Ice sheets and corals: tipping points threaten from as little as 1.5 degrees

Researchers have identified 16 tipping points in the climate system. In an interview, the polar researcher Winkelmann explains what these mechanisms are and why some of them could be triggered from a global warming of 1.5 degrees.

tagesschau.de: The Paris climate agreement aims to ensure that our earth does not warm up to more than 2 and if possible not more than 1.5 degrees. You write in one Study shows that there is already a risk of changes starting from this rise in temperature, which will be irreversible. What exactly could happen?

Ricarda Winkelmann: It’s about so-called tipping points. These are key parts of the climate system where, once in a critical state, a small perturbation like a rise in temperature is enough to trigger really big changes.

For example, the Greenland Ice Sheet is one such tipping element. And we all know the mechanism that makes Greenland a tipping element from mountaineering: when we descend from the top of a mountain into the valley, it gets warmer around us. And it’s the same with the ice sheets. If the surface of the ice sheets melts, which we are already seeing in Greenland, then at some point the surface may sink to lower elevations. It then gets warmer there, which leads to even more melting, the surface sinks further, it gets warmer again and so on.

In other words, it is a self-reinforcing mechanism that, at a critical point, can lead to this momentum taking over and Greenland almost completely melting away.

“Some irreversible changes”

tagesschau.de: Science has identified 16 of these tipping points. They systematically recorded these in their study and evaluated the temperature rise at which their tipping points are triggered. For some it’s pretty quick.

Winkelmann: The tipping elements include, for example, the Antarctic ice sheet, the Amazon rainforest, the Atlantic-Ocean Circulation and the coral reefs. We now understand the mechanisms that turn these areas into tipping points and that there can also be irreversible changes.

And what we show in our study is that even at one and a half to two degrees – i.e. in the temperature range of the Paris climate agreement – we come into this risk area for some of these tipping elements. However, the two ice sheets on Greenland and in the Antarctic are among the most vulnerable tipping elements, as are the coral reefs.

The problem is “self-reinforcing mechanisms”

tagesschau.de: With rising temperatures, there are more and more extreme weather events worldwide. Does this extreme weather also exist in polar regions?

Winkelmann: Yes, there is also extreme weather on the ice. For example, just last year we observed an extreme melting event on the Greenland ice sheet. This is one in a whole series of extreme melt events. It was caused by a high pressure area that got stuck over Greenland and then just increasingly led to the melt. And in extreme cases, for example in 2012, this meant that almost the entire surface of the ice sheet was covered with meltwater for several days.

tagesschau.de: Why does the temperature rise especially at the poles?

Winkelmann: The temperature rises in the polar regions even faster than the global mean temperature. And that’s because of what’s called polar amplification. This is an effect that comes about again through such a self-reinforcing mechanism, namely the so-called ice albedo feedback.

You can imagine it like this: Everyone knows that a dark surface absorbs more radiation than a light surface. Bright surfaces, on the other hand, reflect more. And that’s how it is on a large scale, so to speak, in the climate system. Bright surfaces – such as the ice surfaces – radiate part of the solar radiation back into space and have a cooling effect, so to speak.

However, as the ice melts, the bright surface decreases. Instead, the dark ocean surface appears, which we are already increasingly observing in the Arctic. So it gets darker and thus, so to speak, warmer again. And that’s one of the effects that leads to this polar reinforcement.

tagesschau.de: In 2020 we had a temperature of 38 degrees in the Arctic for the first time. Did that surprise you?

Winkelman: Yes. You can’t really prepare for such extreme weather events. We all know that with global warming, extreme weather events are also increasing in frequency, becoming more severe and also lasting longer. But that’s why you can’t necessarily predict individual events and in this respect the high temperatures of 38 degrees in the Antarctic and 18 degrees on the Antarctic Peninsula were a surprise for us too. So record temperatures from pole to pole.

What is happening under the ice?

tagesschau.de: What do you still need to understand scientifically better in polar research?

Winkelmann: One of the greatest uncertainties is what is actually happening under the ice. Because of course we can’t take a good look at it. There are observation techniques that you can use to try to take a closer look at the soil under the ice, for example. We know that the increased melting on the surface means that more meltwater gets into the ice sheet and thus also under the ice sheet, i.e. on the ground, and can lead to an acceleration of the ice flow. Simply by the fact that the ice slides on the water instead of being frozen to the ground.

And these are effects on the underside of the ice, where it is very important that we have more observations, collect more data in order to better understand what is actually happening under this ice, which is almost five kilometers thick in Antarctica.

tagesschau.de: Where is global warming easier to read at the moment: at the North or South Pole?

Winkelmann: Drastic changes can already be seen in both polar regions, including changes that surprised even us researchers. Sea ice is shrinking in the Arctic and it is expected that even under the most optimistic climate scenario, the Arctic will be ice-free for the first time in summer by mid-century. And that, of course, is a drastic change. One of the many in the ice landscapes.

We also see this in the mountain glaciers. I myself was in the Andes two years ago and went there to examine the glaciers for microplastics. When climbing the Chimborazo, we actually expected a glacier at around 5000 meters and wanted to take our measurements there. And when we got there – as you can imagine, that’s quite an arduous way at high altitude – we had to realize that the glacier tongue was actually no longer where we would have expected it to be a few years ago. And that was one of those moments where I saw how strongly and really comprehensively we are intervening in the climate system.