Satellite image showing the Artic sea ice annual minimum on 19 September 2023. The sea ice has shrunk during the northern hemisphere summer and reached its minimum extent. At 4.23 million square kilometres, this was the sixth-lowest year of sea ice cover in the satellite record. The yellow line shows the median ice cover at this time of year for period 1981 to 2010. Scientists track the seasonal and annual fluctuations because sea ice plays a large role in Earth?íG polar ecosystems and global climate. Data collected by microwave sensors (SSM/I and SSMIS) on the United States Space Force's Defense Meteorological Satellite Program (DMSP) satellite and by the Scanning Multichannel Microwave Radiometer (SMMR) on NASA's Nimbus-7 satellite.