Sea Ice Extent
D5. Coastal processes, sea-level, cryosphere and ocean observation scienceDefinition
Total area where ice concentration exceeds a threshold, usually 15 percent.
Sea ice extent is the total ocean area where ice concentration exceeds a threshold, conventionally 15%, and is the headline metric for tracking polar ice loss. NSIDC derives it from passive-microwave satellites and reports Arctic and Antarctic figures monthly. Arctic September minimum extent has declined about 13% per decade since 1979; Antarctic extent held steadier until a sharp drop from 2023. Extent counts any cell above the threshold, so it differs from ice area, which weights by concentration.
Source: NSIDC