Swiss GAW/GCOS community at 2nd Swiss National GAW/GCOS Symposium 2026, Switzerland; four strategic recommendations for future development.

Swiss GAW/GCOS community at 2nd Swiss National GAW/GCOS Symposium 2026, Switzerland; four strategic recommendations for future development.

MeteoSchweiz_Fachbericht

Technical Report MeteoSwiss No. 292 2nd Swiss National GAW/GCOS Symposium 2026 White Paper Swiss GAW/GCOS Office

MeteoSwiss Operation Center 1 CH-8044 Zürich-Flughafen T +41 58 460 99 99 www.meteoschweiz.ch ISSN: 2296-0058 Technical Report MeteoSwiss No. 292 2nd Swiss National GAW/GCOS Symposium 2026 White Paper The following conference report was prepared by the Swiss GAW/GCOS Office: Michelle Stalder, Andrea Rossa, Nicole Glaus, and Debora Bötticher.

With contributions from the Scientific Programme Committee of the Symposium Iris Feigenwinter, Isabelle Gärtner-Roer, Martin Gysel-Beer, Stelios Kazadzis, and Martin Steinbacher and contri- butions from Mischa Croci-Maspoli.

Final review by: Stefan Brönnimann on behalf of the Swiss GAW/GCOS Scientific Steering Commit- tee.

Recommended citation: MeteoSwiss: 2026, 2nd Swiss National GAW/GCOS Symposium 2026: White Paper, Technical Report MeteoSwiss, 292 39 pp. Editor: Federal Office of Meteorology and Climatology © 2026 MeteoSwiss

V Technical Report MeteoSwiss No. 292 White Paper 2026

Executive Summary The Swiss National GAW/GCOS Symposium 2026 brought together more than 100 experts to review progress since the last Symposium in 2021 and to identify priorities for the coming years. The sym- posium confirmed Switzerland’s strong contribution to the WMO Global Atmosphere Watch (GAW) and Global Climate Observing System (GCOS) programmes and highlighted the continued im- portance of coordinated long-term Earth system observations. The presentations demonstrated major progress in integrating in-situ observations, remote sensing, modelling, and data science and AI/ML approaches, while advancing societally relevant applications related to urban climate, glacier retreat, drought monitoring, biosphere-atmosphere interactions, and atmospheric composition changes. A central outcome of the symposium was the reaffirmation that sustained long-term observations remain the foundation of robust climate and atmosphere research. Continuous, high-quality observational records are essential for detecting environmental change, validating emerging measurement techniques and AI-based approaches, and ensuring reliable cli- mate services and policy-relevant information at national and global levels. Safeguarding the continu- ity, quality, and long-term sustainability of observing systems therefore remains the highest strategic priority of the programmes. The symposium also highlighted the growing importance of integrating remote sensing, process- relevant observations, modelling, and AI/ML approaches with in-situ observations. Advances in data science and machine learning offer major opportunities for improved analysis, prediction, and service development. However, the application of these novel approaches requires rigorous validation against high-quality reference observations and depend on accessible, interoperable, and well- documented data infrastructures. Another key finding was the growing importance of translating observations into actionable climate services and decision-support products. Effective knowledge transfer requires stronger engagement with stakeholders and users, co-development of services, and communication approaches tailored to societal needs. This is particularly relevant for Switzerland as an Alpine country, where climate change impacts are amplified and adaptation needs are increasing rapidly. Overall, the Symposium 2026 demonstrated that the progress presented by the Swiss GAW and GCOS communities was well in line with the recommendations formulated in the White Paper 2022. Given their long-term strategic nature, all recommendations remain relevant and valid, while the dis- cussions at the symposium also highlighted emerging priorities and led to the following four strategic recommendations for the future development of Swiss GAW and GCOS activities: High-quality long-term observations: Ensuring the continuity of high-quality long-term observa- tions is of fundamental importance, as they provide the essential ground-based reference (“ground

VI Technical Report MeteoSwiss No. 292 truth”) for the validation, calibration, and long-term consistency assessment of emerging measure- ment techniques, remote sensing products, and model outputs. This requires i.a. rigorous, cutting- edge science. In addition, these activities should be complemented by an agile scientific component that enables timely responses to new developments in measurement methods (such as advances in instruments or data analysis techniques), emerging trends, and processes that are currently under- explored. At the same time, the long-term sustainability of Swiss observing systems should be regu- larly assessed, including the prioritization of observation sites and variables, in order to ensure that available resources are focused on scientifically and societally most relevant observations. Data management and integration: Quality control, homogenization, traceability, and comprehen- sive documentation for global-, regional-, and national-scale measurements remain critically im- portant and must be ensured in the long term. Related data and metadata need to be stored/archived in curated and trustworthy repositories and ideally in interoperable data ecosystems. In addition, regular re-evaluation of historical datasets is essential to enhance their stability, robustness, and long-term consistency and compatibility. Progress towards more comprehensive observation cover- age should be achieved by systematically extending in-situ monitoring through the integration of process-relevant and remote sensing data and/or through the integration of observations based on simplified techniques with (sparse) high-quality observations in blended, tiered networks. A more encompassing and comprehensive data management is a prerequisite for efficient inclusion of di- verse data sets in AI/ML analysis frameworks. Strengthening the integration between in-situ observa- tions, remote sensing products, modelling, and reanalysis frameworks is essential to improve spatial and temporal coverage and to enable robust cross-validation of datasets. This attributes particular value to data obtained in under-observed regions, such as the cryosphere and high-mountain areas. Knowledge transfer and science for services: There is a clear need to strengthen the transfer of knowledge from science to society, ensuring effective connections across the full chain from obser- vations and research to climate services and communication. This is especially relevant for moun- tainous countries like Switzerland, where the warming is roughly twice as high as in the global aver- age and impacts are likely to be more severe. A key priority is to more clearly demonstrate the im- pact of scientific findings and to strengthen the translation of scientific results into policy-relevant actionable information, thereby enhancing the interface between monitoring, science, and decision- making. Effective climate services require early and continuous engagement with relevant stakehold- ers and users in order to better identify needs, co-develop services, and improve usability and socie- tal relevance of scientific information. In parallel, knowledge transfer represents a significant oppor- tunity for international cooperation and capacity development. Interdisciplinary and cross-institutional collaboration: Next-generation numerical weather and climate prediction models are now complemented by AI/ML models and should be recognised, uti- lised, and further developed as key platforms for interdisciplinary collaboration. Data science can play a key part in enabling stronger integration across observational and modelling communities, crucial to better describe and understand the Earth System. Joint efforts remain necessary to ensure the continued development and long-term sustainability of existing observing systems, as well as to address and close critical measurement gaps.

VII Technical Report MeteoSwiss No. 292 White Paper 2026

Contents Executive Summary V 1 Introduction 1 1.1 Context and Motivation 1 1.2 GAW-CH in Brief 1 1.3 GCOS-CH in Brief 1 2 Goal & Structure of the Symposium 2026 3 Recommendations of the 1st Swiss National GAW/GCOS Symposium 3 3 Sessions 5 3.1 Keynote presentations 5 3.1.1 AI/ML - from NWP to atmospheric composition forecasting, a game changer - Laurence Rouil, Director of CAMS, ECMWF 5 3.1.2 ETH Swiss GeoLab - Transforming Earth Observation Into Action - Felix Seidel, Managing Director, ETH Swiss GeoLab 5 3.2 Recent Progress based on the White Paper 2022 6 3.3 Increasing Importance of Earth System Data 7 3.4 New Generation of scientific leadership in GAW-CH/GCOS-CH 7 3.5 Earth System Data for impactful applications 9 3.6 Panel Discussion 9 4 Conclusions and Recommendations for Future Activities 11 4.1 Conclusions 11 4.2 Recommendations 12 Abbreviations 14 References 15 Acknowledgement 16 Appendices 17 A Symposium Programme 17 B Summaries of the Presentations 19 C List of Posters 24 D List of Participants 27

1 Technical Report MeteoSwiss No. 292 White Paper 2026 1 Introduction 1 Introduction 1.1 Context and Motivation Based on the WMO Global Atmosphere Watch (GAW) programme launched in 1989, and the co- sponsored Global Climate Observing System (GCOS) programme launched in 1992, the Swiss Fed- eral Council has mandated MeteoSwiss to implement these two programmes at the national level, respectively in 1994 and 2006 (BBI, 2002). The goal of this engagement is to contribute to the global- scale systematic observation of the chemical composition of the atmosphere as well as of a large number of essential climate variables (ECVs). MeteoSwiss as the host of the Swiss GAW/GCOS Office coordinates the implementation of the programmes on a national level through a network of national partners. Today, the GAW and GCOS programmes remain important, but are challenged by limited funding at the WMO and countries’ levels, not least in Switzerland. Also, the climate priority is overshadowed by geopolitical crises which further jeopardizes an adequate level of funding for moni- toring efforts such as GAW and GCOS. The Swiss contribution to GAW and GCOS has been sub- stantial and important throughout the existence of these programmes, and it is all the more important for this contribution to be maintained and be made as targeted and effective as possible. The Swiss National GAW/GCOS Symposium aims to provide a dedicated platform for the Swiss GAW and GCOS communities to exchange knowledge and ideas and to present progress achieved in recent years. One important objective of the symposium is to identify the strategic priorities for both national programs for the forthcoming period which are published in the form of the present White Paper. The first one was published in 2022, followed by this updated edition. This process ensures the coherent and continuous advancement of the Swiss GAW and GCOS strategies in alignment with the international GAW Science and Implementation Plan and the GCOS Implementa- tion Plan. Relating to the GCOS-CH programme, the present White Paper supersedes the GCOS Switzerland Strategy 2017–2026 (MeteoSwiss, 2017) beyond 2026. 1.2 GAW-CH in Brief Launched in 1989, the Global Atmosphere Watch programme (GAW) is a partnership of about 100 countries to monitor the composition of the atmosphere. The programme supports a global network of high-quality monitoring stations measuring greenhouse gases, ozone, UV radiation, aerosols, reactive gases and precipitation chemistry with high accuracy and worldwide comparability. The GAW Science and Implementation Plan (WMO, 2025) provide the international guidelines for the Swiss GAW programme (GAW-CH). The Swiss GAW/GCOS Off