Abstract
Abstract. We present the UK's input into the Pliocene Model Intercomparison Project phase 2 (PlioMIP2) using the Hadley Centre Climate Model version 3 (HadCM3). The 400 ppm CO2 Pliocene experiment has a mean annual surface air temperature that is 2.9 ∘C warmer than the pre-industrial and a polar amplification of between 1.7 and 2.2 times the global mean warming. The Pliocene Research Interpretation and Synoptic Mapping (PRISM4) enhanced Pliocene palaeogeography accounts for a warming of 1.4 ∘C, whilst the CO2 increase from 280 to 400 ppm leads to a further 1.5 ∘C of warming. Climate sensitivity is 3.5 ∘C for the pre-industrial and 2.9 ∘C for the Pliocene. Precipitation change between the pre-industrial and Pliocene is complex, with geographic and land surface changes primarily modifying the geographical extent of mean annual precipitation. Sea ice fraction and areal extent are reduced during the Pliocene, particularly in the Southern Hemisphere, although they persist through summer in both hemispheres. The Pliocene palaeogeography drives a more intense Pacific and Atlantic meridional overturning circulation (AMOC). This intensification of AMOC is coincident with more widespread deep convection in the North Atlantic. We conclude by examining additional sensitivity experiments and confirm that the choice of total solar insolation (1361 vs. 1365 Wm−2) and orbital configuration (modern vs. 3.205 Ma) does not significantly influence the anomaly-type analysis in use by the Pliocene community.
Highlights
The Pliocene Model Intercomparison Project phase 2 has a dual focus: (1) to improve understanding of Pliocene climate and (2) to evaluate climate model uncertainty for a warmer-than-present climate
We have described the incorporation of PlioMIP2 (PRISM4) mid-Piacenzian (Pliocene) enhanced boundary conditions into the Hadley Centre Climate Model version 3 (HadCM3) global climate model
Compared to the pre-industrial control (E280), we find Pliocene surface warming focussed within the high latitudes and whose spatial distribution is similar to that obtained with HadCM3 for PlioMIP1 under PRISM3 boundary conditions www.clim-past.net/15/1691/2019/
Summary
The Pliocene Model Intercomparison Project phase 2 (hereafter PlioMIP2; Haywood et al, 2016) has a dual focus: (1) to improve understanding of Pliocene climate and (2) to evaluate climate model uncertainty for a warmer-than-present climate. This dual focus is referred to as Pliocene4Pliocene (P4P) and Pliocene4Future (P4F). The PlioMIP2 protocol specifies a standard and enhanced boundary condition dataset. We conduct all CORE and tier 1 experiments as well as the Pliocene4Future tier 2 experiments as described within Haywood et al (2016). The following definitions are used: pre-industrial (PI), tier 1 (T1), tier 2 (T2), Pliocene for Future (P4F), Pliocene for Pliocene (P4P) and total solar irradiance (TSI)
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