I have heard that proposed as a cause, but I have no idea what research if any backs it up. It sounds more plausible than the connection between pirates and global warming.
Basically, on the statistical side, there is a heavy correlation between lead exposure through leaded gasoline and crime ~18 years later. 18 years after leaded gasoline use starts, violent crime skyrockets. It tracks overall with the usage of leaded gasoline, and cities, with the heaviest, densest use, see the most crime increase. 18 years AFTER use of leaded gasoline ceases, crime drops. This tracks with multiple locations, so cities that stopped usage first saw their crime rates drop first. Cities that stopped last, had violent crime last the longest. They were even able to come up with formulas for X amount of leaded gasoline burned = Y amount of violent crime a couple decades later.
On the medical side, various studies have shown that lead damages the emotional control parts of the brain, leading to increased violence.
https://en.wikipedia.org/wiki/Lead-crime_hypothesishttps://www.motherjones.com/kevin-drum/2018/02/an-updated-lead-crime-roundup-for-2018/In a nutshell, this article argues that atmospheric lead from gasoline tailpipes rose steadily after World War II, affecting babies born in the late 40s and beyond. The leading edge of this generation became teenagers in the late 60s and was more prone than previous generations to committing violent crime. Every year the population of teenagers with lead poisoning increased, and violent crime increased with it. This is why the 70s and 80s were eras in which crime skyrocketed.
In the early 70s the United States began to phase out leaded gasoline and newborns became steadily less lead poisoned. Like clockwork, as the leading edge of this generation became teenagers in the early 90s, the crime wave started to recede. By 2010, an entire generation of teenagers and young adults—the age group responsible for most crime—had grown up nearly lead free, and the violent crime rate had plummeted to half or less of its high point. This happened across the board: in big and small cities; among blacks and whites; in every state; in every city; and, as it turns out, in every other country that also phased out leaded gasoline.
It’s important to emphasize that the lead-crime hypothesis doesn’t claim that lead is solely responsible for crime. It primarily explains only one thing: the huge rise in crime of the 70s and 80s and the equally huge—and completely unexpected—decline in crime of the 90s and aughts. The lead-crime hypothesis is the answer to the question mark in the stylized chart below:
https://www.brookings.edu/blog/up-front/2017/06/01/new-evidence-that-lead-exposure-increases-crime/etc...
It even helps show why flight from the cities was such a deal, and why young people are flocking back into them now, as violent crime and pollution inside cities is no longer so prevalent as to make them unlivable to anybody who can afford to get out.
It is one of the reasons why, even I'm mostly libertarian, I'm generally for the EPA. Because it is entirely possible to put things in the atmosphere that harms others. No different than if somebody stuck a pipe from their toilet into your bedroom. And it's a bill that most can't pay.
