Why is Arctic sea ice decreasing while Antarctic sea ice is not?
Sea ice extent is affected by winds and ocean currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean seems to be responding more directly to atmospheric warming, while changes in winds and in the ocean seem to be dominating the patterns of climate and sea ice change in the ocean around Antarctica.
Sea ice in the Arctic has decreased dramatically since the late 1970s, particularly in summer and autumn. Between 1978, when the satellite record began, and 2025, the long-term trend in yearly minimum Arctic sea ice extent (which occurs in September) has been a decrease of 12% per decade [Figure 5a]. Ice cover expands again each Arctic winter, but the ice is thinner than it used to be. The reduction has been much less since 2007, and this is attributed to changes in wind patterns that may themselves be linked to warming. The reprieve is expected to be temporary and further reductions in ice extent are predicted. Estimates of past sea ice extent suggest that this decline may be unprecedented in at least the past 1,450 years.
In contrast to the Arctic, Antarctic ice extent slightly increased until 2007, then became very variable from year to year, culminating in a sharp decline in 2016. The trend since 2010 has been strongly negative with 2023, closely followed by 2024, easily the lowest on record. It is thought that a strengthening of westerly winds in the Southern Ocean initially drove ice away from the continent allowing more to be produced near the Antarctic coast, but that more recently the same winds have mixed warm water towards the surface where they can melt the sea ice.
Although changing winds and currents have made the records highly noisy from year to year, both polar regions now have much less sea ice than they did 50 years ago. This is certainly a result of polar warming and is expected to continue. Because sea ice is highly reflective, warming is amplified as the ice decreases and more sunshine is absorbed by the darker underlying ocean surface.
Figure 5: September Arctic (minimum) sea ice extent during the satellite era, according to the OSI SAF Sea Ice Index (Lavergne et al., 2023), with linear trend and 1981-2010 average indicated (panel a). September Antarctic (maximum) sea ice extent during the satellite era, according to the OSI SAF Sea Ice Index (Lavergne et al., 2023), with linear trend and 1981-2010 average indicated. https://www.metoffice.gov.uk/research/approach/monitoring/sea-ice/2025/arctic-and-antarctic-end-of-season-report---october-2025
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