How heat affects the mind

For local governments, heat mitigation is one of the primary ways to attempt to soften the psychological impacts of heat. “When you cool down a neighborhood, it benefits your physical and your emotional health,” said Ali Frazzini, a policy adviser with a background in public health at 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 said. “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.

In Los Angeles, city planners are looking at cool surfaces, such as roads coated with heat-reflecting materials, and other strategies to reduce the urban heat effect, Frazzini said. “Right now, one of our big areas of focus is just increasing the tree canopy,” which can provide shade and mitigate temperature spikes, she said. “Many of our most vulnerable neighborhoods have poor tree canopy.”

Across the United States, the link between poverty and vulnerability to heat comes up repeatedly. In Meidenbauer’s analysis of Chicago’s neighborhoods, people reporting high economic hardship were also likely to live in areas impacted the most by the urban heat effect. In Miami, data from heat-related hospital visits also show disparities. “We have ZIP codes that have 4 to 5 times the rates of heat-related illness compared to other ZIP codes,” Gilbert said. “The top correlating factors are high poverty rates, high land surface temperatures, families with children, and a high percentage of outdoor workers.”

Unhoused individuals are also at high risk during heat waves, Gilbert said. Not only is it difficult for people without shelter to escape the heat of the day, many people who are unhoused also have mental health diagnoses that may be exacerbated by heat.

These disparities aren’t limited to urban areas. In Watsonville, tree cover is at only about 8%, Faulstich said, and much of the housing stock for agricultural workers is in poor condition without sufficient cooling. The city is working with the nonprofit conservation organization Watsonville Wetlands Watch to develop a 40-year plan for sustainable tree cover in the city, with a goal of eventually reaching 30% canopy.

Heat doesn’t happen in a vacuum. With heat comes drought, and with drought comes wildfire, which can lower air quality. Pollution is also linked with both mood and cognition problems. One study in China that used portable monitors to measure participants’ exposure to air pollution in real time found that exposure to fine particulate matter (P.M. 2.5) impaired executive control on cognitive tasks (Ke, L., et al., Environment International, Vol. 170, 2022). In a longitudinal population study in Sweden, exposure to fine particulates was linked to cognitive decline in adults over the age of 80 (Grande, G., et al., Journal of Alzheimer’s Disease, Vol. 80, No. 2, 2021). And a meta-analysis of studies between 1974 and 2017 found that particulate exposure was linked to depression, anxiety, and suicide (Braithwaite, I., et al., Environmental Health Perspectives, Vol. 127, No. 12, 2019).

[Related: Extreme heat and poor air quality are threatening childrens’ mental health]

Researchers also worry about the knock-on effects of mass migrations caused by climate change, which have the potential to increase intergroup conflict. Climate refugees, especially children, experience stressors that are well-known to impact mental health and cognition, Anderson said. And large-scale migration can lead to political conflict and violence that further impact those involved. According to the UN Refugee Agency, 110 million people are currently displaced around the globe because of persecution, conflict, and violence, a number that has steadily risen from about 32.3 million in 2008.

“The proportion of the world’s population that is exposed to a number of these risk factors is going to increase,” Anderson said. “In fact, it already has increased.”

The good news, Anderson said, is that psychological research on heat, mental health, and violence is starting to get more traction outside of psychology: “It’s only recently that we’ve started publishing [heat research] in climate change journals,” he said.

There are still urgent questions that psychologists need to answer, Meidenbauer said. She and her team are looking at how uncomfortable, but not dangerous, levels of heat might affect cognition. They’re also interested in trying to unravel individual differences in heat tolerance. People report becoming uncomfortable in heat at very different temperatures, she said, and it’s a combination of warmth and discomfort that seems to cause psychological symptoms. There is also a dearth of research on ways to reduce the negative impacts of heat, and that needs to change quickly, she said.

“Knowing that it’s only going to get worse from here,” she said, “really emphasizes the importance of understanding the effects so that we can intervene.”