CMIP7 and the Assessment Fast Track: Launching the Next Phase of Climate Model Intercomparison

The Coupled Model Intercomparison Project (CMIP) has long been a cornerstone of international climate research and assessment. The newly published article “An evolving Coupled Model Intercomparison Project Phase 7 (CMIP7) and Fast Track in support of future climate assessment” (Dunne et al., 2025) presents the scientific motivation and experimental framework for CMIP7 and outlines the revised mandatory Diagnostics, Evaluation, and Characterization of Klima (DECK) and optional Assessment Fast Track experiments designed to provide timely scientific input to upcoming policy assessments, including the seventh IPCC Assessment Report (AR7)

Published in Geoscientific Model Development, the article sets out the objectives, structure, and scientific rationale for the next phase of CMIP, CMIP7, continuing its legacy of coordinated multi-model experimentation and global collaboration.

Advancing Climate Science Through Coordinated Modelling Intercomparison

CMIP7 builds on the successes of CMIP6, aiming to support four overarching objectives: advancing scientific understanding of the Earth system, providing scenarios and projections, facilitating model evaluation, supporting climate services, and underpinning assessments such as the IPCC reports.

Key elements of CMIP7 include:

• Scientific framing of CMIP7 through a set of four fundamental research questions requiring new coupled modelling in line with WCRP 2019-2028 Science Objectives
• A robust core of long-standing mandatory “entry card” experiments (DECK) to ensure continuity.
• Updated and harmonised forcing datasets extending to at least 2021.
• New scenario experiments to reflect current and plausible future policy pathways.
• A suite of targeted diagnostics to understand effective radiative forcing, feedback processes, and carbon cycle responses.

The newly introduced Assessment Fast Track is a subset of CMIP7 experiments drawn from the community MIPs intended to support upcoming policy assessments and downstream climate services applications, such as regional downscaling (CORDEX), impacts modelling (ISIMIP), ice sheet modelling (ISMIP) and climate services (VIACS). This includes near-term policy-relevant scenarios, model characterisation experiments, attribution studies, and process understanding experiments designed to isolate key feedbacks and uncertainties in climate projections.

What’s New Since CMIP6?

While CMIP7 maintains continuity with CMIP6, in response to community feedback there are some important changes to address known gaps and evolving research needs:

1.Introduction of the Assessment Fast Track

A focused subset of experiments—aligned with pressing policy and scientific priorities—will provide data to support assessments, including the IPCC AR7 report.

2. Updated and Expanded Historical Forcings

CMIP7 incorporates improved datasets, with specific updates for solar variability, improved volcanic eruption representation, refined land-use change harmonisation, aerosols, and improved comparability of regional short-lived climate forcers (SLCFs) to observations. All historical forcing datasets are extended through to at least 2021.

3. New Scenario Experiments

CMIP7 sees a move away from the ‘business as usual’ vs ‘current policy’ framework for scenarios from CMIP6. Instead, CMIP7 features a ‘Medium’ (M) emissions scenario reflecting current policy, plus a suite of comparative scenarios representative of High (H) emissions (a “policy failure” scenario), and Medium Low (ML), Low (L), Very Low with Limited Overshoot (VLLO), and Very Low after High Overshoot (VLHO) emissions (different “mitigation policy success” futures).

4. Emissions-Driven Simulations

CMIP7 introduces a new focus on CO₂ emissions-driven simulations, providing a more realistic representation of how the climate responds to changes in emissions. New experiments include idealised ‘flat10’ experiments to estimates of the policy relevant Transient Response to Cumulative Emissions (TCRE) and Zero Emissions Commitment (ZEC) metrics.

5. Enhanced Model Documentation

There is now a greater emphasis on providing standardised documentation of models via the Essential Model Documentation protocol.

6. Coordination Support

A dedicated CMIP International Project Office (IPO), hosted by the European Space Agency since 2022, provides centralised support for the development and delivery of CMIP and community engagement practices. This enhances transparency and inclusivity across the global modelling community.

A Foundation for Model Intercomparison and a Pathway Towards CMIP Sustained Mode

CMIP7 and the Assessment Fast Track, through its research-driven foundation, represents a critical evolution in global Earth system model intercomparison. Its experiments are tailored not only to address key scientific questions but also to deliver information relevant to policymakers, planners, and the public. The paper also paves the way to the development of a CMIP sustained mode activity

For further details, see:

Dunne et al., (2025): An evolving Coupled Model Intercomparison Project phase 7 (CMIP7) and Fast Track in support of future climate assessment, Geosci. Model Dev., 18, 6671–6700, https://doi.org/10.5194/gmd-18-6671-2025, 2025.