Retreat of Southern Hemisphere Sea Ice, 127 000 years BP

In Retreat of Southern Hemisphere Sea Ice, 127 000 years BP

Our Research

Retreat of Southern Hemisphere Sea Ice, 127 000 years BP

Start date: 1 January, 2017
End date: 31 December, 2021

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Sea ice is the cause of the largest uncertainties in climate model projections of polar change in the Southern Hemisphere (SH). During the Last Interglacial (LIG), between 130 000 and 116 000 years Before Present (BP), there was a substantial retreat in Southern Hemisphere sea ice. This period provides an excellent analogue for the decrease of up to 58% in SH sea ice predicted for the end of the 21st century.

**September SH sea ice concentration**: a) observed mean sea ice concentration since 1979 (**NASA-TEAM**), b) modelled mean sea ice concentration during the last interglacial period (**Holloway at al., 2016**), c) projection for the future state of sea ice concentration (mean calculated over the period 2100-2200) as predicted by the UK Earth System Model under the CMIP5 high-emissions scenario (Stocker et al, 2013).
The dashed line represents the sea ice extent calculated using a standard 15% concentration threshold.

Our group recently identified a substantial retreat (of 50-60%) in Southern Hemisphere (SH) sea ice during the Last Interglacial period (Holloway et al., 2016, Nature Comms; Holloway et al. 2017, GRL). See Our Research for details.

According to the most recent IPCC report, sea ice is expected to decline in both the Southern and Northern Hemispheres in the future. In particular, current climate models predict a reduction of the Antarctic sea ice of about 50–60% by the next two centuries. The analogy between the Last Interglacial and the projected sea ice retreat events offers a unique opportunity to improve our understanding of what drives a (major) sea ice retreat. Indeed, while reconstructions of the last interglacial sea ice extent are based on (and constrained by) ice cores evidences, projections of the future sea ice extent cannot be tested against any existing data.

In this NERC-funded project, we will test a set of hypotheses on the causes of the LIG sea ice retreat and assess whether the UK’s Coupled Model Intercomparison 6 (CMIP6) model (UKESM1) can accurately simulate a major Southern Hemisphere sea ice retreat.

By delivering the lig127k experiment for the CMIP6 archive (Otto-Bleisner et al., 2017), this work will be part of the UK’s contribution to the next Coupled Model Intercomparison project. See the CMIP6 section for details.

This work is supported by the 2017-2020 NERC grant NE/P013279/1 and the 2016-2019 NSFGEO-NERC grant NE/P009271/1.

References

Holloway, Max D., et al. “Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse.” Nature communications 7 (2016): 12293.

Holloway, Max D., et al. “The spatial structure of the 128 ka Antarctic sea ice minimum.” Geophysical Research Letters 44.21 (2017).

Otto-Bleisner, Bette L., et al. “The PMIP4 contribution to CMIP6–Part 2: Two interglacials, scientific objective and experimental design for Holocene and Last Interglacial simulations.” Geoscientific Model Development 10.11 (2017): 3979-4003.