Global warming has driven a sharp decline in Arctic sea ice “area” in recent decades. This has been matched by a harder-to-see, but equally sharp, drop in sea ice “thickness”.
In all there has been a stunning collapse in sea ice “volume”.
In 1979 the volume was 16,855 cubic kilometres.
In 2016 this has dropped to 4,401 cubic kilometres.
So, the volume of Arctic ice has crashed to about one quarter of what it was just 37 years ago.
Think Progress: 15 Oct 2016