The Temperature Toll

Image courtesy of Noora Said.

Today, climate change is not only at our doorstep—it’s in our living rooms, on our kitchen tables, and even in our pockets, through near-constant coverage on television news, newspapers, and social media. Climate stories are often accompanied by aggressive images: wind- and rain-battered palms, neighborhoods swallowed up by churning floodwaters, forests consumed by flames, disturbingly vibrant thermal maps. 

While these photographs impactfully illustrate the physical devastation wrought by extreme weather, recent research suggests they may fail to capture a less visible but key consequence of climate change: its impact on mental health. Studies conducted by Eun-hye Yoo, associate professor of geography at SUNY Buffalo, and Kai Chen, assistant professor of epidemiology at the Yale School of Public Health, identified a possible link between extreme temperatures and increased mental health-related emergency room (ER) visits. Such an association, though still subject to further research, may have meaningful implications for how we think about climate change. 

A Gap in the Literature

While climate research has increased significantly over the past two decades, not all ramifications of the impending crisis have been investigated equally. Yoo and Chen are seeking to address a consequential gap in the literature: the effect of extreme temperature, both hot and cold, on mental disorders. To that end, they co-authored two studies with other collaborators on potential associations between extreme temperature events and ER visits for mental health reasons in New York State. While the first study examined a wider array of mental disorders, the second study investigated specific conditions, such as anxiety disorders, mood disorders, substance abuse, and dementia, as reasons for ER visits. 

Though prior studies suggesting probable links between heat and negative mental health outcomes have been conducted, the field remains relatively sparse in comparison to the larger body of climate research. To account for this, Yoo points to the fact that psychologists are primarily interested in analyzing individual behaviors, while epidemiologists engage almost exclusively with population-level data. As a result, overlap between research in environmental epidemiology and mental disorders is relatively rare. 

For their part, these two researchers come to the field from different backgrounds—Chen, an environmental health epidemiologist, has long harbored an interest in the health implications of climate change, while Yoo’s area of expertise is geographic information science and spatial statistics. Nevertheless, they share a deep concern for this under-investigated correlation, and the two enjoy an amiable relationship, each quick to credit the other for their unique contributions to the study. 

Exploring the Effects of Extreme Temperature

To investigate the relationship between exposure to extreme temperature and risk of increased ER visits, the researchers employed a time-series analysis. Time-series models, a common type of statistical analysis, use a series of data points collected at fixed time intervals to make a prediction or estimate an association. In Yoo and Chen’s studies, the model consisted of two time series—temperature and ER visits—which both varied daily. “What we do in this model is try to find an association between these two time-series,” Chen said. “But in the meantime, there are a lot of other things going on that may influence this relationship, so we need to use our model to control them.”

Data on daily ER visits for mental health disorders were collected from the New York State Department of Health and compared to climate and air pollution data obtained from the National Center for Environmental Information Climate Data Online System. The ER records, dating from January 2009 to December 2016, included demographic information like race, age, and sex, as well as the primary diagnosis code, which the researchers used to identify mental disorders in ER patients. Daily precipitation and minimum, average, and maximum temperatures were examined as part of the temperature time-series. Separate time-series analyses were conducted in ten labor market regions in New York State, and a meta-analysis was performed to pool the result for the whole state. 

Notably, the model was designed to consider any delayed effects on mental health caused by temperature exposure. While a lag period of seven days was used to identify short-term exposure effects on increased ER visits, their analysis also evaluated this exposure-response relationship for a longer period of twenty-one days. 

Climate Consequences for Mental Health

The first study, which focused solely on Erie and Niagara counties, indicated a strong positive association between maximum temperature and increased ER visits for mental illness. Significant risk was observed at temperatures above twenty-nine degrees Celsius and below eight degrees Celsius. Across all lag periods, heat effect was found to elevate one’s risk of visiting an ER for mental illness. For maximum daily temperatures under eight degrees Celsius, the researchers observed a delay of zero to fourteen days between exposure to extreme cold temperatures and increased ER visit risk. In other words, the cold effect on ER visits was not always evident until up to fourteen days after exposure to temperatures below eight degrees Celsius. However, neither precipitation nor air pollution were found by this study to alter the observed temperature-mental illness relationship.

Though the first study suggested that extreme temperatures may induce adverse mental health effects for people of all ages and races, it also indicated a disproportionate effect for certain subpopulations. Youth and elderly populations, defined as ages zero to nineteen and over sixty-four, respectively, seemed more susceptible to heat effects. Additionally, the model suggested greater risk of ER visits for African Americans ages fifty to sixty-four exposed to intense heat as compared to other racial groups in the same age category. Some posit that the observed vulnerability of African Americans, the elderly, and young people to extreme temperatures may reflect disparities in access to healthcare, housing, and technology on a larger, societal scale. 

To examine how differences in geography, climate, and population impacted exposure-response relationships, the researchers expanded the study to include ten different labor regions in New York State. Unlike in the first study, they did not find short-term exposure to extreme cold to be associated with increased ER visits for any mental disorder. However, the findings did suggest a positive association between maximum daily temperatures above 27.07 degrees Celsius and elevated risk for ER visits. Diverging from the findings of the first study, no racial group or age cohort was observed to be more vulnerable to the effects of heat than any other group. 

The varying results between northwestern New York counties and New York State as a whole suggest that the results of any particular analysis are subject to geographic and climatic limitations and that further expansion of the study is required to make more generalizable conclusions. Foremost, both studies support the researchers’ hypothesis that extreme temperatures increase one’s risk for visiting the ER for mental health reasons. 

New Possibilities for Public Health

Measures currently in place to protect the public from the effects of severe weather include radio warnings of impending extreme temperatures, required heating systems in New York housing, and publicly available cooling and heating centers in urban areas. Unfortunately, such efforts often fail to meet the needs of the most vulnerable populations. Cooling and heating centers are rarely adequate in number or capacity in low-income, under-resourced neighborhoods, the very areas where they are needed most. Additionally, unlike heating systems, air conditioning in housing is not necessitated under New York law. This places an additional financial burden on tenants and, in many cases, effectively removes their access to such systems altogether.

Chen cautioned that while improving existing measures is necessary, as they provide immediate support to vulnerable groups, adaptive actions like air conditioning are ultimately “double-edged swords.” Air conditioning increases energy demand and emissions, thus exacerbating climate change. Chen and Yoo pointed instead to research suggesting that the cultivation of green spaces in so-called “heat islands,” urban areas that retain high levels of heat, can reduce temperatures naturally. By adding green spaces, communities can promote better mental and physical health without compromising the environment. 

Ultimately, however, most climate research indicates that effective prevention of climate change will require efforts on a much larger, societal scale, including the commitment of governments and corporations to achieve net zero emissions. 

An Expansive Research Landscape

Yoo and Chen know that their work is far from done. For all the questions this study answers, it raises just as many new ones. Both highlighted the need for future research to intimately involve psychologists. “While we were working on this study, I had a lot of conversations with psychologists,” Yoo said. “We have a lot of interesting hypotheses that need to be verified, but in some cases, this is hard to do with population data… We need to combine population-level studies with cohort studies.” 

Yoo emphasized that future studies should investigate new or more diverse populations in different climatic regions to better understand the variation observed between the county- and state-level studies as well as discrepancies in outcomes between subgroups.

Chen expressed particular interest in further exploring how and why short-term exposure to extreme temperatures can exacerbate more long-lasting, chronic conditions. “That’s something we don’t know much about,” Chen said. “There must be something, through biological or societal mechanisms, that can explain how temperature [has this effect]. This is paving the way for more research on this topic.”

As climate change accelerates, it seems that the urgency of Yoo and Chen’s research will only become more apparent. Without a proper understanding of how extreme temperature events might increase potential for severe mental health episodes, we cannot be adequately prepared for the full range of climate consequences. After all, as the oft-repeated climate activism saying goes, the climate is changing—why aren’t we?

Further Reading

Yoo, E. H., Eum, Y., Gao, Q., &; Chen, K. (2021). Effect of extreme temperatures on daily emergency room visits for mental disorders. Environmental Science and Pollution Research, 1-14. 

Yoo, E. H., Eum, Y., Roberts, J. E., Gao, Q., &; Chen, K. (2021). Association between extreme temperatures and emergency room visits related to mental disorders: A multi-region time-series study in New York, USA. Science of The Total Environment, 148246.