The human body is a finely tuned instrument, intricately attuned to the environment in which it exists. Consider, for a moment, the delicate balance of our body’s internal temperature regulation. A mere one-degree Celsius increase in our body temperature can signal the onset of fever, triggering a cascade of physiological responses as our immune system rallies to restore equilibrium. This sensitivity to temperature fluctuations underscores the profound interconnection between our physical and mental health.

From the subtle shifts in ambient temperature to the onslaught of extreme weather events, our bodies and minds are inextricably linked to the ever-changing climate that surrounds us. Yet, while the visible impacts of climate change may dominate headlines and capture our attention, it is the subtle, long-term variations in temperature that often wield the most profound influence on our mental well-being (Palinkas & Wong, 2020).

The unexpected increase in temperature could impact mental health through various mechanisms. Physiological changes, like shifts in blood flow or serotonin levels, and cognitive alterations due to disrupted sleep and effects on brain connectivity are possible. Societal shifts induced by temperature changes, such as heightened aggression and stress from economic downturns or increased alcohol consumption, also contribute (Hou et al., 2023). Additionally, individuals with pre-existing mental illnesses, possibly due to impaired thermoregulation from psychiatric medications, may be especially vulnerable (Mullins & White, 2019).

Research has shown that long-term shifts in temperature patterns can have a significant impact on our psychological well-being, with implications that ripple through our daily lives in ways both seen and unseen. For instance, rising ambient temperatures have been linked to increased suicide rates in many countries, further underscoring the urgent need to address the mental health implications of climate change. The World Health Organization (WHO), in a recent policy brief (2022), emphasises the exacerbation of social, environmental, and economic risk factors for mental health problems by climate change, along with the existing gaps in mental health systems and services to address these needs.

Of particular concern are the vulnerable populations among us — women, children, and the elderly — who are less capable of dealing with ambient temperature changes in the context of climate change. Just as a fever may have more negative effects, and more easily, on such populations, so too do the subtle temperature variations brought about by climate change exert a disproportionate toll on their mental health.

In short, the slow, steady creep of rising temperatures, and the gradual erosion of familiar climate patterns — these too exert a silent but profound influence on our psychological well-being, with vulnerable populations bearing a disproportionate burden.

There is ample evidence for this. A current systematic review (Thompson et al., 2023) shed light on the intricate relationship between ambient temperature and various aspects of mental health, examining how fluctuations in temperature are linked to suicidal behaviour, hospital attendance or admission for mental illness, and the overall health and well-being of communities.

Methods

This systematic review aims to answer the research question: what is the link between increased temperature and mental health? To look at this review question more conclusively, both qualitative narrative and meta-analysis were used to find the relationship between temperature rise and mental health. Researchers searched the eligible articles from various databases, including Web of Science, Embase, Psych INFO, and PubMed, screening articles published up to April 7, 2022. The review finally included 114 research articles, and 19 studies are eligible to run a meta-analysis to look at the overall effective size of the association between temperature and mental health.

To be eligible for inclusion, included studies could address such relationships in both clinical and non-clinical populations. Moreover, the articles’ method includes epidemiological and observational studies in humans of all ages, evaluating real-world responses to ambient outdoor temperature, with documented mental health outcomes. Researchers intentionally excluded studies focusing solely on physical health outcomes or those involving manipulated or controlled temperature conditions.

Two reviewers evaluated the quality of the included studies, and the Newcastle-Ottawa Scale and the Office of Health Assessment and Translation (OHAT) approach were adopted to assess the risk of bias in individual studies. Furthermore, qualitative synthesis was employed to extract meaningful insights from eligible studies. For the meta-analysis, a random-effects model was applied, combining studies that reported similar or equivalent effect statistics and shared comparable exposure, outcome, and metric parameters.

Results

Overall, the findings support the link between outdoor temperature and mental health outcomes over the world. The study divided temperature measurements into three categories: absolute temperatures, temperature variability, and heatwaves, noting that each category had different metrics and definitions. While greater temperatures compared to the local norm were typically linked with poorer mental health outcomes, the complex nature of contextual variables and inconsistent adjustments in the literature indicate a nuanced, non-linear, and culturally dependent connection. An overview of the findings is presented below:

Suicide outcomes

• 86 studies are relevant to climate change and suicide and were narratively synthesised
• A 1°C increase in mean monthly temperature correlated with a 1.5% rise in suicide incidence
• A 1°C increase in mean daily temperature was associated with a 1.7% increase in suicide incidence
• A 1°C increase in mean monthly temperature resulted in a risk ratio of 1.01 for suicides.

Hospital attendance or admission

• 43 studies reported hospitalisation or admissions for mental illness
• Heatwaves led to a 9.7% higher incidence of hospital attendance or admission for mental illness
• Higher daily mean temperatures (99th percentile vs. 50th percentile) showed a risk ratio of 1.02
• No significant association was found between a 10°C increase in daily mean temperature and hospital attendance.

Community mental health and wellbeing

19 studies reported an association between ambient outdoor temperature and community mental health and well-being outcomes. Heatwaves were not investigated in this category, and questionnaires used to assess mental health and well-being had inconsistent findings (68% of studies). The relationships between ambient outdoor temperature (including absolute temperatures, temperature variations, and heatwaves) and mental health are shown below:

• 84% of studies reported a significant association between temperature metrics and mental health
• 74% of studies showed higher temperatures were generally associated with worse mental health and well-being outcomes
• Some exceptions were noted, such as improved wellness in “comfortable weather hours” and improved mood outside in spring
• 17% of studies did not find a significant association between temperature and mental health or wellbeing.

Conclusions

This systematic review and meta-analysis show compelling evidence that rising temperatures are associated with worse mental health outcomes. The study found a link between high absolute temperatures, changing temperatures, and heat waves and an increased risk of suicide, suicidal behaviour, and hospital admissions for mental illness. It also demonstrates links between community mental health and wellness, as well as absolute and variable temperatures.

However, methodological heterogeneities and varying impact sizes require a careful interpretation, making the overall confidence of these findings low.

Despite a considerable body of supportive data, the authors emphasise the need for more high-quality research to increase confidence in determining the impact of ambient outdoor temperature on suicide risk. This detailed knowledge is critical for informing targeted interventions and strategies in mental health policy and practice.

Strengths and limitations

This systematic review incorporated a substantial sample size, with three meta-analyses encompassing 156,109 participants. To comprehensively explore the link between outdoor temperature changes and mental health outcomes, researchers employed both qualitative synthesis for heterogeneous studies and quantitative synthesis through meta-analysis. Clearly indicating the sample size for each synthesis method aids readers in a concise interpretation of research findings. Additionally, the study defined ambient temperature changes in three categories: absolute temperatures, temperature variability, and heat waves. While this added complexity to data analysis, it distinctly highlighted differences between each category due to varying metrics and definitions. The review also tackled an increasingly important topic—how climate change impacts human mental health. Recent studies on climate change anxiety indicate that global climate change significantly amplifies worries and concerns about our existence and that of future generations. It alters our cognitive perception of the environment, exerting a psychological impact on us. As a result, the current systematic review provides convincing synthesised data to support the hypothesis that rising outdoor temperature is negatively associated with our mental health in terms of suicide rate, mental illness admission rate, and community mental well-being.

This study has a few limitations worth noting. First, the included studies were diverse, making data analysis a bit complicated and the outcomes measured were inconsistent. Another thing is, while researchers defined ambient temperature change and mental health outcomes, there is not a set method or universal measurement for these. Mental health itself is a broad topic, and even though the authors categorised it into three, measurements for these outcomes differ. Interestingly, studies on anxiety-related outcomes were not included, and we know anxiety related to climate change is getting more attention. Therefore, there is room for improvement in how we approach and measure these connections.

Implications for practice

This study highlights the relationship between ambient temperature and mental health globally. Notably, research on absolute temperature frequently accounted for seasonal and temporal patterns, demonstrating the impact of exceptional temperatures during that season. The findings emphasise the need for evidence-based policies in addressing and mitigating the mental health effects of climate-related temperature increases, particularly for disadvantaged groups and individuals who face biological, sociocultural, and economic stresses from high temperatures.

The evidence can inform practical considerations for public health, policymaking, and nature-based interventions. In terms of public health, the findings emphasise the significance of focused awareness initiatives aiming at teaching communities about the complex links between ambient temperature variations and psychological health. Recognising that severe temperatures worsen mental health inequities, there is an urgent need for the provision of accessible mental health resources, particularly in populations that have been disproportionately affected (Frumkin et al., 2008; Hondula et al., 2015). From a policy viewpoint, including mental health issues in wider climate change measures is critical. Policies should not just identify but actively address the mental health vulnerabilities worsened by changes in temperature, with a particular emphasis on protecting marginalised people (Camargo et al., 2020).

Nature-based interventions have emerged as an important component in addressing these difficulties. Investments in green areas and intentional urban design that prioritises mental well-being can operate as effective barriers to the negative effects of severe heat (Parker et al., 2020). Simultaneously, the promotion of nature-based treatments acknowledges the therapeutic potential of natural areas in addressing mental health issues (Eaton et al., 2022).

When managing the intricate connection between climate and mental health, the synthesis of various solutions is critical. These holistic methods pave the way for a more sustainable and psychologically healthy future by developing resilience and well-being, particularly among those most vulnerable to the numerous stresses caused by increasing temperatures.

Statement of interests

None.

Links

Primary paper

Thompson, R., Lawrance, E. L., Roberts, L. F., Grailey, K., Ashrafian, H., Maheswaran, H., … & Darzi, A. (2023). Ambient temperature and mental health: A systematic review and meta-analysis. The Lancet Planetary Health, 7(7), e580-e589.

Other references

Camargo, J., Barcena, I., Soares, P. M., Schmidt, L., & Andaluz, J. (2020). Mind the climate policy gaps: climate change public policy and reality in Portugal, Spain and Morocco. Climatic Change, 161(1), 151-169.

Eaton, J., Nwefoh, E., Duncan, J., Sangare, O., Weekes, Y., & Adams, B. (2022). Addressing mental health and wellbeing in the context of climate change: Examples of interventions to inform future practice. Intervention, 20(1), 107-107.

Frumkin, H., Hess, J., Luber, G., Malilay, J., & McGeehin, M. (2008). Climate change: the public health response. American journal of public health, 98(3), 435-445.

Hondula, D. M., Balling, R. C., Vanos, J. K., & Georgescu, M. (2015). Rising temperatures, human health, and the role of adaptation. Current Climate Change Reports, 1, 144-154.

Hou, J., Wang, C., Wang, H., & Zhang, P. (2023). Effects of temperature on mental health: Evidence and mechanisms from China. China Economic Review, 79, 101953.

Mullins, J. T., & White, C. (2019). Temperature and mental health: Evidence from the spectrum of mental health outcomes. Journal of Health Economics, 68, 102240.

Palinkas, L. A., & Wong, M. (2020). Global climate change and mental health. Current opinion in psychology, 32, 12-16.

Parker, J., Simpson, G. D., & Miller, J. E. (2020). Nature-based solutions forming urban intervention approaches to anthropogenic climate change: a quantitative literature review. Sustainability, 12(18), 7439.

World Health Organization (2022). Mental health and Climate Change: Policy Brief.

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