ISIMIP Steering Committee meeting, online, 23 February 2026
The ISIMIP Steering Committee is the main decision-making body within ISIMIP and consists of the Sector Coordinators, the Scientific Advisory Board, and the Cross-sectoral science team at PIK. On 23 February the group met online to discuss upcoming steps and priorities for the ISIMIP4 Fast Track (FT), and beyond, as well as to carve out priorities and key tasks for strong ISIMIP-based contributions to the IPCC AR7 WGII.
The summary of the meeting can be found below and the slides as shwon during the meeting can be accessed here.
Process towards the ISIMIP Fast Track, and beyond:
After the consultation of different ‘downstream users’ such as ISIMIP, CMIP has decided to recommend the prioritization of the Very Low with Limited Overshoot (VLLO) [1], and the High (H) scenario within the CMIP7-ScenarioMIP process. This increases the chances to generate an ensemble of climate model simulations for at least these two scenarios whose impacts can then still be simulated and assessed for the IPCC-AR7.
Based on these decisions, the IAM community has also prioritized these scenarios, and have already provided the associated emission, concentration, and land use data for the CMIP simulations. The LU patterns have been harmonized to observational historical data, while several ESMs have started pre-industrial runs in the meantime. We received the available data sets, as well, and started to derive the direct human forcing (DHF) for the ISIMIP4 Fast Track. We expect the first CMIP7 models to provide H and VL simulations by first of July which we will then pre-process (perform bias adjustment and downscaling), to be able to start the ISIMIP4 Fast Track around July-August 2026.
The ISIMIP4 FT protocol is planned to mostly follow the ISIMIP3 set up including group III simulations, i.e. accounting for future SSP-based changes in DHF, but without accounting for potential adaptation effects on DHFs.
There will be dedicated sessions during the upcoming ISIMIP-CROSS-CASCADE workshop (8-12 June at PIK, Potsdam), to discuss input data for the ISIMIP4 FT, and to clarify any open questions. In case you anticipate open issues in the meantime, please don’t hesitate to contact your sector coordinator who will collect them so we can address them efficiently.
Given the tight timeline for the IPCC-AR7 there is only little flexibility regarding the ISIMIP4-FT set-up. However, after the sprint for the AR7 there will be room for an extension of the protocols. Supported by the HORIZON Europe project FUTURA on coordinated contributions to the IPCC and integrating the Integrated Assessment Modelling Consortium (IAMC), CMIP, CORDEX and ISIMIP, there will be capacities for the
- Completion of the ISIMIP4 ‘noadapt’ runs by their ‘adapt’ counterparts
- Additions of further scenarios (probably addressing overshoot dynamics) to the ISIMIP4 protocols
- Initialisation of a high-resolution ISIMIP4-Europe (and even an ISIMIP4-Africa) branch based on CORDEX simulations forced by the ISIMIP4 global climate models
- Accounting for additional requirements regarding DHFs.
This implies that the ISIMIP4a/4b simulation round will most probably also focus on overshoot dynamics, high-resolution experiments also outside of Europe, as well as regularly updated and improved counterfactual climate forcing data, though this is still depending on available capacities.
Upcoming priorities and key tasks for the IPCC AR7 submission deadline
The timeline for CMIP7-based impact studies to be submitted within the IPCC AR7 submission deadline for WGII will be quite tight. Therefore, we strongly encourage initiating ISIMIP3-based studies, particularly on impact attribution (ISIMIP3a), impact projections including changing socioeconomic conditions and adaptation measures (ISIMIP3b group III), and cross-sectoral studies but also paper ideas using the ISIMIP4 Fast Track data. The upcoming ISIMIP-CROSS-CASCADE workshop will be the perfect event to pitch paper ideas and coordinate with interested colleagues, so please don’t hesitate to get in touch if you would like to use this opportunity.
