Global Climate System Response to Antarctic Meltwater and Implications for Future Climate

Abstract

As the climate continues to warm, the Antarctic Ice Sheet and its surrounding floating ice shelves are becoming increasingly susceptible to rapid collapse. Despite the potential threat this poses to the global climate system, the effects of AIS meltwater are not considered by most existing coupled climate models, including those in the most recent Coupled Model Intercomparison Project (CMIP6). As such, there remains much uncertainty over the impact of this additional meltwater on current global climate change projections. Here we use the coupled atmospheric-ocean general circulation model HadCM3-M2.1 to study the effect of a continuous meltwater discharge from the AIS on the global climate system. This involves carrying out a series of freshwater hosing experiments based on the newly proposed Southern Ocean Freshwater Input from Antarctica (SOFIA) Initiative. We find that 1150 years of continuous meltwater drives global atmospheric cooling, sea ice expansion in both hemispheres and a northward shift of the Intertropical Convergence Zone (ITCZ). Rapid freshening throughout the global oceans is also observed, resulting in the weakening of both the AMOC and AABW. This triggers pervasive ocean warming at depths greater than 5000m.

Two additional sensitivity studies are also conducted. Firstly, the sensitivity of the climate model response to a change in the horizontal distribution of AIS meltwater is tested. We find that changing the horizontal distribution of AIS meltwater input results in a delay in the freshening of water at depth. Additionally, anomalous warming of SATs is simulated in the northern most parts of the Arctic Ocean, resulting in sea ice in this region thinning. However, this does not have an impact on the global climate response to AIS meltwater.

Secondly, several key model parameters that have a large impact on the climate response to additional forcings are modified to investigate how sensitive the climate model response is to model tuning. The untuned version of the model simulated smaller changes in global SATs and sea ice, and the AMOC and AABW. Additionally, the model parameter changes had a significant impact on the ACC response to AIS meltwater. However, the climate response to AIS meltwater is relatively insensitive to the tuning implemented here.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Anita L Ganesan (Supervisor), Dan Lunt (Supervisor) & Tony Payne (Supervisor)