same location where the Kyoto Protocol was established. It is a beautiful conference center in the brutalist style next to a lake populated with both koi fish and swans. The conference started withan overview of the CMIP7 science questions and a report on the Assessment Fast Track status, highlighting the tight deadlines for including any new research into the upcoming IPCC Assessment Report 7. One of my personal highlights as a developer for ESMValTool was the launch of the Rapid Evaluation Framework (REF). The REF is envisioned to be a community owned evaluation framework built upon existing community evaluation packages that aims to disseminate basic model evaluation upon publication of the model output. ESMValTool is one of the four tools currently used by the REF, the only European tool, as well as the only tool that is currently CMIP7 ready: yay us! The REF was received very well, with many suggestions for further expansions. Coming from a terrestrial carbon cycle background, during my poster presentation and also during the breaks I met with some colleagues from that community and discussed possible diagnostics to include in both ESMValTool and potentially also in REF. It was a rewarding meeting for me that renewed old collaborations, forged new ones - and left me with a lot of extra work for the coming months. After working mostly on technical developments lately, it was nice reconnecting with the science and seeing all the new emerging topics and questions to be tackled with CMIP7.

The workshop also aimed to be quite inclusive, with sessions about better inclusion for the Global South, as well as time dedicated to an Early Career Researcher (ECR) workshop, to promote networking and avenues for ECRs to contribute to establishes structures. In the case of CMIP, the “Fresh Eyes on CMIP” initiative was presented, which aims to include the unique insight and fresh perspective ECRs bring. We also had a number in a colored circle on our workshop badges, with a red color denoting an ECR and a blue one a senior researcher who was meant to be a mentor. It was quite hard to match the numbers, but funnily enough my mentor was my colleague from the Met Office in the UK who also works with ESMValTool. Later we found another ECR with the same number - who works at AWI in Bremerhaven. The world can truly feel small!

During the conference dinner, the hosts promoted the Japanese culture by inviting both a band using traditional Japanese drums, as well as a calligrapher artist who painted a blank canvas to the beat of the drums spelling out the word “climate”. In general, Japan seems to be an existence between tradition and modernity. Traditional buildings - temples, castles and old homes - are surrounded by the usual concrete buildings so typical of modern times. Warned against their prevalent use of cash, as a German it’s just life as usual with smaller family-led restaurants often being cash only. Meanwhile you find drink machines around every corner, a museum that upon entering greets you with social robots and high-speed trains that are actually on time.

I was lucky to be there in March when plum blossoms are showing and you can see the first cherry blossoms - by the time I left, Tokyo had many parks in full bloom. Though beware - each tree blooming early will be flooded with tourists and natives with their cameras! Japan is a very popular tourist destination, which can be seen at the hordes surrounding the hotspots and viral attractions. Sometimes you can barely move: While it is touching to see how silent the Memorial Museum in Hiroshima was even when the first rooms were crowded to the point of not being able to move freely, I’m sure some of the stories would have hada stronger impact if you didn’t have to worry about being squeezed from all sides. For many of these tourist hotspots I’d recommend to look on from afar and then moving to the not-so known places which are still beautiful. Even in the main tourist cities of Osaka, Kyoto and Tokyo, you can find quiet places outside the tourist hotspots, just by walking 5 minutes beyond the nearest station in most cases. Sometimes the parks and temples I found by randomly walking through the city left a stronger impression than the main attractions. Temples with less tourists have a serene atmosphere that hits different than when you have to find your way between 5 tripods, 30 selfie sticks, tourists facetiming their family “look where I am” and just the general mass of people. To crown a successful trip, I got a certificate for flying over the north pole on the way back - and I can confirm it’s still covered in ice!

The Earth’s energy budget and other funny aspects of the thermodynamics of the climate system

State-of-the-art climate models still struggle to reproduce a reasonably energetically consistent system, even though outstanding improvements have been achieved in the recent past.

Valerio Lembo, Postdoc in S1

The idea of this subproject is assessing the impact of introducing new numerical schemes and physical parametrizations developed in the TRR181 for the energy closure of state-of-the-art climate models. We provide diagnostic tools that allow for evaluation and intercomparison of climate models, starting from their outputted datasets.

It might sound trivial, expecting that the climate system, if in steady state, is also in thermodynamic equilibrium. This is at least what our studies of classical thermodynamics suggest. The problem is that the system constantly exchanges energy with its exterior, i.e. the outer space, and within its interior. In steady state conditions, the net exchange of energy with the exterior has to be null. In other words, the climate system is in thermodynamic equilibrium, once we averaged out the modulation of the solar energy input to an appropriately long timescale and all the energy exchanges occurring in its interior, shaping the solar “reflection” and the thermal energy output. This is a clear example of what is called a “non-equilibrium dissipative steady state thermodynamical system”.

State-of-the-art climate models still struggle to reproduce a reasonably energetically consistent system, even though outstanding improvements have been achieved in the recent past. This points to the very basic reasons for climate modeling, on one hand reflecting the lack of understanding of some processes involving energy exchanges and the limits of the discretization/truncation of the real world in finite dimension models, on the other hand preventing us from correctly evaluating the impact of the various forcings for reconstructed and projected climate change.

As TRR181, we are participating to the community effort called “ESMValTool”, whose aim is providing a set of standardized diagnostics for the evaluation of state-of-the-art and forthcoming multi-model ensembles. In our diagnostics, we try to address specifically the Earth’s energy budget and its atmospheric and oceanic components, and the atmospheric energy exchanges, including the Lorenz Energy Cycle, which describes the energy exchanges in the extratropical synoptic eddies. We also provide an estimate of the atmospheric material entropy production, i.e. the entropy production through irreversible processes, and the water mass budget, which is known to be one of the main sources of uncertainty for the modeled energy budget.

The diagnostic tool is currently being ported from version 1 to version 2 of ESMValTool, and will be hopefully soon publicly released. A report for the ESMValTool version 2 is being written, with contributions by all groups in the community, and another paper, focused on potential applications of the tool in various fields of climate science, will be submitted.