Sea ice modelling for NZESM development
Antarctic sea ice comes as close as 1,600km to mainland New Zealand in winter. Sea ice fundamentally alters the atmosphere and is instrumental in generating storms that alter our weather. Using the NZESM, this project will investigate persistence and reversibility of the responses to increased freshwater melt and other anthropogenic climate drivers in the Southern Ocean, especially responses involving sea ice.
We intend to make improvements to sea ice representation in the NZESM available to all NZESM users, through porting code to the NeSI supercomputer Maui. Similarly, we will share improved flexibility in the NZESM’s ocean component. This significant work will make the NZESM straightforward for any authorised user to run.
In our first phase, we investigated the impacts of freshwater melt from icebergs and ice shelves that occur in a warming world. We simulated these impacts by artificially increasing the meltwater input to the Southern Ocean in the NZESM. We used fixed pre-industrial forcings, and then ‘idealised’ forcings to see how responses would change under different warming scenarios. We’ll continue this line of research, to determine persistence (or reversibility). We will analyse fresh water impacts on sea ice extent and ocean surface properties, both of which could have implications for New Zealand’s future climate, as well as the climate of countries further from the sea ice.
We’ll further determine whether the climate-related responses we found under idealised conditions hold up in a more realistic setting, when the meltwater input occurs simultaneously with realistic changes in greenhouse gases, stratospheric ozone, and other anthropogenic climate forcings.
Our aim is to ensure that the NZESM can be a ‘ready to use’ tool capable of calculating updated climate projections as new estimates of mass loss rates from specific ice shelves become available. It will be suitable for research into the potential impacts of regionally-specific mass loss acceleration, making it possible to identify areas to target future observation effort.
Lastly, this flexibility will make the representation of ice shelf melt more realistic in the NZESM, by using up-to-date observations to account for spatial and temporal variability in melt rates, without the expense of coupling a dynamic ice sheet model.