What was done
According to the authors, "in Canada, extreme temperature events, especially those during winter, can have many adverse environmental and economic impacts."  Hence, their focus in this paper was "to examine observed trends and variability in the frequency, duration, and intensity of winter (Jan-Feb-Mar) cold and warm spells over Canada during the second half of the 20th century."

What was learned
From 1950-1998, western Canada experienced decreases in the frequency, duration and intensity of winter cold spells.  In the east, however, distinct increases in the frequency and duration of winter cold spells occurred.  With respect to winter warm spells, significant increases in both their frequency and duration were observed across most of Canada, with the exception of the extreme northeastern part of the country, where warm spells appear to be becoming shorter and less frequent.

What it means
In the mean, there appear to be close-to-compensating trends in the frequency and intensity of winter cold spells in different parts of Canada, while winter warm spells appear to be increasing overall.  Hence, the last half-century has seen a positive climatic shift indicative of less adverse consequences of extreme winter weather in Canada.