A single standard-deviation increase in temperature elevates the risk of person-to-person violence by about 2.5 percent and the risk of group-to-group violence by about 11 percent

A Stanford economist named Marshall Burke and two of his colleagues published an article in the Annual Review of Economics about the relationships between climate and conflict.  He begins by telling me that I don’t need to go to Darfur or Damascus to learn about the connections between heat and hot-headedness. “We see this everywhere in the U.S. — in the city level, at the county level — really any way you want to look at it.”  He cites papers that documented the relationship in Phoenix in 1986; in Charlotte in 1988; inMinneapolis and Dallas, between 1997 and 2005. It was there in St. Louis in 2013. Nationwide, 2014. Forget drought: When temperatures alone rise, violence does the same.

Burke and his colleagues estimate that a single standard-deviation increase in temperature elevates the risk of person-to-person violence by about 2.5 percent and the risk of group-to-group violence by about 11 percent. These are events with low underlying likelihoods in the first place — most countries aren’t constantly on the brink of civil war, and most people aren’t constantly on the brink of aggravated assault — but in a warming world, the economists argue the effects are appreciable. Some parts of the world are expected to warm by two to four standard deviations by 2050.

“If future civil conflicts remain as deadly as those that took place recently,” his team writes, projections suggest that the “increase in conflict would result in 393,000 additional battle deaths by 2030” — in Africa alone.

The “began as” and “at least in part” are important qualifiers. It’s the same logic that the Department of Defense uses when it describes climate change as a “threat multiplier” — never the cause of a conflict, always a lens through which societies are focused and refracted; bent over, eventually, some nameless, violent tipping point. Arable land isn’t something you can import, and when livelihoods depend on crop yields, an increased frequency of drought can make or break families.

But that still doesn’t explain why, say, domestic violence spikes in Australia on hotter days. It certainly doesn’t explain why pitchers are more likely tointentionally hit batters at higher temperatures.

“A lot of people naturally gravitate to the income effect story, but in the U.S., we’re usually looking at daily-scale data,” Burke told me. “We’re comparing a hot day to a normal day — and temperature variation on that kind of time scale just does not, or is very unlikely to, induce variation in income.”

In other words, it’s fairly obvious that a creeping desert and its accompanying heat and drought could dry out a wallet — and that, on average, this financial stress could feasibly influence the likelihood of someone committing a violent act — but it makes less sense that rising temperatures on their own should have anything to do with violence.

Burke put it bluntly: “You can piss people off and get them to be mean to each other if you put them in a room and crank up the heat.”

Craig Anderson was one of those psychologists. “Even as a child I was interested in aggression,” the Iowa State researcher writes in his contribution to a forthcoming essay collection, ambitiously titled Scientists Making a Difference: The Greatest Living Behavioral and Brain Scientists Talk about Their Most Important Contributions.

What had begun as a childhood fascination with Westerns and World War II shows would develop into a meticulous scholarly pursuit, he writes. As a young Stanford graduate student in the late 1970s, Anderson’s first professional publicationdemonstrated a linear relationship between temperature and the likelihood of civil riots in the United States. Pinning down a psychological explanation, though, was easier said than done.

When I called him up, Anderson explained the line of questioning that had fueled his early work: “If this effect is real, what’s going on? Are people just more irritable? Can you replicate this in a lab?”

The problem with that line of experimentation is that people tend to be suspicious of psychologists. “If your research participants know what you’re doing, they start to behave pretty weirdly,” said Anderson. But where previous psychologists had made the game too obvious — “a kerosene heater sitting in the lab,” he recalled — Anderson and his colleagues were a bit more covert. Their solution: Use a shitty office.

“With a set of crappy cubicles in an old building, participants could reasonably believe it was just the building’s heating system acting up,” he said, reflecting on a set of studies his team conducted in the early 1980s. “They couldn’t believe that we had any control over the temperature.” And when the psychologists ran experiments testing for aggressive thinking and hostile feelings in the aging cubicles, lo and behold, the observations held. People were more aggressive at higher temperatures.

Throughout the ’80s and ’90s, Anderson and his collaborators would continue to probe the temperature–aggression link for explanations. As the experimenters plodded on, a theory began to take shape.

It seemed that many of the upticks in aggression came down to over-interpreting a situation. It wasn’t that Anderson’s subjects were automatically more aggressive at higher temperatures — though feelings of hostility often did increase — it was that higher temperatures more easily lent themselves to escalation. In hotter rooms, for example, people would perceive a video as depicting a more aggressive interaction. “That’s what we think is happening in the real-world data at a psychological level,” he said. People over-interpret and overreact. “That’s how bar fights turn into shootings in the parking lot.”

Intuitively speaking, this has the taste of truth. “Hot-headedness” is called what it is for a reason. I know I, for one, am probably more likely to tense up on a crowded bus if it’s a hot day. There’s a fine line between discomfort and a hair trigger.

But the psychological explanation has that twisty tautological rub that comes with a lot of psychological explanations. It might offer clues as to why an increase in heat corresponds with an increase in aggression — because of over-interpretation, perhaps — but it fails to answer why an increase in heat corresponds with an increase in over-interpretation.

Answering that would require zooming the lens a bit and research in this area has not been funded yet.  But admitting that the climate might have something to do with the way people behave — might already be exerting that influence, in places like the Sahel, in places like Syria, in places like St. Louis — means recognizing that people are at risk of losing far more than coastal property or crops, and that maybe we really should be throwing ourselves at solutions. The alternative is throwing ourselves at each other: out with a bang and not a whimper after all.

Excerpt from:  http://grist.org/climate-energy/hunting-for-the-neuroscience-of-heat-and-violence/