September is the month of the year when historically the minimum annual in Arctic sea ice extent occurs. This year we have broken the record again, and by a decent margin. The sea ice area had shrunk to below 4 million square kilometers by the 5th September.
Image from: http://nsidc.org/arcticseaicenews/
Information on the data used: http://nsidc.org/arcticseaicenews/about-the-data/