At the height of the last ice age, about 20,000 years ago, the sea level was 120 meters lower than it is today. As the weather warmed and the ice began to melt, sea levels rose rapidly.

At its peak, sea level was less than 4 cm per year, more than ten times the current rate. In a lifetime, the water will rise several meters. Global warming was much slower then than it is now.

How sea levels rise so fast in the past has long been a mystery to scientists, says Tigen Berends. He is a paleontologist at the University of Utrecht who studies the effects of climate change on ice sheets in the past and future.

(Part) The answer now seems to be in the picture: the instability at the edge of the iceberg. This causes the ice on land to quickly disappear into the sea, where it will melt and sea level rise. “The only thing we ‘ve been able to bring so far is that it’s causing such a rapid increase,” Berends said.

The ice sheet is receding faster and faster

Unstable ice sheets threaten to become a major problem in the future because global warming is still creating warmer oceans, causing Antarctic ice to melt faster.

The ice sheets at the South Pole are ‘supported’ by ice shelves. They are actually stretches of ice floating in the ocean. “Those ice shelves make sure the ice from the ice sheet that wants to flow into the ocean can’t do it as fast as it wants to,” Berends explains. “The ice shelf is on the way.”

If the ice shelf disappears or breaks due to overheating, the ‘contact line’ of the ice sheet may recede more quickly. That’s where the edge of the ice sheet lies at the bottom of the ocean, where it melts into a floating ice shelf.

If that retraction occurs when the ice sheet is on a slope as shown in the image below, more and more ice will be submerged. “As a result, more ice will flow into the water and the contact line will retract more,” Berends says. A vicious circle.

Much is unknown about the geography of Antarctica

Such a melting cycle is likely to occur on the Twaits Glacier in western Antarctica. Scientists Found Last year there were cracks in the ice shelf in front of that glacier, and it is feared that it will completely collapse in a few years. Then the ice loss from the glacier will increase rapidly and the sea level will rise significantly.

But it is not known exactly how many regions of Antarctica are susceptible to this phenomenon. We do not know much about the geology of large parts of the continent.

We know this from radar data. “There were explorations that went up the ice sheet using a radar station on the sled to measure how thick the ice was,” Berends says. “The continent is bigger than Europe, so you need a lot of such explorations.” That too in summer at temperatures tens of thousands of degrees below zero.

There are big differences between computer models

So it is still very uncertain how quickly the ice sheets will recede if the ice shelves disappear. To get an idea, the scientists conducted a digital experiment. Many universities have used their own computer models to estimate what would happen if all the ice sheets in Antarctica disappeared at once. This is not a realistic situation, Berends emphasizes, but is intended to give an idea of ​​the consequences of losing ice shelves.

Problem: The results of different models were far apart. While one model was expected to rise only 1 meter above sea level in 500 years, another model was expected to be no less than 12 meters. “There has to be a right answer,” Berends says. “But apparently we as ice model scientists have no clue.”

Where is the tipping point?

The disappearance of glaciers and glaciers in western Antarctica is likely to cause flooding in large parts of the Netherlands, raising the sea level by several feet. But we do not know how fast that rise will be, and it is not clear how hot the ice shelves will be to disappear.

“It simply came to our notice then Tipping point “If climate change exceeds that limit, the western Antarctic ice sheet will disappear one by one, due to warming of the atmosphere and partly warming oceans.”

No one knows where that tipping point is. “The best way to find out from an academic perspective is to let it happen, and then we’ll see,” says Berends. “But it’s already too late.”