Sea-ice-free Arctic during the Last Interglacial supports fast future loss

Abstract

The Last Interglacial (LIG), a warmer period 130-116 ka before present, is a potential analog for future climate change. Stronger LIG summertime insolation at high northern latitudes drove Arctic land summer temperatures 4-5 • C higher than the preindustrial era. Climate model simulations have previously failed to capture these elevated temperatures, possibly because they were unable to correctly capture LIG sea-ice changes. Here, we show the latest version of the fully-coupled UK Hadley Center climate model (HadGEM3) simulates a more accurate Arctic LIG climate, including elevated temperatures. Improved model physics, including a sophisticated sea-ice melt-pond scheme, result in a complete simulated loss of Arctic 1 sea ice in summer during the LIG, which has yet to be simulated in past generations of models. This ice-free Arctic yields a compelling solution to the longstanding puzzle of what drove LIG Arctic warmth and supports a fast retreat of future Arctic summer sea ice. Both land air temperatures and sea surface temperatures in high northern latitudes were considerably warmer during the LIG (≈ 130 000-116 000 years before present) 1-5 and global sea level was likely 6-9 m higher than present 6, 7. Previous climate model simulations of the LIG, forced by appropriate greenhouse gas (GHG) and orbital changes, have failed to capture the observed high temperatures 8-11. This suggests that these models may not have accurately captured Arctic key climate processes in warmer climates. Whilst knowledge of past Arctic temperatures is robust thanks to the available observations 2, 10 , interpretation of Arctic sea ice changes during the LIG has previously been afflicted by uncertainty 8, 10, 12, 13. Water-isotope measurements from ice cores have been interpreted to suggest that, alongside the Arctic warming, there was a reduction in mean annual sea ice area 8. Microfauna in LIG marine sediments recovered from boreholes on the Beaufort Sea Shelf have been interpreted as implying a lack of perennial Arctic sea ice cover 14 , as have planktonic foraminifera recovered from some Arctic marine cores 15, 16. Similarly, ostracodes on the Lomonosov and Mendeleyev Ridges and Morris Jesup Rise have been interpreted as indicative of minimum sea ice coverage during peak LIG warmth 17. On the other hand, measurements of the recently-developed sea ice proxy IP25 (a carbon-25 highly-branched isoprenoid lipid), when combined with terrestrial and open-water phytoplankton biomarkers, have been interpreted as evidence of perennial LIG ice cover in the central

Sea ice feedbacks influence the isotopic signature of Greenland ice sheet elevation changes: last interglacial HadCM3 simulations

“…The lowering of the elevation also leads to a weakened ice sheet barrier effect, permitting cyclonic systems to get into more central and northern areas of Greenland. These modelled results are in agreement with the findings of Merz et al (2014a) and Hakuba et al (2012), who show that a decrease in the height and size of the GIS weakens the barrier effect, permitting more moisture to be advected to the plateau. The reduction in cyclogenesis over the Norwegian Sea and off the southeast coast of Greenland due to lowering of the GIS elevation leads to the growth of further sea ice, especially during the winter months ( Fig.…”

A Comparison of the CMIP6midHoloceneandlig127kSimulations in CESM2

“…CESM2 has a high equilibrium climate sensitivity (ECS) of 5.3 °C (Gettelman et al, 2019); HadGEM3 similarly has a high ECS of 5.5 °C. Both predict an almost ice‐free or ice‐free Arctic in their lig127k experiments and the predicted year of disappearance of September sea ice in the SSP8–8.5 scenario of 2038 and 2035, respectively (Guarino et al, 2020). The CMIP6 and PMIP4 paleoclimate simulations with CESM2 combined with proxy reconstructions allow an assessment of whether this high ECS is plausible (Feng et al, 2020; Zhu et al, 2020).…”

Antarctic Ice Sheet Elevation Impacts on Water Isotope Records During the Last Interglacial

“…It is less clear if the East AIS (EAIS) also reduced or expanded during interglacials (Sutter et al., 2020; Wilson et al., 2018). Last Interglacial (LIG) changes in insolation are also known to directly impact polar sea ice extent (Guarino et al., 2020; Kageyama et al., 2020).…”