Obtaining reliable measurements of sea ice as it changes was difficult until the satellite era began in the early 1970s. Useful satellite data concerning sea ice began in late 1978 with the launch of NASA’s Scanning Multichannel Microwave Radiometer (SMMR) satellite.
Today, scientists from NSIDC primarily use to monitor Arctic sea ice, the Special Sensor Microwave/Imager (SSM/I) instrument on the Defense Meteorological Satellite Program (DMSP) satellite. The satellite passes over the polar region several times each day to gather data; researchers can then form the data into images for analysis and publication.
When scientists compare average sea ice conditions between years, they often use a 30-year reference period of 1981 to 2010. This reference period allows a consistent comparison of changes in extent over individual years.
Scientists monitor both Arctic and Antarctic sea ice, but Arctic sea ice is more significant to understanding global climate because much more Arctic ice remains through the summer months, reflecting sunlight and cooling the planet. Antarctica and the Arctic are reacting differently to climate change partly because of geographical differences.
Antarctica is a continent surrounded by water, while the Arctic is an ocean surrounded by land. Wind and ocean currents around Antarctica isolate the continent from global weather patterns, keeping it cold. In contrast, the Arctic Ocean is intimately linked with the climate systems around it, making it more sensitive to changes in climate.