This document describes the versioning strategy for CMIP7 data specifications, including the data_specs_version global attribute.

1. Overview¶

CMIP7 files include three versioning-related global attributes:

2. Attribute Definitions¶

2.1 Conventions¶

Identifies the CF (Climate and Forecast) conventions version followed by the file.

• All CMIP7 data must conform to CF-1.12 or later
• This attribute is defined by CF conventions
• Software may parse this to check CF compliance

2.2 drs_specs¶

Identifies the Data Reference Syntax (DRS) used for file naming and directory structure.

• Fixed at MIP-DRS7 for all CMIP7 data
• Defines how filenames and directories are constructed
• Does not include the CV values themselves (only the structure)
• Allows software to know the "shape" of file paths without opening files

2.3 data_specs_version¶

Identifies the version of data specifications used when creating the file.

Initial value for CMIP7: MIP-DS7.1.0.0

The detailed versioning scheme (what triggers version increments) is still under discussion.

3. Current Version¶

MIP-DS7.1.0.0¶

Release date: February 2026

Components:

4. Versioning Policy¶

4.1 Key Constraint¶

Any changes to CVs or Data Request must NOT break data intercomparability.

This is a strict requirement for the CMIP7 Fast Track. Files produced under different data_specs_version values must remain comparable.

4.2 Permitted Changes¶

4.3 QA/QC Behaviour¶

• QA/QC should respect the data_specs_version recorded in the file
• Files are validated against the specifications that were in place when they were produced
• This allows modelling groups to publish data produced under previous (but still valid) specifications

5. Version History¶

Future versions will be documented here with detailed changelogs.

6. Background¶

This versioning strategy was developed through extensive discussion within the CMIP7 CV Task Team (January 2026). Key contributors: Guillaume Levavasseur, Zebedee Nicholls, Karl Taylor, Matthew Mizielinski, Martin Juckes.

The full discussion is archived in the WCRP-CMIP collaboration platform.

Key Design Decisions¶

1. Separate DRS from CVs: drs_specs identifies structure; data_specs_version covers CV content
2. Backward compatibility: New versions must not invalidate previously published data
3. QA/QC flexibility: Tools validate against the version in the file, not necessarily the latest
4. Transparency over complexity: A single version string cannot capture all nuances; detailed CHANGELOGs are essential

7. References¶

• CMIP7 Global Attributes Specification
• CMIP7 Controlled Vocabularies
• esgvoc Library