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Marshall Burke (Department of Earth Sciences at Stanford University) and his colleagues correlated the evolution of the gross domestic product (GDP) of 166 countries, over the period 1960-2010, with the fluctuations of the column of mercury. Productivity - the efficiency with which societies transform natural resources, energy, capital and labor into goods or services - "reaches its peak at an average annual temperature of 13 ° C", beyond which it "declines strongly" . An excessively hot climate not only harms agricultural production, the authors explain, but also the performance and health of workers in all sectors of activity.
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http://www.lemonde.fr/cop21/article/201 ... 27432.html
Interesting this number, because the average temperature of the globe is precisely around 13 ° C ... but not for long ...