New Scientist - Average Polar Ice Thickness, 2004 - 2.6 Meters; Average Thickness, 2007 - 1.3 Meters

Last spring we broke the news that the North Pole could be ice-free this summer. Now we've got some numbers that show just how thin the ice at the North Pole has become over the past 17 years, and they suggest that Santa isn't sitting very pretty.

Christian Haas of the Alfred Wegener Institute for Polar and Marine Research in Germany and colleagues estimated the thickness of late summer ice at the North Pole in 2001, 2004 and 2007. They found that the ice was on average 1.3 metres thick at the end of the summer in 2007. By contrast, it was 2.3 metres thick in 2001 and 2.6 metres thick in 2004.

Measuring polar ice thickness has always presented a bit of a challenge, particularly in remote areas like the North Pole. Haas and colleagues flew a helicopter equipped with a device that detects ice thickness remotely by measuring its conductivity.

Previously, glaciologists had gone to the same region and measured ice thickness by placing instruments directly on the ice. Records from 1991 show that the summer ice that year was 3.1 m thick.

EDIT

http://www.newscientist.com/blog/environment/2008/07/just-how-thin-is-north-pole-ice.html?DCMP=ILC-hmts&nsref=specrt12_head_Santa%20on%20thin%20ice

Wikipedia helped me out

http://youtube.com/watch?v=PtS45bh_INY