Arctic sea ice has shrunk to its lowest level since satellite records began in 1979.
NASA says the extent of the ice is currently 410 square km compared with a previous low of 417 square km on 18 September 2007.
The volume was also down on 21 September 2005.
Sea ice normally reaches a low point in September so it is thought likely this year's melt will continue to grow.
The BBC reports the sea ice cap grows during Arctic winters and shrinks when temperatures climb again, but during the past three decades, satellites have observed a decline of 13% per decade in the summertime minimum.
The thickness of the sea ice is also declining, so overall the ice volume has fallen far - although estimates vary about the actual figure.