These are the September averages on 2000-2018 (in millions km2):

Year Extent
10^6 km2
1980′s Avg. 7.21
1990′s Avg. 6.66
2000′s Avg. 5.65
2010′s Avg. 4.68
2000 6.25
2001 6.73
2002 5.83
2003 6.12
2004 5.98
2005 5.50
2006 5.86
2007 4.27
2008 4.69
2009 5.26
2010 4.87
2011 4.56
2012 3.57
2013 5.21
2014 5.22
2015 4.62
2016 4.53
2017 4.82
2018 4.71