01 Aug 2022
01 Aug 2022
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Internal climate variability and spatial temperature correlations during the past 2000 years

Pepijn Bakker1, Hugues Goosse2, and Didier M. Roche1,3 Pepijn Bakker et al.
  • 1Department of Earth Sciences, Vrije Universiteit Amsterdam, the Netherlands
  • 2Earth and Life Institute (ELI), UCLouvain, Louvain-la-Neuve, Belgium
  • 3Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, Université Paris-Saclay, Gif-sur-Yvette, France

Abstract. The spatio-temporal structure of natural climate variability has to be taken into account when unraveling observed climatic changes and simulate future climate change. However, based on the comparison of temperature reconstructions and climate model simulations covering the past two millenia, it has been argued that climate models are biased. They would simulate too little temporal temperature variability and too high correlations between temperature time series from different continents. One of the proposed causes is the lack of internal climate variability in climate models on centennial time scales, for instance variability related to the Atlantic Meridional Overturning Circulation (AMOC).

We present a perturbed-parameter ensemble with the iLOVECLIM earth system model containing various levels of AMOC-related internal climate variability to investigate the effect on the spatio-temporal temperature variability structure. The model ensemble shows that indeed enhanced AMOC variability leads to more continental-scale temperature variability, but it also increases the spatio-temporal temperature correlations between different continents. However, combining the iLOVECLIM results with CMIP5 model results and various PAGES-2K temperature field reconstructions, we find that neither model results or reconstructions are robust. We show overall agreement for the magnitude of continental temperature variability in models and reconstructions, but both the simulated and the reconstructed ranges are large. This is even more true when considering higher order metrices like inter-continental temperature correlations or temperature variability land-sea contrasts. For such metrices, uncertainties in both model results and temperature reconstructions are so large that they hamper our ability to constrain simulated spatio-temporal structure of centennial temperature variability. As a result, we cannot determine the importance of AMOC variability for the climatic evolution over the past two millenia.

Pepijn Bakker et al.

Status: open (until 26 Sep 2022)

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Pepijn Bakker et al.

Pepijn Bakker et al.


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Short summary
Natural climate variability plays an important role in the discussion of past and future climate change. Here we study centennial temperature variability and the role of large-scale ocean circulation variability using different climate models, geological reconstructions and temperature observations. Unfortunately, uncertainties in models and geological reconstructions are such that more research is needed before we can describe the characteristics of natural centennial temperature variability.