DW: MOSAiC is a large-scale expedition led by Germany's Alfred Wegener Institute (AWI). It starts on September 20. What's it about?

Christian Haas: On the expedition we want to better understand the processes and energy flows between the air, the ocean and the ice. To do this, we will freeze ourselves in the Arctic for a whole year with our research icebreaker, Polarstern.

The processes and conditions there change greatly over the course of the seasons. In winter, we'll investigate the factors that affect the freezing and how the ice grows. In summer, the conditions are reversed. Then, the ice melts and the ice cover breaks open to form ice floes.As the ice gets older, it's important to understand the interplay between winter freezing and summer melting, so we can judge whether the ice is getting thicker or thinner.

Read more: Climate research on the high, warming seas

The Polarstern will drift with the ice through the Arctic Ocean. How exactly does this work?

The Arctic sea ice is only a few meters thick. Because it is so thin, it can easily break and be driven away by winds and currents, so it is constantly in motion. We use this movement, the so-called ice drift, to drift from Siberia via the North Pole to Greenland.

There is also a decisive advantage to drifting with the same ice, because only then can we judge how the ice is exposed and changed by all the external influences.

There have already been several expeditions to the Arctic. What makes MOSAiC so special?

The special thing about MOSAiC is that we'll be there for the course of a year, throughout the entire freezing and melting seasons. We'll observe the processes in all their diversity. We are also a huge team of researchers from 19 nations. A total of 300 scientists are involved. But everyone will only be on board for two months. We take turns and travel with Russian icebreakers to the Polarstern and back. There are a total of six sections, each with 50 scientists on board. I myself will be there from December to February. 

And what's your task on site?

I am the expedition leader for my section. This means that I will assume overall responsibility for the entire undertaking during the two months. Our group is concerned with the properties of ice, with a focus on ice cover measurement.

In the past, you had to drill holes to measure the thickness of the ice, which is very time consuming. We developed a new method for this at AWI. We can use electromagnetic probes to measure the conductivity of the substrate.

Ice is solid and therefore a poor electrical conductor, while the salt water underneath conducts electricity very well. That enables us to determine the distance from the surface to the border between the ice and the water, which is the thickness of the ice.

We will then compare the data with satellite data, in particular with the European CryoSat, which was specifically launched for ice cover measurements. This will allow us to observe how the ice grows and becomes thinner.
You've mentioned a number of processes. Tell us more.

The main focus is to investigate why the thickness of the ice changes. This depends on a huge number of influences, such as the air temperature and humidity of the winds, solar radiation and how much heat from the water reaches the ice.

All these factors are measured simultaneously in high temporal resolution. We want to know how this affects the thickness of the ice.

You have been in the Arctic quite often. What are the working conditions?

There are risks that we don't have at home. You can get frostbite, break into the water or cross paths with polar bears. I have met many polar bears. Everyone who moves in the Arctic carries a weapon.

But Polarstern has never fired a shot at a polar bear. Because first and foremost, they are curious about us, and that's why they appear. Since they are also very anxious, they can easily be driven away by noise. So, these are not risks that bring great dangers, if you respond correctly.

The far greater challenges lie more in the extreme situation of being so far away from home for so long. Especially in winter we work in complete darkness. In addition, we are constantly together with many other people, there is no privacy. Communication via the internet, satellites and telephone, is also limited because there is only one satellite communication system that still functions north of 75 degrees north.

Read more: Scientists say atmosphere carrying microplastics to the Arctic

Nevertheless, this expedition is very important — keyword, climate change?

The whole world is worried about climate change. The Arctic is a hotspot, or epicenter, of global climate change. Because in the Arctic, we observe the strongest climate changes.

These can be observed particularly well due to the retreat of ice. The Arctic is warming faster than the rest of the world. Therefore, you have to go to the Arctic to understand what is happening there and to make predictions for the world.

And how is the sea ice at the moment?

The area of Arctic ice in summer has decreased by more than 50% in the last 40 years. Right now, in September, the ice retreats the most every year before it expands again in autumn and winter.

This year we observed the second smallest extension of the sea ice that has ever been observed in the Arctic.

So, it is good that MOSAiC is starting now. With it the original conditions are the most extreme and that is exactly what we want to investigate, how the Arctic has changed in the last years and what the state of the 'new Arctic' is.

Prof. Dr. Christian Haas is a geophysicist and head of the sea ice section at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven.

Interview by Liyang Zhao.