I'm sorry Ellis - but your statement "for the first time in recorded memory the fabled north west passage around the north of Canada in navigable to non-specialised ships" is simply false. (I'm not saying you're lying, but simply misinformed by a media who salivates for sensationalist headlines)
It is called the "Northwest Passage" for a reason, meaning ships have used it before. And yes, it certainly did, and does exist.
-Norwegian explorer Roald Amundsen made the passage in 1906.
-In 1940 Canadian RCMP officer Henry Larsen did it, and repeated it again in 1944
-The United States Coast Guard cutter Storis did it in 1957
-A reinforced tanker did it in 1969 (granted a "specialized" ship), with an ice-breaker as an escort. This was done to test the economics of commercially using the Northwest Passage, but was deemed not to be cost-effective.
-In June 1977 sailor Willy de Roos, did it in his his 13.8 m (45 ft) steel yacht Williwaw (hardly a "specialized" ship).
-More recently, in 2005, a 14.3 m (47 ft) aluminum sailboat, Northabout, built and captained by Jarlath Cunnane successfully navigated the Northwest Passage.
This is all available on the northwest passage wiki http://en.wikipedia.org/wiki/Northwest_Passage
As far as how this may, or may not relate to GW - I'm not at all convinced the warming of the Artic (and yes, I agree it is warming), is indicative of a global trend.
Here's a graph of northern hemisphere ice anomalies http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg
You can see the ice really started dropping around 2001.
Now, let's look at the estimate of global average temperature http://www.metoffice.gov.uk/research/hadleycentre/obsdata/HadCRUT3.html
Scroll down, and you can find the plot of monthly temp anomalies. It's sort of hard to tell, but from 2001 onwards, it looks like temperature has been trending downward, or at least having no trend. But certainly not trending up.
So, we have constant, or even cooling global temps over the past 6-7 years, but a significant reduction in ice cover in that same time. Still think this local warming is indicative of a global warming trend?
Combine this with the fact that Antarctica is not warming, or that rural stations in Africa or South America show no warming, or that since Hanson's "error" has been corrected, the US has an almost flat temp trend - shows (to me at least), the recent Artic warming is much more likely to be a regional effect, then a global effect.