Now that the summer is in full swing, it is incumbent upon the psychiatric and mental health community to learn about the specific effects on behavior, psychiatric risks, and outcomes – and to plan for ways to protect our patients and communities.
Extreme heat has significant effects on mental health and behavior. Research shows1 that the number of people exposed to extreme heat is expected to rise in many American cities, particularly across the southern United States. Records were set in May 2018 across the United States and around the world. In the United States, those May temperatures were the warmest ever recorded, representing the hottest spring ever.2 Around the world, the warmer-than-average conditions that engulfed much of the land and sea surfaces made May the fourth-warmest since records started being kept in 1880.2
In short, these trends are not remitting. Extreme heat and climate disruption are the new normal.
Extreme heat makes many people cranky, agitated, or listless. However, heat waves are not benign, uncomfortable periods; they have profound health risks tied to increasing rates of anxiety, depression, posttraumatic stress disorder, and even death. In fact, extreme heat is now considered to be the single largest weather-related cause of death, exceeding hurricanes, lightning, tornadoes, floods, and earthquakes combined. The Centers for Disease Control and Prevention reports 7,800 deaths attributable to extreme heat between 1999 and 2009 – and predicts more frequent and extreme heat.3
In addition, extreme heat has been linked to increases in aggression and violence. One standard deviation of temperature increase and rainfall is associated with a 4% increase in interpersonal violence and 14% increase in intergroup violence.4 Anecdotal stories underscore the well known lore among prison staff of increased inmate violence during heat waves.5
Complex cognitive tasks such as working memory (spatial span test, pattern recognition) have been observed to be significantly impaired through heat stress.6 Increased heat also contributes to insomnia and worsens with increased humidity.7 A study in England and Wales showed a link between a possible association between hot weather and an increased risk of suicide.8 People with mental illness and those who abuse substances are considered an especially vulnerable population to the impacts of extreme heat and other climate change–related events. Co-occurring variables such as poverty, substandard housing, and lack of access to cool environments all contribute to this increased vulnerability. Homeless mentally ill have little control over their environments and have very limited ability to protect themselves from heat exposures and therefore are at extreme risk.9. Regretfully, these kinds of cooling systems are out of reach for many people who live on the margins of society.
Furthermore, patients with severe psychotic or mood disorders, substance abuse disorders, and cognitive impairments who are able to compensate with marginal executive functioning during periods of normal weather are challenged during intense heat, and can lose their fragile ability to make plans, have good judgment, and care effectively for themselves. These patients are more likely to experience heat stroke and other heat-related morbidity.
Here is evidence that supports the greater impact of extreme heat on psychiatric patients: