Tuesday, December 18, 2012

Evidence of climate change: Snow depth and chance of white Christmas decreasing

When a major storm hits, some people say 'climate change'. But should avoid doing so, since individual events by themselves, no matter how record-breaking, cannot be used to determine a long-term trend.

Telling evidence of climate change can only come from looking at long term changes, i.e. comparing certain averages from lengthy periods many years ago to the same data for more recent periods.

Environment Canada has a very interesting page documenting the likelihood of a white Christmas. In it they compare data from the period 1992-2011, to the period 1963-1982 (my childhood to my adulthood). The results are startling.

Snow depth: Out of 39 cities, 33 have seen a decrease in snow depth, and only four (Vancouver, Victoria, Hamilton and Brandon) have seen an increase. 12 cities now see less than half the snow they used to on Christmas day: The following are the percent changes in depth:

Fredericton -72.7%
Halifax -70.0%
Kamloops -63.6%
Saint John -63.6%
Moncton -60.9%
Penticton -60.0%
Charlottetown -58.8%
Sarnia -55.6%
Stephenville -52.2%
Quebec -51.2%
Kelowna -50.0%
Montreal -50.0%

Chance of a white Christmas: 31 of the 49 cities have seen chances of a white Christmas drop. Only three (St. John's, Victoria and Vancouver) have seen an increase. Sarnia holds the record, having a 56% lower chance of a white Christmas; Toronto Airport is not far behind at 46% lower.

This is clear evidence of climate change right across Canada. The regional differences are particularly interesting. Decreases in depth can be noted from Whitehorse to most of the Prairies, throughout Ontario, Quebec, and the Atlantic provinces.

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