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Does heat make us more aggressive? Researchers put it to the test


We're going to turn now to an experiment that seems excruciating in the midst of the current global heat wave. Researchers at University of California, Berkeley put thousands of people in hot rooms to find out if high temperatures could make us all more violent. NPR's Nurith Aizenman reports.

NURITH AIZENMAN, BYLINE: The subjects of this experiment included college students in Nairobi, Kenya. In groups of six, they were ushered into one of two possible rooms. The first was a comfortable 68 degrees. The second was that hot room cranked up to 86 degrees. Berkeley economist Edward Miguel is one of the researchers.

EDWARD MIGUEL: We hid the heaters so that participants didn't know that we were actively heating the room. We had different screens in parts of the room.

AIZENMAN: I kind of feel for these test subjects.


AIZENMAN: He stresses that ethics rules barred them from forcing people to stay.

MIGUEL: In fact, in one of the sessions I was observing, somebody was like, I'm out of here.

AIZENMAN: But the vast majority sweated it out and spent the next hour playing a series of computer games, including one called The Joy of Destruction.

MIGUEL: This is a direct measure of aggressive, antisocial behavior.

AIZENMAN: Essentially, you're shown how much money another player has just won playing their own game. Then you're given the option of totally anonymously erasing that person's payoff. And Miguel says, here's the key. When it comes to this payoff...

MIGUEL: It isn't like, oh, I'm taking it away from them. I'm getting it myself. I don't get the money.

AIZENMAN: And it's actual money, as much as $30.

MIGUEL: You're really harming somebody and not benefiting yourself other than the pleasure of seeing other people do worse.

AIZENMAN: So did being in the hot room increase people's interest in doing this? Before we get to the answer, here's why Miguel and his collaborators were so keen to find out. Over the last 20 years, scientists have been uncovering how in countries, mostly lower-income ones, where there's been lots of political conflict, it's tracked with bouts of extreme heat. During those periods...

MIGUEL: There's more likelihood of civil war. There's more violence. There's more political instability. And that's just been shown now around the world in scores and scores of studies.

AIZENMAN: Nina Harari is an economist at University of Pennsylvania's Wharton School. She says the upshot is that with climate change, the world isn't just going to get hotter, it's probably going to get more violent.

NINA HARARI: That is disheartening and concerning going forward.

AIZENMAN: Harari and a collaborator have shown that in sub-Saharan Africa, it's only when extreme heat and consequent drought hit during the growing season that there's been an increase in civil conflict - riots, battles, recruiting by rebel groups.

HARARI: So the idea is my agricultural yields are very low, so that makes me more likely to engage in conflict activity the following year.

AIZENMAN: But Harari says Edward Miguel's hot room study breaks new ground by rigorously testing for a factor that economic analyses like hers can't get at. See - more recent research has found that in countries of all income levels, even when there's not an economic impact of heat, it still correlates with many types of aggression - ranting on social media, fights on sports fields, murder rates. So could there also be a psychological effect of extreme heat?

HARARI: You really need something like a lab experiment.

AIZENMAN: Which brings us back to Miguel and company's findings, first revealed in a National Bureau of Economic Research working paper. He says in Kenya's cool room, about 1 in 7 students chose to destroy the other player's winnings, in line with what's been found in other studies using this game, including in the U.S. But in Kenya's hot room, 1 in 5 students chose destruction, still within that normal global range but nearing the top end and 50% higher than in the cool room.

MIGUEL: A very sharp increase in these antisocial behaviors.

AIZENMAN: But it wasn't all the Kenyan students who reacted this way. The experiment had been done amid a tense and, at times, violent election.

MIGUEL: The opposition felt really aggrieved, and they felt the election was being stolen from them. And they were protesting.

AIZENMAN: And the hot room only drove up the aggression of students from ethnic groups aligned with that politically marginalized opposition. In fact, the researchers had also tested students in the U.S. and found no difference between their behaviors in the hot and cold rooms. But that testing had been done well before the upheaval of the U.S.'s 2020 presidential election. The potential implication - heat could be an accelerant.

MIGUEL: For people who already feel a sense of grievance, experiencing extreme temperature could really be the last straw.

AIZENMAN: An additional psychological stress that tips them into violence. Nurith Aizenman, NPR News. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

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