Understanding Antarctica’s impact on sea level rise

Will melting of the Antarctic Ice Sheet (AIS), Earth’s largest ice mass, cause global sea levels to rise by 5 metres, 2 metres or even less in the coming decades and centuries?

This is a difficult question to answer: the Antarctic and Southern Ocean environments are dynamic and unpredictable, which means there is uncertainty in our understanding of AIS behavior and how it will affect future sea-level rise.

Now scientists from Australia, the United States and Canada have identified actions that can help reduce uncertainties about projections of the ice sheet’s future trends and sea level rise.

Current data available from the Australian Antarctic Data Centre will also aid research to reduce the uncertainties faced by policy makers, decision makers and communities who need to plan and adapt to a changing world.

Sources of uncertainty

A research team led by Australian Antarctic Division glaciologist Dr Ben Galton-Fenzi reviewed research on the key processes and potential feedbacks that could be accelerating the AIS retreat.

“We looked at how Antarctica will affect sea level change over the coming decades and centuries, and where there are uncertainties that make it difficult to predict the future course of the ice sheet,” Dr Galton-Fenzi said.

“We then considered what processes and areas future scientific research should focus on to reduce these uncertainties.”

If the AIS were to melt completely, global sea levels would rise by about 58 metres. The massive East Antarctic Ice Sheet (covering two-thirds of the continent) would account for about 52 metres of this sea-level rise, with the West Antarctic Ice Sheet and the Antarctic Peninsula accounting for the rest.

Simply put, the Antarctic ice sheet expands as snowfall compresses into ice, and shrinks as icebergs calve and melt from beneath the ice shelves.

However, these physical processes and ice transport involve many complex interactions and feedback mechanisms, making the behaviour of the ice sheet difficult to predict, and critical thresholds, if exceeded, could dramatically increase Antarctica’s contribution to sea level rise.

Further uncertainties are due to the limitations of current climate and ice sheet models in simulating these physical processes and feedback mechanisms, and the lack of data that can capture physical processes at appropriate time and spatial scales.

Sea level rise is also occurring unevenly around the world due to what are called “gravitational, rotational, and deformation effects.”

“As the Antarctic ice sheet loses mass through melting and flowing into the ocean, the gravitational pull on the continent weakens, causing sea levels to fall closer to the continent and rise further away,” Dr Galton-Fenge said.

“The loss of ice mass and redistribution of water in the oceans also cause changes in the Earth’s rotation and shape, contributing to spatial variations in sea level.”

Areas for action

Among the priority areas for future research identified by the team are higher-resolution measurements focused on areas thought to be particularly vulnerable to rapid change, to better understand the physical processes affecting the ice sheet.

Building on these observations and improving our understanding will help improve models and analytical tools, leading to better predictions of sea level rise for effective policy decisions.

“Reducing the uncertainties associated with the Antarctic ice sheet and sea level rise can provide policy and decision makers with better information to develop coastal planning measures, resilient infrastructure and adaptation strategies,” Dr Galton-Fenzi said.

“Interdisciplinary and international collaboration, especially in areas vulnerable to the rapid retreat of the East Antarctic Ice Sheet, will accelerate progress in improving the overall quality of our research and reducing levels of uncertainty.”