On December 10, 1972, the world of sea ice data changed forever. For the first time in history, as the Electrically Scanning Microwave Radiometer (ESMR) launched aboard the NASA Nimbus-5 satellite, scientists gained the ability to track changes in sea ice cover over the Polar Regions every day via passive microwave data. Today, they can piece together a half century’s worth of data from several instruments and satellite missions, including ESMR, to better understand how global warming is affecting Arctic and Antarctic sea ice.