Impacts of Warming Temperatures on Education and Learning

The Issue:

The summer of 2019 was tied with 2016 for the hottest on record for the Northern Hemisphere, and the winter was the warmest one yet for the contiguous United States. Eight of the ten hottest years on record have occurred in the past decade, and given current emissions trajectories, some parts of the world are expected to experience over 100 additional days above 90F per year by 2040. New research suggests that extreme heat contributes to gaps in educational achievement: both across as well as within countries. Temperature is a surprisingly disruptive factor for students — both for high stakes test-taking and for learning over the longer term, across a wide range of educational settings. Due in part to differences in access to air conditioning and where people live, these disruptions appear to be highly unequal across socioeconomic status and race.

Due in part to differences in access to air conditioning and where people live, heat disruptions on education appear to be highly unequal across socioeconomic status and race.

The Facts:

• Hot temperatures have been shown to affect human performance in a variety of tasks. There is a long-standing ergonomics and medical literature that documents clear relationships between hotter temperature and task performance, such as soldiers doing arm curls and completing cognitive tasks, as well as a literature that shows heat to increase mortality risk and hospitalizations. However one of the big unknowns has been whether lab-based findings that find decreased human performance in hot temperatures would hold up in the "real world", where people could be expected to try to engage in various adaptations or "defensive investments" to mitigate heat, especially if the stakes are high. 
• Heat during standardized exams reduces student performance and can have real-world consequences. In a study of over 1 million New York City public school students, I find that students taking an exam on a day when the outdoor temperature is 90F perform 13% of a standard deviation worse than they would have on a 65F day. While air conditioning provides an adaptation to deal with hot temperatures, only 62% of NYC schools reported having some form of air conditioning as of 2012, and over 40% of those that did reported some form of deficiency in their equipment. I am able to compare test scores for the same student for tests taken over days with differing outdoor temperatures, providing a more credible estimate of the potential causal impact of hotter temperature on test performance. The consequences of reduced performance can be lasting. For some students in this study, hot temperature during high stakes tests leads to lower likelihood of graduating. A one standard deviation increase in test-time temperature reduces the likelihood that a student graduates on time by over 4%. In fact, the data suggests that, over the period 1998 to 2011, upwards of 90,000 students that otherwise would have passed likely received failing grades due to hotter exam conditions. Recent evidence from China suggests that such test-day effects are likely not limited to the United States, finding that increased temperatures during the National College Entrance Examination decreases test scores and the probability that a student is admitted to a first-tier university.
• Beyond impacting performance on test days, there is some evidence that hotter temperatures can reduce the rate of actual learning taking place over the school year. In a separate study, my co-authors and I find that hotter temperature during the school year reduces the rate of learning, at least as evidenced by improvements on the PSAT, a major standardized exam that tests knowledge and skills learned in secondary school. In the study we look at standardized performance for roughly 10 million students from over 12 thousand U.S. high schools who have taken the PSAT more than once. We ask whether students score lower immediately following a hotter year relative to their own score immediately following a cooler school year. We find that a 1F hotter school year lowers subsequent scores by 0.2 percent of a standard deviation, or roughly one percent of an average student’s learning-gain over a school year. Extreme heat is particularly damaging. A day with temperature in the 90s (F) reduces achievement by one-sixth of a percent of a year’s worth of learning: a day above 100F has an effect that is up to 50 percent larger. Importantly, the effect appears to be driven mostly by hot temperature that occurs during school days – as opposed to summer vacation, weekends, or other holidays – suggesting that heat’s disruption of instructional time is responsible for the observed drop in test scores. These disruptions to learning appear to have enduring effects. The effect of hotter school days two, three, and even four years prior to the test also appear to lower scores, so that the cumulative effect of elevated temperature over multiple school years is substantially larger than that of a single school year. In other words, these small cuts appear to add up over time, and once disruption to pedagogy occurs, many students find it difficult to make up for lost time.
• Air conditioning appears to offset most of the disruptive impacts of heat on learning. Based on the first nationwide survey of school air conditioning penetration, we find that up to 40% of U.S. schools may not be fully air-conditioned. Those that do have air conditioning appear to experience far less learning disruption due to heat. Our estimates suggest that the effects of hotter temperature in a school that is fully air-conditioned are approximately 78% smaller than a school without any air conditioning. It is possible that schools that have the means to invest in air conditioning have also made other investments in resources that could explain why their students experience less learning disruption. However, the mitigating effect of air conditioning remains even after we take into account zip-code level income and the racial composition of the school's test takers, as well as a triple-difference strategy that leverages changes in AC penetration within a given school over time. Using estimates from other studies that look at the effect of learning on later life outcomes, such as earnings, we estimate that the present value of classroom air conditioning in a place like Houston may be more than $2million per year for a 1,000 student school. 
• Access to air conditioning is unequally distributed, however. Black and Hispanic students are 9% less likely than white students to report having school air conditioning. Lower income (below median neighborhood income) students are 6% more likely to report having inadequate school air conditioning. Black and Hispanic households are 6% and 7% less likely, respectively, to report having air conditioning at home for any given climate and income group. Importantly, these gaps in air conditioning access appear to persist within geographies. It would be less surprising that students in Maine or Minnesota reported less air conditioning than students in Georgia or Florida. But we find evidence that, in addition to such geographic differences, racial minorities and lower income students appear to be significantly less likely to have access to air conditioning even within localities. 
• The effect of heat on learning is larger for Black and Hispanic students and for lower income students, meaning that climatic factors already appear to contribute to racial and geographic achievement gaps, and that without remedial investments, these gaps may grow over time. We find that hotter temperature’s disruptive effects on learning appear to be roughly three times larger for Black and Hispanic students compared to Whites. This means that, according to our estimates, approximately 5% of the gap in standardized achievement (on the PSAT) between White students and Black and Hispanic students can be explained by differences in the temperature environment experienced by students in each group: that is, the combination of a hotter local climate and less access to air conditioning at school or at home. 
• If heat can disrupt learning in the United States, one of the wealthiest, most highly air conditioned countries in the world, what are the potential implications for students in other countries? Whereas the average American student experiences approximately 40 days above 80F per school year, students in Indonesia, Brazil, and Mexico experience 240, 120, and 140 such days respectively. In a new study, my co-authors and I find that heat seems to have similarly disruptive impacts on exam performance and learning across countries with a wide range of climates and levels of development. The effects appear to be larger for poorer countries than richer ones, perhaps due in part to differences in the level of air conditioning and other investments that might help students and teachers adapt to the disruptive impacts of heat.