Arctic marine heatwaves forced by greenhouse gases and triggered by abrupt sea-ice melt

Abstract

Since 2007, unprecedented marine heatwave events are occurring over the Arctic Ocean. Here we identify the fraction of the likelihood of Arctic marine heatwaves magnitude that is attributable to greenhouse gas forcing. Results reveal that Arctic marine heatwaves are primarily triggered by an abrupt sea-ice retreat, which coincides with the maximum downward radiative fluxes. Up to 82% of the sea surface temperature variability over the shallow Arctic marginal seas, where marine heatwaves are prone to occur, can be explained by net accumulation of seasonal surface heat flux in the ocean. Event attribution analysis demonstrates that the 103-day long 2020 event – the most intense (4 ^∘C) recorded so far in the Arctic – would be exceptionally unlikely in the absence of greenhouse gas forcing in terms of both intensity and duration. Our further results imply that if greenhouse gas emissions continue to rise, along with the expansion of first-year ice extent, moderate marine heatwaves in the Arctic will very likely persistently reoccur.