Extreme heat is already transforming our world in subtle and not-so-subtle ways. Reporting from Phoenix, Arizona, this story describes how people are learning to cope with heatwaves and the potential consequences of more extreme temperatures. The link between heat and violence is particularly intriguing. “There is growing evidence of a psychological mechanism that is impacted by heat, although we can’t yet say exactly what that is,” says Solomon Hsiang, a professor of public policy at Berkeley and Lab co-director. Some scientists speculate that higher temperatures impact neurotransmitters in the brain, resulting in lower levels of serotonin, which has been shown to lead to aggressive behavior. So rising heat may literally alter the chemistry in our brains. One study showed that police officers were more likely to fire on intruders during training exercises when it was hot.