Since 2007, unprecedented marine heatwave events are occurring over the Arctic Ocean. This study identifies the fraction of the likelihood of Arctic marine heatwaves magnitude attributable to greenhouse gas forcing. Results reveal that Arctic marine heatwaves are primarily triggered by an abrupt sea-ice retreat, coinciding with maximum downward radiative fluxes. Up to 82% of sea surface temperature variability in shallow Arctic marginal seas (where marine heatwaves are prone to occur) is explained by net accumulation of seasonal surface heat flux in the ocean. Event attribution analysis demonstrates that the 103-day 2020 event—the most intense (4 °C) recorded—would be exceptionally unlikely without greenhouse gas forcing. Continued greenhouse gas emissions, along with expanding first-year ice extent, will very likely lead to persistent moderate marine heatwaves in the Arctic.

Armineh Barkhordarian, David M. Nielsen, Dirk Olonscheck, Johanna Baehr