More than 100 researchers from across the globe gathered at the Potsdam Institute for Climate Impact Research (PIK) this week for the joint CROSS-CASCADE and ISIMIP Workshop 2026 — five days of intensive exchange on how to make climate impact science more robust, more comprehensive, and better prepared for the challenges ahead.
Rigorous Model Intercomparison to Foster Robustness of Climate Impact Assessments
The workshop’s core focus reaffirmed ISIMIP’s foundational role: systematic, cross-sectoral climate impact model intercomparison is not merely an academic exercise, but a critical process for building the reliable, evidence-based understanding necessary for effective climate adaptation and mitigation, and at the same time produces scientific results that can withstand scrutiny — including from politically motivated critics seeking to cast doubt on climate research.
By systematically comparing results across independent impact models targeting various sectors such as Water, Agriculture, Health, Energy, and many more, driven by the same climate forcing data, ISIMIP produces findings whose robustness can be explicitly quantified. Where models agree, confidence is high; where they diverge, the reasons can be investigated and communicated transparently. This multi-model approach is perfectly suited to counter critics dismissing individual results as model artefacts or cherry-picked outcomes.
Workshop participants stressed that in an era of intensifying political pressure on climate science, this transparency and reproducibility is not merely a scientific virtue — it is a strategic necessity. Openly documented protocols, publicly archived model outputs, and clearly communicated uncertainty ranges are among the strongest defenses the research community has against bad-faith attacks on the scientific consensus around climate change and its impacts.
Towards CMIP7-Based Climate Impact Assessments in Time for IPCC AR7
A key discussion centered on ISIMIP’s strategic alignment with the next generation of climate projections. Participants actively explored the pathway for ISIMIP to integrate CMIP7 (Coupled Model Intercomparison Project Phase 7) data as it becomes available. The goal is clear: to ensure that cutting-edge climate impact studies – vital for informing national adaptation plans, infrastructure resilience, and the upcoming IPCC Seventh Assessment Report (AR7) – are grounded in the most current and comprehensive climate forcing data. Timely adoption of CMIP7 would allow ISIMIP to deliver impact projections with state-of-the-art climate physics, directly supporting AR7’s mandate to assess impacts, adaptation, and vulnerability with the highest possible confidence.
CMIP7 delivers updated climate projections incorporating the latest advances in Earth system modelling, and there is strong scientific and policy motivation to base sectoral impact assessments — on water, food, ecosystems, health, infrastructure, and more — on this most current forcing data. At the same time, running the full suite of ISIMIP impact models on new climate inputs is a major undertaking requiring careful planning, data infrastructure, and community buy-in.
Participants discussed pathways for a timely and strategically prioritised uptake of CMIP7 data within ISIMIP, with the explicit goal of ensuring that high-quality, multi-sector climate impact results are available to contribute to the IPCC AR7 process. The discussions addressed how to handle bias adjustment and statistical downscaling of the new data, and how to coordinate the modelling community to achieve the necessary throughput within the AR7 timeline.
In his opening keynote, PIK Co-director Johan Rockström emphasized the urgency and relevance of cross-sectoral climate-impact research for science, policy, and society, and spoke out strongly in favour of ISIMIP’s core focus, namely the development of process-based climate impact simulation data that is as robust as possible.
Keynote speaker Bart van den Hurk (IPCC WG II co-chair) underlined that the IPCC's ability to make robust statements on sectoral impacts depends critically on the kind of systematic, multi-model evidence ISIMIP provides, and stressed that methodological transparency is the research community's most important asset under political scrutiny. Additionally, Marina Romanello (Lancet Countdown Europe) highlighted in her keynote the growing demand for health impact attribution — quantifying how much of today's observable health burden is caused by anthropogenic climate change. This requires carefully constructed counterfactual climate scenarios: simulations of a world without human-induced warming, against which observed outcomes can be compared. Her keynote set the stage for discussions on aligning ISIMIP with the Lancet Countdown, including plans to produce a cross-community standard counterfactual dataset within the ISIMIP framework for use across Lancet Countdown health indicators — strengthening comparability, reproducibility, and the defensibility of attribution statements.
Outlook
The workshop produced concrete next steps for both the CROSS-CASCADE networking project that underpins certain ISIMIP activities and the broader ISIMIP community, including a roadmap for ISIMIP’s Phase 4 activities to integrate CMIP7 and to produce robust findings for IPCC AR7, as well as for strengthening links with CROSS-CASCADE to provide even more holistic risk assessments for decision-makers navigating complex climate futures.
By fostering this environment of rigorous, collaborative scrutiny, the ISIMIP and CROSS-CASCADE communities reaffirm their commitment to producing science that doesn’t just project the future – it helps build a resilient one, founded on evidence that withstands the test of both peer review and real-world application.
