As global temperatures continue to climb, heat waves present a growing threat to human mental health and emotional well-being. A recent review published in the journal American Psychologist suggests that rising temperatures can worsen existing psychiatric conditions, increase aggressive behaviors, and impair basic cognitive functions. The findings suggest that climate change poses widespread risks to the nervous system, affecting even those without prior psychological conditions.
Extreme heat is already recognized as a leading cause of weather-related deaths, typically due to physical emergencies like heat stroke or cardiovascular failure. Conversations around climate change regularly focus on these physical health risks or environmental damages. The threat to psychological health tends to receive much less attention from both the general public and medical professionals.
To address this gap in the literature, a researcher sought to create a comprehensive overview of how heat exposure changes the way people think and feel. Prior studies have scattered their focus across isolated mental health outcomes, making it difficult to see the full picture. The author aimed to consolidate this information to highlight exactly how heat alters the nervous system.
“I’ve always been interested in integrated healthcare, bridging physical and mental health together,” said Joseph Taliercio, a clinical psychologist in integrated behavioral health at NewYork-Presbyterian Brooklyn Methodist Hospital and Weill Cornell Medicine. “As climate disasters have become more obvious, my curiosity naturally expanded to question how the environment impacts our health.”
The review provides evidence that exposure to extreme heat consistently degrades general mood and emotional stability. Even for individuals without a diagnosed psychiatric disorder, temperatures above 21 degrees Celsius (around 70 degrees Fahrenheit) are associated with reduced positive emotions and increased fatigue. Prolonged exposure to hotter weather is linked to higher rates of depression and anxiety in the general population.
Taliercio noted that these widespread effects were unexpected. “I was surprised to see how grand the psychiatric consequences are of extreme heat, including that those without a preexisting condition could feel the consequences,” he told PsyPost.
Social media activity tends to reflect this widespread emotional drop. During unusually hot days, local social media posts show a measurable increase in depressed language. Because negative moods can spread through social networks, the review notes that heat can indirectly depress the mood of individuals who are not even outside.
For those with preexisting mental health conditions, the risks are more severe. Higher temperatures and increased humidity are closely linked with increased hospitalizations for individuals with bipolar disorder. Extreme heat and bright sunlight can disrupt regular sleep cycles, which tends to trigger manic episodes in these individuals.
People diagnosed with psychotic spectrum disorders face particularly high risks during heat waves. The review provides evidence that individuals with conditions like schizophrenia have a significantly higher risk of early death during extreme heat compared to people with severe physical illnesses. This vulnerability is often worsened by social factors, as these individuals may experience homelessness and lack access to air conditioning.
Heat exposure also tends to increase aggressive behaviors and violence. As temperatures rise, crime rates, domestic violence, and gun violence all reliably increase. The author notes that prolonged heat exposure drains the mental resources needed to control aggressive urges.
This increase in violence also extends to self-inflicted harm. Suicide rates and emergency room visits for self-harm spike notably during warmer months. The research suggests a linear relationship here, meaning that as temperatures climb higher, the rate of self-directed violence continues to rise.
Beyond emotional regulation, heat physically impairs basic cognitive functioning. People exposed to hot environments demonstrate slower reaction times, increased impulsivity, and worsened working memory. Working memory is the brain’s ability to hold and process temporary information, like remembering a phone number just long enough to dial it.
To explain these outcomes, the scientist reviewed several biological mechanisms. Regulating body temperature requires a massive amount of physical energy. When a person is already using mental resources to manage a psychiatric condition, the added physical stress of cooling the body can overwhelm their system.
Heat exposure also alters the production of essential neurotransmitters, which are the chemical messengers the brain uses to communicate. For instance, extreme heat changes levels of serotonin and dopamine, both of which are heavily involved in regulating mood and stress. Abnormalities in these chemicals provide an explanation for why anxiety and depression spike during the summer.
Additionally, severe heat can disrupt the production of heat shock proteins. These are specific proteins that cells produce to protect themselves under stressful conditions. When these proteins fail to function correctly due to prolonged heat, it can disrupt the hypothalamic-pituitary-adrenal axis, a major hormone system that controls how the body responds to stress.
Physical consequences like dehydration and poor sleep also play a massive role. Dehydration slows down blood flow and impairs brain enzyme function, leading to confusion and fatigue. Poor sleep during hot nights increases inflammation in the brain, further degrading a person’s emotional and mental defenses.
Socially, the review highlights the routine activity theory to explain increases in summer crime. This theory proposes that warmer weather simply drives more people outside and into public spaces. With more people interacting in public, there are statistically more opportunities for conflicts to occur.
Cognitively, the author points to the temperature-aggression hypothesis. This concept suggests that heat makes people perceive neutral actions as hostile. Because heat strains the brain, individuals lose their critical thinking skills and default to aggressive responses when interacting with others.
The review also examined compounding factors that make certain individuals more vulnerable to heat. Older adults face the highest risk of hospitalization and mortality, as aging bodies are less efficient at managing blood pressure and hydration.
Geography and urban planning heavily influence heat exposure. Cities often experience the heat island effect, where concrete and asphalt absorb heat, making urban centers much hotter than surrounding rural areas. Neighborhoods with fewer trees and more dense buildings trap heat, putting the residents of these areas at a severe disadvantage.
Historically marginalized communities suffer the most from these urban planning issues. The review provides evidence that neighborhoods formerly subjected to redlining are significantly hotter today. Redlining was a discriminatory practice where banks refused to offer loans in specific, often minority-populated neighborhoods, leading to a lack of investment in green spaces and cooling infrastructure.
Finally, the use of psychiatric medications is a major risk factor during heat waves. Many common medications used to treat anxiety, depression, and psychosis interfere with the body’s ability to sweat and regulate blood flow. Individuals taking these prescriptions are significantly more likely to be hospitalized for heat-related emergencies.
A common assumption is that certain geographical regions are safe from these climatic shifts. Taliercio warns against this false sense of security.
“Some areas were previously considered ‘climate havens,’ or areas where the impact of rising temperatures was expected to be limited,” he said. “We now know those havens were driven by naive hopes. Even within the last year, we see these areas are also experiencing significant rises in temperature.”
Studying the exact impacts of extreme weather on mental health presents a variety of challenges. The delayed effects of heat exposure mean that individuals might not experience a mental health crisis until days after a heat wave has passed. This delay makes it difficult for medical professionals to accurately connect a psychiatric emergency to environmental temperatures.
Additionally, cognitive impairments can be hard to measure consistently across different populations. Scientists often use different testing methods to measure traits like memory and reaction time, making it challenging to compare data from different studies. It is also difficult to determine whether cognitive decline is caused directly by the high temperatures or indirectly by the dehydration that accompanies the heat.
Future research needs to establish more consistent testing methods to better track mental health changes across different climates. The author also suggests exploring how much patients actually know about the heat risks associated with their psychiatric medications. Identifying this knowledge gap could help doctors better educate their patients on how to stay safe during extreme summer weather.
Moving forward, the author plans to expand on this area of study. “I continue to be interested in ecopsychology, and am actively attempting to build insight around different facets of climate change, such as the impacts of pollution and the role of green spaces,” Taliercio said.
Overall, the reality of climate change requires a broad shift in public awareness. “Climate change represents a health crisis, and one that none of us are immune to,” Taliercio added.
Despite the grim reality of rising temperatures, there is room for optimism. “Despite the existential threat posed by climate change, we need to recognize there is promising ongoing work and that great strides can be made to protect ourselves and our future,” he concluded.
The paper, “Heat on the Brain: The Impacts of Rising Temperatures on Psychiatric Functioning, Potential Causes, and Related Compounding Factors,” was authored by Joseph R. Taliercio.