Paper Reviewed
Wang, X.L., Feng, Y. and Vincent, L.A. 2014. Observed changes in one-in-20 year extremes of Canadian surface air temperatures. Atmosphere-Ocean 52: 222-231.

According to Wang et al. (2014), "there have been a few studies on extreme indices of temperature in Canada (e.g., Bonsal et al., 2001), generally finding that there are fewer cold nights, cold days, frost days, and more warm nights, warm days, and summer days across Canada (Vincent and Mekis, 2006)." And they note that an increase of 1.5°C in the national average annual mean temperature over the 1950-2010 period has been reported by Vincent et al. (2012). However, they state that "there has not been a study of Canada-wide temperature extremes with return periods of several years to decades nor any assessment of changes in temperature extremes as inferred from extreme value distribution analysis."

In an effort designed to fill this void, Wang et al. analyzed data from 115 Canadian weather stations that recorded daily temperature observations for at least 90 years during the 1910-2011 period, as well as 31 northern stations that have at least 44 years of data spanning the 1951-2011 period. In doing so the three researchers report finding that "warming is strongest for extreme low temperature and weakest for extreme high temperature," as well as "stronger in the Canadian Arctic than in southern Canada." And they also report that "warming is stronger in winter than in summer and stronger during nighttime than daytime of the same season."

"Overall," in the concluding words of Wang et al., "our results are consistent with those reported in previous studies, particularly in the sense that Canada has become much less cold but not much hotter."

References
Bonsal, B.R., Zhang, X., Vincent, L.A. and Hogg, W.D. 2001. Characteristics of daily and extreme temperatures over Canada. Journal of Climate 14: 1959-1976.

Vincent, L.A. and Mekis, E. 2006. Changes in daily and extreme temperature and precipitation indices for Canada over the twentieth century. Atmosphere-Ocean 44: 177-193.

Vincent, L.A., Wang, X.L., Milewska, E.J., Wan, H., Yang, F. and Swail, V. 2012. A second generation of homogenized Canadian monthly surface air temperature for climate trend analysis. Journal of Geophysical Research 117: 10.1029/2012JD017859.