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Hot-headed: Heat waves really can make tempers boil. In fact, from 1950 to 1995, rates of serious and deadly assaults were higher during hotter years, according to research in the Journal of Personality and Social Psychology in 1997. The authors suggest that uncomfortably high temperatures increase annoyance-provoked crimes, in which the primary goal is to hurt someone. (Crimes like burglary, where the incentive is money, did not increase.) They predicted at least 115,000 additional serious and fatal assaults a year in the United States due to global warming.

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