Satellite data from 1979-2023 show the Arctic sea-ice melt season stopped lengthening consistently after 2010, averaging about 108 days despite large year-to-year swings.
A roughly 40-day extension since 1979 came mostly from later autumn freezing, while earlier spring melting played a smaller role.
The biggest increase occurred in 2000-2009, when darker open water, thinner ice and cloud changes boosted solar energy absorbed at the surface.
Cloud patterns later shifted to cut some incoming sunlight, helping explain the plateau, but researchers say that does not mean sea ice recovered because the ice pack remains thinner.
NASA said melt-season length and ice condition are separate measures, and continued observations are needed to see whether the post-2010 plateau persists.