New study in the journal Communications Earth & EnvironmentHeat Waves in the Arctic Ocean to Become Regular Occurrence in the Future

Photo: Universität Hamburg / CLICCS / A. Barkhordarian

To date, the strongest heat wave occurred in 2020, lasting over 103 days.

Since 2007, the conditions in the Arctic have shifted— this is revealed in data published in the journal Communications Earth & Environment. Between 2007 and 2021, 11 heat waves occurred on the fringes of the Arctic Ocean, during which the water temperature was, on average, 2.2 degrees Celsius warmer on the surface than the annual mean. The heat waves last 37 days on average. From 2015, they occurred annually.

The strongest heat wave to date occurred in 2020 and lasted 103 days with peak temperatures 4 degrees Celsius above the long-term average. The probability that such heat waves would have happened without human activity is less than one percent, calculated Barkhordarian’s team in the Cluster of Excellence Climate, Climatic Change, and Society (CLICCS). As a result, they narrowed down the range of plausible future developments in the Arctic. Annual heat waves will be the rule in the future.

The Arctic is entering a new phase

Barkhordarian has also proved, for the first time, that Arctic heat waves occur when the sea ice melts early and quickly after the winter. As a consequence, a lot of heat can have accumulated in the water by the time of maximum solar irradiance in July. “A new phase began in the Arctic in 2007,” says the expert in climate statistics at Universität Hamburg. “There is less and less thick ice that is several years old. Instead, the proportion of year-old thin ice is steadily increasing.” However, the thin ice is less durable and melts faster, which allows solar irradiance to warm the water’s surface unhindered.

Officially, a marine heat wave is when the temperatures at the water’s surface are higher than 95 percent of the measurements from the last 30 years for at least 5 consecutive days.

“Not only the ongoing loss of sea ice but also the warmer water can dramatically harm the Arctic ecosystem,” says Barkhordarian. This can lead to a breakdown in food chains, damaged fish stocks, and a decline in overall biodiversity.

Background:

Are humans responsible? Using attribution research, we can compare how the world would have developed with and without human impact. The present study calculated how likely the occurrence of individual heat waves would be in a world without greenhouse gas emissions caused by humans. Barkhordarian and her team also assessed satellite data and used coupled climate models for their analyses.

Journal articles:

Barkhordarian A, Nielsen DM, Olonscheck D, Baehr J (2024): Arctic marine heatwaves forced by greenhouse gases and triggered by abrupt sea-ice melt. Communications Earth & Environment.