Satellite image showing the Arctic polar ice cap at its annual minimum extent on 16th September 2021. The yellow line shows the average minimum extent for the years 1981 to 2010. The Arctic sea ice (white, centre) reaches a minimum in September, at the end of the Arctic summer. This minimal ice area is called the perennial ice cover. The perennial ice has been steadily decreasing since satellites began observing it in 1979, at a rate of about 10 percent per decade. The sea ice here covers 4.72 million square kilometres. This decrease is attributed to global warming. Data from the Japan Aerospace Exploration Agency's Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument aboard the Global Change Observation Mission 1st-Water (GCOM-W1).