| Summary: | The severe ecological and socioeconomic consequences of marine heatwaves (MHWs) have motivated many studies aimed at understanding their drivers and occurrences. However, much less attention has been received by the MHWs over the Arctic Ocean, where these events are possibly more damaging than those in climatologically warmer ocean. Here we show that the magnitude of Arctic MHWs has significantly increased since 2007, and has exceeded the pre industrial climate bounds since then. These amplified extreme MHWs in the Arctic have each been accompanied by a record decline in Arctic Sea ice, in particular in the years 2007, 2012, 2016 and 2020. The aim of this study is to identify the fraction of the likelihood of Arctic MHW event’s magnitude that is attributable to greenhouse gases (GHG) forcing. The probability of necessary causation of Arctic MHWs intensity indicates that any MHW over the Arctic with an intensity higher than 2°C is entirely attributable to the inclusion of GHG forcing. Our further results provide evidence that the prolonged Arctic MHWs, triggered by faster early summer sea ice melt, will accelerate Arctic warming, and cause Arctic Sea ice extent to shrink even faster in the near future.
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