PlioMIP2 simulation with NorESM-L and NorESM1-F

Abstract. As a continuation of the Pliocene Model Intercomparison Project (PlioMIP), PlioMIP Phase 2 (PlioMIP2) coordinates a wide selection of different climate model experiments aimed at further improving our understanding of the climate and environments during the late Pliocene with updated boundary conditions. Here we report on PlioMIP2 simulations carried out by the two versions of the Norwegian Earth System Model (NorESM), NorESM-L and NorESM1-F, with updated boundary conditions derived from the Pliocene Research, Interpretation and Synoptic Mapping version 4 (PRISM4). The two NorESM versions both produce warmer and wetter Pliocene climate. Relative to the pre-industrial period, the simulated Pliocene global mean surface air temperature is 2.1 ℃ higher with NorESM-L and 1.7 ℃ higher with NorESM1-F, respectively, and the corresponding global mean sea surface temperature enhances by 1.5 ℃ and 1.2 ℃. The simulated precipitation for the Pliocene increases by 0.14 mm day−1 globally in both model versions, with large responses in the tropics and especially in monsoon regions. In the simulated warmer and wetter Pliocene world, Atlantic meridional overturning circulation (AMOC) become deeper and stronger, with the maximum AMOC levels increasing by ~ 9 % (with NorESM-L) and ~ 15 % (with NorESM1-F), while the meridional overturning circulation slightly strengthens in the Pacific and Indian Oceans. Although the two models produce similar Pliocene climates, they also generate some differences, in particular for the Southern Ocean, which should be investigated through the PlioMIP2 in the future. As compared to PlioMIP1, the simulated Pliocene warming with NorESM-L is weaker in PlioMIP2, but otherwise show very similar responses.