Quantifying Human Influence on Ocean Melting of the West Antarctic Ice Sheet

The West Antarctic Ice Sheet (WAIS) is a huge slab of glacier ice about the size of Europe, and a few kilometres thick. Satellite observations show that the WAIS is losing ice, and this is causing global sea level to rise. If the current rate of ice loss continues, the WAIS alone will cause 50 cm of global sea-level rise by 2100. The ice loss is caused by increased ocean melting beneath areas of floating glacial ice called ice shelves. In the Amundsen Sea region of Antarctica, ocean melting is causing the ice shelves to thin very rapidly.

The ultimate cause of these changes in melting is not known. Earth's climate experiences large natural variations, and we know that these variations have a strong influence on the Amundsen Sea. As a result, we don't know whether the increased melting of the WAIS is caused by human-induced climate change, or by natural variability. This project will address that question.

Scientists in the UK and Japan are leading the world in developing computer models of the ice and ocean in the Amundsen Sea. We will force these models with a wide range of atmospheric conditions for the past and future, including both natural variability and human-induced changes. These forcings will be taken from global climate model simulations. By considering the results of all these models together, and averaging over many possible examples of the natural variability, we will be able to determine the importance of human-induced changes.

In order to be confident in these results, we need to know what ocean processes are causing the model behaviour that we find. We will quantify the importance of different processes by progressively disabling each process in the model and investigating the result. We must also be sure that the models are a good representation of ocean conditions in the region. However, this is difficult because the Amundsen Sea is remote and very poorly observed. To provide the crucial model validation, we will create a new record of ocean currents in the region over the last 25 years, using the latest satellite processing techniques to determine ocean currents even in regions covered by thick sea ice.

These results will allow us to determine whether the present ice loss was caused by human activities in the past, and whether melting in the future can be reduced by lower emissions of greenhouse gases. This will enable politicians and the public to decide how best to respond to sea-level rise from the WAIS.

Our conclusions will form key evidence addressing the question of anthropogenic forcing of sea-level rise, which must be communicated at a range of levels.

At the international level, the Intergovernmental Panel on Climate Change (IPCC) is the primary forum by which such findings are communicated to policymakers. The project team has a strong track record of involvement with the IPCC, including authoring the Special Report on Oceans and the Cryosphere and the Fifth Assessment Report. We are well-placed to lead the pull-through of our science into forthcoming reports.

Further opportunities for international impact will be afforded by our extensive external links. For example, Holland co-authored the State of the Polar Oceans report, commissioned by the UK Foreign and Commonwealth Office and the Norwegian Ministry of Foreign Affairs, and Jenkins is Chair of the Forum for Research into Ice Shelf Processes, an expert group of the Scientific Committee on Antarctic Research.

At the national level, our research will be communicated in many ways, including direct routes to key stakeholders, for example through Naveira Garabato, who sits on NERC Science Board; Aoki, whose work is integral to the current program of the Japanese Antarctic Research Expedition; and Jenkins, who sits on the NERC-Met Office Joint Marine Modelling Programme.

Our results will further be communicated to the general public through a project website and Twitter account, BAS and JAMSTEC joint press releases, and public lectures that include simple laboratory experiments illustrating the dynamics of marine ice sheets. The UK-Japan elements of the project will be particularly emphasised, highlighting that Antarctica provides an exemplar of international scientific collaboration.