The record melting of Arctic sea ice observed this summer and fall led to record-low levels of ice in both September and October, but a record-setting pace of re-freezing in November, according to the NASA Earth Observatory. Some 58,000 square miles of ice formed per day for 10 days in late October and early November, a new record.
Still, the extent of sea ice recorded in November was well shy of the median extent observed over the past quarter century, as the image from Nov. 14 (above, right) shows. The dramatic increase in ice is evident, when compared to the record-low amount observed Sept. 16 (below, right). In both images, 100% sea ice is shown in white, and the yellow line encompasses the area ion which there was at least 15% ice cover in at least half of the 25-year record for the given month.
The record melting of Arctic sea ice this summer was widely viewed as a harbinger of global warming, though unusual wind patterns played a role and many factors affecting fluctuations in Arctic ice are poorly understood by scientists. Still, so much ice melted that the fabled Northwest passage opened for the first time in history, and the melting broke a record, set just two years ago and by a country mile, that at the time was seen as unprecedented and worrying.
The area of persistent open water north of Alaska and eastern Siberia, according to NASA, is unusual for this time of year, though not unprecedented. This area was also largely free of ice in November 2002 and especially November 2006.
Here's how NASA explains the record re-growth of ice over that 10-day period in October and November:
Record sea ice growth rates after a record low may sound surprising at first, but it is not completely unexpected. The more ice that survives the summer melt, the less open water there is for new ice to grow. When summertime ice extent hits a record low, on the other hand, large areas of open water provide room for the ice to grow once temperatures cool off enough. While summer warming of the upper ocean surface can cause wintertime sea ice regrowth to lag initially, as the fall season progresses and sunlight weakens, the rate of energy loss from the ocean increases. That heat loss coupled with a large area of open water creates ideal conditions for sea ice to form rapidly over large areas.
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