But knowledge of the sea-ice extent and motion are still not enough—scientists need to also know the ice’s thickness.

For a long time, satellite-based thickness measurements were considered the holy grail.

The most direct way to measure sea ice thickness on a global scale is with satellite altimetry—using the same technique as hardware store laser tape measures.

Satellites can send down a pulse of laser light or radar energy, measure the time taken for that signal to reflect off the ice and travel back, and then estimate the distance to the ice surface.

By calibrating this space-based tape measure using nearby sea surface height, they can accurately measure the height of the ice floating above the water, and hence estimate its thickness.

But this technique is tricky for two reasons: as with icebergs, only around 10 per cent of the ice thickness lies above the water; and researchers don’t accurately know the thickness or density of the overlying snow cover.

So although scientists have been able to estimate sea-ice thickness with altimeters since the 2000s, these estimates have had fairly large uncertainty.

Estimating the sea ice thickness, as well as that of its snow cover, are currently very active areas of research, but with more work, most researchers feel that the holy grail is nearly within their grasp.

Sea-ice extent, motion and thickness are three big-ticket items from researchers’ shopping lists, but they also need to know more about the sea ice to fully understand how it might change in the future.

One thing to know more about is where different types of ice are found around Antarctica.

Sea ice can be classified by its age, for example, first-year ice, which has not survived the summer melt versus multi-year ice; whether it moves (pack ice) or not (landfast ice, which is attached to the coastline or grounded icebergs); and whether or not it is affected by waves and swell from the open ocean (in the so-called marginal ice zone).

Each of these ice types has distinctly different climate roles and interactions—for example, in the marginal ice zone, ice floes can be broken by large waves, and this fracturing into smaller floes can result in accelerated melt in the springtime.

Understanding of different sea-ice types is progressing, and with the launch of more advanced satellites, researchers gain more knowledge each year, but knowledge of these ice types is still comparatively limited.

After every quantum leap in understanding of sea ice properties and types, climate modellers then implement this new knowledge into their models.

With each model generation, new complexity is added in order to represent ice in a more realistic way, and the resulting increase in model skill is investigated.

As an example, the third major version of the Australian Community Climate and Earth System Simulator ocean/ice model is now under development.

For the first time, researchers will soon be able to differentiate between pack and landfast ice, and include waves in order to represent the marginal ice zone in the model.

Accurate monitoring and modelling of this complex Earth system component is an expensive undertaking—leveraging billion-dollar, multi-national satellite constellations, sea-ice research voyages costing tens of millions of dollars, supercomputer time worth hundreds of thousands of dollars and researcher salaries to bring it all together.

But the societal cost of not being able to accurately understand and predict Antarctic sea ice is too great to comprehend, especially in an era of rapid climate change.

Dr Alexander Fraser is a senior research fellow with the Australian Antarctic Program Partnership at the University of Tasmania. He is a recipient of the 2024 Japan Society for the Promotion of Science BRIDGE Fellowship. His research interests are in the field of cryospheric remote sensing. He will begin an Australian Research Council-funded Future Fellowship investigating the puzzle of landfast sea ice in April.

Assistant Professor Takenobu Toyota works for the Institute of Low Temperature Science at Hokkaido University in Japan. His research interests include growth and decay processes of sea ice in the seasonal ice zone, ice floe size distribution, properties of sea ice and overlying snow, and estimation of ice thickness distribution with remote sensing.

Originally published under Creative Commons by 360info.

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