Do heat waves cause crime waves? That’s the impression one might get reading media coverage of a recent study purporting to show that climate change will increase crime. As reported in the Los Angeles Times:
The study by Matthew Ranson of Abt Associates, a research and consulting firm in Cambridge, Mass., suggests global warming will trigger more crimes including murders and rapes over the next century, with social costs estimated to run as high as $115 billion.
Between 2010 and 2099, climate change can be expected to cause an additional 22,000 murders, 180,000 cases of rape, 1.2 million aggravated assaults, 2.3 million simple assaults, 260,000 robberies, 1.3 million burglaries, 2.2 million cases of larceny and 580,000 cases of vehicle theft, the study published this week in the Journal of Environmental Economics and Management says.
Compared with the number of crimes expected to occur during this period in the absence of climate change, these figures represent a 2.2% increase in murders, a 3.1% increase in cases of rape, a 2.3% increase in aggravated assaults, a 1.2% increase in simple assaults, a 1% increase in robberies, a 0.9% increase in burglaries, a 0.5% increase in cases of larceny and a 0.8% increase in cases of vehicle theft, the study says.
The year 2099 is, of course, very far in the future. If you’re reading this in 2014, chances are you will be dead by then (sorry). So how exactly are we supposed to tell the effect of climate on crime 85 years from now?
Looking at the study itself, the estimated increase in crime is derived by comparing the crime rates of U.S. counties based on how hot it was in a given month. As it turns out, many crimes have a degree of “seasonality” – they are less likely to occur when it is cold outside than when it is warmer. Since warmer days have more crime, and climate change leads to more warmer days, the study concludes that climate change will lead to more crime. QED.
The study makes no attempt to control for other variables that might cause a spurious connection between crime and the weather. The late Senator Daniel Patrick Moynihan once noted that one of the strongest predictors of school quality was the school’s distance from the Canadian border. He might’ve added that school attendance falls sharply during hot summer months. No doubt one could conclude based on these facts that climate change will lead to a sharp decrease in school quality. That might make headlines, but it wouldn’t tell us much.
More interesting, though, is the mechanism by which higher temperatures are supposed to lead to more crime. The study gestures at research suggesting that higher temperatures might make people more aggressive. But, as the study also notes, the connection between warmer weather and property crime vanishes once temperatures hit 50 degrees. And both violent and non-violent crimes tended to be more seasonal in colder parts of the country. Clearly something else is going on here.
As alternatives, the study’s author speculates that “weather conditions are an input that affects both the probability of successfully completing a crime and the probability of escaping undetected afterward,” and that “weather conditions that foster social interactions are likely to increase crime rates.” An earlier version of the paper, puts the matter more plainly: “pleasant evening weather may increase the number of opportunities for mugging,” and “mild weather that encourages people to go shopping would also have the effect of increasing the frequency of property crimes such as larceny.”
In other words, if climate change does cause an increase in crime, it’s liable to be because people are more likely to leave the house when the weather is nice. But aside from a few misanthropes, most people view the advantages of “social interactions” as worth the risk that you might get mugged. If they didn’t, they could easily reduce their risk of being robbed by staying home, even on a beautiful summer day.
Of course, a study that concluded climate change would lead to more pleasant weather might not have attracted the same attention (or at least not the same sort of attention) as the crime and climate study. Perhaps unsurprisingly, the references to climate change leading to more “pleasant” weather have disappeared from the final paper.
If you spend enough time on the web, you may have come across the idea of “clickbait.” Articles are given headlines that are deliberately provocative or surprising in order to drive traffic to the publisher’s website. The substance of the article in question may not live up to the hype, but by the time you’ve read far enough to establish this, it’s too late. You’ve already clicked on the article. While certain websites specialize in this sort of thing (you know who you are), the phenomenon is rapidly becoming universal.
In recent years a similar trend has, sadly, increasingly infected science journalism. If a paper has a counter-intuitive or politically salient conclusion, the media will run with it regardless of any uncertainties or caveats included in the paper itself, or even whether the paper’s underlying methodology is fundamentally sound. In fact, on one level clickbait science is easier to get away with, as virtually no one who reads about the latest shocking scientific study is going to track down the original paper to see how robust the findings are.
The crime and climate study is just one example of how clickbait science can give a distorted picture of the findings of scientific research. And in a society where people increasingly look to experts to form their views on a variety of social and political matters, that’s a problem.