First Ice-free Day in Arctic Ocean will Occur with Multiple Compounding Events: Earliest within 3 Years but 7-20 Years Most Likely

Nature Communications, 3 December 2024

This new study used a range of climate models to predict when we could see the first ice-free day in the Arctic Ocean, which IPCC AR6 noted was likely to occur by mid-century even under low emissions scenarios. The study found that the earliest ice-free day could occur within just 3 years’ time compared to 2023-equivalent conditions, with the highest probability occurring within 7–20 years’ time. The most rapid transitions to ice-free conditions were primarily related to internal variability rather than degree of warming, and most likely to occur following warm atmospheric conditions in the previous winter and spring.

Authors were careful to note that the first occurrence of ice-free conditions is primarily symbolic, however a transition to an Arctic Ocean that regularly has a sea ice area of less than 1 million km2 (the agreed threshold for “ice-free” conditions) in summer would have profound effects on the rest of the climate system. These include greater warming of the upper ocean, accelerating loss of sea ice year-round, negative impacts on the already-stressed Arctic ecosystem, and possibly more extreme weather events at mid-latitudes. They conclude that the rapidity and scale of emissions reductions would decide the overall future of Arctic Ocean sea ice, with ambitious mitigation pathways consistent with the lower Paris Agreement limit of 1.5C potentially delaying the first ice-free day by over 50 years, as compared to current NDCs that will lead to around 2.3C warming or more.

全文 https://www.nature.com/articles/s41467-024-54508-3
News briefing with informative NSIDC sea ice graphic: https://www.ft.com/content/63fbcf2b-9acc-4ccb-ac12-9f3b78e85b68