Not all Antarctic sea ice is the same—here are the finer details that will help you understand its impact on climate change
Antarctic sea ice was in the headlines for all the wrong reasons in 2023.
It started with the lowest extent ever recorded in January, based on a satellite record going back to 1978—a worrying sign in itself. Normally Antarctic sea ice reaches a minimum extent of around 3 million square km in February. In 2023, it could only muster around 2 million square km.
But what came later in the year really blew the socks off experts: not only was the extent at record lows for almost all the year, but the magnitude of this record was far beyond what many scientists considered possible at the start of the year.
There is usually a steady increase to a maximum of around 19 million square km in September, but in 2023 Antarctic sea ice didn’t even hit 17 million square km. The failure to grow this extra almost 2 million square km over winter is of huge concern and points to major upheavals in the climate system.
Researchers have been expecting Antarctic sea ice extent to start slowly shrinking for a while now—as the warming of the atmosphere and ocean takes hold—but it’s fair to say that this huge anomaly took climate scientists by surprise.
Full understanding of the 2023 Antarctic sea ice anomaly still eludes scientists, and while ice-ocean modellers work furiously toward the answers, there’s also the recognition that despite their best efforts, scientists still don’t know enough about many crucial properties of the sea ice.
Where is sea ice?
Because of the vast area occupied by the ice, satellite measurements hold the key to large-scale monitoring.
Since 1978 researchers have been able to determine the extent of sea ice on a near daily basis. This is done by polar-orbiting satellites which can observe the subtle microwave emissions from the surface, and these measurements continue to this day.
But extent is only one piece of the sea ice puzzle. To fully understand sea ice, more needs to be known about its properties, and the different types of sea ice which play different roles in the climate system.
What is sea-ice motion?
Like sea-ice extent, the drift speed of pack ice is what is called an essential climate variable.
Without knowledge of the motion of the sea ice, there would be no way of accounting for ice which is produced in one area and “exported” to another region—it would be like trying to understand a book by reading only its last page.
Again, thanks to satellite observations of the Earth, researchers have been able to remotely monitor sea-ice motion on a daily basis since the 1990s.