Sea Ice Extent

September's Northern Hemisphere
Sea Ice Extent plot

According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere (Arctic) sea ice extent — which is measured from passive microwave instruments onboard NOAA satellites — averaged for September 2015 was 4.63 million square km (1.79 million square miles), 1.88 million square km (720,000 square miles), or 28.88 percent, below the 1981-2010 average. This was the fourth smallest September Arctic sea ice extent in the 37-year satellite record and 1.01 million square km (390,000 square miles) above the record low monthly average for September that occurred in 2012. Overall, September Arctic sea ice extent is decreasing at an average rate of 13.1 percent per decade. According to the NSIDC, sea ice extent was below average in nearly all regions of the Arctic, with the exception of the Barents Sea and part of the northern area around the Canadian Archipelago. For the entire month of September, the Roald Amundsen's route through the Northwest Passage and the Northern Sea Route were both ice free and navigable by ship. This is the fifth time in recorded history that the Northwest Passage has been open, the other times occurring in 2007, 2008, 2010, and 2011.

September's Northern Hemisphere
Sea Ice Extent plot

On September 11^th, the Artic sea ice extent reached its annual minimum, four days earlier than average. The 2015 minimum was 4.41 million square km (1.70 million square miles), 1.81 million square km (699,000 square miles) below the 1981-2010 average, but 1.02 million square km (394,000 square miles) larger than the smallest annual minimum extent that occurred in 2012. The 2015 minimum extent was the fourth smallest in the satellite record behind 2012, 2007, and 2011. The nine lowest minimum extents in the satellite era have all occurred in the last nine years. From the annual maximum extent that occurred on February 25^th to the minimum extent, the Arctic lost a total of 10.13 million square km (3.91 million square miles) of ice, which was 1.68 million square km (651,000 square miles) less than the record ice loss that occurred in 2012.

September's Southern Hemisphere
Sea Ice Extent plot

The September 2015 Southern Hemisphere (Antarctic) sea ice extent was 18.69 million square km (7.22 million square miles), 100,000 square km (30,000 square miles), or 0.53 percent, below the 1981-2010 average. This was the 16^th smallest September Antarctic sea ice extent on record and smallest since 2008. Sea ice expanded slowly during much of September, with the extent even decreasing at certain points of the month. The ice growth accelerated towards the end of the month, with the daily sea ice extent above average on September 30^th. September Antarctic sea ice extent is increasing at an average rate of 1.1 percent per decade. The Antarctic sea ice extent continued to expand until October 6^th when the maximum extent occurred at 18.83 million square km (7.24 million square miles), 120,000 square km (46,000 square miles) above the average. This was the 16^th largest maximum extent on record. Additional details on the Antarctic sea ice maximum extent will be available in the October report released in November.

When combining the Northern Hemisphere and Southern Hemisphere sea ice extents, the globally-averaged sea ice extent during September was 23.32 million square km (9.00 million square miles), 7.79 percent below the 1981-2010 average and the third smallest September global sea ice extent on record. This was the smallest September global sea ice extent since 2012. September global sea ice extent is decreasing at an average rate of 2.53 percent per decade.

For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.

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