Frequent marine heatwaves in the Arctic Ocean will be the norm

Since 2007, conditions in the Arctic have shifted, as confirmed by data recently published in the journal Nature Communications Earth & Environment. Between 2007 and 2021, the marginal zones of the Arctic Ocean experienced 11 marine heatwaves, producing an average temperature rise of 2.2 degrees Celsius above seasonal norm and lasting an average of 37 days. Since 2015, there have been Arctic marine heatwaves every year.

The most powerful heatwave to date in the Arctic Ocean was in 2020; it continued for 103 days, with peak temperatures intensity that were four degrees Celsius over the long-term average. The probability of such a heatwave occurring without the influence of anthropogenic greenhouse gases is less than one percent, as calculated by Barkhordarian's team at the Cluster of Excellence CLICCS. By doing so, they have narrowed down the number of plausible climate scenarios in the Arctic. According to the study, annual marine heatwaves will be the norm.

The Arctic entered a new phase

In the study, Barkhordarian also proves for the first time that heatwaves are produced when sea ice melts early and rapidly after the winter. When this happens, considerable heat energy can accumulate in the water by the time maximum solar radiation is reached in July.

"In 2007, a new phase began in the Arctic," says Barkhordarian, an expert on climate statistics. "There is less and less of the thicker, several-year-old ice, while the percentage of thin, seasonal ice is consistently increasing." However, the thin ice is less durable and melts more quickly, allowing incoming solar radiation to warm the water's surface.

Officially, it is considered to be a marine heatwave when temperatures at the water's surface are higher than 95 percent of the values from the past 30 years for at least five consecutive days.

"Not just the constant loss of sea ice but also warmer waters can have dramatic negative effects on the Arctic ecosystem," says Barkhordarian. Food chains could collapse, fish stocks could be reduced, and overall biodiversity could decline.

Background

Are human beings responsible? Attribution research allows us to compare how the world would have developed without human influences. For the study at hand, the calculations focused on the probability of each heatwave occurring in a world without anthropogenic greenhouse gases. In addition, Barkhordarian and her team reviewed satellite data and drew on coupled climate models for their analyses.