Heat waves disrupt attention in firefighters after 15 minutes, then return in 20

A dangerous heat wave can be more than “just uncomfortable.” In a study Catherine Thompson, a cognitive psychologist at Liverpool Hope University, has been running with firefighters, 15 minutes of intense heat exposure made it harder to focus and control attention immediately after the exposure. The good news, if you can call it that: the firefighters’ skills returned to normal after about 20 minutes of cooling down. The sobering part is what Thompson does not yet know, because the test is hard to scale: she does not know what a days-long heat wave does to cognition, or how long impacts might last.

Thompson is not the only researcher pushing on the brain question. Joshua Wortzel, who directs the Heat-Mind Lab at Hartford HealthCare in Connecticut, describes heat as a “million-dollar question” area where biology and mental-health outcomes collide, especially when temperatures rise above what’s typical for a region. In a review of evidence published in 2023, Emma Lawrence at the University of Oxford and her colleagues found that during heat waves there was a 9.7% increase in the hospital admission rate for people with mental-health conditions. Lawrence ties susceptibility to the physical impacts of heat, and that makes this story relevant well beyond weather watchers.

Start with the immediate reality: it’s been hot in London this week, in Western Europe more broadly. The UK recorded its highest ever June temperature at 36.1 °C, about 97 °F. It “felt like” 39 °C on a weather app, underscoring how heat stress is about more than the thermometer. For context, the Met Office says June temperatures peaked at an average 19 °C, about 66 °F, in England between 1991 and 2020. When the environment shifts that far beyond typical, second-order effects begin stacking: deaths, plus knock-on damage to agriculture, infrastructure, and the health system. The brain effects are part of that cascade.

Why does heat mess with thinking in the first place? In Thompson’s firefighter work, the challenge is experimental design. It’s difficult to directly study a heat wave’s effects on cognitive skills “in the wild,” so her team studied scheduled training that includes entering a burning building. That matters because it gives researchers pre- and post-exposure measurements. Even so, the exposure in that setup was intense but short. Thompson explicitly notes she does not know the effects of living through days-long heat, and she suggests one possible approach that highlights the practical barriers: shipping cognitive test kits to thousands of people during the few days’ notice of an impending heat wave. Her quote frames the problem as difficulty, not a lack of concern: “My guess [is] that no one’s done it because it’s just so difficult to do.”

If cognitive impairments can show up quickly after heat exposure, the mental-health angle suggests a longer runway. The 2023 review by Lawrence and colleagues points to worse outcomes during heat waves, with the 9.7% increase in hospital admissions for people with mental-health conditions. Wortzel describes a correlation: “the hotter it gets, especially during the hottest times of the year, the worse the mental-health outcomes.” The mechanism could be indirect, but the evidence for biological pathways is emerging. Lab research in rats and mice suggests that excessive heat can alter chemical signaling in the brain. Levels of neurotransmitters like serotonin seem to increase with high temperatures, according to multiple studies. Heat may also interfere with how brain networks communicate, and with oxygen reaching brain cells. Wortzel points to “so many biological reasons” that brains may be negatively affected.

For executive decision-makers, the youth angle is where risk modeling gets uncomfortable. Emerging research suggests children and young people are among the most vulnerable. In research published earlier this week, Wortzel and colleagues saw a 2.97% increase in the suicide rate among people in the US aged 15 to 24 for every 1 °C increase in average monthly temperature. That increase was more than double the increase seen in people over age 24. Separate work hints at potential long-term impacts on brain development: babies exposed to either extreme heat or cold appeared to have altered white matter by the time they were nine to 12 years old, though it’s not clear how that translates to individual outcomes. This is where the “public health” story meets “operational continuity.” Mental health systems do not just face more demand, they face demand with complexity and timing.

And timing is the whole problem with adaptation. Sleep, socializing, and exercise are important for mental health, and heat disrupts all three. Some people end up stuck indoors, avoiding outdoor play and exercise. Getting a good night of sleep can become harder. So even if “unusual heat” does not have a single specific mechanism, the environment is still reshaping the brain through a bundle of pressures. Wortzel’s lab framing, the Oxford review, and Thompson’s cognitive measurements all converge on one managerial reality: you can’t treat heat as only a respiratory or cardiovascular story. It is also a cognitive and mental-health load that can spike fast.

For boards and leaders, the strategic stake is that climate adaptation is no longer only about resilience for infrastructure. It is about workforce performance, emergency response readiness, and mental-health capacity. Thompson’s work suggests attention and focus can degrade immediately after intense exposure, with recovery after cooling in minutes, but the key unknown is what days-long events do. Lawrence’s review suggests that when temperatures surge, hospital admissions for mental-health conditions jump measurably. And Wortzel’s youth data suggests that the human cost concentrates in younger cohorts. In other words, heat waves can turn “weather” into measurable, operational strain across hospitals, caregivers, and organizations that rely on outdoor labor, caregiving, and youth development.

There is urgency here because climate change is changing the frequency and intensity of what counts as “extreme.” Children born in 2020 are predicted to experience around seven times the number of heat waves their grandparents did, according to Lawrence. She says, “[We] need to be serious about adapting to a warming world.” Researchers are still learning why heat affects the brain. But the decisions are already here: if you lead a hospital, staff emergency services, run outdoor operations, or govern public health, heat wave planning has to include cognitive and mental-health effects, not as an afterthought, but as a core risk.