Heat and Learning

6 min readMay 28, 2021

The impacts of climate change are all around us. Wildfire seasons are increasingly severe, hurricane seasons are longer, and coastal flooding is more frequent. A more subtle, but perhaps more pernicious, impact has been the steady and inexorable march upwards in global average temperatures. True, we pay attention to a particularly long or intense heat wave, but the slow shift in the day-to-day averages often goes unremarked upon.

That lack of attention belies the serious potential consequences of increasingly frequent high temperatures. Higher temperatures will impact many more individuals than any increase in wildfires or storms whose impacts, though intense, fall upon people within specific geographic regions. Conversely, nearly everyone in the world will be exposed to higher temperatures and these higher temperatures have a range of consequences.

In a recent study, we focus on one consequence of increased temperatures that is relevant for anyone with children or who cares about how we educate future generations. We examine how exposure to higher temperatures during the school year impacts how much students learn when they are in school.

In what is unlikely to come as a surprise to anyone who has tried to do a mentally demanding task while sitting in a sweltering room, it has been known for some time that acutely high temperatures reduce students’ performance on exams. When asked to take a high stakes exam on particularly hot days, students in New York City do worse in ways that have implications for whether they ultimately graduate from high school. The acute impact of heat on exam performance makes sense. It is hard to concentrate when heat makes you physically uncomfortable; that difficulty in concentrating might reasonably translate into reductions in performance.

But it remains unclear whether the same mechanisms that are at play in an acute exam setting are also at play during the rest of the school year. Specifically, if students have trouble concentrating on hot days, do they learn less material if there are more hot days during that school year? The implications of such a finding are farther reaching than the finding that students do worse on exams when they take them on a hot day. If students learn the same amount during a hot year and just perform poorly when exams are scheduled on hot days, we can adapt by changing the scheduling of the exams. That avoids the negative consequences of a poor exam performance and the students are otherwise just as well off because they have learned the same amount. But if they actually learn less during a hot year, the adaptations to ensure adequate learning happens are more difficult than simply rescheduling an exam.

There are several reasons to expect that students might learn less in hotter years. Students may find it harder to concentrate. They may also attend school less frequently. This is particularly true in less developed countries where they may be needed to provide agricultural labor for their families to offset reductions in agricultural performance driven by the heat. Reductions in agricultural performance driven by heat might also reduce the nutritional content of their diets in ways that impact either attendance or concentration or both. Finally, teacher absenteeism might be aggravated by hotter temperatures.

We use two large datasets on student performance over time to determine how exposure to hotter temperatures during the school year impacts how much students learn. The first is the Stanford Educational Database (SEDA) that contains information on the performance of millions of students in the United States from 2009–2015 on state mandated exams. We combine that with data from the PISA international assessment, given to representative samples of 15-year-olds from 58 countries around the world every three years to see how our estimates vary in settings outside of the United States. We measure the total number of hot school days (days >80°F) that the students were exposed to in the years prior to the exam and take advantage of natural randomness in the distribution of hot days to estimate the impact of these days on student learning leading up to the exams.

Our results indicate that students learn substantially less on hotter school days. Across all the countries in our sample, we find that each additional day >80°F reduces student performance on the exam by 0.18% of a standard deviation. To put that number in more intuitive terms, the difference in average temperatures between Brazil and South Korea suggests that Brazilian students learn as much as 6% less in a typical school year than their South Korean counterparts. Our estimates control for the temperature on the day of the exam so they are not driven by the acute impacts of heat but rather reflect differences in what the students knew going into the exam.

These effects are larger for those who are more disadvantaged. We find substantially larger effects in less wealthy countries around the world. We also find that within the U.S. the effects are much larger in lower income school districts. They are as much as 3x larger in school districts with larger minority populations. In fact, we find that heat has very little effect on White students and has the largest effects for Black students. This likely reflects differences in the average level of air conditioning between school districts.

Our results suggest that heat plays an important role in the learning process. Students who are more frequently exposed to heat learn less over the course of their education. Because heat exposure is strongly correlated with income and minority status these impacts can help to explain some of the gaps that education researchers have long-documented between socio-economically advantaged students and those who are more disadvantaged.

They also underline the importance of considering the impacts of heat on human performance when calculating the costs of climate change. Reductions in the amount that students learn can have persistent effects that ripple across society. Reducing the average level of education in a society reduces its level of innovation and productivity and can lead to meaningful reductions in long-term economic growth. Solving climate change won’t just reduce our exposure to deadly and costly disasters, it will also help our children learn more and grow up to be more productive and better educated.

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