Readers may recall that in the past couple of winters I've mentioned the odd reluctance of the Yukon River to freeze up properly at Dawson in the Yukon Territory. This has created a problem for residents of West Dawson who in years past relied on an ice bridge for seasonal access to the main town on the east side of the river.
Perhaps not surprisingly, the same problem has occurred this winter, and efforts to stimulate ice growth across the stubbornly open channel were called to a halt last week. Here are a couple of news articles on this winter's lack of success:
Here's a view from the webcam in Dawson a few days ago, looking out across the river; as in past winters, a narrow strip of open water is visible.
The lack of an ice bridge has been deemed sufficiently important that Canada's National Research Council looked into the issue last year, and a report was issued in October; it makes for very interesting reading. The report discusses a variety of hypotheses about what may have caused the change, but there are no definitive conclusions; there may be multiple factors at play, some of which we've speculated about before on this blog (including good comments from readers).
As we've noted before, the change in ice conditions can't simply be pinned on warmer winter weather, because temperature data from Dawson doesn't show substantially warmer conditions in the winters when freeze-up failed. The accumulated total of freezing degree days has been slightly lower this winter than the two-decade normal, but 2016-17 and 2017-18 were both near normal through this point in the season (see below). Of course it is possible that ground and/or river water temperatures have risen, as noted in the NRC report.