Articles | Volume 10, issue 1
Clim. Past, 10, 79–90, 2014

Special issue: Progress in paleoclimate modelling

Clim. Past, 10, 79–90, 2014

Research article 15 Jan 2014

Research article | 15 Jan 2014

Evaluating the dominant components of warming in Pliocene climate simulations

D. J. Hill1,2, A. M. Haywood1, D. J. Lunt3, S. J. Hunter1, F. J. Bragg3, C. Contoux4,5, C. Stepanek6, L. Sohl7, N. A. Rosenbloom8, W.-L. Chan9, Y. Kamae10, Z. Zhang11,12, A. Abe-Ouchi9,13, M. A. Chandler7, A. Jost5, G. Lohmann6, B. L. Otto-Bliesner8, G. Ramstein4, and H. Ueda10 D. J. Hill et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK
  • 2British Geological Survey, Keyworth, Nottingham, UK
  • 3School of Geographical Sciences, University of Bristol, Bristol, UK
  • 4Laboratoire des Sciences du Climat et de l'Environnement, Saclay, France
  • 5Sisyphe, CNRS/UPMC Univ. Paris 06, Paris, France
  • 6Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 7Columbia University – NASA/GISS, New York, NY, USA
  • 8National Center for Atmospheric Research, Boulder, Colorado, USA
  • 9Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan
  • 10Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
  • 11UniResearch and Bjerknes Centre for Climate Research, Bergen, Norway
  • 12Nansen-zhu International Research Centre, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 13Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

Abstract. The Pliocene Model Intercomparison Project (PlioMIP) is the first coordinated climate model comparison for a warmer palaeoclimate with atmospheric CO2 significantly higher than pre-industrial concentrations. The simulations of the mid-Pliocene warm period show global warming of between 1.8 and 3.6 °C above pre-industrial surface air temperatures, with significant polar amplification. Here we perform energy balance calculations on all eight of the coupled ocean–atmosphere simulations within PlioMIP Experiment 2 to evaluate the causes of the increased temperatures and differences between the models. In the tropics simulated warming is dominated by greenhouse gas increases, with the cloud component of planetary albedo enhancing the warming in most of the models, but by widely varying amounts. The responses to mid-Pliocene climate forcing in the Northern Hemisphere midlatitudes are substantially different between the climate models, with the only consistent response being a warming due to increased greenhouse gases. In the high latitudes all the energy balance components become important, but the dominant warming influence comes from the clear sky albedo, only partially offset by the increases in the cooling impact of cloud albedo. This demonstrates the importance of specified ice sheet and high latitude vegetation boundary conditions and simulated sea ice and snow albedo feedbacks. The largest components in the overall uncertainty are associated with clouds in the tropics and polar clear sky albedo, particularly in sea ice regions. These simulations show that albedo feedbacks, particularly those of sea ice and ice sheets, provide the most significant enhancements to high latitude warming in the Pliocene.