Project 2436 sy: Defining a common PMIP-carbon protocol (PMIP)

The PMIP-carbon community is drafting a shared science plan and experimental design in order to perform coupled climate-carbon simulations within the next phase of PMIP.

Abstract

Simulating the carbon cycle during past climates provides a unique opportunity to investigate the importance of different mechanisms contributing to glacial-interglacial atmospheric pCO2 variations and to evaluate the model representation of biogeochemical processes. Confronting these simulation results within intercomparison
projects (such as PMIP) can then improve our understanding of model behaviours and biases.

However, the first opportunistic phase of PMIP-carbon (2019-2021) highlighted the need for a common protocol: we achieved the participation of nine climate models, but the various modelling choices related specifically to the carbon cycle undermined the interpretation of the model ensemble as a whole (Lhardy et al., 2021; Bouttes et al.,
2021). Still, preliminary results within the PalMod project (Liu et al., in prep) demonstrate again that a structured effort of different modelling groups has great potential to achieve comparable model outputs and address outstanding scientific questions which are still not elucidated despite decades of research.

Thanks to the support of a single-year project from INQUA, the opportunity of a wider-scale and more robust intercomparison phase for coupled carbon-climate simulations under past conditions is arising again at the start of a new CMIP7/PMIP5 phase. Our project has thus organized a workshop to gather much-needed community input, in view of publishing a PMIP-carbon protocol paper.

Objectives:

• define key questions and experiments to be prioritized during CMIP7/PMIP5;
• assess feasibility of simulations; discuss challenges, barriers and facilitators, in view of reaching the best compromise between a shared protocol and maximum inclusiveness for models of various complexity;
• establish a long-term strategy to extend the initial project.

Project leaders:

• Fanny Lhardy, France
• Nathaelle Bouttes, France
• Bo Liu, Germany