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Testing for a temperature effect on homicides in New York and London

26 May 2021 | Science Notes

From CO2Science: One of the social-related concerns of CO2-induced global warming is that rising temperatures will affect societal temperature-crime relationships, producing more violent crime in the future, including murder. In a newly published paper on this topic, Lynch et al. (2020) present a detailed overview of this “heat hypothesis” in which warming temperatures are postulated to produce more crime. In doing so, they note key shortcomings in prior analyses conducted on this topic, where temperature and crime data are often analyzed on seasonal time scales ranging from days to months and on differing geographic scales, which can give false impressions of a climatic signal. And in this regard they opine that “it is entirely plausible, given that crime trends fluctuate over time, that evidence of an association between climate and crime may be an outcome of the time period employed for examination.”

Paper Reviewed: Lynch, M.J., Stretesky, P.B. and Long, M.A. 2020. Climate change, temperature, and homicide: A tale of two cities, 1895-2015. Weather, Climate, and Society 12: 171-181.

In an attempt to overcome such shortcomings, the three researchers set out to conduct their own study of the subject by examining the relationship between annual mean temperature and homicide in two cities, New York and London, over the period 1895-2015. The use of a long time series allowed the scientists the ability to best assess trends using proper statistical methods to correct for nonstationarity and heterogeneity in the underlying data.

The results of the analysis revealed there was a positive correlation between annual homicide rates and temperature on a bivariate level that “became statistically insignificant in both New York and London when gross domestic product is controlled.” Furthermore, they report that “the bivariate relationship between temperature and homicide is statistically insignificant when correcting for nonstationarity,” where they add that “changes in temperature do not predict changes in homicide when correcting for heteroscedasticity, autocorrelation, and multicollinearity.”

In commenting on their work, Lynch et al. say that “despite several adjustments, we were unable to uncover a relationship between temperature and homicide in New York or London, and we suggest that such an association is likely not to exist in these data.” Therefore, they conclude that “in our century-long analysis of temperature and homicide in New York and London there appears to be little support for the heat hypothesis.”

And there we have it. When proper methods are utilized to examine temperature-crime relationship, the heat hypothesis melts away.

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