The Sensitivity of Sea Ice and Ocean to the Representation of Antarctic Mass Loss in a Climate Model

Shona Mackie1, Inga Smith1, David P Stevens2, Jeff K Ridley3 and Pat Langhorne1, (1)University of Otago, Dunedin, New Zealand, (2)University of East Anglia, Norwich, United Kingdom, (3)Met Office, Hadley Centre for Climate Prediction and Research, Exeter, United Kingdom
Mass loss from Antarctica is increasing, but is constant in most climate models. We looked at the sensitivity of modelled sea ice and ocean to this assumption in the fully coupled climate model, HadGEM3-GC3.1. Firstly, we held all external forcings (except the mass loss) fixed in order to isolate effects attributable to this process, and then, in a second experiment, we increased CO2 by 1% per annum. Our findings address not only the sensitivity of the model to the increasing mass loss, but also whether the same sensitivities occur in a world of increasing CO2. Furthermore, we looked at whether the effects of the additional melt on sea ice and ocean could offset, or enhance, effects attributable to the rising CO2. Some models represent Antarctic mass loss as a surface melt flux around the coast, while in others the melt enters the ocean at depth. Icebergs are included in some models, either explicitly, or represented as a surface melt flux entering the ocean at some distance from the coast. In two further experiments, we assessed whether it was possible to discriminate between effects of increasing melt that are separately attributable to iceberg and ice shelf melt. Our results demonstrate the need for appropriate representation of these separate melt processes in climate models, and also provide insights into the effect of neglecting the increasing rate of mass loss in calculations of future climate.