1. Introduction

Heat stress is one of the most significant environmental and occupational health challenges. Prolonged exposure to high temperatures, humidity, and other severe climatic factors can result in partial or complete inability of the human body to regulate its temperature. Evidence shows that exposure to elevated temperatures, both indoors and outdoors, is strongly associated with adverse health outcomes. These include cardiovascular, respiratory, infectious, and other physical ailments, increased heat-related mortality and morbidity, and heightened risks of mental health issues, such as schizophrenia, dementia, and mood disorders [1–3]. Moreover, rising temperatures are associated with increased incidences of violent behaviour, including assaults, and higher suicide rates [4,5].

Cognition encompasses the brain’s ability to perform tasks such as attention, memory, learning, action, reasoning, decision-making, planning, and communication. These processes demand considerable conscious mental effort [6]. The impact of high temperatures and heat stress on human capital productivity and cognitive performance is a well-documented area of research [7]. Most studies indicate that exposure to excessive heat detrimentally affects working memory, information processing, and knowledge retention, thereby impairing overall cognitive performance [8–10]. However, there are studies that have reported statistically non-significant effects of heat on cognitive function [11,12].

Two main theoretical models explain the relationship between thermal stress and human performance: (a) the Inverted U model and (b) the Extended U model [7]. The Inverted U model is derived from the arousal theory known as the Yerkes-Dodson law [13]. According to this model, there is an optimal level of arousal at which task performance is maximized. Performance declines when arousal levels fall below or rise above this optimal level. Environmental psychologists have applied the arousal theory to understand how thermal environments influence cognitive performance. They propose an inverted relationship between cognitive performance and the intensity of environmental stress, where there is an optimal temperature that enables peak cognitive performance [14].

According to the Extended U model, there is a broad central plateau of acceptable temperatures, or the comfort zone, where human performance remains stable and near-optimal performance is achieved. On either side of the comfort zone, there is the maximum adaptability zone, in which acceptable and improved cognitive performance can still be maintained through psychological adaptive actions [15]. Heat stress occurs outside the maximum adaptability zone and can result in a sharp decline in cognitive function, potentially leading to life-threatening conditions.

2. Methodology

We conducted a comprehensive search of six major scientific databases, including PubMed, Scopus, PsycINFO, Web of Science, Science Direct, and Google Scholar. Additionally, we hand-searched field-specific journals and examined the references of relevant papers. The search was limited to the last 15 years, up to December 2024. The search was conducted from January to December 2024. Our search terms were relevant to: 1. the cumulative impact of heat exposure on the cognitive performance of students, 2. The adaptation and heat mitigation measures and technologies used, 3. The social and economic inequalities caused within and across countries, and 4. Future projections for the effects of long-term exposure to heat to students’ cognitive abilities (Fig 1, S2 Checklist).

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Fig 1. PRISMA diagram of study selection.

https://doi.org/10.1371/journal.pclm.0000618.g001

Two reviewers (Konstantina Vasilakopoulou and Matthaios Santamouris) searched the databases independently and screened articles based on title and abstract. After removing duplicates, the full texts were screened to identify the articles that met the inclusion criteria. We excluded any type of review articles, theses, articles on short-term exposure to heat and cognitive performance, clinical trials and general articles on cognitive performance.

We focussed on studies investigating the long-term impact of indoor or outdoor temperature on students’ learning capacity. Our review considered all categories of students, including primary, secondary, and college/university students. We selected only studies that reported analysis and results from a very high number of students, typically several thousand per study to avoid bias. All types of cognitive functions and tasks were included in our review. No review protocol was prepared or registered for this paper.

3. Results

Six articles reporting seven studies on the impacts of long-term exposure to heat on students’ cognitive performance were selected and assessed by both reviewers, individually and collaboratively. The studies’ characteristics are detailed in Table 1, as a quick reference. Further analysis of the included papers’ findings is included in the paragraphs below.

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Table 1. The characteristics of the studies analysed in this review.

https://doi.org/10.1371/journal.pclm.0000618.t001

All studies are based on the results of national examinations and cognition tests, with each study involving between 8,000 and 10 million students. Based on the reported figures, the studies include data from 61 countries, and the total number of participating students exceeded 14.5 million. The studies include results from cognition tests in various subjects: Mathematics (six studies), Reading (four studies), English Language (three studies), Science (one study), and History (one study). Seven studies reported results from high school students, while three included results from both high school and elementary school students. The effects on student cognition are reported in terms of academic achievement, i.e., test scores decrease as compared to the scores of cooler days/years/periods, per subject or as a mean of multiple subjects. There was no handling of the data of the included studies.

However, no articles describing adaptation measures, social and economic inequalities and future projections were based on long-term exposure of large student cohorts to heat. The respective paragraphs follow a narrative review and analysis of studies which are relevant but do not meet all the inclusion criteria for the systematic review process, followed for the first research question.

Park et al. (2020) analysed test scores of approximately 10 million American high school students who participated at least twice in the Preliminary Scholastic Aptitude Test (PSAT), a national standardized exam, between 2001 and 2014. They associated the test scores with local daily average maximum ambient temperatures and the number of days exceeding a given multiple of 10°F (~5.55°C) in the 365 days before the test. Racial, economic, and demographic data were also collected and associated with the temperature data [24].

The study found that exposure to high ambient temperatures during school days, up to four years prior to the test, has a significant impact on students’ cognitive capacity. An increase of 1°F (0.55°C) above 26.7 C, during school days in the year prior to the test decreases the mean learning gain of students by almost 1% over a complete year. Each additional school day with an average maximum temperature of 90°F (32.2°C) or 100°F (37.77°C), relative to a day with a temperature close to 60°F (15.55°C), lowers cognitive gains by 0.17% and 0.26% of the annual worth of learning, respectively [24].

Exposure to high temperatures during school days up to four years prior to the test causes a considerably higher cognitive loss than exposure during the year prior to the test. Sustained exposure to daily maximum ambient temperatures up to 2°C higher compared to the current temperatures, reduces cognitive gains by 7% compared to the average worth of learning. Exposure to high temperatures outside the school period was not found to impact students’ cognitive capacity.

Garg et al. (2020) analysed two sets of cognitive test results in India. The analysis included Mathematics and Reading test scores for over 4.5 million primary school students, based on the Annual Status of Education Report (ASER). It also incorporated data from the Young Lives Survey (YLS), which included 1,008 children born between January 1994 and June 1995, and 2,011 children born between January 2001 and June 2002. The test results were associated with local temperature and other climatic data from the year before the tests. Temperature data were classified into 10 different bins, with the coldest bin including average daily temperatures below 13°C and the warmest bin including temperatures above 29°C. The YLS test results were also linked to local socioeconomic information [22]. A flexible econometric model was used to associate the scores with temperature, humidity, and rainfall, drawing on previous research by Deschenes and Greenstone (2011) [33] and Hsiang (2016) [34].

It was found that one additional day in the previous year with an average daily temperature higher than 29°C, compared to a day with a temperature between 15°C and 17°C, decreases Reading and Mathematics performance by 0.002 and 0.003 standard deviations, respectively, in the present year. Ten extra days with an average daily temperature above 29°C in the previous year were found to reduce Reading scores by 0.02 and Mathematics scores by 0.03. Additionally, story reading ability and division-solving ability were reduced by 1 percentage point, while the impact on word or letter reading skills was insignificant. These results were statistically significant, with the impact of hot days being significant only for the harder questions in both reading and mathematics tests. The study did not identify any impact of short-term temperatures on test scores, and heat stress over the four days prior to the test did not have a significant impact on student performance [22].

Park et al. (2021) analysed global test score data from more than 500,000 students in 58 developing and developed countries that participated in the PISA International Student Assessment between 2000 and 2015, administered by the Organisation for Economic Co-operation and Development. The assessment involves representative samples of 15-year-old students taking harmonized exams in mathematics, reading, and science. The test scores were associated with country-specific temperature and income data to identify the impact of heat stress on students’ cognitive performance. Data on the daily maximum temperature of each station were used, clustered into temperature bins of 5.5°C, ranging from −17.7°C to 60°C. The number of days in each bin over the previous 5 years was counted for each station. The study investigated the impact of all days with a daily maximum temperature above 26.7°C on student performance. The analysis concluded that school days with high temperatures during the last 3 years prior to the PISA exam impacted students’ performance. Each additional school day above 26.7°C during the 3 years prior to the exam decreased exam scores by 0.18% of a standard deviation, while an increase by a standard deviation of the days above 26.7°C, conditional on year and station, resulted in 14 school days. Robustness tests showed that the findings were robust and not driven by false associations between long-term cognitive achievement trends and local warming patterns. School days before the exam were found to exclusively impact exam scores and human capital accumulation, while the impact of high temperature during non-school days was insignificant, indicating that exposure to heat interferes with learning time [19].

Park et al. (2021) analysed the test scores in mathematics and English Language Arts (ELA) from schools in over 12,000 US districts. The tests were administered to third and eighth graders. The data were sourced from the Stanford Education Data Archive (SEDA). In total, over 270 million test scores covering the period from 2009 to 2015 were analysed. The test data for each district were associated with the corresponding climatic data, particularly the daily maximum temperature for school days from June 1 to February 28 in the year before the test, collected from 3,400 climatic stations [19].

The analysis showed that exposure to high temperatures during the school period significantly affects student performance. For each additional school day with temperatures above 27.6°C, student performance was reduced by almost 0.04% of a standard deviation. Specifically, mathematics scores were reduced by 0.11% and ELA scores by 0.04% of a standard deviation, with the average score reduction being close to 0.07% of a standard deviation [19].

Graff Zivin et al. (2018) analysed data from 8,003 children and young people aged 14–22, participating in the National Longitudinal Survey of Youth (NLSY) in the USA. The study examined the short- and long-term exposure to high temperatures on mathematical test scores. To assess the impact of long-term exposure to high temperatures, three climatic indicators were used: a) the average of the degree days base 21°C over the relevant period, b) the percentage of days in each 2°C bin, and c) the average temperatures during January to February and July to August. All days, including school and non-school days, were considered. Two models were defined and used. The first model investigated the impact of the sum of temperature between successive tests, while the second model examined the impact of accumulated temperature from birth until the date of the test. It was found that the impact of high temperatures on mathematical scores was not significant for both models. A 1-degree day increase in temperature across all days between two tests, a rather substantial change, decreased mathematics performance by only 0.630 percentile points. The lack of impact is attributed to potential adaptation measures undertaken to minimize the impact of high temperatures on students’ cognitive performance [21].

Roach and Whitney (2022) analysed data provided by the Stanford Educational Data Archive (SEDA), USA, including assessment outcomes from 2008-09–2014–15 for students in third through eighth grade for both English/language arts and mathematics tests. The test scores of each district were correlated with the corresponding median daily maximum ambient temperature. The study included data only for the school period, excluding non-school days. Daily temperature data were clustered into bins of 5.5°C (10°F), centred at 37.77°C (100°F), 32.22°C (90°F), 26.66°C (80°F), and so on. It was found that in areas with an average maximum temperature of 55°F (12.77°C), an increase in temperature by 1°F (0.55°C) decreased the average score by 4.71%, while in areas with a warmer average maximum temperature of 75°F (23.88°C), the corresponding average decrease was 2.6%. Additionally, for each additional day above 100°F (37.77°C), the mean student achievement was found to decrease by 2.3% [23].

Cho (2017) analysed test data from the Korean college entrance exam in reading, mathematics, and English language from 1,729 high schools located in 164 cities in Korea. The sample included almost 1.3 million observations of tests performed in November over the period 2009–2013. The test scores were associated with the corresponding daily maximum ambient temperature data. It was observed that high ambient temperatures during the previous summer had negative effects on the scores of the current year. An additional summer day with a maximum daily ambient temperature above 34°C, compared to a summer day with temperatures between 28–30°C, resulted in a decrease in mathematics and English language scores by 0.0042 and 0.0064 standard deviations, respectively. Ten additional warm days decreased the test scores by 0.042 and 0.064, respectively. In contrast, the impact on reading scores was insignificant [20].

4. Climate adaptation techniques and their impact on student cognitive performance

Various techniques aiming to lower indoor temperatures, improve thermal comfort and increase wellbeing have been implemented and studied.

5. Social heterogeneities in cognitive performance caused by overheating

Existing studies have identified significant racial and geographic heterogeneities in the cognitive performance of students caused by cumulative exposure to heat. Differences in access to air conditioning and higher ambient temperatures in deprived geographic areas are considered the main reasons for these disparities.

Past research has shown that fewer schools in disadvantaged areas in the USA have air conditioning compared to those in wealthier areas [85,86]. According to Park et al. (2020), lower-income students in the USA are 6.2% more likely to attend schools with inadequate air conditioning compared to higher-income students [24]. Additionally, previous research has shown that disadvantaged households in the USA, Australia, and Europe live in warmer neighbourhoods where the urban heat island effect can be up to 6°C higher than in areas where wealthier people live. These disadvantaged areas also have a lower density of green spaces, public goods, and environmental amenities [87–91].

Racial inequalities in educational outcomes are well-documented and are primarily attributed to social discrimination, racial bias, and cultural differences [92,93]. Additionally, cumulative exposure to heat can have varied impacts based on income, race, and geographic location. Studies by Park et al. (2020), Garg et al. (2020), Park et al. (2021), Roach and Whitney (2022), and Cho (2017) have shown that cumulative heat exposure significantly affects the cognitive performance of minorities and disadvantaged low-income students more than their advantaged counterparts [19,20,22–24]. The reasons for these disparities include a) Substantially lower access to school and home air conditioning for minorities and low-income students. b) Higher ambient temperatures in neighbourhoods where minorities and low-income students live. c) The lack of capacity for disadvantaged families to compensate for cognitive loss due to overheating, such as through private tutoring. d) Advantaged students may attend schools where teachers can compensate for lost learning [24].

Several studies have documented that cumulative exposure to excess heat significantly contributes to racial disparities in educational outcomes. According to Park et al. (2020), the cognitive performance of Black and Hispanic students in the USA is almost three times more inhibited by potential heat exposure during the previous school year compared to white students. The impact of heat exposure from the previous year was nearly twice as high for students living in low-income zones compared to those in high-income zones [24].

Exposure to a 1°F, (0.55 C), warmer school year over the past four years has been found to cause an almost 80% larger impact on Black and Hispanic students than on white students. Additionally, one extra day above 90°F (32.2°C) in each of the four previous school years has a nearly 40% higher impact on Black and Hispanic students compared to white students. These performance differences are due to discrepancies in heat exposure during the school period, caused by the partial lack of air conditioning in schools in the poorest geographic zones, as well as significant differences in ambient temperatures between the zones where various racial groups live. Cognitive losses due to cumulative heat exposure seem to explain between 3% and 7% of the gap in PSAT scores between white, Black, and Hispanic students. The authors estimate that heat exposure accounts for up to 13% of the racial achievement gap in the USA.

Garg et al. (2020), in their analysis of the cumulative impact of heat on the cognitive performance of students in India, found that students from the poorest families receiving state subsidies had lower test scores compared to students from wealthier families [22].

Park et al. (2021) analysed the performance of students in PISA exams and concluded that the impact of heat exposure on cognitive performance is higher in poorer countries compared to richer ones. The effect of the same temperature event was almost three times greater for low-income students than for high-income students. Based on their analysis, it was concluded that Brazilian students may learn 6% less than their South Korean counterparts due to much higher heat exposure, which accounts for almost 33% of the differences in exam performance [19].

Park et al. (2021) analysed the impact of cumulative heat exposure on students in grades three to eight in the USA and concluded that low-income and disadvantaged students living in deprived neighbourhoods are more affected than their advantaged counterparts. Each additional school day above 26.7°C results in a 0.12% decrease in test scores for low-income schools, while no significant impact is observed in higher-income schools. For each week above 26.7°C, the average cognitive performance of Black and Hispanic minorities is reduced by an amount equivalent to reducing teacher value-added by 5–6% of a standard deviation. This disparity is explained by significant differences in the availability of air conditioning in schools and homes between the White population and other minorities [19].

Roach and Whitney (2022), in their study on the impact of cumulative heat exposure on elementary and middle school students in the USA, found that their data aligns with previous research on the impact of heat on different racial groups. Asian students were found to perform better than White, Hispanic, and Black students [23].

The impact of heat and the corresponding differences in performance seem to be more significant in cooler geographic regions than in warmer ones. Goodman et al. (2018) found that cognitive losses in the USA are more significant in heating-dominated zones compared to cooling-dominated zones [94]. Similarly, Cho (2017) found that exposure to high summer temperatures in Korea mainly affects students living in cooler parts of the country, while the impact on students living in relatively warm cities was not statistically significant. In cities with an average maximum daily temperature below 28.5°C, one additional day at or above 34°C, compared to a day with a maximum daily temperature between 28°C and 30°C, decreased students’ scores in reading, mathematics, and English by 0.0073, 0.0124, and 0.0105 standard deviations, respectively [20].

6. Expected impact of climate change on the future cognitive performance of students

Considering the significant impact of cumulative exposure to excess heat on the cognitive performance of students and the considerable increases in environmental temperatures by even moderate future projections, it is useful to collate information on the potential cognitive performance of students. Three studies have assessed the potential future cognitive losses due to global warming and their main findings are summarized below [22–24].

Garg et al. (2020), using a longitudinal study from Southern India and future climatic projections for the years 2075–2099 obtained from the Community Climate System Model (CCSM v4, Gent et al., 2011), reported that the expected temperature increase would decrease reading and mathematics scores by 0.03 and 0.04 standard deviations (SD) each year, respectively [95]. Over the course of a student’s education, this corresponds to a schooling loss equivalent of nearly two years. Using the assumptions and methodology proposed by Evans and Yuan (2019) [96], and assuming that an increase in literacy skills by one standard deviation corresponds to a 51% increase in wages, it was estimated that a potential rise in hot days by 10 could result in a 3% decrease in wages [22].

Park et al. (2020) estimated the magnitude of heat-related learning disruptions caused by global warming for an average high school student by 2050, relative to a student attending school in 2010. Considering climatic model predictions that foresee an average increase in ambient temperature in the USA by 5°F (~2.8°C) and a 10-year cumulative impact of heat on students’ lives before the PSAT exams, it is estimated that future overheating would reduce the 2050 cognitive achievement of students by 0.1 standard deviations, assuming no additional penetration of A/C systems in schools and homes and neglecting potential non-linearities in the association between temperature and cognitive losses for temperatures outside the range of historical values. If A/C use in schools increases according to the existing trend, the loss in cognitive performance could be less than 0.05 standard deviations. If all schools are air-conditioned by 2050, the damage would be less than 0.025 standard deviations. The impact of overheating on cognitive performance is found to be higher in the Northeast and other cooler geographic zones of the country, where the cognitive impact per degree of temperature increase is greater [24].

Additionally, the damage will be considerably higher for poorer populations in the USA and globally due to reduced penetration of air conditioning, especially among low-income groups. As reported by Pavanello et al. (2021), air conditioning penetration in developing countries is unevenly distributed across various income groups, with very low penetration figures for the poorest people [97]. Despite a significant increase in air conditioning penetration by 2050 [98], it is estimated that between 64–100 million families with electricity access in countries like India, Mexico, Indonesia, and Brazil will not be able to adequately satisfy their cooling needs.

Roach and Whitney (2022) have also assessed the potential cognitive loss caused by global warming in the USA by 2050. Using the IPCC forecast for a temperature increase of 1.5°C, they estimated that the average performance of elementary school students may decrease by about 9.8%, assuming no adaptation measures are taken. Similar to Park et al. (2020), they found that in geographic zones with average temperatures below 65°F (18.3°C), cognitive loss will be significantly higher than in warmer zones. An increase in temperature by one degree in cooler parts (<18.3°C) may significantly reduce students’ cognitive performance, while the impact in warmer areas (>84°F or 28.9°C) is not expected to be statistically significant [23].

7. Discussion and conclusions

We reviewed seven existing studies that investigated the effects of prolonged heat exposure on students’ cumulative cognitive performance. Collectively, these studies analysed an extensive dataset comprising nearly 14.5 million students from 61 countries, linking individual learning outcomes to heat exposure. The findings suggest that long-term heat exposure negatively impacts students’ cumulative learning. Six of the seven studies identified a statistically significant negative relationship between extended heat exposure and cognitive performance, while one study found the impact to be minimal [21].

The studies examined the influence of heat exposure over periods ranging from one to five years prior to the tests. However, the estimated timeframes during which heat exposure affected cognitive performance varied across the studies. Two studies focusing on the PISA exam concluded that high temperatures influenced cognitive performance up to three and four years before the tests, respectively [19,24]. Meanwhile, two studies observed the impact as limited to the previous school year [20,22], and another two studies restricted the effects to the current school year [19,23].

Significant differences in the modelling approaches adopted by these studies may explain the observed discrepancies. The choice of temperature data used as a proxy appears to have a substantial impact on the results of the analyses. Two studies linked cognitive performance to the average daily temperature, while the remaining studies used the daily maximum temperature as a proxy [21,22]. The use of daily maximum temperature seems to be a more appropriate choice, as schooling typically takes place during the hours when maximum temperatures occur. In contrast, the average daily temperature includes nighttime data, which is unlikely to influence cognitive performance significantly.

The effect of the selected temperature proxy becomes particularly evident in analyses of the same dataset of Brazilian students. Melo and Suzuki (2021), who based their analysis on temperature during the exam, found a pronounced impact of heat on students’ performance [99]. Conversely, Li and Patel (2021), who used the average daily temperature, arrived at opposite conclusions [11]. A further analysis of the dataset by Melo and Suzuki (2021), employing both temperature proxies, demonstrated that using the average daily temperature significantly reduces the effect estimates [99].

There remains an open question as to whether cognitive loss occurs primarily during the school period or if exposure to high temperatures during non-school days in previous periods affects students’ cognitive performance. Four studies have excluded weekends and non-school days from their analysis of the relationship between temperature exposure and learning performance [23,24,66], while the others have included them. Park et al. (2020, 2021) investigated the impact of weekends and holidays on student performance using econometric models and found no evidence of diminished achievements among students [19,24]. None of the studies concluded that the impact of non-school days is significant. Although further research is required, it appears that time spent in school plays a decisive role in human capital loss and accumulation.

The characteristics of cognitive tasks performed and assessed determine the magnitude of the loss associated with heat exposure. Cognitive tasks of varying types and complexities activate different regions of the brain. Heat stress affects the temperature of different brain regions in distinct ways, and potential cognitive loss depends on the specific thermal load experienced by the brain areas involved [58,100]. According to Ayres and Paas (2012), the Cognitive Load Theory of instructional design posits that the cognitive system consists of Working Memory (WM) and Long-Term Memory (LTM) [101]. Working Memory has limited capacity and duration and is utilized to hold and process information needed for immediate tasks, such as problem-solving, decision-making, and learning [102]. In contrast, Long-Term Memory is theoretically limitless in capacity and serves as a repository for informative knowledge stored indefinitely. Under conditions of heat stress, the limited resources of Working Memory may struggle to handle demanding cognitive tasks, such as complex mathematical operations. In contrast, cognitive tasks like reading comprehension and proofreading, which rely on the participants’ skills and are primarily based in long-term memory, require less attention since the information is already assimilated [103]. As a result, these tasks may be less sensitive to temperature compared to more complex tasks [36].

The conclusions from long-term exposure studies appear to align with the previous findings. Four studies have separately analyzed the impact of cumulative heat stress on mathematics and reading. Three of these studies found that the effect of prolonged heat exposure was significantly greater for mathematical tasks compared to reading tasks [19,20,22]. In contrast, one study reported that the cognitive loss for both tasks was nearly identical [24]. Park et al. (2021) observed that the long-term exposure to heat had approximately three times the impact on mathematics as it did on reading and verbal tasks [19]. Meanwhile, Cho (2017) found that during days with maximum temperatures between 28°C and 30°C, mathematics and reading scores decreased by 0.0105 and 0.0073 standard deviations, respectively [20].

Besides temperature, a wide range of factors—environmental, task-related, and performer-related—may influence students’ cognitive performance [7]. Environmental confounding factors include climatic variables such as humidity, precipitation, wind speed, and solar radiation, which can affect the body’s thermoregulation system. Additionally, perceived indoor environmental elements—such as lighting quality, acoustics, indoor pollution, spatial layout, decoration, furniture, and cleanliness—impact students’ mental well-being and satisfaction [3].

Numerous studies have investigated the impact of humidity on thermal comfort [104]; however, little is known about its effect on human cognitive performance [105]. Laboratory research on short-term reductions in cognition under humid conditions revealed that humidity negatively impacts mean skin temperature, as well as the accuracy and response time of participants during cognitive tests [105]. Additionally, three studies on long-term heat exposure examined the influence of humidity, wind speed, and pressure on students’ cognitive performance [20,22,24]. All these studies concluded that humidity and other climatic parameters have minimal effects on point estimates.

The impact of non-temperature-related Perceived Indoor Environmental Characteristics (PIEC) on cognition has been extensively studied among office workers [9]. Research highlights that factors such as improved visual quality, spatial layout, furniture, and privacy positively influence occupants’ mental well-being and satisfaction. However, limited research exists on the effects of PIEC on students’ cognitive performance, despite evidence showing that children are more susceptible to environmental conditions than adults. Comparative studies suggest that indoor environmental conditions in classrooms have a greater impact on students’ performance than on office workers’ productivity [106,107]. This is because children sweat rate is lower than that of adults, while children absorb more heat because of their smaller body and the higher ratio of surface area to body mass [108].

Most short-term classroom studies examining the effects of PIEC on students’ cognitive function have focused on indoor temperature and thermal comfort [109]. Only a few, however, have explored the role of lighting [110,111]. Notably, classroom lighting conditions significantly affect cognitive performance, particularly attention span, working speed, and accuracy. Strategies such as utilizing LED lighting, balancing artificial and natural light, and implementing high Correlated Colour Temperature (Cool White light) systems appear to enhance students’ cognitive and psychological processes [111].

The confounding impact of perceived indoor environmental characteristics (PIEC) on students’ cumulative cognitive performance remains unaddressed in existing long-term heat exposure studies. These studies rely on macro-level statistical data provided by national authorities, which lack detailed, classroom-specific information. However, findings from short-term studies suggest that PIEC may significantly influence students’ cognitive performance over time. Therefore, it is crucial to design and implement long-term heat exposure studies that combine experimental data on perceived indoor environmental conditions and other mediating factors with statistical insights into students’ cognitive outcomes. Such studies would help uncover the relative impact of key confounding variables.

Performer related factors influencing the cognitive performance of young people primarily include thermal acclimatization, gender, hydration levels, emotional state, and skill level [7]. Individuals living in warmer climates are better acclimatized to heat compared to those in colder regions, making them more adept at managing heat exposure [112]. This adaptation arises from behavioural, cultural, and environmental responses to heat stimuli, such as enhanced sweating efficiency, improved blood circulation, and other cardiovascular adjustments [113,114]. The degree of heat acclimatization depends on the intensity of heat exposure and individual characteristics.

Limited research exists regarding the effects of heat acclimatisation on cognitive performance. A study examining the impact of acclimatisation on soldiers’ performance under heat-stress conditions found that non-acclimatised participants demonstrated reduced response accuracy on complex tasks. However, no significant effects were observed on attention-related tasks [115].

Three studies on the long-term effects of heat exposure on students’ cognitive performance found that students living in cooler regions experience greater cognitive disruption per unit of temperature increase compared to those in warmer areas [20,23,24]. Park et al. (2020) reported that an additional day with temperatures exceeding 32.2°C impairs cognitive performance in students from cooler regions three times more than in those from warmer regions in the U.S. Furthermore, the cumulative impact of a 1°F, (0.55C), rise in temperature throughout the school year is nearly twice as significant in cooler areas. Similarly, the cumulative effect of each extra day above 32.2°C per year is five times greater in cooler regions [24]. Roach & Whitney, (2022), found that increase of the ambient temperature by 1F, decreases the performance of students in the cooler and warmer areas of the country by 4.71% and 2.6% respectively [23]. Additionally, Cho (2017) found that an extra school day with a maximum daily temperature of 34°C or higher impairs reading scores by 0.0073 standard deviations in cooler regions and 0.000 standard deviations in warmer regions. For maths, the corresponding decreases were 0.0124 and 0.0011 standard deviations, respectively [20]. The pronounced differences in cognitive loss between students living in cooler and warmer geographic areas, attributed to cumulative heat exposure, may result from a combination of long-term heat acclimatisation among students and the more extensive use of air conditioning in households located in warmer regions.

Long-term exposure to heat appears to have a greater impact on the cognitive performance of younger students compared to older ones. Park et al. (2021) found that each additional hot day at school reduces the performance of third to fifth graders by 0.08-0.13% of a standard deviation, while the effect on students in grades six to eight was negligible [19]. This aligns with earlier findings indicating that children have a reduced capacity to adapt to heat due to their less developed and less efficient biological systems for regulating body temperature, as well as their limited ability to sweat effectively [116].

Limited knowledge exists regarding the impact of heat exposure on the performance distribution of students. Graff Zivin et al. (2020) found that short-term heat exposure during exams disproportionately affects the success rates of high-performing students, while low-performing students remain largely unaffected by environmental conditions. Given the already low expected success rates of low-performing students, the relative decrease due to heat exposure may be statistically negligible. In contrast, for high-performing students, the absolute reduction in success rates can be significantly higher in absolute terms [67]. Adverse conclusions are drawn from short term studies assessing the impact of heat exposure during normal courses period. Porras Salazar et. al. (2018), found that higher exposure to heat disproportionally affected the less able 11-year-old pupils while decrease of the classroom temperature had more beneficial impact for them compared to the high-performance pupils [63].

Considering the reduced adaptability of children to heat, as well as findings from several short-term school experiments on students’ temperature preferences, it has been suggested that indoor classroom temperatures should be 2–3°C lower than those recommended for adults [17]. However, while implementing such lower indoor temperature conditions poses significant energy challenges, further research is required to thoroughly assess the physiological and cognitive benefits of these measures across varying climatic conditions.

Research on the physiological responses and heat adaptability of individuals working under natural ventilation (NV) and air conditioning (AC) conditions has demonstrated that those in NV environments exhibit superior physiological acclimatisation and a greater ability to cope with heat compared to their AC counterparts [117]. This raises questions about whether reliance on AC is the most effective adaptation strategy for climate change. Consequently, the potential risks and negative impacts of prolonged AC usage in classrooms—particularly when not accompanied by substantial improvements in students’ cognitive performance—should be thoroughly evaluated and documented.

The penetration of air conditioning in poorer developing countries is low and unevenly distributed among various income groups [97]. In low-income groups, the availability of air conditioning is severely limited due to reduced economic affordability [118]. Systemic cooling poverty, driven by economic and social deficiencies alongside a lack of supporting infrastructure, restricts the ability of lower-income households and neighbourhoods to maintain comfortable living temperatures.

In developed countries, the adoption of air conditioning among low-income and ethnic minority households is significantly lower compared to middle- and high-income households. In regions of the USA with above-average temperatures, the percentage of households without air conditioning is 12% for the low-income group (less than $25,000 per year), 7% for the middle-income group (less than $80,000 per year), and 3% for the high-income group [119].

Additionally, ethnic minority households —namely Black, Hispanic, and Asian-led households — are less likely to have air conditioning compared to white households. In these warm regions, 14% of Asian-led, 13% of Black-led, 9% of Hispanic-led, and 4% of white-led households do not have air conditioning [119]. Furthermore, financial challenges prevent 12% of Black-led and 10% of Hispanic-led households from using air conditioning, compared to 5% of white-led households. In these areas, approximately 22% of low-income households experience unhealthy indoor temperatures, and 42% report reducing or foregoing necessities due to high energy bills. By comparison, these issues affect only 3% and 7% of upper-income households, respectively [119].

The additional energy consumption and costs associated with air conditioning usage reveal significant disparities between countries and income groups. The electricity consumption penalty for air conditioning is notably higher in developing nations compared to developed ones [120]. For example, De Cian et al. (2025) reported that, on average, households in Indonesia and the U.S. allocate approximately 1.6% and 3.5% of their expenditures to electricity, respectively. However, air conditioning usage increases electricity consumption by 66% in Indonesian households and by 29% in U.S. households, placing a significantly greater economic burden on Indonesian households [120].

Predictions regarding the penetration of air conditioning in developing countries indicate that cooling devices will remain largely inaccessible to low-income groups [97]. Given the anticipated significant rise in temperatures in almost all parts of the world, along with the increasing frequency and duration of extreme heat events, serious concerns emerge about the potential cognitive losses among younger generations due to overheating. The development and implementation of zero- or low-energy heat mitigation and adaptation technologies for educational premises appear to be essential strategies to prevent a decline in learning capacity and to avert substantial societal and developmental consequences for low-income population in developing and developed countries.

8. Limitations

There are several limitations of this study that need to be mentioned and considered. Firstly, direct comparison of the results of the seven reported long-term heat exposure studies is not possible. This is due to the use of populations with varying characteristics, such as age, heat acclimatization, knowledge, and cultural backgrounds. Additionally, the methodologies employed in these studies differ significantly, including variations in the proxy temperatures considered and the statistical approaches used.

Moreover, the absence of data on indoor classroom climatic conditions limits the analysis of how indoor environmental quality may affect cognitive performance.

Finally, none of the studies address the magnitude or characteristics of other environmental stressors beyond temperature, such as indoor pollution, lighting quality, and their impact on cognitive decline in students. As a result, these factors cannot be adequately assessed.

Further research is essential to fully understand the magnitude and impact of key environmental stressors on the long-term cognitive performance of students.

9. Conclusions

Impairments related to cognitive and human capital loss of the young generation may affect the future progress of nations because of the associated dramatic economic, social and cultural implications caused by persistent disruptions to the learning process. The social cost of global overheating on human capital associated to the potential reduced capacity of young people to undertake intensive cognitive activities, will unfortunately affect equity and quality of life of vulnerable and low-income population unable to be protected from the climatic phenomena. It will accelerate societal discrepancies and will impede economic progress in less developed countries suffering from excessive heat exposure. There is an urgent need to adopt a new perspective on the cognitive implications of climate change by advancing technologies and implementing robust, targeted policies to safeguard both current and future human capital.

Supporting information