Sea Ice Extent

The polar oceans are among the most rapidly changing oceans in the world. The yearly cycle of the build-up and melting of Arctic sea ice is one of the earth’s vital signs and a key climate variable monitored by scientists.

Loss of sea ice increases global heating. White snow reflects sunlight, whereas water absorbs it. Declining Arctic sea ice, therefore, amplifies the warming up of the Arctic. Temperatures increased by around 0.5°C per decade between 1982 and 2017, primarily due to increased absorbed solar radiation accompanying sea ice loss since 1979.

Arctic sea ice increases its extent during the northern hemisphere winter, reaching a maximum in March. “Under the influence of global heating caused by human-induced greenhouse gases emissions, we have seen a sharp decrease in the extent of Arctic sea since 1979". (UN Environment)

Assisted by the August slowdown in melt, the 2021 minimum extent (September) was greater than in recent years but still well below the 1981-2010 average, representing the 12th lowest minimum ice extent in the 43-year satellite record. (WHO)

As it does in the Arctic, the surface of the ocean around Antarctica freezes over in the winter and melts back each summer. Antarctic sea ice usually reaches its annual maximum extent in mid- to late September, and reaches its annual minimum in late February or early March.

The sea ice satellite record dates back to 1978. Unlike the Arctic, where sea ice extent is declining in all areas in all seasons, Antarctic trends are less apparent. From 1979–2017, Antarctic-wide sea ice extent showed a slightly positive trend overall, although some regions experienced declines. Overall, the long-term trend in Antarctic sea ice is nearly flat. Spanning over four decades, the satellite record shows periods of increasing and decreasing sea ice, but few of those trends have been statistically significant. (NOAA).

Sea-ice extent across the Southern Ocean during the first 9 months of 2021 was generally below the 1981–2010 mean, with a relatively low February minimum but near- average conditions during the summer melt season (WHO).

Infographic: summary of cryosphere indicators (Copernicus)