10 Aug 2022
10 Aug 2022

Summer surface air temperature proxies point to near sea-ice-free conditions in the Arctic at 127 ka

Louise Claire Sime1, Rahul Sivankutty1, Irene Vallet-Malmierca1, Agatha M. de Boer2, and Marie Sicard2 Louise Claire Sime et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2Department of Geological Sciences, Stockholm University, Sweden

Abstract. The Last Interglacial (LIG) period, which had higher summer solar insolation than today, has been suggested as the last time that Arctic summers were ice-free. However, the latest suite of Coupled Modelling Intercomparison Project 6 Paleoclimate (CMIP6-PMIP4) simulations of the LIG produce a wide range of Arctic summer minimum sea ice area (SIA) results, ranging from a 30 % to 96 % reduction from the pre-industrial (PI). Sea ice proxies are also currently neither abundant nor consistent enough to determine the most realistic state. Here we estimate LIG minimum SIA indirectly through the use of 21 proxy records for LIG Summer Surface Air Temperature (SSAT) and 11 CMIP6-PMIP4 models for the LIG. We use two approaches. First, we use two tests to determine how skilful models are at simulating observed proxies for ΔSSAT (where Δ refers to LIG-PI). This identifies a positive correlation between model skill and the magnitude of ΔSIA: the most reliable models simulate a larger sea ice reduction. Averaging the most skilful two models yields an average SIA of 1.3 mill. km2 for the LIG. This equates to a 4.5 mill. km2, or a 79 %, SIA reduction from the PI to the LIG. Second, across the 11 models, the averaged ΔSSAT at the 21 proxy locations is inversely correlated with ΔSIA (r = -0.86). In other words, the models show that a larger Arctic warming is associated with a greater sea ice reduction. Using the proxy record-averaged ΔSSAT of 4.5 ± 1.7 K and the relationship between ΔSSAT and ΔSIA, suggests an estimated ΔSIA of 4.4 mill. km2 or 77 % less than the PI. The mean proxy-location ΔSSAT is well-correlated with the Arctic-wide ΔSSAT north of 60° N (r=0.97) and this relationship is used to show that the mean proxy record ΔSSAT is equivalent to an Arctic-wide warming of 3.7±0.1 K at the LIG compared to the PI. Applying this Arctic-wide ΔSSAT and its modelled relationship to ΔSIA, results in a similar estimate of LIG sea ice reduction of 4.5 mill. km2. The LIG climatological minimum SIA of 1.3 mill. km2 is close to the definition of a summer ice-free Arctic, which is a maximum sea ice extent less than 1 mill. km2. The results of this study thus suggest that the Arctic likely experienced a mixture of ice-free and near ice-free summers during the LIG.

Louise Claire Sime et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-594', Pepijn Bakker, 23 Aug 2022
  • RC2: 'Comment on egusphere-2022-594', Anonymous Referee #2, 06 Oct 2022

Louise Claire Sime et al.

Louise Claire Sime et al.


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Short summary
It is not known if the Last Interglacial (LIG) experienced Arctic summers that were sea ice-free: models show a wide spread in LIG Arctic temperature and sea ice results. Evaluation against sea ice markers is hampered by too few observations. Here, assessment of 11 climate model simulations against summer temperatures shows that the most skilful models have a 77–79 % reduction in LIG sea ice. A LIG area of sea ice (1.3 mill. km2) indicates a likely mix of ice-free and near ice-free LIG summers.