What was done
For three areas of the world -- (1) North Carolina, USA, (2) South Finland, comprising all of Finland except the northern provinces of Oulu and Lapland, and (3) Southeast England, comprising Greater London, Essex, Kent, Sussex, Hampshire, Surrey, Berkshire, Oxfordshire, Buckinghamshire and Bedfordshire -- the authors determined the mean daily May-August 3°C temperature band in which deaths of people aged 55 and above were at a minimum.  Then they compared heat- and cold-related deaths that occurred at temperatures above and below this optimum temperature interval for each region, after which they determined how heat-related deaths in the three areas changed between1971 and 1997 in response to the 1.0°C temperature rise that was experienced in North Carolina over this period (from an initial temperature of 23.5°C), the 2.1°C temperature rise experienced in Southeast England (from an initial temperature of 14.9°C), and the unchanging 13.5°C temperature of South Finland.

What was learned
First, it was determined that the 3°C temperature band at which mortality was at its local minimum was lowest for the coolest region (South Finland), highest for the warmest region (North Carolina), and in between for the "in between" region (Southeast England), which suggests that the populations of the three regions were somewhat acclimated to their respective thermal climates.  Second, for each region it was determined that cold-related mortality, expressed as excess mortality at temperatures below the 3°C temperature band at which mortality was at its local minimum, was greater than heat-related mortality, expressed as excess mortality at temperatures above the 3°C temperature band at which mortality was at its local minimum.

As for the third aspect of the study, i.e., changes in heat-related mortality from 1971 to 1997, it was determined that in the coldest of the three regions (South Finland, where there was no change in temperature over the study period), heat-related deaths per million inhabitants in the 55-and-above age group declined from 382 to 99.  In somewhat warmer Southeast England, however, where it warmed by a whopping 2.1°C over the study period, heat-related deaths per million of the at-risk age cohort still declined, but this time from only 111 to 108.  Last of all, in the warmest of the three regions (North Carolina, where mean daily May-August temperature rose by 1.0°C over the study period), corresponding heat-related deaths also fell, and this time from 228 to a mere 16 per million.

What it means
First of all, people can adapt to both warmer and cooler climates to some degree.  Beyond that, however, local cooling tends to produce many more deaths than local warming in all three of the areas studied, as has also been demonstrated to be the case in a number of other locations around the world [see Mortality (Cold Weather) in our Subject Index].  As for the dramatic decline in the number of heat-related deaths over a period of warming in the hottest area of this specific study (North Carolina), the authors attribute this phenomenon to "the increase of air conditioning in the South Atlantic region of the U.S.A.," where they note that "the percentage of households with some form of air conditioning in that region rose from 57% in 1978 to 72% in 1997."  With respect to the declining heat-related deaths in the other two regions, they say "the explanation is likely to lie in the fact that both regions shared with North Carolina an increase in prosperity [our italics], which could be expected to increase opportunities for avoiding heat stress."

In summary, cold kills far more people than heat; and prosperity brings with it an enhanced ability to protect oneself even further from the stress of high temperatures.