Abstract
Abstract. The mid-Piacenzian warm period (3.264 to 3.025 Ma) is the most recent geological period with present-like atmospheric pCO2 and is thus expected to have exhibited a warm climate similar to or warmer than the present day. On the basis of understanding that has been gathered on the climate variability of this interval, a specific interglacial (Marine Isotope Stage KM5c, MIS KM5c; 3.205 Ma) has been selected for the Pliocene Model Intercomparison Project phase 2 (PlioMIP 2). We carried out a series of experiments according to the design of PlioMIP2 with two versions of the Institut Pierre Simon Laplace (IPSL) atmosphere–ocean coupled general circulation model (AOGCM): IPSL-CM5A and IPSL-CM5A2. Compared to the PlioMIP 1 experiment, run with IPSL-CM5A, our results show that the simulated MIS KM5c climate presents enhanced warming in mid- to high latitudes, especially over oceanic regions. This warming can be largely attributed to the enhanced Atlantic Meridional Overturning Circulation caused by the high-latitude seaway changes. The sensitivity experiments, conducted with IPSL-CM5A2, show that besides the increased pCO2, both modified orography and reduced ice sheets contribute substantially to mid- to high latitude warming in MIS KM5c. When considering the pCO2 uncertainties (+/-50 ppmv) during the Pliocene, the response of the modeled mean annual surface air temperature to changes to pCO2 (+/-50 ppmv) is not symmetric, which is likely due to the nonlinear response of the cryosphere (snow cover and sea ice extent). By analyzing the Greenland Ice Sheet surface mass balance, we also demonstrate its vulnerability under both MIS KM5c and modern warm climate.
Highlights
The mid-Piacenzian warm period (MPWP; 3.264 to 3.025 Ma) is the most recent geological period with a present-like pCO2 concentration and exhibited significant warming relative to today
The warming in Eoi400 relative to PlioMIP1 can be attributed to the closure of the Bering Strait and the Canadian Arctic Archipelago, which is the major difference in the boundary conditions between these two experiments
We describe the results of modeling the warm interglacial MIS KM5c (3.205 Ma), located in the MPWP interval of 3.0–3.3 Ma, while driving the model with the new PRISM4 boundary conditions (Dowsett et al, 2016)
Summary
The mid-Piacenzian warm period (MPWP; 3.264 to 3.025 Ma) is the most recent geological period with a present-like pCO2 concentration and exhibited significant warming relative to today. This interval has been intensively studied during the past 3 decades as this time period is generally considered to be a potential analog of the future warmer climate. The reconstructed pCO2 for the MPWP ranges from 350 to 450 ppmv (Bartoli et al, 2011; Pagani et al, 2010; Martínez-Botí et al, 2015), which bracket the present-day level. The MPWP is thought to be globally warmer by 2–4 ◦C than pre-industrial climate (e.g., Dowsett et al, 2009). A large warming amplification of 7–15 ◦C is estimated in Arctic regions derived
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