Peter Wadhams on the Catlan Arctic Survey

This is an excellent description of the need to measure the Arctic sea ice's thickness physically during the winter by using upward-looking radar of British submarines or manually drilling into it.  The thickness during the winter is the greatest factor for how much the extent will decline during the summer.
  https://www.youtube.com/watch?feature=endscreen&NR=1&v=q190H5MHmn4