The first reason for warming

The Antarctic ice sheet was formed relatively recently in geological terms. “I think most people would say the ice sheet first formed in Antarctica 34 million years ago. Before that, most of the ice sheet was similar to northern Canada today; tundra and coniferous forests.”– says Eric Wolf, a paleoclimatologist at the University of Cambridge.

Global temperature is a major factor affecting the size of the ice sheet. Closed 50 million years ago the world was about 14 degrees warmerwas higher than today, but temperatures decreased steadily over the next 16 million years. By 34 million years ago, a time period known as the Eocene-Oligocene boundary, the climate was already 8 degrees Celsius warmer than today.

So what caused such a drop in temperature and was it enough for the ice sheet to form?

There are two factors, and both were probably at play. One is the change in the concentration of carbon dioxide in the atmosphere, the other is the movement of the continents, and in particular the opening of the Drake Passage, the strait between South America and Antarctica that connects the South Atlantic with the South Pacific Ocean.
– says Wolf.

The more carbon dioxide in the atmosphere, the more heat is trapped and the hotter the planet becomes, which is exactly how our current global warming works. About 60 to 50 million years ago, the concentration of carbon dioxide in the Earth’s atmosphere was very high, somewhere between 1,000 and 2,000 parts per million. 2.5-5 times higher than today’s level.

Tina van de Flierdt of Imperial College London says it is well known to science that carbon dioxide levels fell between the Eocene and Oligocene. This decline was accompanied by a cooling of the global climate, which would have likely led to the formation of ice sheets.

The reason is the second

But that’s not the only reason why Antarctica is freezing. Eric Wolf adds that local cooling on the continent is also likely due to: plate tectonicsAround the time carbon dioxide concentrations dropped, South America and Antarctica finally separated from each other, opening up what is now called the Drake Passage.

This has led to a circular current of water moving around Antarctica. This isolates Antarctica from the rest of the world and makes it much harder for warm air masses to penetrate the Southern Ocean, making Antarctica colder.
– explained Wulf.

Drake Strait on the world map / Collage 24 Channel / Google

Plate tectonics also directly affect carbon dioxide levels, he added. Rock weathering and volcanic activity are part of the carbon cycle, so geological processes can change the balance of gases in the atmosphere over thousands of years.

Although some uncertainties remain, researchers are fairly certain that this transition occurred 34 million years ago, as can be seen from chemical traces in rock sediments.

When you look at oxygen isotopes in the carbonate shells of tiny marine organisms in ocean sediments, you see a jump of about 34 million years ago.
– says Wolf.

The future of Antarctica

As for whether Antarctica could become ice-free again, “it’s certainly possible,” says Tina van de Flierdt: “Planet Earth has done it before. Planet Earth can do it again.”

He added that while human activity is unlikely to lead to complete melting of the ice sheet, it is important to do everything possible to limit ice loss in Antarctica.