This sight will irritate: water everywhere, as far as you can see. Nothing to see of the sea ice that has shaped the Arctic Ocean for over 40 million years. This picture could present itself in the next decade. And the polar sea could be ice-free for a whole month for the first time in living memory, i.e. September, when the sea ice expands at its lowest rate of the year. This is the conclusion reached by a team led by atmospheric scientist Yeon-Hee Kim from Pohang University of Science and Technology in South Korea in the journal Nature Communications. Accordingly, the Arctic Ocean could lose its frosty character earlier than previously thought.
For decades, Arctic sea ice has been shrinking as a result of global warming, and this trend has accelerated since 2000. The current report by the Intergovernmental Panel on Climate Change (IPCC) also says that the Arctic will probably be practically free of sea ice at least once before 2050. Only from the middle of the century can it be expected that the polar sea will also be “practically ice-free” on average in September – unless the world pursues ambitious climate protection. Then ice could still be preserved in relevant quantities on the ocean.
The team led by Yeon-Hee Kim now assesses this differently: Even under the lowest emission scenarios, the first ice-free September could already occur between the 1930s and 1950s. And then more and more often, until at least September will be more often without ice than with it in the second half of the century, regardless of how quickly the world community makes progress on climate protection. “We can no longer prevent the sea ice from disappearing in September,” says climate researcher Dirk Notz from the Center for Earth System Research and Sustainability at Universität Hamburg, one of the authors of the study. “Summer sea ice will be the first major element in the climate system that we will lose.”
“You can still save August”
The reason why the models on which the IPCC report is based come to significantly more optimistic prospects or “fundamentally underestimate” the ice loss, as Notz puts it, can be explained by the choice of method: In the case of the Nature Communicationsstudy, the authors first wanted to find out how large the human contribution was to the sea ice retreat. To do this, they ran the model simulations for the years 1979 to 2019 several times, each time considering individual factors such as the level of carbon dioxide or aerosols in the air, but also volcanic eruptions or natural variability in isolation. “If we only considered the non-human contributions, there was almost no ice loss,” says Notz. And the best explanation for the decline in Arctic sea ice was man-made climate change.
The next step was how well the models were able to depict past developments. “With this knowledge, we were able to correct the errors in the models and continue the development into the future,” explains Notz. As a result, in all future scenarios, the ice disappeared in the September months. It didn’t disappear completely, but it only stayed below the one million square kilometer threshold. In climate science, this is considered “practically ice-free”, since the residual amounts of sea ice on the north coast of Greenland, for example, are of little practical relevance for the Arctic ecosystems or shipping.
Dirk Notz doesn’t want the bad news to be understood as a call to stop worrying about Arctic sea ice. Because only the September ice is lost in the long run. “You can still save August,” says Notz. As well as all other months when the Arctic Ocean still carries ice.