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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-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Feb 2020

Submitted as: research article | 04 Feb 2020

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This preprint is currently under review for the journal CP.

Contribution of the coupled atmosphere–ocean–sea ice–vegetation model COSMOS to the PlioMIP2

Christian Stepanek1, Eric Samakinwa1,2,3, and Gerrit Lohmann1,4 Christian Stepanek et al.
  • 1Alfred-Wegener-Institut - Helmholtz-Zentrum für Polar and Meeresforschung, Bremerhaven, Germany
  • 2Geographisches Institut, Universität Bern, Bern, Switzerland
  • 3Oeschger Centre for Climate Change Research, University of Bern, Switzerland
  • 4Institut für Umweltphysik, Universität Bremen, Bremen, Germany

Abstract. We present the Alfred Wegener Institute's contribution to the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) where we employ the Community Earth System Models (COSMOS) that include a dynamic vegetation scheme. This work builds on our contribution to Phase 1 of the Pliocene Model Intercomparison Project (PlioMIP1) where we employed the same model without dynamic vegetation. Our input to the PlioMIP2 special issue of Climate of the Past is twofold. In an accompanying manuscript we compare results derived with the COSMOS in the framework of PlioMIP2 and PlioMIP1. With the manuscript on hand we present details of our contribution with COSMOS to PlioMIP2. We provide a description of the model and of methods employed to transfer reconstructed Mid-Pliocene geography, as provided by the Pliocene Reconstruction and Synoptic Mapping Initiative, Phase 4 (PRISM4), to model boundary conditions. We describe the spin-up procedure for creating the COSMOS PlioMIP2 simulation ensemble and present large scale climate patterns of the COSMOS PlioMIP2 Mid-Pliocene core simulation. Furthermore, we quantify the contribution of individual components of PRISM4 boundary conditions to characteristics of simulated Mid-Pliocene climate and discuss implications for anthropogenic warming. When exposed to PRISM4 boundary conditions, the COSMOS provide insight into a Mid-Pliocene climate that is characterized by increased rainfall (+0.17 mm d−1) and elevated surface temperature (+3.37 °C) in comparison to the Pre-Industrial (PI). About two-thirds of the Mid-Pliocene core temperature anomaly can be directly attributed to carbon dioxide that is elevated w.r.t. PI. The contribution of topography and ice sheets to Mid-Pliocene warmth is in contrast much smaller – about one-fourth and one-eighth, respectively. The simulated Mid-Pliocene climate comprises pronounced polar amplification, a reduced meridional temperature gradient, a northward shifted tropical rain belt, an Arctic Ocean that is nearly free of sea ice during boreal summer, as well as muted seasonality in Northern Hemisphere high latitudes. Simulated Mid-Pliocene precipitation patterns are defined by both carbon dioxide and PRISM4 paleogeography. The COSMOS confirm longstanding characteristics of the Mid-Pliocene Earth System, among these increased meridional volume transport in the Atlantic Ocean, an extended and intensified equatorial warm pool, as well as pronounced poleward expansion of vegetation cover. By means of a comparison of our results to a reconstruction of sea surface temperature (SST) of the Mid-Pliocene we find that the COSMOS reproduce reconstructed SST best if exposed to a carbon dioxide concentration of 400 ppmv. In the Atlantic to Arctic Ocean the simulated Mid-Pliocene core climate state is too cold in comparison to the SST reconstruction. The discord can be mitigated to some extent by increasing carbon dioxide that causes increased mismatch between model and reconstruction in other regions.

Christian Stepanek et al.

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Christian Stepanek et al.

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Short summary
Future climate is expected to be warmer than today. We study potential future climate characteristics based on simulations of the Mid-Pliocene (about 3 million years ago), that is known to have been warmer than today. Our results are provided towards a comparison to both geologic evidence and output of other climate models. We simulate a Mid-Pliocene climate that is both warmer and wetter than today. Some of its characteristics can be more directly transferred to near-future climate than others.
Future climate is expected to be warmer than today. We study potential future climate...
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