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High temperatures cause violent crime and implications for climate change, also some suggestions about how to better summarize these claims

Solomon Hsiang writes:

I [Hsiang] have posted about high temperature inducing individuals to exhibit more violent behavior when driving, playing baseball and prowling bars. These cases are neat anecdotes that let us see the “pure aggression” response in lab-like conditions. But they don’t affect most of us too much. But violent crime in the real world affects everyone. Earlier, I posted a paper by Jacob et al. that looked at assault in the USA for about a decade – they found that higher temperatures lead to more assault and that the rise in violent crimes rose more quickly than the analogous rise in non-violent property-crime, an indicator that there is a “pure aggression” component to the rise in violent crime.

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 [click to view the graphs]:

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.

This seems important to me. Just one graphics tip (to Ronson, not to Hsiang, who is merely reporting this work): The graphs are great, but they’d be even better if they were rearranged slightly. First, put the labels on the top rather than bottom of the graphs. As it is, when I first looked, I thought that the results for Murder were in the second row, not the first row. You can make more space for the titles by removing the boxes around the graphs (in R notation, bty=”l” rather than bty=”o”). The x-axes are too busy, it would be enough to label temperature every 20 degrees rather than 10. (I’d actually prefer Celsius but that’s more of a judgment call.) The zero line should be gray rather than black so as not to so strongly distract from the results. The y-labels would be improved by (redundantly) naming the crime: thus, Murder Rate, Manslaughter Rate, Rape Rate, etc., rather than the identical “Number of Crimes” for each.

Finally, I’d prefer the scales of the y-axis to be directly interpretable. Instead of presenting changes in monthly crime rate per 100,000 persons, I’d present changes in crime rates per crime. For example, if there were 15,000 murders in the U.S. in one year, that’s 15,000/(12*100,000)=0.0125 murders per 100,000 people per month. A change in 0.002 in the upper-left graph then corresponds to 0.16 or 16% of the murder rate. Maybe I got the numbers wrong here; in any case, my point is that percentages of the murder rate will be much more relevant than crime rate per person.

13 Comments

  1. Paul says:

    At least part of this effect must come from people being out more at late hours when the temperature is high, especially the rape aspect. This doesn’t change the statement that high temperature causes violent crime, but it definitely changes our interpretation.

    • K? O'Rourke says:

      Yes and puts a spin on the vehicle theft http://www.youtube.com/watch?v=QsxV49pmnL8

      The world is enormously complicated (but can be seen as funny)

    • I don’t doubt that this effect matters as temperatures rise up to around 70 degrees, which is probably why there is rise in all types of property crime up to that temperature. But above 70 degrees, only the violent crimes, like rape and assault, continue to go up. If the entire response was due to simply having more people out on the street at night, I think we would expect to see the property crimes continue to rise above 70F as well.

      • Jacob H. says:

        Unless being out on the street has different effects on property crime than on violent crime. You could imagine that being observed by lots of people might make stealing a car less likely and getting into a fight more so.

      • There is also public alcohol consumption, which probably increases steadily with temperature. That would be an interesting analysis: The effect of global warming on the global alcoholic beverage industry.

  2. Jacob Hartog says:

    I wrote a paper on this topic a few years back for a class on climate change policy, analyzing crime data from Philadelphia in 2007 and looking at day-to-day variation in temperature in the metropolitan area. I wrote it concurrently with my first real statistics class, so the analyses are very clumsy, but it’s a bit interesting…
    https://docs.google.com/file/d/0B5pZvpGKg-s1S2R4bl9kSnpXaDg/edit

  3. Brian says:

    Crime rates have been in steady decline for decades. Temperature has been steadily increasing for decades. US population has been steadily shifting southward for decades. And higher temperature is associated with higher crime. Mix this all together… Can we conclude that whatever is causing crime to drop (and I’ve heard lots of theories) is actually stronger than what we are observing due to the attenuating effect of temperature?

    • idiot says:

      True, but that’s why it’s even more important that studies like this get published (otherwise we might miss an important effect that can be swamped by various other factors).

  4. mpledger says:

    It might not be the termperature but what people do when they are hot i.e. drink, especially alcohol. People who get drunk are easier to victimise and it can also make some people more aggresive towards others.

  5. Steve Sailer says:

    It’s fascinating how Climate Change and Crime is a respectable topic but Demographic Change and Crime is hatestat.

    • Andrew says:

      Steve:

      This is not so clear. I was curious so I did some googling.

      *demographic change crime*: 3.5 million hits
      *climate change crime*: 91 million hits

      So it looks like you’re right. But a careful look shows that many of the *climate change crime* links point either to that single study I mentioned above or to pages such as “Forbes: Climate Change Hoax is Crime of the Century” and “Cate Blanchett Exposed For ‘Crime’ Of Speaking Up On Carbon Tax.”

      So I tried Google Scholar. There we see:

      *demographic change crime*: 174,000 hits
      *climate change crime*: 339,000 hits

      Again, though, there is a discrepancy. The *demographic change crime* links seem mostly to be about demographics and crime, whereas the *climate change crime* links include papers such as “Mountain pine beetle and forest carbon feedback to climate change.”

      So overall it seems like a tough call to assess which research topic is more popular. Now you could argue that even the closeness of this comparison makes your point, given that, if you’re studying crime, demographics is so evidently more relevant than climate change. But, when it comes to the research literature, demographic change and crime does seem to be studied.

  6. Kevin Kind says:

    Decades ago we saw some research suggesting “personality”, really reoccurring individual behavior, is determined 90% by ecosystem-climate-topography-etc. Makes sense. Then another study that more sunlight affects the brain to produce more impulsive behavior.

    So individuals near the equator will have more impulsive behavior. Have not been able to find those studies since. Belief they were in a Brit mag or newspaper.

    Of course, what we want to know is what does heat do to young men’s brains of which the crime is a behavioral “symptom.” We should also find this heat effect in other animals – from which we have descended.

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