Turning the tide on climate modelling

Climate change is causing profound changes to the Earth’s ice cover, including the frozen surface of the ocean known as sea ice.

Sea ice covers approximately 15% of the ocean surface at some point during the year, and the winter advance and summer retreat of sea ice is one of the world’s largest seasonal cycles. It is crucial to the global climate system as it reflects sunlight and drives ocean circulation carrying cool water towards the equator. Loss of sea ice is one of the most sensitive indicators of climate change and an agent of climate change. Sea ice models are crucial components of earth system models used to forecast future scenarios for the global climate.

But there are inadequacies in sea ice models used in climate studies and Intergovernmental Panel on Climate Change (IPCC) reports have ‘low confidence’ in models of Antarctic sea ice. In particular, sea ice models miss key physical processes in the dynamic region between the open and ice-covered ocean, which controls the advance and retreat of the ice cover and is known as the marginal ice zone. The marginal ice zone is characterised by the presence of ocean waves generated by distant storms and an unconsolidated ice cover due to these waves.

A research project undertaken by Dr Jordan Pitt and Associate Professor Luke Bennetts from the School of Mathematical Sciences is seeking to understand the critical connections between ocean waves and sea ice in the marginal ice zone.

The constant action of ocean waves affects both the formation and destruction of sea ice. Whilst collecting accurate sea ice data is challenging in such a highly dynamic and variable environment, new expeditions are gathering data from both the Arctic and Antarctic.

“With this new data, we have the opportunity to develop better models of the interaction of ocean waves and sea ice and better understand the advance and retreat of sea ice,” explains Dr Pitt.

As applied mathematicians, the researchers are seeking to combine data with fundamental physics to derive equations that describe wave–ice interactions.

“By resolving physical processes underpinning the climate of the planet, climate models will be able to more precisely predict the response of sea ice cover to the changing climate,” says Dr Pitt.

The team have already made significant progress in developing physical models which incorporate more detailed information on wave–ice interactions, such as the breakup of the ice cover caused by waves. They are working to improve current large-scale versions of these models to incorporate in sea ice and wave prediction models.

Such models are important not only for the climate prediction but for weather forecasting in the region as well.

What’s next?

Current climate models are the culmination of specific technical knowledge across multiple research disciplines into a model of the most complex system humans have ever tried to understand. They are a remarkable achievement which would not be possible without specialised research into physical processes such as the focus of Dr Pitt’s project on the interaction of sea ice and ocean waves. 

“The next step will be to extend this work to produce a complete coupling between the atmosphere, ocean waves and the sea ice,” says Dr Pitt. “With thermodynamic and wave-ice models it would be possible to more precisely model the seasonal advance and retreat of the sea ice which would empower future climate models.”

The local effects that the team are interested in the medium term are collisions between sea ice, the break-up of sea ice, the effects of waves overtopping the sea ice and the drift of floes due to waves and currents.