Here is the summary of the Summer melt season from the NSIDC.
And here is a graph.
Interesting explanation about the North West Passage; this year’s event truly is exceptional. Shame about the Northern Sea Route, though.
Though I think it may be slightly contentious, the observation of a decline of 10% per decade, for five decades, (or even if you choose to allow lower numbers and less time) probably counts as a definitive trend.
EDIT: Andy Revkin’s article for the NY Times says it so much more eloquently than I have managed… and note that statistic at the end; ‘Old ice’ down from 80% to 2%…