1. Nature

   Two ways to measure the same ice differ by a factor of 1.5

   Arctic, September 2025: area within the ice edge, 4.75 million km²; area of the ice itself, without open water inside, 3.08 million km².

   Source: NOAA/NSIDC Sea Ice Index v4Open on the chart →

   More

   Extent counts entire cells with ≥15% ice concentration; area weights cells by ice concentration. The polar observation gap is also treated differently. Their ratio is not presented as an exact ice-cover concentration.

   Bars share one scale. The source values and their units are listed below.

   • Extent million km²

     4.747 (2025-09)

     Sea ice in both hemispheres: area and extent

   • Area million km²

     3.076 (2025-09)

     Sea ice in both hemispheres: area and extent

   Two different fields from the same NSIDC version and month. Extent/area illustrates the effect of the definition; neither is converted into ice volume.

   Fetterer et al. (2025), Sea Ice Index v4, DOI 10.7265/a98x-0f50. Northern/Southern Hemisphere are not countries. Extent counts whole grid cells with ice concentration ≥15%; area weights by concentration. Monthly satellite estimates in million km², not volume or land glaciers. Recent points may be preliminary. The published annual mean is calendar-day weighted and retained only with all 12 months present. Hemispheres are not summed into a universal climate index.

   A question for this picture

   Which measure would change this story?

More findings

• Atmospheric methane barely grew for seven years. The pause ended
• Do human-made things already outweigh all life on Earth, or will they by 2037?
• Concrete and gravel make up 79% of the mass of everything humans have made
• Everything humans have built and made weighs 27 times as much as in 1900
• A magnitude 9.5 earthquake releases roughly 5,600 times the energy of a magnitude 7
• A magnitude 7.7 earthquake struck 675 km down

All findings →