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Effects of Diurnal Temperature Range on Human Mortality
Kan, H., London, S.J., Chen, H., Song, G., Chen, G., Jiang, L., Zhao, N., Zhang, Y. and Chen, B. 2007. Diurnal temperature range and daily mortality in Shanghai, China. Environmental Research 103: 424-431.

What was done
Using daily weather and mortality data from Shanghai, China, the authors examined the association between Diurnal Temperature Range (DTR, defined as daily maximum temperature minus daily minimum temperature) and human mortality over the period 1 January 2001 to 31 December 2004 via a semi-parametric generalized additive model after controlling for covariates including time trend, day of week, temperature, humidity and outdoor air pollution levels.

What was learned
For cold days (below 23C), according to Kan et al., "a 1C increase of the 3-day moving average of DTR corresponded to 1.41%, 1.76% and 1.47% increases in total non-accidental, cardiovascular and respiratory mortality," while for warm days (above 23C), "an increase of 1C DTR corresponded to 1.13%, 1.91% and 0.54% increases in total non-accidental, cardiovascular and respiratory mortality."

What it means
Kan et al. say their data suggest that "even a slight increase in DTR is associated with a substantial increase in mortality." In addition, they correctly note that over the course of the past century, global warming has been characterized by "the daily minimum temperature increasing at a faster rate ... than the daily maximum, resulting in a decrease [our italics] in the DTR for many parts of the world." Consequently, their results suggest that in addition to the reduction in human mortality typically provided by the increase in daily mean temperature (see Health Effects (Temperature - Hot vs. Cold Weather) in our Subject Index), the accompanying decrease in DTR should also have been tending to reduce human mortality. The result thus adds up to a truly phenomenal (double-barreled) blessing for most of the world's inhabitants.

Reviewed 16 May 2007