World of change: Arctic ice sea extent
source: http://earthobservatory.nasa.gov/Features/WorldOfChange/sea_ice.php
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Layers of frozen seawater, known simply as sea ice, cap the Arctic Ocean. Ice grows dramatically each winter, usually reaching its maximum in March. The ice melts just as dramatically each summer, generally reaching its minimum in September. These image pairs show Arctic sea ice concentration for the month of September (left) and the following March (right) for a time series beginning in September 1999 and ending in March 2009.
The yellow outline on each image shows the median sea ice extent observed by satellite sensors in September and March from 1979 through 2000. Extent is the total area in which ice concentration is at least 15 percent. The median is the middle value. Half of the extents over the time period were larger than the line, and half were smaller.
Since 1978, satellites have monitored sea ice growth and retreat, and they have detected an overall decline in Arctic sea ice. The rate of decline steepened after the turn of the twenty-first century. In September 2002, the summer minimum ice extent was the lowest it had been since 1979. Although the September 2002 low was only slightly below previous lows (from the 1990s), it was the beginning of a series of record or near-record lows in the Arctic.
This series of record lows, combined with poor wintertime recoveries starting in the winter of 2004-2005, marked a sharpening in the rate of decline in Arctic sea ice. Sea ice did not return to anything approaching the long-term average (1979-2000) after 2002.
end of excerpt.
The yellow outline on each image shows the median sea ice extent observed by satellite sensors in September and March from 1979 through 2000. Extent is the total area in which ice concentration is at least 15 percent. The median is the middle value. Half of the extents over the time period were larger than the line, and half were smaller.
Since 1978, satellites have monitored sea ice growth and retreat, and they have detected an overall decline in Arctic sea ice. The rate of decline steepened after the turn of the twenty-first century. In September 2002, the summer minimum ice extent was the lowest it had been since 1979. Although the September 2002 low was only slightly below previous lows (from the 1990s), it was the beginning of a series of record or near-record lows in the Arctic.
This series of record lows, combined with poor wintertime recoveries starting in the winter of 2004-2005, marked a sharpening in the rate of decline in Arctic sea ice. Sea ice did not return to anything approaching the long-term average (1979-2000) after 2002.
end of excerpt.
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