Abstract
Abstract. In the Pliocene Model Intercomparison Project (PlioMIP), two sets of experiments are suggested. One includes a reference and a mid-Pliocene experiment run with atmosphere general circulation models (AGCM experiments, referred to as Experiments I), the other includes a pre-industrial and a mid-Pliocene experiment run with coupled ocean-atmosphere general circulation models (AOGCM experiments, referred to as Experiments II). In this paper, we describe the AGCM experiments with the atmosphere component in the low-resolution version of the Norwegian Earth System Model (NorESM-L), and also assess the potential uncertainties in analyzing mid-Pliocene climate anomalies that might result from the choice of the sea surface temperature (SST) forcing for the reference experiment (pre-industrial or modern). We carry out a mid-Pliocene experiment, a control experiment forced by the modern SST fields, and a pre-industrial experiment forced by the monthly SST fields from HadISST averaged between 1879 and 1900. Our experiments illustrate that the simulated mid-Pliocene global mean annual surface air temperature (SAT) is 17.1 °C. It is 2.5 °C warmer than the control experiment, but 2.7 °C warmer than the pre-industrial experiment. We find that the uncertainties in analyses of mid-Pliocene climate anomalies are small on a global scale, but still large on a regional scale. On the regional scale, these uncertainties should be noted and assessed in future PlioMIP studies.
Highlights
The mid-Pliocene period, the most recent period in Earth’s history, is thought to be a potential analog for the long-term fate of the climate system in the coming future (e.g. Jansen et al, 2007; Dowsett et al, 2010; Meehl et al, 2007)
A recent midPliocene simulation (Lunt et al, 2010) and reconstruction of pCO2 in the Pliocene (Pagani et al, 2009) indicate that climate sensitivity to the Earth system feedbacks is larger than climate sensitivity to the fast feedbacks. δ18O records from coral skeletons found in Philippines demonstrate that permanent El Nino conditions did not exist during the Pliocene warm period (Watanabe et al, 2011)
In the coupled simulation with NorESM-L (Zhang et al, 2012), we find that the cldfrc rhminl set to 0.835 and the cldfrc rhminh set to 0.800 are the best options
Summary
The mid-Pliocene period, the most recent period in Earth’s history, is thought to be a potential analog for the long-term fate of the climate system in the coming future (e.g. Jansen et al, 2007; Dowsett et al, 2010; Meehl et al, 2007). In order to better understand the dynamics behind the mid-Pliocene warm climate, and to further reduce gaps between simulations and reconstructions, the Pliocene Model Intercomparison Project (PlioMIP) has been recently. The first set includes a reference and a mid-Pliocene experiment run with atmosphere-only climate models (AGCM experiments, referred to as Experiments I). The second set includes a pre-industrial and a midPliocene experiment run with coupled ocean-atmosphere climate models (AOGCM experiments, referred to as Experiments II). As the PlioMIP experimental guidelines suggest, the reference experiment is called pre-industrial experiment, but carried out based on local modern SST fields (Haywood et al, 2010). In this paper, we consider the potential influence of SST fields used in the reference experiment in analyses of the mid-Pliocene climate anomalies.
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