How do we know that sea ice at the poles is melting? VIDEOGRAPHIC
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00:00How do we know that sea ice at the poles is melting?
00:05Sea ice forms when seawater freezes on the surface in cold weather.
00:09In summer, part of it melts and reforms in winter.
00:14To measure its extent, weather agencies use satellite data, which can distinguish between
00:19the sea and the ice at the surface.
00:22At a certain concentration of white, generally 15%, a zone is considered covered by sea
00:28ice.
00:30By adding together the ice surfaces detected, the total area of sea ice can be measured
00:34each day.
00:36This is how we know that in September 2023, the month with the least ice in the North
00:41Pole, the sea ice extent was about 30% less than compared to the September average during
00:47the 20th century.