High temperatures cause violent crime and implications for climate change
A new working paper "Crime, Weather, and Climate Change" by recent Harvard grad Matthew Ranson puts together an impressive data set of all types of crime in USA counties for 50 years. The results tell the aggression story using street-level data very clearly:
Note that all crime increases as temperatures rise from 0 F to about 50 F. It seems reasonable to hypothesize that a lot of this pattern comes from "logistical constraints", eg. it's hard to steal a car when it's covered in snow. But above 60 F, only the violent crimes continue to go up: murder, rape, and assault. The comparison between murder and manslaughter is elegantly telling, as manslaughter should be less motivated by malicious intent.
Ranson goes on to make projections about the expected effect of climate change:
Between 2010 and 2099, climate change will cause an additional 30,000 murders, 200,000 cases of rape, 1.4 million aggravated assaults, 2.2 million simple assaults, 400,000 robberies, 3.2 million burglaries, 3.0 million cases of larceny, and 1.3 million cases of vehicle theft in the United States.
This is pretty serious stuff. Ranson also shows that these effects haven't changed much over time, so the prospects for adaptation may be low. And there's no reason to believe that this relationship, which is probably neuro-physiological, doesn't hold outside of the USA.