Researchers have identified 16 turning points in the climate system. In an interview, polar researcher Winckelmann explains what these mechanisms are and why some of them could be triggered by 1.5 degree global warming.

tagesschau.de: The Paris climate agreement aims to ensure that the Earth’s temperature does not rise to more than 2 degrees, and if possible no more than 1.5 degrees. write in one The study shows that there is indeed a risk of changes starting from this rise in temperature, which will be irreversible. What could happen exactly?

Ricarda Winkelmann: It concerns the so-called critical points. These are essential parts of the climate system, where, once you’re in a critical state, a perturbation as small as a temperature rise is enough to cause really big changes.

For example, the Greenland ice sheet is an element of the inversion. And we all know the mechanism that makes Greenland a reversal of mountaineering: When we descend from a mountaintop to a valley, it gets warmer around us. It’s the same with ice sheets. If the surface of the ice sheets melted, which is what we already see in Greenland, at some point the surface could plummet to lower elevations. Then it gets warmer there, which causes more melt, the surface sinks more, it gets warmer again and so on.

In other words, it is a self-reinforcing mechanism that could, at a critical point, cause that momentum to take over and almost completely melt Greenland.

„Some irreversible changes”

tagesschau.de: Flag identified 16 of these critical points. They systematically recorded them in their study and assessed the temperature rise at which their tipping points are triggered. For some, it’s too fast.

Winkelman: Solstice elements include, for example, the Antarctic ice sheet, the Amazon rainforest, the Atlantic circulation, and coral reefs. We now understand the mechanisms that turn these domains into tipping points and that there can also be irreversible changes.

And what we’ve shown in our study is that even at 1.5 degrees to 2 degrees — that is, in the temperature range of the Paris Climate Agreement — we come into this danger zone for some of these inversions. However, the Greenland and Antarctic ice sheets are among the overturning elements most at risk, as are coral reefs.

The problem is „self-reinforcing mechanisms”

tagesschau.de: As temperatures rise, there are more and more extreme weather events all over the world. Does this extreme weather also exist in the polar regions?

Winkelman: Yes, there is also severe ice weather. For example, just last year we observed an extreme melting of the Greenland ice sheet. This is one of a whole series of extreme melt events. It was caused by the area of ​​high pressure that hung over Greenland and then 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?

Winkelman: The temperature in the polar regions is rising faster than the global average temperature. This is due to the so-called polar amplification. It is this effect that again occurs through this self-reinforcing mechanism, the so-called ice-white reactions.

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

However, when the ice melts, the shiny surface decreases. Instead, the dark ocean surface appears, which we are already increasingly observing in the Arctic. So it gets darker and therefore, so to speak, warmer again. This is one of the effects that leads to this polar reinforcement.

tagesschau.de: In 2020, the temperature reached 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, becoming more severe and also lasting longer. But that’s why you can’t necessarily predict individual events and in this regard the high temperatures of 38 degrees in the Arctic and 18 degrees on the Antarctic Peninsula Surprise us too. So record the temperatures from pole to pole.

What happens under the ice?

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

Winkelman: One of the greatest uncertainties is what is actually happening under the ice. Because of course we can’t take a closer look at it. There are observational techniques you can use to try to get a closer look at the soil under the ice, for example. We know that increased thawing at the surface means that more meltwater is entering the ice sheet and thus also under the ice sheet, i.e. on land, and can lead to an acceleration of the ice flow. Simply by the fact that the ice is sliding on the water instead of freezing on the land.

And these are impacts on the lower side of the ice, where it’s very important that we have more observations, and collect more data in order to better understand what’s really going on under this ice, which is about five kilometers thick in Antarctica.

tagesschau.de: Where is it easier to read global warming at the moment: the Arctic or the Antarctic?

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

We also see this in mountain glaciers. I was myself in the Andes two years ago and went there to check glaciers for microplastic particles. Going up to Chimborazo, we already expected a glacier at an altitude of about 5,000 meters and wanted to take our measurements there. And when we got there – as you can imagine, this was way too strenuous at high altitude – we had to realize that the icy tongue is actually no longer where we expected it to be a few years ago. And that was one of those moments when I saw how powerful and comprehensive our interference with the climate system was.