Guest essay by Eric Worrall
The New York Times has taken the unusual step of publishing something factual about the relative risks of cold and hot weather.
Beware: Winter Is Coming
By JANE E. BRODY DEC. 19, 2016
Most of the Northern Hemisphere is now in the throes of the deadliest time of the year. Cold kills, and I don’t mean just extreme cold and crippling blizzards. I mean ordinary winter cold, like that typically experienced, chronically or episodically, by people in every state but Hawaii from late fall through early spring.
While casualties resulting from heat waves receive wide publicity, deaths from bouts of extreme cold rarely do, and those resulting from ordinary winter weather warrant virtually no attention. Yet an international study covering 384 locations in 13 countries, including the United States, found that cold weather is responsible, directly or indirectly, for 17 times as many deaths as hot weather.
Over time, as global temperatures rise, milder winter temperatures are likely to result in fewer cold-related deaths, a benefit that could outweigh a smaller rise in heat-caused mortality. In winter in the United States, mortality is generally 10 percent to 15 percent higher than on typical summer days.
The study, published in July 2015 in The Lancet, was based on an analysis of more than 74 million deaths and calculated mortality attributable to heat and cold in Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, Britain and the United States.
Furthermore, unlike what you might expect, the overwhelming majority of cold-weather casualties do not result from vehicular accidents, falls on ice or snow-related activities. Rather, they are attributable to leading killers like heart disease, stroke and respiratory disease, and are especially common among those aged 75 and older.
The 2015 Lancet Study is even clearer about what kind of weather causes excess deaths;
Our findings show that temperature is responsible for advancing a substantial fraction of deaths, corresponding to 7·71% of mortality in the selected countries within the study period. Most of this mortality burden was caused by days colder than the optimum temperature (7·29%), compared with days warmer than the optimum temperature (0·42%). Furthermore, most deaths were caused by exposure to moderately hot and cold temperatures, and the contribution of extreme days was comparatively low, despite increased RRs. The study was based on the largest dataset ever collected to assess temperature–health associations, and included more than 74 million deaths from 13 countries (panel). The analysis of data from 384 locations provides evidence for temperature-related mortality risk in a wide range of climates and populations with different demographic, socioeconomic, and infrastructural characteristics. A strength of the study was the application of new, flexible statistical models to characterise the temperature- mortality association and pool estimates across locations. In particular, while previous studies relied on simplification of the exposure-response or lag structure, the approach we used here enabled us to estimate and pool non-linear and delayed dependencies and to identify the temperature of minimum mortality.
We identified a substantial effect of heat and cold on mortality, with attributable figures that varied by country. The optimum temperature at which the risk is lowest was well above the median, and seemed to be increased in cold regions. Cold was responsible for a higher proportion of deaths than was heat, while moderate hot and cold temperatures represented most of the total health burden.
Our study also provides a platform to improve and extend predictions of the effects of climate change; our findings emphasise how a comprehensive assessment is needed to provide an appropriate estimate of the health consequences of various climate-change scenarios.
Looking at the graphs on page 371 of the Lancet Study, the optimum temperature varies significantly between different countries, but in all cases it is warm – around 25c (77F), warmer in countries which are used to hot weather.
While The Lancet stopped short of recommending more global warming, the message is pretty clear. A warmer world is a safer world for humans, especially older humans.