Paper Reviewed
Diaz, J., Carmona, R., Miron, I.J., Ortiz, C. and Linares, C. 2015. Comparison of the effects of extreme temperatures on daily mortality in Madrid (Spain), by age group: The need for a cold wave prevention plan. Environmental Research 143: 186-191.

In this extremely enlightening paper, Diaz et al. (2015) analyzed data on daily deaths due to natural causes in the city of Madrid (Spain) over the period 2001-2009, calculating the impact of both extreme hot and cold temperatures on mortality using Poisson regression models for specific age groups. And what did they thereby learn?

The five Spanish researchers report that "the mean intensity of the heat waves (0.8°C) was half that of the cold waves (1.7°C)." However, they found that the effect of cold on mortality was five times greater than that of heat. And if that sounds a bit extreme, they further note that the recent study of Gasparrini et al. (2015) showed, on a global basis, that cold-induced mortality is fully twenty times higher than that induced by heat.

This being the case, one would hope that any future global warming experienced by the Earth would be more strongly expressed by daily minimum temperatures than by daily maximum temperatures. And, fortunately, this is what has been found to have been the case to date, as has been demonstrated by the studies of Karl et al. (1984, 1991), Easterling et al. (1997), Donat et al. (2013) and Gasparrini et al. (2015), to name but a few.

References
Donat, M.G., Alexander, L.V., Yang, H., Durre, I., Vose, R., Dunn, R.J.H., Willett, K.M., Aguilar, E., Brunet, M., Caesar, J., Hewitson, B., Jack, C., Klein Tank, A.M.G., Kruger, A.C., Marengo, J., Peterson, T.C., Renom, M., Rojas, C.O., Rusticucci, M., Salinger, J., Elrayah, A.S., Sekele, S.S., Srivastava, A.K., Trewin, B., Villarroel, C., Vincent, L.A., Zhai, P., Zhang, X. and Kitching, S. 2013. Updated analyses of temperature and precipitation extreme indices since the beginning of the twentieth century: The HadEX2 dataset. Journal of Geophysical Research (Atmospheres) 118: 2098-2118.

Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K. 1997. Maximum and minimum temperature trends for the globe. Science 277: 364-367.

Gasparrini, A., Guo, Y., Hashizume, M., Kinney, P.L., Petkova, E.P. and Lavigne, E. 2015. Temporal variation in heat-mortality associations: a multi-country study. Environmental Health Perspectives: 10.1289/chp.1409070.

Karl, T.R., Jones, P.D., Knight, R.W., Kukla, G., Plummer, N., Razuvayev, V., Gallo, K.P., Lindseay, J., Charlson, R.J. and Peterson, T.C. 1984. A new perspective on recent global warming: asymmetric trends of daily maximum and minimum temperature. Bulletin of the American Meteorological Society 74: 1007-1023.

Karl, T.R., Kukla, G., Razuvayev, V.N., Changery, M.J., Quayle, R.G., Heim Jr., R.R., Easterling, D.R. and Fu, C.B. 1991. Global warming: evidence for asymmetric diurnal temperature change. Geophysical Research Letters 18: 2253-2256.