Paper Reviewed
Huang, C., Chu, C., Wang, X. and Barnett, A.G. 2015. Unusually cold and dry winters increase mortality in Australia. Environmental Research 136: 1-7.

In a study involving five major cities in Australia -- Sydney, Melbourne, Brisbane, Perth and Adelaide -- Huang et al. (2015) split "seasonal patterns in temperature, humidity and mortality into their stationary (seasonal) and non-stationary (unseasonal) parts," where "a stationary seasonal pattern is consistent from year-to-year, and a non-stationary pattern varies from year-to-year," with the aim to determine "how unseasonal patterns in temperature and humidity in winter and summer were associated with unseasonal patterns in death."

Working with daily mortality data from 1 January 1988 to 31 December 2009 for each city -- which totaled more than 1.5 million deaths -- the four researchers found there were "far more deaths in winter," such that "death rates were 20-30% higher in a winter than a summer" (see figure below) And they add that "this seasonal pattern is consistent across much of the world, and many countries suffer 10% to 30% excess deaths in winter," citing the studies of Healy (2003) and Falagas et al. (2009).

Stationary seasonal patterns of mortality (standardized to January) in the five Australian cities studied (1988–2009). Adapted from Huang et al. (2015).

Also of note, Huang et al. report that winters that were colder or drier than a typical winter had significantly increased death risks, whereas "summers that were warmer or more humid than average showed no increase in death risks." And, therefore, we continue to find ever more evidence that warming of the globe actually leads to fewer deaths from all causes combined than does maintaining the thermal status quo.

References
Falagas, M.E., Karageorgopoulos, D.E., Moraitis, L.I., Vouloumanou, E.K., Roussos, N., Peppas, G. and Rafailidis, P.I. 2009. Seasonality of mortality: the September phenomenon in Mediterranean countries. Canadian Medical Association Journal 181: 484-486.

Healy, J.D. 2003. Excess winter mortality in Europe: a cross country analysis identifying key risk factors. Journal of Epidemiology and Community Health 57: 784-789.