With climate change, Arctic summers are becoming longer and warmer. It can already be observed that the Arctic sea ice is shrinking drastically. The first day of summer completely free of sea ice in the Arctic could come as early as the next decade, a new study suggests. That would be significantly earlier than predicted based on previous calculations. When and for how long entire months remain ice-free depends on the further course of climate change and anthropogenic greenhouse gas emissions.
Our greenhouse gas emissions are warming the earth and melting snow and sea ice in the Arctic. As the ice cover dwindles, more sunlight hits the dark, open waters of the Arctic Ocean and warms it, which in turn accelerates ice melting. Numerous measurements have already shown that Arctic sea ice is rapidly decreasing. This has consequences for the animals living there, such as polar bears and seals, who find it difficult to survive without the ice. Researchers also predict that invasive fish species from southern areas could disrupt the marine ecosystem in the future. Without the protection of sea ice, ever larger waves will hit the Arctic coast, causing the land to continue to erode.
However, the loss of sea ice also has positive effects - at least for shipping: Because more and more sea areas become ice-free in summer, the Northeast Passage is already navigable more and more often. This route along the northern coast of Siberia significantly shortens the transportation of goods between Europe and Asia. A Northern Sea that is completely ice-free in summer could even enable trips across the Arctic Ocean and through the Northwest Passage north of Canada. Climate scientists typically define the Arctic Ocean as “ice-free” when less than a million square kilometers of its surface is covered with ice. In recent years between 2015 and 2023, the annual low in September was an average of around 3.3 million square kilometers.
The first day without sea ice in the Arctic is approaching
In order to find out exactly when the sea ice will have “completely” disappeared according to this definition, a team led by Alexandra Jahn from the University of Colorado Boulder evaluated existing measurement data, satellite images and projections of previous and future ice loss. The researchers also compared this data with modern climate models, which can predict future changes down to the day. It found that the first “ice-free” day, when less than a million square kilometers of the Arctic Ocean is covered with ice, could occur up to 18 years before the first “ice-free” month. According to the forecasts, this will probably be a September in the middle of the century, between 2035 and 2067. By then the earth will have warmed by 1.8 degrees compared to pre-industrial levels.
The first day without sea ice could therefore occur as early as the next decade, in the late 2020s or early 2030s. That would be more than ten years earlier than previous studies have predicted. Although the result of Jahn and her team applies regardless of our further emissions, it is still subject to a high degree of uncertainty despite the refined methodology. The first day without sea ice in the Arctic could not be until the 2040s. What is certain, however, is that it will be a summer day at the end of August or beginning of September.
Future emissions will determine the length of the ice-free summer
According to the models, it will take until the end of the century for the Arctic Ocean to remain ice-free for several months in summer, as climate scientists report. When exactly and how regularly this will happen and whether all summer months will be affected depends on our future greenhouse gas emissions. If we don't lower these and carry on as before, not only the summer months, but even some winter months could remain ice-free - up to nine months in a row from May to January. “This would transform the Arctic into a completely different environment, from a white summer Arctic to a blue Arctic,” said Jahn.
However, if the currently announced measures are taken to reduce emissions, the Arctic Ocean will probably only be ice-free from August to October at the end of the century. If humanity even reaches net-zero emissions, there will only be no ice in the Arctic summer in September. “Even if short-term ice-free conditions are unavoidable, we still need to keep our emissions as low as possible to avoid prolonged ice-free conditions,” says Jahn.
After all, the results also contain some good news: Even if all Arctic sea ice were to melt due to climate change, it could quickly return as soon as the atmosphere cools down again. “Unlike the ice sheet in Greenland, which took thousands of years to form, the Arctic sea ice will return within a decade if we can recover CO2 from the atmosphere and reverse global warming in the future,” explains Jahn. According to their results, there is no irreversible tipping point for the Arctic sea ice.
Source: Alexandra Jahn (University of Colorado Boulder) et al., Nature Reviews Earth & Environment, doi: 10.1038/s43017-023-00515-9