The end of white Christmases in southwestern Ontario?

According to a report from CTV News (a major Canadian network) out of southern Ontario:

Climate change making white Christmases a thing of the past: UW [University of Waterloo] prof... The chances of a white Christmas in southwestern Ontario are getting slimmer and slimmer.

To better understand whether this extraordinary claim could be true, here are the snow amounts on the ground on Christmas Day of each year dating back to the 1955 start of on-the-ground snow records in the Environment Canada online historical climate database for the three major long-term stations crossing southwestern Ontario in a diagonal.

There are no significant trends (not even remotely close) in the datasets, indicating that the average amount of snow on the ground at these sites on Christmas Day is not declining with time.

If the number of Christmas Days without snow on the ground in each running five-year period is plotted over time, none of the three sites shows any evidence whatsoever for an increasing likelihood of encountering a green Christmas.

If we divide up the period of record into 10-year-long blocks starting in 1955, there aren't any clear trends towards an increasing number of green Christmases, either.

Assuming that 2014 was a green Christmas throughout the region, adding another one to the last row doesn't change the conclusion that we are not seeing some historically anomalous increase in green Christmas probability throughout southwestern Ontario due to climate change.

Thus, there appears to be some difficulty reconciling historical trends with these statements from the CTV article:

That's what Jason Thistlethwaite thinks.

A professor at the University of Waterloo focused on climate change adaptation, Thistlethwaite says the 'quintessential' white Christmas is already 15 per cent less likely to occur in southern Ontario than it was in the 1970s and 1980s -- a trend he doesn't expect to shift anytime soon.

'The temperature's just going to be too high,' he said.

'If you do get a white Christmas, cherish it. A green Christmas is going to be the new normal.'

Specifically, Thistlethwaite points to a slow rise in the average local December temperature, to the point where it now sits only a degree or two below freezing.

Well, it is also important to note that the "average local December temperature" has not been rising over the last three decades at any of the stations in the Environment Canada Adjusted and Homogenized Canadian Climate Data database south of – and including – Toronto.  There are no statistically significant increasing trends in average December temperatures, and all but one of the stations in this area of southern Ontario have either cooling or nearly perfectly flat trends during the past 30 years.

It is difficult to say where the climate is headed, but if historical trends are any indication, concerns over the death of white Christmases may be overstated.

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