More modest peak temperatures during the Last Interglacial for both Greenland and Antarctica suggested by multi-model isotope simulations [preprint]

The Last Interglacial (LIG) period, approximately 130,000 to 115,000 years ago, represents one of the warmest intervals in the past 800,000 years. Here we simulate water isotopes in precipitation in Antarctica and the Arctic during the LIG, using three isotope-enabled atmosphere-ocean coupled climate models: HadCM3, MPI-ESM-wiso, and GISS-E2.1. These models were run following the Paleoclimate Modelling Intercomparison Project, phase 4 (PMIP4) protocol for the LIG at 127 ka (kilo-years ago), supplemented by a 3000-year Heinrich Stadial 11 (H11) experiment run with HadCM3. The long H11 simulation has meltwater from the Northern Hemisphere applied to the North Atlantic which causes large-scale changes in ocean circulation including cooling in the North Atlantic and Arctic and warming in the Southern and Global Ocean. We find that the standard 127 ka simulations do not capture the observed Antarctic warming and sea ice reduction in the Southern Ocean and Antarctic regions, but they capture around half of the warming in the Arctic. The H11 simulations align better with observations: they capture more than 80 % of the warming, sea ice loss, and δ18O changes for both Greenland and Antarctica. Decomposition of seasonal δ18O drivers highlights the dominant role of sea-ice retreat and associated changes in precipitation seasonality in influencing isotopic values in all simulations, alongside a small common response to orbital forcing. We use the H11 and multi-model 127 k simulations together to infer LIG surface air temperature (SAT) changes based on ice core measurements. The peak inferred LIG Greenland SAT increase is +2.89 ± 1.32 K at the NEEM ice core site. This is less than half the previously inferred warming. Peak inferred LIG Antarctic SAT increases are +4.39 ± 1.45 K at EDC, dropping to +1.67 ± 3.67 K at TALDICE. These calculated warming values are from climate effects alone, and do not take account of any ice flow or site elevation related impacts. Coastal sites in Greenland and Antarctica appear to have experienced less warming compared with higher central regions.

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