The Arctic Ocean is the mass of water positioned approximately above latitude 65° N. Arctic Sea Ice refers to the area of the Arctic Ocean covered in ice. The Arctic sea ice minimum is the day in a given year when Arctic sea ice reaches its smallest extent. It occurs at the end of the summer melting season, normally during September. Arctic Sea ice maximum is the day of a year when Arctic sea ice reaches its largest extent near the end of the Arctic cold season, normally during March. Typical data visualizations for Arctic sea ice include average monthly measurements or graphs for the annual minimum or maximum extent, as shown in the adjacent images.
An article in Popular Mechanics, published in March 1912, described open waters in the Arctic regions in 1911, a year with exceptional above average temperatures.
Observation with satellites show that Arctic sea ice area, extent, and volume have been in decline for a few decades. Sometime during the 21st century, sea ice may effectively cease to exist during the summer. Sea ice extent is defined as the area with at least 15% ice cover. The amount of multi-year sea ice in the Arctic has declined considerably in recent decades. In 1988, ice that was at least 4 years old accounted for 26% of the Arctic's sea ice. By 2013, ice that age was only 7% of all Arctic sea ice.
Scientists recently measured sixteen-foot (five-meter) wave heights during a storm in the Beaufort Sea in mid-August until late October 2012. This is a new phenomenon for the region, since a permanent sea ice cover normally prevents wave formation. Wave action breaks up sea ice, and thus could become a feedback mechanism, driving sea ice decline.
For January 2016, the satellite based data showed the lowest overall Arctic sea ice extent of any January since records begun in 1979. Bob Henson from Wunderground noted: