21 Jun 2022
21 Jun 2022
Status: this preprint is currently under review for the journal CP.

Causes of the weak emergent constraint on climate sensitivity at the Last Glacial Maximum

Martin Renoult1, Navjit Sagoo1, Jiang Zhu2, and Thorsten Mauritsen1 Martin Renoult et al.
  • 1Department of Meteorology, Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 2Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, USA

Abstract. The use of paleoclimates to constrain the equilibrium climate sensitivity (ECS) has seen a growing interest. In particular, the Last Glacial Maximum (LGM) and the mid-Pliocene Warm Period have been used in emergent constraint approaches using simulations from the Paleoclimate Modelling Intercomparison Project (PMIP). Despite lower uncertainties regarding geological proxy data for the LGM in comparison with the Pliocene, the robustness of the emergent constraint between LGM temperature and ECS is weaker at both global and regional scales. Here, we investigate the climate of the LGM in models through different PMIP generations, and how various factors contribute to the spread of the model ensemble. Certain factors have large impact on an emergent constraint, such as state-dependency in climate feedbacks or model-dependency on ice sheet forcing. Other factors, such as models being out of energetic balance and sea-surface temperature not responding below -1.8 °C in polar regions have a limited influence. We quantify some of the contributions and find that they mostly have extratropical origins. Contrary to what has previously been suggested, from a statistical point of view, the PMIP model generations do not differ substantially. Finally, we show that the lack of high or low ECS models in the ensembles critically limits the strength and reliability of the emergent constraints.

Martin Renoult et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-52', Anonymous Referee #1, 02 Aug 2022 reply
  • CC1: 'Comment on cp-2022-52', Matthew Huber, 12 Aug 2022 reply

Martin Renoult et al.

Martin Renoult et al.


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Short summary
The relationship between Last Glacial Maximum and the sensitivity of climate models to a doubling of CO2 can be used to estimate the true sensitivity of the Earth. However, this relationship has varied in successive model generations. In this study, we assess multiple processes at the Last Glacial Maximum which weaken this relationship. For example, how models respond to the presence of ice sheets is a large contributor of uncertainty.