Tuesday, August 28, 2007

Deadly resonance

Anne Fouillet, Grégoire Rey, Eric Jougla, Philippe Frayssinet, Pierre Bessemoulin and Denis Hémon just released a paper on the correlation between weather temperature and mortality rate. This is in part due to the 2003 abnormal death rate sustained in France during a heat wave that killed upward 18,000 people above what would have been expected. In recent memory, there were 4 other hot weather incident in France: summer 1975, 1976, 1983 and 2003. The figures shown below are from the paper and they tell a story:

When I saw these graphs, I could not but notice the following, there seems to be a resonance when the maximum temperature goes above 35 C (35 degree Celsius = 95 degree Fahrenheit). The average body temperature is 37 degree Celsius (or 98.6 degree Fahrenheit), skin temperature is an average of 34 C and we also know that water is very anomalous, and in particular that the specific heat capacity (CP) has a minimum at 36°C.
One can always imagine the following, between 34C and 37 C, the body (made of 90 % water) starts taking in heat from the surrounding (mainly from radiation) and it does so more quickly at around 36 C. Since, we are only accustomed to heat warming the body slowly at lower temperature (higher Cp at T less than 30 C), there is a compounding effect taking place above 34 C that yields catastrophes on populations not accustomed to these heat fluxes. One also wonder, if a lower-tech version of DARPA cooling glove would not be an efficient tool in these situations (besides drinking and air conditioning).

[1] A predictive model relating daily fluctuations in summer temperatures and mortality rates.

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