Preprints
https://doi.org/10.5194/gmd-2021-412
https://doi.org/10.5194/gmd-2021-412
Submitted as: model evaluation paper
06 Jan 2022
Submitted as: model evaluation paper | 06 Jan 2022
Status: this preprint is currently under review for the journal GMD.

CMIP6 simulations with the compact Earth system model OSCAR v3.1

Yann Quilcaille1,a, Thomas Gasser1, Philippe Ciais2, and Olivier Boucher3 Yann Quilcaille et al.
  • 1International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria
  • 2Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, Université Paris-Saclay, CEA – CNRS – UVSQ, 91191 Gif-sur-Yvette, France
  • 3Institut Pierre-Simon Laplace, Sorbonne Université, CNRS 75252 Paris, France
  • anow at: Institute for Atmospheric and Climate Science, Department of Environmental Systems Sciences, ETH Zürich, Zürich, Switzerland

Abstract. While Earth system models (ESMs) are process-based and can be run at high resolutions, they are only limited by computational costs. Reduced complexity models, also called simple climate models or compact models, provide a much cheaper alternative, although at a loss of spatial information. Their structure relies on the sciences of the Earth system, but with a calibration against the most complex models. Therefore it remains important to evaluate and validate reduced complexity models. Here, we diagnose such a model the newest version of OSCAR (v3.1) using observations and results from ESMs from the current Coupled Model Intercomparison Project 6. A total of 99 experiments are selected for simulation with OSCAR v3.1 in a probabilistic framework, reaching a total of 567,700,000 simulated years. A first highlight of this exercise that the ocean carbon cycle of the model may diverge under some parametrizations and for high-warming scenarios. The diverging runs caused by this unstability were discarded in the post-processing. Then, each physical parametrization is weighted based on its performance against a set of observations, providing us with constrained results. Overall, OSCAR v3.1 shows good agreement with observations, ESMs and emerging properties. It qualitively reproduces the responses of complex ESMs, for all aspects of the Earth system. We observe some quantitative differences with these models, most of them being due to the observational constraints. Some specific features of OSCAR also contribute to these differences, such as its fully interactive atmospheric chemistry and endogenous calculations of biomass burning, wetlands CH4 and permafrost CH4 and CO2 emissions. The main points of improvements are a low sensitivity of the land carbon cycle to climate change, an unstability of the ocean carbon cycle, the seemingly too simple climate module, and the too strong climate feedback involving short-lived species. Beyond providing a key diagnosis of the OSCAR model in the context of the reduced-complexity models intercomparison project (RCMIP), this work is also meant to help with the upcoming calibration of OSCAR on CMIP6 results, and to provide a large group of CMIP6 simulations run consistently within a probabilistic framework.

Yann Quilcaille et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-412', Anonymous Referee #1, 04 Mar 2022
  • RC2: 'Comment on gmd-2021-412', Anonymous Referee #2, 04 May 2022
  • EC1: 'Comment on gmd-2021-412', Gunnar Luderer, 04 May 2022

Yann Quilcaille et al.

Yann Quilcaille et al.

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Short summary
The model OSCAR is a simple climate model, meaning its representation of the Earth system is simplified but calibrated on models of higher complexity. Here, we diagnose its latest version using a total of 99 experiments in a probabilistic framework and under observational constraints. OSCAR v3.1 shows good agreement with observations, complex Earth system models and emerging properties. Some points for improvements are identified, such as the ocean carbon cycle.