The summer months, when temperatures soar and pedestrians flock to the shady side of the street, when even breathing seems to leave you sticky, is when violent crimes peak. It’s a well-known pattern, and psychologists have published vast rafts of papers investigating whether the heat, rather than any other factor, like day length, or the kids being out of school, might be responsible. Though a clear causal effect remains elusive, the research has found that heat does appear to boost aggression, as anyone who’s stood in a sweltering subway station with a bunch of surly looking fellow commuters can attest.
The link between environment and human behavior can be writ much larger too. For decades, archaeologists and historians have uncovered evidence that extreme weather events that cause crop failures can lead to unrest, uprisings, and downfalls—from Babylon to dynastic China to modern-day Africa—usually in concert with other factors. And in recent years, thanks perhaps to the looming specter of climate change, research into the connection between climate fluctuation and conflict has snowballed, with papers often looking at one particular geographic area, or one particular weather event.
