Aug 7, 2023

Towards the definition of a solar forcing dataset for CMIP7

In 2017, solar forcing recommendations were provided for the 6th round of the Coupled Model Intercomparison Project (CMIP6), which for the first time included all relevant solar irradiance and energetic particle contributions (https://solarisheppa.geomar.de/cmip6). Since then, this dataset has been extensively used in climate model experiments and tested in various intercomparison studies. New datasets have also become available.

Recently, a SPARC SOLARIS-HEPPA and International Space Science Institute (ISSI) working group was established to review these recent achievements and to outline a roadmap for the construction of a revised and extended historical solar forcing dataset for the upcoming 7th round of CMIP (CMIP7). This working group has outlined the process in a document that has just come out as a GMD perspective discussion paper at https://gmd.copernicus.org/preprints/gmd-2023-100/

A vital aspect of this work is the need for community feedback, as this will ultimately help us to translate these suggestions into recommendations for CMIP7. The authors, led by CMIP7 Forcings Task Team member Bernd Funke, welcome constructive feedback on the GMD discussion paper. Your feedback can be submitted in the form of traceable community comments on the paper’s GMD page.

Discussion is open until 21 September 2023.

Paper details


The solar forcing prepared for the 6th round of the Coupled Model Intercomparison Project (CMIP6) has been used extensively in climate model experiments and has been tested in various intercomparison studies. Recently, an International Space Science Institute (ISSI) Working Group has been established to revisit the solar forcing recommendations, based on the lessons learned from CMIP6, and to assess new data-sets that have become available, in order to define a roadmap for building a revised and extended historical solar forcing data-set for the upcoming 7th round of CMIP. This paper identifies needs for improvements and outlines a strategy to address them in the planned new solar forcing dataset. Proposed major changes include the adoption of the new TSIS-1 solar reference spectrum for solar spectral irradiance and an improved description of top of the atmosphere energetic electron fluxes, as well as their reconstruction back to 1850 by means of geomagnetic proxy data. In addition, there is an urgent need to consider the proposed updates in the ozone forcing data-set in order to ensure a self-consistent solar forcing in coupled models without interactive chemistry. Regarding future solar forcing, we propose consideration of stochastic ensemble forcing scenarios, ideally in concert with other natural forcings, in order to allow for realistic projections of natural forcing uncertainties.


Funke, B., Dudok de Wit, T., Ermolli, I., Haberreiter, M., Kinnison, D., Marsh, D., Nesse, H., Seppälä, A., Sinnhuber, M., and Usoskin, I.: Towards the definition of a solar forcing dataset for CMIP7, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2023-100, in review, 2023.

Link to paper


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