Paper Reviewed
Todd, N. and Valleron, A.-J. 2015. Space-time covariation of mortality with temperature: A systematic study of deaths in France, 1968-2009. Environmental Health Perspectives 123: 659-664.

Minimum mortality temperature (MMT) is defined as the temperature at which the lowest mortality rate for a given location occurs over a given time period of examination. Above and below this value mortality rates increase as temperatures rise and fall, respectively.

Writing as background for their work, Todd and Valleron (2015) note that MMT values in comparative studies from different latitudes are repeatedly shown to be higher in locations where the mean summer temperature is higher. Such observations, according to the two French researchers, have led to the interpretation that humans are capable of adapting to local climatic conditions. However, they additionally note that "drawing conclusions from this geographic observation about the possible adaptability of human populations to future climate change requires observing that, similarly, MMT at a given location changes over time when climate changes." And with this caveat in mind, Todd and Valleron set out to investigate whether or not the MMT for a given location does indeed change over time as climate changes.

To accomplish their objective, the two scientists examined the change in MMT in France over (1) the entire 42-year period from 1968-2009, and (2) three 14-year subsets: 1968-1981, 1982-1995 and 1996-2009. Data utilized in their study included two hundred and twenty eight 0.5 x 0.5 degree latitude/longitude grid squares of daily mean temperature and individual death certificate information for persons > 65 years old who died in France over the 42-year period of examination (approximately 16.5 million persons).

Their results indicate that MMT was strongly correlated with, and had a positive linear relationship with, mean summer temperature over the entire period. It was also determined that mean MMT increased from 17.5°C in the first 14-year period (1968-2981) to 17.8°C and 18.2°C in the second (1982-1995) and third (1996-2009) time periods examined. And in light of these findings, coupled with the fact that there was an increase in temperature between each of these time periods, Todd and Valleron conclude that their "spatiotemporal analysis indicated some human adaptation to climate change, even in rural areas."