As the world gets warmer, extreme heat days – once a phenomenon of midsummer, are now an inevitable fact of life. You’re not just imagining it – the summers are getting hotter for longer spans of time. Just last year, 2023 set a record for the hottest year since humans have been keeping track, and all signs suggest 2024 will be worse. We may be living in the first year on record to exceed 1.5°C of warming since the preindustrial age.
“Extreme heat can make people more depressed or irritable, it can bring on psychotic outbreaks, and people on certain psychiatric medications are more sensitive to heat,” says Jane Gilbert, the first appointed Chief Heat Officer in the world, a government position the Miami Dade County officials felt the need to create in 2021.
However, Gilbert is just one of several local-level policy makers across the United States who is devoted to handling the consequences of extreme heat as a full blown crisis. While this is addressed on the policy level, a number of psychologists are also working to determine how the heat impacts our short term moods, as well as behavior and cognition. While unraveling the scope of the damage, they’re becoming increasingly vocal about the need to respond.
“The way we are headed right now, things are only going to get worse,” says Dr. Kim Meidenbauer, assistant professor of psychology from Washington State University. Meidenbauer studies the impact of heat stress combined with other environmental factors on thought and emotion. “If we don’t even understand the scope of the effect heat is having on us, that bodes poorly for our ability to protect people from the negative psychological consequences.”
Your mental health under fire
The most apparent danger from heat is physical. Losing too much water and sodium by sweating can shortly result in heat exhaustion – symptoms of dizziness, clammy skin, and an accelerating pulse. Untreated, this condition quickly progresses into heat stroke, where the body’s central air condition system completely collapses, causing a catastrophic rise in your internal body temperature. This hyperthermia does not spare the brain: Around 10% and 28% of heat stroke survivors suffer from persistent brain damage, according to a 2022 study.
While heat stroke can be very lethal on its own, there are also other lingering consequences to constant exposure to extreme temperatures. “We’re only looking at emergency department visits, so we’re only looking at the most extreme presentations,” says Dr. Amruta Nori-Sarma, Assistant Professor in the Environmental Health Department at Boston University School of Public Health. “There might be a lot of other people who see a primary-care physician or a mental health provider. Or there might be a lot of people who are having symptoms who will never come into contact with the medical system.”
While heat waves can be physically dangerous to older adults, mental health symptoms associated with heat also hit this demographic particularly hard, as a new systematic review with meta-analysis led by Jingwen Liu of the University of Adelaide School of Public Health indicates. The review showed a 2.2% increase in mental health-related mortality as well as a 0.9% increase in mental health morbidity attached to every 1.8°F increase in temperature. The largest display in mortality overall was seen in individuals who had substance use disorders. Those who lived in either subtropical or tropical environments and those who were over age 65 suffered disproportionately.
Though seasonal mood problems are mostly associated with winter, there is also a subset of people who struggle with summer-related major depression. “It’s understudied,” says Dr. Kelly Rohan, a clinical psychologist at the University of Vermont whose area of concentration is seasonal affective disorder (SAD). Summer-related depression cases are much rarer than winter-related SAD, associated with short daylight hours in winter months. Summer SAD, however, is associated with individual experiences with heat and humidity, according to Rohan.
“Some of the same neurotransmitters, like norepinephrine, dopamine, and serotonin, that are involved in mood regulation are also involved in thermoregulation,” she says, “so maybe there is some dysfunction in one or more of those neurotransmitter systems that confers a risk of depression as well as the inability to tolerate heat and humidity.”
Cooling down
Local governments see heat mitigation as a primary way to reduce the psychological harmfulness of heat. “When you cool down a neighborhood, it benefits your physical and your emotional health,” says Ali Frazzini, who is a policy adviser on matters of public health for the L.A. County Chief Sustainability Office.
Policies range from those directed toward individuals, such as making public service announcements and maintaining cooling centers in the summer, to those focused on making city infrastructure more climate resilient, such as planting trees and installing green infrastructure. Because of the known socioeconomic disparities in heat impacts, many of these policies are focused on those who are financially precarious, Gilbert said.
“It’s gotten cost-prohibitive for many households to keep their homes cool,” Gilbert explains. “Or if the wall unit breaks down in July and they can’t afford to replace it or the landlord doesn’t fix it, they can be in a dangerous situation.”
Miami-Dade County has a financial assistance program for low-income residents and maintains a list of resources for Florida incentives and rebates for energy savings and home cooling. The county’s HOMES plan, a housing affordability initiative announced in 2022, includes $7 million for retrofitting and weatherizing older homes and includes requirements that new construction funded by the county include cool roofs—light-colored roofs made with materials that reflect instead of absorb heat, which can reduce cooling costs considerably. The city is also focused on improvements to the power grid, especially since hurricanes can leave residents sweltering without electricity for days or weeks.
Los Angeles city planners are looking into cool surfaces – like a roads coated in heat-reflecting materials to mitigate the urban heating effect. “Right now, one of our big areas of focus is just increasing the tree canopy, which provides shade and reduces temperature spikes,” Frazzini said. “Many of our most vulnerable neighborhoods have poor tree canopy.”
Throughout the United States, the relationship between both poverty and vulnerability to warm temperatures surfaces regularly in research. Meidenbauer’s analysis of Chicago’s neighborhoods found that those describing high degrees of economic hardship were the most likely to live in neighborhoods hit hardest by urban heat effect. In Miami, literature from heat-related hospital visits display similar disparities. “We have ZIP codes that have 4 to 5 times the rates of heat-related illness compared to other ZIP codes,” says Gilbert. “The top correlating factors are high poverty rates, high land surface temperatures, families with children, and a high percentage of outdoor workers.”
Houseless individuals are dangerously at risk in heat waves, says Gilbert. It’s not only difficult for them to evade the daytime heat, but those with mental health issues could suffer from the effects being exacerbated by the heat.
With high temperatures come the droughts, and with droughts, come wildfires, that can also reduce air quality – as 2023’s forest fires in Canada brought hazardous conditions across much of the northern United States. Pollution has also been linked to both mood and cognition issues. A study from China used portable monitors for measuring the participants’ exposure to air pollution and discovered exposure to fine particulate matter was detrimental to executive control in performing cognitive tasks. A longitudinal population study from Sweden linked fine particulate exposure to later cognitive decline in adults over 80. A meta-analysis made from studies throughout 1974 and 2017 discovered a link between particulate exposure and depression, anxiety, and suicide.
Researchers also fear the effect of mass migration due to climate change, especially since there’s the potential for intergroup conflict to break out. These so-called climate refugees, particularly children, experience stressors well-documented for their impact on both mental health and cognition. As per the UN Refugee Agency, there are 110 million people currently displaced across the globe due to persecution, conflict, or violence. This number has steadily hiked from around 32.3 million in 2008 – making climate change a matter of global security.
“The proportion of the world’s population that is exposed to a number of these risk factors is going to increase,” says Anderson. “In fact, it already has increased.”
