Key points
- Heat impairs memory, attention, and executive functions like problem-solving and decision-making.
- People without AC performed measurably worse on cognitive tests during a heat wave.
- Long-term heat exposure is linked to lasting cognitive decline across large populations.
- Some models project a 5–7% drop in average human cognitive function due to heat by 2100.
Heat waves are becoming more common, with severe health consequences ranging from cardiovascular, respiratory, and renal difficulties to death due to extreme heat exposure or heat stroke. But even setting aside those direct risks, heat has severe indirect consequences. A large number of studies have shown that high temperatures impair cognitive functions, which in turn leads to poor decisions.
The reasons why high temperatures cloud your brain are probably related to changes in brain blood flow. When air temperature is too high, your body attempts to protect you by diverting blood and energy to cool you down, a process called thermoregulation. Unfortunately, this alters blood flow to the brain, and although the exact mechanisms are not yet fully understood, the consequences are not good. Heat also causes fatigue and sleep impairments, which compound the cognitive toll.
Your Brain Without AC
Cedeño Laurent and coauthors (2018) conducted a study on university students’ cognitive functions during the 2016 heat wave in Boston, MA. Over 12 days in July, students completed two tests daily. One was a numerical task requiring addition or subtraction of two-digit numbers. The other was the Stroop task, a classic in cognitive psychology that measures the ability to inhibit impulses and direct attention.
What made the study particularly interesting is that some students lived in buildings with air conditioning (AC), while others did not. The AC group experienced temperatures in the 17–25°C range, averaging 21°C (70 °F). The non-AC group endured temperatures in the 20–30°C range, averaging 26°C (79 °F). That difference was enough: students in the non-AC group gave fewer correct responses per minute on the numerical task and were slower on the Stroop task.
Studies like this one have limitations, including small and specific samples (38 university students, in this case). But they have been accumulating over the years. Laboratory studies, in which people are randomly assigned to different ambient temperatures, have consistently found that those exposed to higher temperatures display impaired memory, reduced attention, and lower performance in executive functions, including problem-solving, understanding complex tasks, and decision-making. So, yes: heat might quite literally make you dumber.
Evidence Linking Long-term Heat Exposure to Cognitive Decline
We are also beginning to accumulate data from large panel studies. Yin and coauthors (2024) used data from the China Family Panel Study, tracking over 53,000 participants across eight years. The researchers examined the relationship between high-temperature exposure, defined as the proportion of time above 32°C (90°F), and cognitive test scores (verbal and mathematical) collected as part of the panel. The results show that both exposure to extreme temperatures and sustained, long-term exposure are associated with cognitive decline. On average, in the data, a 10% increase in the number of days with peak temperatures above 32°C was associated with a 2% drop in cognitive capacity.
That might not sound like much. But how many additional high-temperature days will we face in the near future? 10% more, or 40% more? Under standard climate-change scenarios, the study of Yin et al. concluded that average cognitive function in humans might decrease between 5 and 7% by 2100. That is a sobering prospect. The effects are also uneven: they are worse for the elderly, for people with high body-mass index, and for males compared to females. And the long-term averages do not capture everything. In the data of Yin et al., a high proportion of extreme-temperature hours in the days before a test was already associated with declined cognition, meaning that a single heat wave may leave your brain clouded for some time afterward.
Practical Strategies During Heat Waves
As discussed in a previous post, carrying too much in your mind (what psychologists call “cognitive load”) can lead to poor decisions. That is why “multi-tasking” is a bad idea, and you should single-task instead. Financial worries cloud judgment in much the same way, which is the reason that poverty is often found to cloud your brain. The mechanism behind heat-impaired judgment is different and more directly physiological. But the practical takeaways are similar.
The old expression “in the heat of the moment” usually refers to poor choices driven by strong emotions, but it turns out to hold more literally as well. As climate change makes heat waves more frequent and high-temperature days more frequent, you should be wary of when and how you make decisions. Beware of decisions made during or shortly after a heat wave.
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Avoid important decisions on high-temperature days when you can. Maybe you should delay buying that big-ticket item if it’s a hot day (unless it is an AC system!). As always with consequential choices, give yourself time. Do not trust your gut. Check your reasoning carefully. Seek outside advice. Wait until you can achieve some emotional and cognitive distance.
And if it is hot outside and you have to make an important decision, cool down first.
Cedeño Laurent, J.G., A. Williams, Y. Oulhote, A. Zanobetti, J.G. Allen, and J.D. Spengler (2018), “Reduced Cognitive Function during a Heat Wave among Residents of Non-Air-Conditioned Buildings: An Observational Study of Young Adults in the Summer of 2016,”PLOS Medicine 15, no. 7: e1002605.
Yin, B., W. Fang, L. Liu, Y. Guo, X. Ma, and Q. Di (2024), “Effect of Extreme High Temperature on Cognitive Function at Different Time Scales: A National Difference-in-Differences Analysis.”Ecotoxicology and Environmental Safety 275: 116238.
