Ice caps and corals: tipping points threaten from 1.5 degrees

Status: 11/13/2022 11:18 AM

Researchers have identified 16 tipping points in the climate system. In an interview, polar explorer Winkelmann explains what these mechanisms are and why some can be activated by 1.5 degrees of global warming. The Paris climate agreement aims to ensure that our earth does not warm by more than 2 and if possible no more than 1.5 degrees. In a study you write that as soon as this temperature rises, irreversible changes are on the way. What exactly can happen?

Ricarda Winkelmann: These are so-called tipping points. These are important parts of the climate system where, once in a critical condition, a small disturbance such as a temperature rise is enough to bring about really big changes.

The Greenland ice sheet, for example, is one such tilting element. And we all know the mechanism that makes Greenland a tilting element of mountaineering: As we descend from the top of a mountain into the valley, it gets warmer around us. And so it is with the ice caps. 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’s a self-reinforcing mechanism that, at a critical point, could lead to this momentum taking over and Greenland almost completely melting away.

Ricarda Winkelman

The polar researcher works at the Potsdam Institute for Climate Impact Research and mainly studies changes in the ice sheets in the Arctic and Antarctic waters.

“Some irreversible changes” Science has identified 16 of these tipping points. They systematically recorded these in their research and evaluated the rise in temperature at which their tipping points are triggered. For some it goes quite quickly.

Winkelmann: The tilting elements are, for example, the Antarctic ice sheet, the Amazon rainforest, the Atlantic Ocean circulation and the coral reefs. We now understand the mechanisms that make these areas tipping points and that irreversible changes can also occur.

And what we show in our study is that even at one and a half to two degrees — that is, in the temperature range of the Paris Climate Agreement — we get into this risk area for some of these tipping elements. However, the two ice sheets in Greenland and Antarctica are among the most vulnerable tilting elements, as are the coral reefs.

The problem is “self-reinforcing mechanisms” With rising temperatures, there are more and more extreme weather events worldwide. Does this extreme weather also exist in the polar regions?

Winkelmann: Yes, there is also extreme weather on the ice. For example, last year we observed an extreme melting moment on the Greenland ice sheet. This is one in a slew of extreme melting events. It was caused by a high pressure area that got stuck over Greenland and only led more towards the melt after that. 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. Why does the temperature rise especially at the poles?

Winkelmann: The temperature in the polar regions is rising even faster than the global average temperature. And that’s because of what’s called polar amplification. This is an effect that is again brought about by 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 so it is on a large scale, so to speak, in the climate system. Clear surfaces – such as the ice surfaces – radiate some of the solar radiation back into space and have a cooling effect, as it were.

However, as the ice melts, the clear surface diminishes. Instead, the dark ocean surface, which we are already increasingly seeing in the Arctic, appears. So it gets darker and thus warmer again, so to speak. And that’s one of the effects that lead to this polar amplification. In 2020 we had a temperature of 38 degrees in the Arctic for the first time. Did that surprise you?

Shopkeeper: Yes. You can’t really prepare for such extreme weather conditions. 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 regard the high temperatures of 38 degrees in the Arctic and 18 degrees in the Antarctic Peninsula were a surprise to us too. So record temperatures from pole to pole.

What’s going on under the ice? What else do you need to better understand scientifically in polar research?

Winkelmann: One of the biggest uncertainties is what really happens under the ice. Because of course we can’t look at it properly. There are observation techniques with which you can try to get a closer look at the ground under the ice, for example. We know that due to the increased melting at the surface, more meltwater enters the ice sheet and therefore 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’s very important that we have more observations, collect more data to better understand what’s really going on under this ice, which is almost three miles thick in Antarctica. Where is global warming currently more readable: at the North or South Pole?

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

We also see this with the mountain glaciers. I myself went to the Andes two years ago and started researching the glaciers there for microplastics. When climbing the Chimborazo we actually expected a glacier at about 5000 meters and wanted to take our measurements there. And when we got there – as you can imagine, that’s quite a tough road at high altitudes – we had to realize that the glacier tongue was actually not where we expected it to be a few years ago. And that was one of those moments when I saw how strong and truly all-encompassing we are intervening in the climate system.

The interview was conducted by Cornelia Eulitz-Satzger, hr

Ricarda Winkelmann: Early warning signs that we are approaching a tipping point

Lennart Pyritz, DLF, 7.11.2022 5:38 PM

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