Climate crisis in the Arctic: “Melting is accelerating”

taz: Ms. Humbert, you often visit Greenland for your research. What did summer look like this year?

Angelika Humbert: It started off very cold, very cold. My first expedition took me to northeast Greenland, and I was seriously worried that we would be able to measure anything at all: there was no meltwater on the surface yet and that's exactly what we wanted to measure.

has a doctorate in glaciology and has headed the ice sheet modeling working group at the Alfred Wegener Institute in Bremerhaven since 2012. One of her areas of expertise is the Greenland Ice Sheet. She also teaches as a professor at the University of Bremen.

Humbert: That happens every now and then, we also had a very cool summer in 2018. However, this year the temperatures suddenly rose sharply and a really drastic meltdown set in. I wanted to fly to the southeast for my measurements, but it rained at an altitude of 2,000 meters and the weather was so bad that we couldn't fly at first. Most recently I was traveling in the northwest, where there was so much meltwater and rain that the road was washed away - although the road was a gravel road.

Humbert: Absolutely! It started cool, and then there was an extremely strong, incredibly rapid rise in temperature with a very intense melt.

taz: When the meltwater hits the glaciers: What happens then?

Humbert: Meltwater reduces the albedo effect, i.e. the ability of the glacier surface to reflect. Dry snow reflects a lot of sunlight back into space, meltwater changes it, and as a result more energy penetrates the ice body and the glacier melts faster. Meltwater increasingly flows down the glacier and penetrates crevasses and glaciers accelerate over the summer.

taz: Greenland is considered one of the tipping points in the world climate system. Why?

Humbert: The meltwater is changing the surface of the Greenland ice sheet, and the ice sheet is becoming thinner and so the surface is at lower altitudes. However, it is warmer further down, which accelerates melting - a feedback effect that can lead to tipping.

taz: And the tipping point means: Once the melting has started, it can no longer be stopped?

Humbert: That's exactly how it is. The tipping point doesn't necessarily say anything about the exact timing, but it marks the moment at which we can't get out of this mechanism again.

taz: A study by the Geological Survey of Denmark and Greenland concluded in 2023 that we have passed the tipping point. Is this an individual opinion or scientific consensus?

Humbert: I wouldn't call that the current state of research. Based on current data, it is not possible to clearly prove that the tipping point has been reached. But there are many indicators that show that we are close to reaching that point. We are seeing increased amounts of meltwater on the surface of Greenland; the area over which meltwater flows has increased by 29 percent between 1985 and 2020.

taz: But that also means: It's not melting everywhere in Greenland yet?

Humbert: No, there is still a very large area inland that is a dry snow area in summer. But this area is getting smaller. And that's not surprising either. There are not only a lot of measuring stations around Greenland, but also several manned weather observatories. In the mid-1990s, a jump in the average annual temperature of 1 degree Celsius was recorded there. And there is this coupling: higher temperature means more meltwater.

taz: Research projects are constantly trying to precisely quantify the amount of meltwater. For example, one study concluded: Since the 1980s, Greenland has lost around five trillion tons of ice; about half of them since 2010. How do you measure something like that?

Humbert: There is no direct measurement of meltwater volume. What it does give is a measurement of the change in the volume of the ice sheet. This is carried out using satellites: pulses are sent out from orbit and the time is measured as to how long the pulse takes to get back to the satellite. And the satellite flies over the same areas over and over again with a certain repetition frequency. Since the 2000s, there have been continuous satellite missions that cover the whole of Greenland: they measure how the altitude decreases, i.e. how much glacier volume is lost, and use this to calculate the weight.

Humbert: That would be 169 billion tons per year between 1992 and 2020, with large differences between years, such as only 86 billion tons in 2017 and 444 billion tons in 2019. These differences come from large differences in surface melting between cold and warm years. Today, annual mass loss in Greenland is five times higher than in the 1990s.

taz: At the beginning of the year, another study came to the conclusion that the ice-free areas of Greenland have grown 23 centimeters in height over the past ten years. How come?

Humbert: The process is called glacial-isostatic compensation movement: Trillions of tons of ice weigh on the island's subsoil, which has pushed the earth's crust downwards over thousands of years. The loss of ice reduces this load and the land slowly springs back again. The landscape on the edge of the island looks a bit like the fjord landscape in Norway. To put it simply, scientists have installed GPS stations on the ice-free points. And thanks to these stations we know how the rock lifts.

taz: One of your research focuses is the “Zachariæ Isstrøm”, a glacier in northeast Greenland that drains an area three times the size of Brandenburg. What does it look like there?

Humbert: This summer I was only able to devote a little time to the Zachariæ Isstrøm. But what we see is that the glacier is retreating further and further and huge meltwater lakes are forming at ever higher altitudes. There is now one at about 1,200 meters altitude that is 21 square kilometers in size. To get a picture: This is almost half the size of Lake Ammersee. These lakes drain.

taz: Do you drain water through the ice body into the sea?

Humbert: Exactly. Through gigantic cracks and crevices through which water finds the base of the glaciers, where there is a hydrological system. We measured how large these channels are at the base in 2018, then again in 2021 and 2024. Some of these channels are not 1 meter or 2 meters, but several hundred meters. We suspect that these drainages from the large lakes are responsible for the fact that hundreds of meters high channels were created in the ice 30 to 50 kilometers further down the slope of the glacier. We, but also other research teams, have never seen such a change in such a short period of time.

taz: You not only observe this drama on site, you also measure it. How do you actually deal with it when you come home and find politicians that are not interested in climate change and are passing the wrong laws?

Humbert: My personal approach to the drama in Greenland is to create a basis on which decision-makers could act: I try to explain as often and as well as possible what is happening to the Greenland ice sheet. When I talk to experts from the ministries, I get the impression that they all have a good idea. Of course, what comes out is often not appropriate to the problem: we have to reduce our emissions.