I should think that it is the Great Circle Route by way of Alaska, the reverse of how they flew the Freedom Birds out of VietNam or how one would fly to SYK's paradise in Singapore. When we flew to Zurich from Dulles last summer, it was by way of Gander, Newfoundland. Do you all remember when they grounded all of the airtraffic after the 9/11 attacks? This little town of Gander was swamped by some 60 or more trans-Atlantic jumbo jets that were not able to be turned around in time. The locals rallied and provided true hospitality for everyone for the next couple of days before they were able to fly out again. Try to remember that the North Atlantic Air Corridor is the busiest in the world and it was suddenly gounded for two days.
I am not certain why flying so far north is the most efficient way, but it seems to be whether you are going to Europe or to East Asia.