AN UPDATED ASSESSMENT OF THE CHANGING ARCTIC SEA ICE COVER

Sea ice is an essential component of the Arctic climate system. The Arctic sea ice cover has undergone substantial changes in the past 40+ years, including decline in areal extent in all months (strongest during summer), thinning, loss of multiyear ice cover, earlier melt onset and ice retreat, and later freeze-up and ice advance. In the past 10 years, these trends have been further reinforced, though the trends (not statistically significant at p <0.05) in some parameters (e.g., extent) over the past decade are more moderate. Since 2011, observing capabilities have improved significantly, including collection of the first basin-wide routine observations of sea ice freeboard and thickness by radar and laser altimeters (except during summer). In addition, data from a year-long field campaign during 2019-2020 promises to yield a bounty of in situ data that will vastly improve understanding of small-scale processes and the interactions between sea ice, the ocean, and the atmosphere, as well as provide valuable validation data for satellite missions. Sea ice impacts within the Arctic are clear and are already affecting humans as well as flora and fauna. Impacts outside of the Arctic, while garnering much attention, remain unclear. The future of Arctic sea ice is dependent on future CO2 emissions, but a seasonally ice-free Arctic Ocean is likely in the coming decades. However, year-to-year variability causes considerable uncertainty on exactly when this will happen. The variability is also a challenge for seasonal prediction.

Automated summary

Sea ice in the Arctic has undergone significant changes in the past few decades, including decline in extent, thinning, loss of multiyear ice, and changes in melting and freezing patterns. These trends have been reinforced in the past 10 years, with improved observation capabilities providing valuable data. The impacts of sea ice on the Arctic and its surrounding regions are clear, but the impacts beyond the Arctic are still uncertain. The future of Arctic sea ice depends on future CO2 emissions and the timing of a seasonally ice-free Arctic Ocean remains uncertain due to year-to-year variability.