Global Warming's Impact on Thinking

Even in auto factories, most presumably air-conditioned, a week of six days above 90 degrees reduces production by 8 percent. Perhaps more startling, rising temperatures seem to cause more violence.

“The relationship is really clear,” said Edward Miguel, an economist at the University of California, Berkeley, who has studied the issue. “Extremes in climate lead to more violence, more killing, more war, more land riots in Brazil, more sectarian violence in India. It’s pretty stunning how the relationship between climate and violence holds across the globe.”

The starting point is that heat makes people irritable. Researchers have found hot days linked to more angry honking in Arizona, and more road rage and car accidents in Spain. Scholars have done the math and found that on hot days a major-league baseball pitcher is more likely to retaliate for a perceived offense and deliberately hit a batter.

“High temperatures,” that study finds, are “lowering inhibitions against retaliation.”

On hot days, property crimes aren’t more common, but murders go up with the temperature. Likewise, researchers find that police officers are more likely to draw and fire their weapons during a training session conducted on a hot day.