Since satellite monitoring began in 1979, sea ice in the Arctic has been on the decline, shrinking by about 10 to 12 percent per decade. In the summer of 2007, Arctic sea ice cover shrank to an unprecedented low. At this rate, researchers project that the Arctic may experience a summer completely devoid of ice by the end of the century.   

Vast expanses of sea ice make the Arctic and Antarctic oceans perilous and inhospitable, but they’re also vital guardians of Earth’s climate.

Sea ice forms when ocean water is cooled to the freezing point by cold polar air. Freezing begins in fall, when the amount of light from the sun decreases, and ice continues to expand and thicken during the dark winter months. When summer returns, the sun’s energy warms the surface of the ice, causing portions of it to melt.