Extreme heat and climate mental health

Heat waves are increasing in the climate crisis

Global warming has become the new normal, threatening our health and well-being and, in some places, our ability to live on our lands.

As the average annual temperature increases, we are also experiencing more periods of extreme heat, including heat waves. Heat waves are occurring both in places where high temperatures are the norm and in places with more moderate climates.

Heat waves, or extreme heat events, are defined as two to three days of high temperature and humidity levels that are above the normal levels you’d see in a region. These heat waves are becoming more frequent, severe, and long-lasting across the globe.

During heat waves, it is not only the high temperatures but also the degree of humidity that threatens people’s health and well-being. This combination of temperature and humidity level is called the heat index.

Extreme heat is a killer; Sometimes it’s even called the silent killer. Extreme heat is now considered one of the deadliest types of weather event—with the death toll in 2021 from heat events exceeding the year’s tolls from hurricanes, lightning, tornadoes, floods, cold weather, and earthquakes.

From June to July 2021 in the Northwestern region of the United States and Canada, an area that normally has mild weather with low humidity, a severe, record-breaking heatwave with a high temperature record of 121.3 degrees F (49.6 degrees C) caused about 1,400 deaths.

During the unprecedented 2022 heat wave in India and Pakistan, residents of Jacobabad, a city of nearly one billion people, lived through 51 consecutive days of temperatures over 100 degrees F (37.78 degrees C), with temperatures registered as high as 124 degrees F (51 degrees C). Researchers anticipate that these long, extreme heat periods will become more common as the climate crisis continues to progress.

How extreme heat affects mental health

Beyond causing potentially lethal physical problems, extreme heat also uniquely impacts human behavior, feelings, thinking patterns, and emotional well-being.

Research confirms that emotional well-being is impacted by extreme heat. Extreme heat makes most of us cranky, more likely to have flares of temper, feelings of agitation, or experiences of listlessness. Researchers have found that high temperatures lead to deceased experiences of joy; increased levels of negative emotion and stress; increased levels of fatigue; and greater limitations on participating in stress-relieving outdoor recreation.

Effects on behavior: aggression and violence

Research linking heatwaves and aggression confirms the general understanding expressed in our colloquial language of hot-headed, and so hot my blood boils. One significant study shows these links, indicating that a temperature increase over normal temperature of one standard deviation leads to a 4% increase in interpersonal violence and 14% increase in group violence.

Women are particularly vulnerable during heat events, with reports indicating significant increases in sexual crimes.

This increase in aggression is found throughout the world and with all ethnicities.

Suicide

Suicide, a form of violence turned onto the self, increases during extreme heat. Research showed an increase in suicide rates of 0.7% in the US and 2.1% in Mexico during a period when temperatures were just 1 degree Celsius higher than average monthly temperatures.

If there is no reduction in green-house gas emissions, projections about future climate change impacts estimate that by 2050 there may be between 9,000 to 40,000 additional suicides in the USA and Mexico, with 26,000 suicides in the USA.

Mood effects and psychiatric symptoms

General sense of emotional well-being is impacted by heat waves in both the general population and in people who have prior psychiatric conditions. During heat waves, there are increases in depressive language use on social media.

Emergency room visits and hospitalizations for psychiatric conditions increase during periods of extreme heat. Extreme heat can also precipitate manic episodes in those with bipolar illness.

A systematic review of the literature reported that a 1 degree C increase in temperature increased morbidity and mortality for those with mood disorders, schizophrenia, anxiety, organic mental illness, and substance use disorders. The greatest increase in mortality was linked to people with substance use mental disorders.

Effects on thinking and cognition

Studies support our general sense that we don’t think as sharply when it is extremely hot. During those periods many of us avoid doing intellectual activities, and with good reason. Studies show evidence of impaired cognitive performance in extreme heat, with memory, learning, concentration all impacted.

Complex mental tasks are particularly impacted by extreme heat stress. Academic performance decreases.

Concentration and attention are reduced, leading to impaired workplace functioning: more workplace errors, accidents, and injuries than during periods of normal temperature.

Heat stoke is a severe impact: it is a medical emergency and can lead to death. During a heat stroke, people may present with the cognitive and brain symptoms of confusion.

Sleep and insomnia

Periods of extreme heat can interfere with sleep, causing insomnia. This is because falling asleep and staying asleep require a slight decrease in body temperature, which can be impacted by high nighttime temperatures in uncooled spaces.

Although it may feel like just a bad night of sleep, the implications of poor sleep can be quite wide-ranging, affecting mood and thinking. Bad sleep can even trigger the resurgence of otherwise stable psychiatric symptoms.

Effects on medications

Many medications interfere with body’s ability to remain cool. This makes it harder for patients taking these medications in extreme heat.

Some of the medications that contribute to complications during heat waves include:

Most psychiatric medications
Some cardiac medications (some blood pressure pills and beta-blockers)
Diuretics (also called water pills)
Stimulants and recreational drugs
Antihistamines (such as Benadryl)

Psychiatric patients treated with medications are particularly vulnerable during heat waves since many psychotropic medications interfere with the body’s ability to maintain core body temperatures

Body heat regulation and mental health

The body’s ability to maintain core temperature and respond to environmental temperature changes is a complex interplay of interconnected biological processes. Movement of blood to the skin promotes the primary cooling mechanism of sweating. This is regulated by both central (brain) and peripheral (non-brain) thermoregulatory processes. A variety of brain neurotransmitters, chemicals that communicate between cells in the body, are involved in the delicate process of maintaining core temperature.

Neurotransmitters, heat, and mental health

Serotonin is a neurotransmitter that has wide-ranging impacts on our emotions, brain, behavior, attention, cognition, reward systems and well-being. The serotonin system also has a role in heat regulation and other biological functions that impact mental well-being, such as sleep regulation. Other neurotransmitters, including but not limited to dopamine and noradrenaline, also have important roles in the brain and in mental functions – as well as in body temperature regulation.

Adequate functioning of these important neurotransmitters can be adversely impacted by heat. Heat has been implicated in altering serotonin levels and functioning.

Because of the multiple roles that neurotransmitters play, and the way heat impacts on these neurotransmitters, there is a strong plausible hypothesis that changes in heat to biological functions such as neurotransmitters contribute to the mental health impacts of heat.

Additionally, since psychiatric medications impact many of these neurotransmitters, the added biologically-driven impacts of psychiatric medications add to risks for patients treated with these medications.

Unequal impacts

Although all of us are affected by hot spells, we are not all affected equally.

There are particularly vulnerable groups who often experience more intense impacts. These groups include:

The elderly, especially those with medical conditions
Pregnant women
People of color
Indigenous populations
Children – especially babies, toddlers, and children who play outdoors
Outdoor workers and confined indoor factory workers
Unhoused people
Those with pre-existing mental health conditions, who die at three times the rate of those without conditions
Low-income urban residents
Rural residents, who live close to the land
First responders to disaster and emergency

Low-income people and people of color, living both within the United States and internationally, bear the greatest burdens of heat impacts. Race and poverty are the most significant factors in how vulnerable someone is to heat. Communities in the Global South, particularly in Southeast Asia, Indochina, and on islands in the Pacific Ocean, are at the greatest risk.

What do we still need to learn about extreme heat?

We need to improve responses to managing heatwaves in ways that will improve mental health.

We need to develop:

Better communications and messaging that uniquely focus on vulnerable populations, outlining ways to protect those groups from extreme heat.
Multi-language materials on how to protect individuals from extreme heat that resonate with different ethnic and cultural groups.
Better ways for individuals, neighbors, and communities to work more collaboratively with already-existing public health departments and governmental and non-governmental entities to assist at the individual and collective levels.
Clinical guidelines and extensive professional education for managing safe use of psychiatric medications.

More technical things we need to learn through research:

How specific medications, especially psychiatric medications, adversely impact the human body’s physiologic capacity for maintaining effective cooling.
How people acclimate to heat, and how to facilitate helping this process.

How to protect mental health in heat

There are many ways to limit the severity of extreme heat. Extreme heat can be managed!

Individuals can protect themselves by learning the signs of heat stress and developing strategies to prepare for and manage periods of extreme heat. There are many guides, such as these surviving heat extremes handouts.

Communities can develop plans for response. They can:
Assist those who are vulnerable. For instance, they can set up buddy-system check-ins for elderly, isolated, or otherwise vulnerable people.

Provide public cooling respite centers as well as assistance getting to these centers in locations such as libraries, malls, and movie theaters.

Create heat alert systems that are accessible in many languages.

Local, regional, national, and international policies must address the underlying risks of extreme heat with a wide range of actions aimed to improve our communities and responses.

All efforts to reduce our reliance on fossil fuels and transition to a clean energy economy are essential to curb escalating heat and its effects on health.

Author and version info

September 25, 2022: Robin Cooper, MD, UCSF

Extreme heat and climate mental health

Heat waves are increasing in the climate crisis

How extreme heat affects mental health

Unequal impacts

What do we still need to learn about extreme heat?

How to protect mental health in heat

Further reading

RESOURCES FOR COPING

US GOVERNMENT RESOURCES

ARTICLES AND ONLINE SOURCES

Selected Research/Scientific Papers

Author and version info

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