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A closer look at sea ice: An interview with AMAP expert Sebastian Gerland

Sebastian Gerland is a geophysicist at the Norwegian Polar Institute in Tromsø. As a specialist for sea ice and climate, he has contributed to several projects and reports of the Arctic Monitoring and Assessment Programme (AMAP). In this interview, Sebastian speaks about the shrinking Arctic sea ice cover and why its important to not just look at the annual minimum extent to understand trends and effects of a changing Arctic.

The sea ice cover of the Arctic Ocean drops to a minimum in early fall. Are we approaching another record minimum extent in 2019?

The middle of September is usually the time of the year, when the sea ice cover in the Arctic reaches its minimum. If we look at satellite images now, we can see that we do have a very low sea ice extent this year. At the moment it does not look like we are going to have another record low, but 2019 definitely comes in line with those years that have had a low ice cover – and reaffirms a trend we have observed over many years now: the summer sea ice extent is declining.

The Arctic sea ice underlies a strong season cycle. The ice forms in winter, when both the water and air are cold. Then we get an ice cover that spans across most parts of the Arctic Ocean and areas of neighboring seas. We see slight decreases in the winter sea ice cover, but it still ranges between 14 to 15 million square kilometers – compared to the about four million square kilometers we can observe in summer. Once summer approaches, the sea and air warms and the ice begins to melt. It is important to note that we also see a decline of sea ice extent during other months than September, which has a wide range of implications.

Which are the other months scientists are looking at?

Important months are in fall at the onset of freezing, so when the ice is forming, and in spring and early summer, when the sun moves higher above the horizon. How much ice we have during the time the sun is returning after winter until it stands highest in June, is an important factor for a whole range of processes related to our climate and the ecosystem.

What impacts does a shrinking sea ice cover have?

When we look at the impacts of a reduced sea ice cover, we can differentiate between effects on the climate and on the ecosystem. Sea ice for example reflects incoming solar radiation. Therefore, a change of sea ice cover affects the energy balance, the transfer of heat between the atmosphere and the ocean, the rate of evaporation and so on. Since the Arctic is changing, many of the observations we make now are new, there are not always past scenarios we can return to in order to understand certain processes. Also, it’s important to note that the sea ice cover may be different for a given season from year to year. Areas that are ice-free one summer, can be ice-covered the next. If you only look at the amount of the total sea ice extent in the Arctic, you don’t see regional differences.

Retreating sea ice also has severe implications for the ecosystem. It affects prominent species, such as polar bears, seals and whales, as well as a large number of smaller organisms, whose life cycle is also closely connected to sea ice. They all play a role in the system and scientists are trying to find out, who will be losers and who winners related to the Arctic system changes observed. All processes and components of the ecosystems are interconnected, and as a sea ice geophysicist I for example work closely together with biologists to understand the larger picture.

How does the loss of sea ice affect us humans?

Sea ice – or its absence – is for example important for transport. With shorter sea ice seasons, a community that used to cross a frozen fjord in winter, needs to adapt its way of living as it cannot use the ice in the way it traditionally has. On the other hand, shipping can benefit from ice-free routes. The retreating sea ice can also impact fisheries, as new species may migrate to ice free areas and ice-dependent species retreat with the ice. For those who manage Arctic marine areas it is therefore important to have the best available knowledge at hand. That is what we scientists aim at providing them with and we need to work across disciplines to understand the processes and gather the most up-to-date data.

Does a reduced sea ice cover also directly impact weather patterns in lower latitudes?

That is a big question and new research is looking into how the sea ice cover in the Arctic affects other parts of the world. It is important to look at individual studies that link specific lower latitude regions to the Arctic, for example how sea ice retreat affects snow cover in northern Asia, and then to interconnect findings. While connections to areas that are further away from the Arctic can be expected, it is too early to say in detail how the regions are connected.