DER SPIEGEL: In fact, the Arctic is warming more dramatically than any other part of the world. What does that mean for Greenland?
Ahlstrøm: In recent decades, circulation patterns in the atmosphere have changed. We have evidence that warm air is reaching the ice sheet more and more frequently. This has to do with changes in the jet stream. They ensure that the air over Greenland in summer comes less frequently from the far north – and very often from the mid-latitudes, where it is warmer.
The Summit Station was established in 1989. The purpose was to support a research project. In the process, scientists drilled through Greenland’s ice, which is more than 3-kilometers thick. There have been several subsequent drillings since then. The ice cores provide a precise climate archive because of the gas bubbles trapped in the ice, from which the composition of the air in the past can be determined. Among other things, the researchers are interested in finding out how much CO2 was in the atmosphere at a given point. But a lot of other information can also be gained from the ice cores, including ash from volcanic eruptions from all over the world that ended up in the Arctic via the air currents in the atmosphere.
DER SPIEGEL: Ice cores show that temperatures at the Summit Station occasionally have been above the freezing level before. What’s different now?
Ahlstrøm: If you look back thousands of years, you see events like this maybe every 250 years. Now, we’ve had rain in 2012, 2019 and 2021, so three times within a decade. The frequency of such events is without precedent.
DER SPIEGEL: Seven billion tons of rainwater have now landed on Greenland between August 14 and 16 alone. What are the long-term consequences for the ice?
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