Arctic sea ice extent shrunk down to 2.0 million square miles (5.1 million square kilometers) in September 2013—18 percent below the 1981-2010 average, but larger than record low set in 2012.

Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Climate scientists are wondering if a warmer Arctic could explain its odd behavior in recent years.

(Video) Thick, old ice used to dominate the winter ice pack in the Arctic. This animation of maps of sea ice age from 1987 through end of October 2013 shows how little old ice is left in the Arctic.

To be consistent with NOAA's use of 30-year periods for the official "climate normals," the National Snow and Ice Data Center switched its baseline period for sea ice analyses from 1979-2000 to 1981-2010.  Compared to the new normal, the low ice conditions of the recent past will appear less abnormal than they used to.

 

In 2012, sea ice melted to a record-breaking minimum extent. At the end of the summer melt season, ice covered only about half of the average area it did from 1979–2000.

Arctic sea ice extent fell to 1.58 million square miles on August 26, 2012. This was 27,000 square miles smaller than the previous record low of 1.61 million square miles set in 2007.

In September 2011, Arctic sea ice reached its second-lowest minimum extent in the satellite record.

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