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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2020-17
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-17
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 19 Feb 2020

Submitted as: research article | 19 Feb 2020

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This preprint is currently under review for the journal CP.

PlioMIP2 simulations using the MIROC4m climate model

Wing-Le Chan1 and Ayako Abe-Ouchi1,2 Wing-Le Chan and Ayako Abe-Ouchi
  • 1Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, 277-8564, Japan
  • 2National Institute for Polar Research, Tachikawa, 190-8518, Japan

Abstract. The second phase of the Pliocene Model Intercomparison Project (PlioMIP2) has attracted many climate modelling groups in its continuing efforts to better understand the climate of the mid-Piacenzian warm period (mPWP) when atmospheric CO2 was last closest to present day levels. Like the first phase, PlioMIP1, it is an internationally coordinated initiative that allows for a systematic comparison of various models in a similar manner to PMIP. Model intercomparison and model-data comparison now focus specifically on the interglacial at marine isotope stage KM5c (3.205 Ma) and experimental design is not only based on new boundary conditions but includes various sensitivity experiments. In this study, we present results from long-term model integrations using the MIROC4m atmosphere-ocean coupled general circulation model, developed at the institutes CCSR/NIES/FRCGC in Japan. The core experiment, with CO2 levels set to 400 ppm, shows a warming of 3.1 °C compared to the Pre-Industrial, with two-thirds of the warming being contributed by the increase in CO2. Although this level of warming is less than that in the equivalent PlioMIP1 experiment, there is a slightly better agreement with proxy sea surface temperature (SST) data at PRISM3 locations, especially in the northern North Atlantic where there were large model-data discrepancies in PlioMIP1. Similar changes in precipitation and sea ice are seen and the Arctic remains ice-free in the summer. However, unlike PlioMIP1, the Atlantic Meridional Overturning Circulation (AMOC) is now stronger than that of the Pre-Industrial, even though increasing CO2 tends to weaken it. This stronger AMOC is a consequence of a closed Bering Strait in the PlioMIP2 paleogeography. Also, when present day boundary conditions are replaced by those of the Pliocene, the dependency of the AMOC strength on CO2 is significantly weakened. Sensitivity tests show that lower values of CO2 give a global SST which is overall more consistent with the PRISM3 SST field presented in PlioMIP1. Inclusion of dynamical vegetation and the effects of all realistic orbital configurations should be considered in future experiments using MIROC4m for the mPWP.

Wing-Le Chan and Ayako Abe-Ouchi

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Wing-Le Chan and Ayako Abe-Ouchi

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Latest update: 04 Apr 2020
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Short summary
We carry out several modelling experiments to investigate the climate of the mid-Piacenzian warm period (~ 3.205 Ma) when CO2 levels were similar to those of present day. The global surface air temperature is 3.1 °C higher compared to the Pre-Industrial. Like previous experiments, the scale of warming suggested by proxy sea surface temperature (SST) data in the northern North Atlantic is not replicated. Global and tropical SST show much better agreement when CO2 levels are below 400 ppm.
We carry out several modelling experiments to investigate the climate of the mid-Piacenzian warm...
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