Annual minimum Arctic sea ice, 2015. Computer illustration showing the Arctic sea ice (white with blue tint, top) on 11th September 2015, when it reached its annual minimum extent. The Arctic sea ice reaches a minimum in September, at the end of the Arctic summer. This minimum 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. This decrease is attributed to global warming. Image based on data acquired by the Japan Aerospace Exploration Agency's (JAXA) Advanced Microwave Scanning Radiometer 2 (AMSR2) instrument, onboard the Global Change Observation Mission 1st-Water 'SHIZUKU' (GCOM-W1) satellite.