Abstract

The Last Interglacial period (LIG, 129-116 thousand years ago, ka) represents a time when sea-level was at least 6 m higher than today and high latitude summer temperatures were several degrees warmer. For these reasons, along with reasonable palaeo-data coverage and temporal resolution, this time period provides an ideal opportunity with which to understand and test the climate and ice sheet mechanisms that operate under warm climates in order to more robustly inform on future warm climates and their impact on sea-level change.

The IPCC AR5 reported in its Summary for Policy Makers that during the LIG “…the Greenland ice sheet very likely contributed between 1.4 and 4.3 m to the higher global mean sea level, implying with medium confidence an additional contribution from the Antarctic ice sheet”. Here I review this potential reduction in ice-volume of the Greenland ice sheet 130-120ka, derived from modelling and data approaches.

Modelling the Antarctic component to sea-level change is more complex, however. Up until recently, climate model simulations of the LIG were compared with temperature reconstructions representing the warmest temperature for the whole time period, neglecting any temporal variation between regions (e.g. Turney & Jones, 2010). A new compilation (Capron et al, 2014) of high-latitude temperature changes across the LIG shows at 130ka non-synchronous maximum summer temperature changes between the two hemispheres with the Southern Ocean and Antarctica records showing early warming compared with North Atlantic records. Comparison with model simulations selected as part of an ‘ensemble of opportunity’ at the PMIP3 2012 General Meeting (Lunt et al. 2013) shows that the models predict warmer than present conditions earlier than documented in the North Atlantic records, while the reconstructed early Southern Ocean and Antarctic warming is not captured by any model. Not only does this comparison highlight the importance of producing defined time slices rather than one representative climate for the LIG but implies that important missing processes in the models are likely required to account for this temporal mismatch between data and model.

Here I show that by not neglecting the melt of ice sheets from the previous glaciation this mismatch between data and model can partially be resolved. This will have implications for modelling the stability of the West Antarctic Ice Sheet as it provides a mechanism by which to warm the Southern Ocean when other forcings were similar to today.