The Arctic has warmed at more than twice the global average, causing sea ice at the top of the world to melt faster than scientists had projected. This can be measured in square kilometers of ice cover, referred to as the sea ice extent. At the end of summer in 2019, at the time when Arctic sea ice extent reaches its annual minimum, the area covered by Arctic sea ice shrank to its second-lowest level since satellite monitoring began in 1979. The 13 years with the lowest sea-ice area have occurred in the last 13 years.
The loss of Arctic sea ice is a double whammy. Ice helps cool the Earth by reflecting solar energy back into space. Losing reflectivity is bad enough—the ocean around the ice becomes darker and absorbs energy, warming the water and melting more ice. The consequences are global, not only from faster heating, but from potential disruption to large-scale features of weather, such as the Northern winter polar vortex.
Since 1979, a succession of satellites have collected energy radiated from Arctic sea ice and surrounding water, allowing scientists to assemble maps of ice coverage. Unlike visible light, microwave radiation given off at the surface can pass through clouds, allowing the satellites to distinguish ice from water. The ice-extent data are produced by the National Snow and Ice Data Center at the University of Colorado-Boulder.
Short of artificially producing ice with water pumps or other not-yet-feasible means, there’s no direct fix for the melting Arctic besides arresting the overall release of heat-trapping gases. In the meantime, nations around the Arctic rim are busy adapting to the melt. Expect to see more shipping, fishing, fossil-fuel exploration and strategic military activity.