September Sea Ice Outlook: June Report

Release Date: 
14 June 2013

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With 23 pan-arctic Outlook contributions, an increase over the last two years (thank you!), the June Sea Ice Outlook projects a September 2013 arctic sea extent (defined as the monthly average for September) median value of 4.1 million square kilometers, with quartiles of 3.8 and 4.4 million square kilometers (Figure 1).

The consensus is for an increasing downward trend of September sea ice extent. We interpret the split of 2013 Outlooks above and below the 4.1 median to different interpretations of the guiding physics: those who considered that observed sea ice extent in 2012 being well below the 4.1 level indicates a shift in arctic conditions, especially with regard to reduced sea ice thickness and increased sea ice mobility; and those with estimates above 4.1 who support a return to the longer-term downward trend line (1979-2007). It is always important to note for context that all estimates are well below the 1979–2007 September mean of 6.7 million square kilometers.

This month's report includes details on the causes of the 2012 minimum, the use of sea ice volume versus extent, sea ice in climate models, and late spring 2013 conditions. There has been a lot of discussion over the past few years on the use of sea ice volume as a better index than sea ice extent for use in Outlooks. For example, the events of summer 2012 suggest that spring sea ice extent is probably not the best variable on which to base summer Outlooks. Sea ice anomalies at the springtime maximum probably have more to do with what is happening to weather over subarctic seas rather than what is happening to preconditioning of sea ice in the Arctic Basin proper.

Individual responses continue to be based on a range of methods: statistical, numerical models, comparison with previous rates of sea ice loss, estimates based on various non-sea ice datasets and trends, and subjective information (i.e., the "heuristic" category). In addition to the 23 pan-arctic Outlooks, we have four regional Outlooks that provide more detail for the Northwest Passage, the Arctic Bridge (Hudson Bay / Hudson Strait), Nares Strait and the Lincoln Sea, and the Greenland and Barents Seas.

Figure 1. Distribution of individual Pan-Arctic Outlook valuesFigure 1. Distribution of individual Pan-Arctic Outlook values (June Report) for September 2013 sea ice extent (values are rounded to the tenths). Download High Resolution Version of Figure 1.

The Pan-Arctic report was developed by Jim Overland, NOAA, and Helen Wiggins, ARCUS. The Regional report was developed by Adrienne Tivy, National Research Council Canada, with assistance from Kristina Creek, ARCUS.