Arctic sea-ice loss is projected to lead to more frequent strong El Nino events

With an ice-free Arctic, strong El Nino frequency increases 1/3 + . Almost half the increase by 2100 links to Arctic ice loss, not other greenhouse forcing. The Arctic's influence on ENSO may represent a novel driver of changing climate extremes globally. Arctic sea ice has decreased substantially and is projected to reach a seasonally ice-free state in the coming decades. Little is known about whether dwindling Arctic sea ice is capable of influencing the occurrence of strong El Nino, a prominent mode of climate variability with global impacts. Based on time slice coupled model experiments, here we show that no significant change in the occurrence of strong El Nino is found in response to moderate Arctic sea-ice loss that is consistent with satellite observations to date. However, as the ice loss continues and the Arctic becomes seasonally ice-free, the frequency of strong El Nino events increases by more than one third, as defined by gradient-based indices that remove mean tropical Pacific warming induced by the seasonally ice-free Arctic. By comparing our time slice experiments with greenhouse warming experiments, we conclude that at least 37-48% of the increase of strong El Nin o near the end of the 21st century is associated specifically with Arctic sea-ice loss. Further separation of Arctic sea-ice loss and greenhouse gas forcing only experiments implies that the seasonally ice-free Arctic might play a key role in driving significantly more frequent strong El Nino events.

Automated summary

With the disappearance of Arctic ice, the frequency of strong El Nino events increases by more than a third. This study reveals that a significant portion of the increase in strong El Nino events near the end of the 21st century can be attributed to the loss of Arctic sea-ice. The seasonally ice-free Arctic could play a key role in driving more frequent strong El Nino events.