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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2018-180
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2018-180
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Jan 2019

Research article | 08 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

The HadCM3 contribution to PlioMIP Phase 2 Part 1: Core and Tier 1 experiments

Stephen J. Hunter, Alan M. Haywood, Aisling M. Dolan, and Julia C. Tindall Stephen J. Hunter et al.
  • University of Leeds, Leeds, LS2 9JT, UK

Abstract. We present the UK's input into the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) using the HadCM3 climate model. We outline the process of setting up HadCM3 with the enhanced PRISM4 boundary conditions and discuss in detail the assumptions and choices made. We then present the HadCM3 spin-up process from an initial arbitrary atmosphere, zero-momentum ocean state through to a well-equilibriated climatic state. We present data from the spin-up and final climatological mean state of the pre-industrial and Pliocene experiments. We focus on large-scale climatic and oceanic features. Comparing the control Pliocene experiment to pre-industrial the change in palaeogeography and CO2 combined account for a warming in globally integrated air temperature (sea surface temperature) of 1.4 °C (0.8 °C) and 1.5 °C (1.0 °C). For the pre-industrial and Pliocene we see climate sensitivities (for 2 × CO2) of 3.5 °C and 2.9 °C. We derive an approximation of Earth System Sensitivity of ~ 5.5 °C leading to an ESS / CS ratio ~ 1.90. Precipitation change is more complex, with geographic and land surface changes primarily modifying the geographical extent, and increasing CO2 leading to a general wet-get-wetter response. We see a reduction in summer and winter sea ice extent driven by both geographical – land surface changes and CO2 increase. In our model, the Atlantic Meridional overturning is relatively insensitive to CO2 but is strengthened in the Pliocene (from 15.7 to 19.6 Sv) due to the change in palaeogeography. Understanding the change in Antarctic Circumglobal Current within the Pliocene is problematic given an overly intense modern ACC and palaeogeography-driven changes in barotropic model set-up within the Pliocene. We confirm that the modern orbit used throughout PlioMIP2, is a satisfactory substitute for the Pliocene 3.205 Myr KM5c orbit in terms of large-scale climate and a number of important climatic indices. We also quantify the impact of the total solar irradiance choice (1361 versus 1365 W m−2) on the Pliocene – pre-industrial anomaly and absolute climatic state and highlight climatic systems which may present non-linear responses.

Stephen J. Hunter et al.
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Stephen J. Hunter et al.
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Short summary
In this paper we model climate of the mid-Piacenzian warm period (mPWP; 3 million years ago), a geological analogue for contemporary climate. Using the HadCM3 climate model we show how changes in CO2 and geography contributed to mPWP climate. We find mPWP warmth focussed in the high-latitudes, geography-driven precipitation changes and wetter-gets-wetter paradigm under increasing CO2, complex changes in sea surface temperature and intensified overturning in the North Atlantic (AMOC).
In this paper we model climate of the mid-Piacenzian warm period (mPWP; 3 million years ago), a...
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