Irritable in a Heat Wave? It’s Not Just You: How Climate and Environment Leave Their Mark on the Brain

Written by Dazhong Wu

By Yu Xie

The unexplained irritability during a heat wave. The gloom that lingers through days of rain. The flutter of unease before a typhoon makes landfall. Then think about everyday city life: traffic rumbling past all night, neon that never switches off, exhaust fumes at the subway entrance, a rush-hour train packed like a tin of sardines, and a patch of green space you have to walk a long way to reach.

We tend to put all of this down to "stress." But is that really all it is?

In October 2026, Nature Mental Health published the report of the Earth–Brain–Health Commission (hereafter "the Commission"). After reviewing the evidence, about 30 experts in psychiatry, neuroscience, climate science, and ethics concluded that heat, air and noise pollution, extreme weather, urbanization, and the loss of green space are all linked to depression, anxiety, and declines in cognitive abilities such as memory and attention (Schumann et al., 2026). And these effects fall hardest on low-income countries, children, older adults, people with disabilities, and marginalized groups.

Climate change and environmental problems have never been only environmental issues. They are health issues, and they are equity issues.

I. The Body Feels It First, and the Brain Remembers

The environment rarely strikes the brain directly. The Commission emphasizes that most of its effects pass through the body first: the cardiovascular system, immune and inflammatory responses, the endocrine system, breathing, and sleep and circadian rhythms. These pathways intertwine to create what physiologist Bruce McEwen called "allostatic load": the body repeatedly mobilizes resources to cope with stress, which protects us in the short term but, over the long term, adds up to a growing bill for wear and tear (McEwen, 1998). Eventually, that bill is sent to the brain.

Heat is one example. In analyses of the UK Biobank, people living long-term in warmer areas had smaller volumes in several brain regions, including the region responsible for forming new memories. This may show up as being more forgetful or finding it harder to retain new information. Animal studies show that high temperatures disrupt the stress hormone system, keeping the body in a constant state of tension, triggering anxiety-like behavior and weakening memory. At the population level, heat is associated with more psychiatric visits and more suicidal behavior.

Air pollution takes a different route. PM2.5 refers to fine particles no more than 2.5 micrometers across, roughly one-thirtieth the width of a human hair, small enough to travel deep into the lungs and enter the bloodstream. Long-term exposure to PM2.5 and nitrogen dioxide is linked to depression, anxiety, and declining thinking skills. Pollutants may keep the brain in a state of chronic inflammation, damage the blood vessels that supply it, and disrupt the "wiring" between brain regions, slowing thought and reaction.

Noise and artificial light at night work mainly by stealing sleep. The Commission notes that chronic noise is linked to disrupted sleep and to symptoms of depression and anxiety, while artificial light at night throws off the body clock. Cities stack these stressors on top of one another. The share of the world's population living in cities has risen from under 30% in 1950 to more than 55% today, and depression, anxiety, and schizophrenia are more common in urban areas. Brain scans show that city living is associated with a brain "alarm system" that is more sensitive to social stress, making people tense up more easily and calm down less readily.

The good news is that this can change. One controlled study found that after a one-hour walk in nature, the brain's alarm system reacted less strongly under stress. Body and mind have always been a single system. The heat, noise, glare, grime, and crowding of cities wear down the body, and they wear down the mind too.

II. When Home Changes Before Your Eyes: The Mental Toll of Extreme Weather

A flood may last only a few days, but its psychological effects can last for years. The Commission notes that disasters such as floods are often followed by persistent anxiety, depression, and post-traumatic stress disorder (PTSD), especially when people are displaced, their homes are damaged, or support after the disaster is inadequate. Less visible is the knock-on effect: disasters cut off housing, transport, electricity, livelihoods, and healthcare, extending the stress link by link. The storm may last a day, but how things turn out is decided by the days that follow.

The Commission identifies the loss of control and agency as a core psychological pathway. Agency is the sense that "what I do can affect my situation." When people repeatedly go through disasters they cannot control, they learn that "nothing I do makes a difference." This learned helplessness is a major source of depression (Seligman, 1975).

In a survey conducted about a week after the catastrophic rainstorm in Zhengzhou, China, on July 20, 2021, about 20% of residents surveyed showed symptoms of PTSD and more than half reported anxiety. Those who were less satisfied with the relief response and had less social support were at higher risk (Wang et al., 2023). How people experience the response matters as much as the disaster itself. The Commission also notes that poor institutional responses can deepen distrust and trauma, while collective action can help people regain a sense of control over their lives.

There is another kind of distress, called "solastalgia." Australian philosopher Glenn Albrecht coined the term to describe homesickness you feel while still at home: the familiar land, rivers, and seasons falling apart in front of you, with no power to stop it (Albrecht, 2005). The Commission notes that people directly exposed to extreme weather, such as Indigenous communities, farmers, and island residents, are living with disrupted livelihoods, broken cultural ties to the land, and anxiety about the future. Among young people, this worry is often called "climate anxiety," and it is a reasonable response to a real threat.

When home is no longer livable, people have no choice but to leave. The Commission notes that climate-related migration and forced displacement can shake a person's social identity and are associated with higher risks of depression and suicidal thoughts. Yet international law still has no status for "climate refugees."

No point in the Pacific island nation of Tuvalu sits more than six meters above sea level, and its prime minister expects more than half of the country's land to be flooded by tides by 2050. In 2025, the first round of Australia's climate visa for Tuvaluan citizens offered just 280 places but received more than 4,000 applications, from a country with a total population of only about 10,000 (CNN, 2025).

To leave is to say goodbye to ancestral land and community. To stay is to watch your home sink into the sea. Either way, it is a kind of grief.

III. Same Heat Wave, Different Costs: How Inequality Gets Written into the Body

One of the most important shifts in the Commission's report is that it no longer treats poverty as a "background factor."

Scientists use the term "exposome" to describe all the environmental factors a person encounters over a lifetime. The report goes further and proposes a "social exposome": poverty, housing conditions, and discrimination act together with air, heat, and noise, and in this way inequality may become "biologically embedded" in the body.

These exposures rarely come alone. Air pollution, light at night, and noise tend to concentrate in the same disadvantaged neighborhoods. Run-down housing, heat, and scarce healthcare also tend to pile up on the same people. All these harms accumulate and amplify one another.

Living in a poor neighborhood as an adult is linked to higher risks of depression, suicidal behavior, and self-harm. This may be related to changes in the brain regions responsible for self-control and emotional regulation, showing up as greater difficulty concentrating and controlling impulses. The Commission cautions, however, that most of these brain studies show correlation: where you live doesn't decide your fate, but it does change your starting line.

Heat waves show this inequality most clearly. The Commission notes that lower-income people are more likely to work outdoors or in places without air conditioning, to live in poorly ventilated housing, and to struggle to afford cooling. In the summer of 2026, a civil society group in Hong Kong measured conditions in 86 households, most of them living in inadequate housing such as subdivided flats and rooftop structures. The average nighttime indoor temperature was 29.42°C, above the threshold for a "hot night," and some units exceeded 40°C. Nine in ten households had air conditioning, but because of electricity costs they ran it for only a few hours a day, and 70% of residents had their sleep disrupted (The Standard, 2026). Having air conditioning and being able to afford to run it are two different things.

Vulnerable groups face higher risks still. Psychiatric medications increase older adults' risk of heatstroke, and people with disabilities often don't receive warnings in accessible formats, making it hard for them to evacuate in time. Globally, the share of people affected by disasters in the least developed countries is 20% higher than the world average, and disaster death rates are nearly twice as high.

This can turn into a cycle. According to psychologist Stevan Hobfoll's conservation of resources theory, people with fewer resources are more likely to fall into a "loss spiral" (Hobfoll, 1989): more exposure, worse health, less agency, a worse situation, and then more exposure. If interventions ignore equity, the cycle can speed up. The Commission found that cooling measures often benefit wealthier households first, and new greenery often goes to neighborhoods that are already better off. Environmental inequality is not only an outcome. It is also producing more inequality.

IV. A Long Road Ahead: What We Can Do

The Commission sets a clear goal: within ten years, every major environmental, climate, or urban project should include brain and mental health as one of the outcomes measured in its planning and evaluation. The report stresses that the main obstacle to action is not a lack of evidence but organization and funding: the data, tools, and policy levers already exist, they are just rarely connected. Action can start at the individual, community, and institutional levels all at once, but those most affected should benefit first.

A Ladder of Action

Individuals

  • Light and sleep: Get more natural light during the day; dim the lights at night and use blackout curtains. If you can, choose a bedroom away from the street, or use earplugs to cut down on noise.

  • Time in nature: Make walks in a park or by the water a fixed part of your schedule, not something you do "when there's time."

  • Heat and air: Before a heat wave, find a cool place nearby you can go to, and cut back on strenuous outdoor exercise when air quality is poor. If you take psychiatric medication, check with your doctor or pharmacist before summer.

  • Climate anxiety: Turn worry into something you do with others, such as volunteering or community gardening. If worry starts affecting your sleep or daily life, seek professional support.

Communities

  • Heat wave check-ins: Build a care list of older people living alone, people with disabilities, and people with mental illness, and call or visit them during hot spells.

  • Mutual aid and warnings: Open air-conditioned community spaces as "cooling points," share supplies and alerts, and provide warnings in text, audio, and multiple languages.

  • Support after disasters: Social support lowers risk after a disaster. Learn psychological first aid, and organize mutual aid and grief groups.

Policy and institutions

  • Ask the planners: At planning consultations or public hearings, ask, "Has this project assessed residents' mental health?" Push for stress, social trust, and sense of belonging to be included in environmental impact assessments.

  • Equity first, combined measures: Direct cooling and greening first to the most exposed communities, and roll them out together with early warnings, cash assistance, and psychological support.

  • Heat health plans: Make people with serious mental illness a priority group, and carry out medication reviews during heat waves.

  • Employers and society: Upgrade workplaces to reduce heat and noise, and include heat protection for outdoor workers and mental health support for employees in occupational health programs.

In practice, this road is not easy. Greening, air quality programs, and heat action plans rarely measure mental health outcomes. Health, social services, and environmental agencies work in silos. Research resources are concentrated in high-income regions, so the places carrying the heaviest burden often have the least data. Without deliberate design, even good intentions can widen the gap.

But some cities are already leading the way. In Medellín, Colombia, residents of low-income neighborhoods worked with planners to create "green corridors," and the neighborhoods reportedly cooled by 2°C over five years while self-reported depressive symptoms fell by 13%. In South Korea, social workers visited high-risk older adults during heat waves, and emergency hospital admissions for psychological distress fell by 15% over two years. These figures mostly come from program reports and still need independent evaluation, but the direction is clear.

The Commission's guiding principle is that mental health and environmental systems depend on each other, and can be changed together. The environment leaves its mark on our brains, and we leave our mark on the environment too: a phone call to a neighbor who lives alone, a question raised at a public hearing, a tree planted on the hottest street.

The road is long, but we already know which way to go.

A Note on the Evidence

The main points and data in this article come from the Earth–Brain–Health Commission report. The report is a narrative review, not a systematic review. Evidence on heat, air pollution, noise, and urban stress is relatively strong, while evidence on topics such as biodiversity loss and the neural mechanisms of climate anxiety is still developing. Most studies show correlation rather than causation.

The suggestions in this article are not a substitute for professional diagnosis or treatment. If you are experiencing persistent low mood, anxiety, or trauma reactions, please reach out to local mental health services or someone you trust.

References

Dazhong Wu
Previous

Safety or Profit? The High-Stakes Contest Behind the AI Giants
Next

Why Does the Economy Keep Growing While People Still Feel Broke?