While the sea ice melt season has lengthened in most of the satellite era, the trend stabilized around 2010.
For decades, Arctic sea ice has been melting earlier in spring and freezing later in fall, extending the melt season and contributing to ice loss.
The Arctic sea ice melt season is now about 40 days longer than it was in 1979, according to the study. Most of the increase occurred before 2010. Since then, the average melt season length has remained relatively unchanged, despite large year-to-year fluctuations.
Researchers analyzed satellite observations between 1979 and 2023 to track when sea ice begins to melt each spring and refreezes each autumn.
“Previously, there was more of this multiyear ice that didn't melt away each summer,” said Linette Boisvert, a co-author on the study and ice scientist at NASA’s Goddard Space Flight Center.
To understand why, the team examined changes in the Arctic's energy balance—the net difference between incoming heat from the Sun, atmosphere, and ocean and the outgoing infrared radiation emitted back to space.
In the left map above, the reddest areas mark where the melt season grew fastest that decade, by up to 5 days per year. Much of the Arctic ice today is younger and thinner than the multiyear ice that was once more widespread in the Arctic Ocean.
Since 2010, changing cloud patterns have reduced the amount of sunlight reaching parts of the Arctic Ocean.
The study suggests that the Arctic may have entered a new phase, in which annual weather patterns exert a stronger influence on melt season than they once did.