The impact of climate change on youth depression and mental health

Youth depression is a major risk factor for suicide, and a leading cause of disability worldwide,1Murray CJ Lopez AD Evidence-based health policy-lessons from the global burden of disease study.Science. 1996; 274: 740-743Crossref PubMed Scopus (1695) Google Scholar, 2Thapar A Collishaw S Pine DS Thapar AK Depression in adolescence.Lancet. 2012; 379: 1056-1067Summary Full Text Full Text PDF PubMed Scopus (1245) Google Scholar, 3Kessler RC Bromet EJ The epidemiology of depression across cultures.Annu Rev Public Health. 2013; 34: 119-138Crossref PubMed Scopus (1466) Google Scholar hence its impact is both devastating and substantial. Although researchers have suggested several potential causal factors that contribute to the development of youth depression including genetic loading, low socioeconomic status, and adverse life events,2Thapar A Collishaw S Pine DS Thapar AK Depression in adolescence.Lancet. 2012; 379: 1056-1067Summary Full Text Full Text PDF PubMed Scopus (1245) Google Scholar the impact of climate change remains relatively unexplored. In the past three decades, global annual surface temperatures have increased by approximately 0·2°C per decade, giving rise to concerns for planetary and environmental human health.4Hansen J Sato M Ruedy R Lo K Lea DW Medina-Elizade M Global temperature change.Proc Natl Acad Sci USA. 2006; 103: 14288-14293Crossref PubMed Scopus (1363) Google Scholar Furthermore, global scale specific humidity, defined as the ratio of water vapour mass of moist air taken with respect to the total mass of the system, has increased in response to rising temperatures.5Willett KM Gillett NP Jones PD Thorne PW Attribution of observed surface humidity changes to human influence.Nature. 2007; 449: 710-712Crossref PubMed Scopus (272) Google Scholar These planetary changes are believed to be anthropogenic in origin, and are anticipated to increase in extreme precipitation, tropical cyclones, and heat stress events.5Willett KM Gillett NP Jones PD Thorne PW Attribution of observed surface humidity changes to human influence.Nature. 2007; 449: 710-712Crossref PubMed Scopus (272) Google Scholar In this Comment, we highlight the potential value of considering climatological variables in the assessment of young people with mental illness. One position advanced in the literature is that climate change causes extreme heat events, intensification of storms, flooding, and coastal erosion, all of which might disrupt the societal and economic structures that underpin mental health.6Berry HL Bowen K Kjellstrom T Climate change and mental health: a causal pathways framework.Int J Public Health. 2010; 55: 123-132Crossref PubMed Scopus (429) Google Scholar Within this framework, individuals in the developing world would be most vulnerable to these direct environmental effects. For example, climate change might alter the quality of soil, preventing agricultural practices that would otherwise supply populations with food.7McMichael AJ Friel S Nyong A Corvalan C Global environmental change and health: impacts, inequalities, and the health sector.BMJ. 2008; 336: 191-194Crossref PubMed Google Scholar Ongoing climate change could directly result in the degradation of the physical environment, negatively impact food yields and freshwater supplies, leading to the displacement of populations, and eventual loss of livelihoods.7McMichael AJ Friel S Nyong A Corvalan C Global environmental change and health: impacts, inequalities, and the health sector.BMJ. 2008; 336: 191-194Crossref PubMed Google Scholar Therefore, climate change, and its ensuing negative impact on the physical environment could exacerbate poverty, malnutrition, and disease. Each of these factors could, in turn, serve as independent risks for the development of youth depression in young people living in developing nations. Young individuals with depression and anxiety might be at a disproportionately increased risk for worsening symptoms in the face of changing climate.8Frumkin H Hess J Luber G Malilay J McGeehin M Climate change: the public health response.Am J Public Health. 2008; 98: 435-445Crossref PubMed Scopus (401) Google Scholar, 9Norris FH Friedman MJ Watson PJ et al.60,000 disaster victims speak: Part I. An empirical review of the empirical literature, 1981–2001.Psychiatry. 2002; 65: 207-239Crossref PubMed Scopus (2144) Google Scholar Climate change exposes pre-existing psychological vulnerabilities. Individuals with a pre-existing resilience deficit might fail to prepare adequately for extreme events due to the changing climate.10Morrissey SA Reser JP Natural disasters, climate change and mental health considerations for rural Australia.Aust J Rural Health. 2007; 15: 120-125Crossref PubMed Scopus (91) Google Scholar By contrast, individuals and communities who are prepared for natural disasters associated with changing climate might experience less collective distress.10Morrissey SA Reser JP Natural disasters, climate change and mental health considerations for rural Australia.Aust J Rural Health. 2007; 15: 120-125Crossref PubMed Scopus (91) Google Scholar Therefore, young individuals are believed to be at greater vulnerability to the negative effects of climate change by virtue of their developing coping capacity. Although few studies evaluating the impact of climate on mental health exist, some suggest that rising temperature might negatively impact mental health. To date, much of the literature has focused on adult mental health. For example, rising temperature and humidity are associated with increases in emergency department visits for mental health concerns.11Vida S Durocher M Ouarda TB Gosselin P Relationship between ambient temperature and humidity and visits to mental health emergency departments in Quebec.Psych Serv. 2012; 63: 1150-1153Crossref PubMed Scopus (68) Google Scholar One study showed a positive correlation between emergency department visits and mean surface temperatures.11Vida S Durocher M Ouarda TB Gosselin P Relationship between ambient temperature and humidity and visits to mental health emergency departments in Quebec.Psych Serv. 2012; 63: 1150-1153Crossref PubMed Scopus (68) Google Scholar Increased rates of emergency department visits occurred during summer months and the rate of mental health concerns increased between 5–10% at higher temperatures (ie, 25°C as opposed to 20°C).11Vida S Durocher M Ouarda TB Gosselin P Relationship between ambient temperature and humidity and visits to mental health emergency departments in Quebec.Psych Serv. 2012; 63: 1150-1153Crossref PubMed Scopus (68) Google Scholar Furthermore, researchers have proposed an association between humidity and temperature with mental health outcomes.12Ding N Berry HL Bennett CM The importance of humidity in the relationship between heat and population mental health: Evidence from Australia.PLoS One. 2016; 11: e0164190Google Scholar, 13Hansen AL Bi P Nitschke M Ryan P Pisaniello D Tucker G The effect of heatwaves on mental health in a temperate Australian city.Epidemiology. 2008; 19: 1369-1375Google Scholar Increasing temperature and vapour pressure were associated with a significant increase of high distress.12Ding N Berry HL Bennett CM The importance of humidity in the relationship between heat and population mental health: Evidence from Australia.PLoS One. 2016; 11: e0164190Google Scholar Humidity modulates the effect of temperature on distress.12Ding N Berry HL Bennett CM The importance of humidity in the relationship between heat and population mental health: Evidence from Australia.PLoS One. 2016; 11: e0164190Google Scholar In high temperatures, humidity augmented distress, whereas in low temperatures, humidity mitigated distress.12Ding N Berry HL Bennett CM The importance of humidity in the relationship between heat and population mental health: Evidence from Australia.PLoS One. 2016; 11: e0164190Google Scholar Additionally, only a few studies have endeavoured to evaluate the effects of climate on mental health specifically in youth. For example, a study surveyed Nicaraguan adolescents after Hurricane Mitch in 1998, and its findings revealed severe levels of both post-traumatic stress and depressive reactions.14Goenjian AK Molina L Steinberg AM et al.Posttraumatic stress and depressive reactions among Nicaraguan adolescents after hurricane Mitch.Am J Psychiatry. 2001; 158: 788-794Crossref PubMed Scopus (284) Google Scholar These results extend the work conducted by Norris and colleagues,9Norris FH Friedman MJ Watson PJ et al.60,000 disaster victims speak: Part I. An empirical review of the empirical literature, 1981–2001.Psychiatry. 2002; 65: 207-239Crossref PubMed Scopus (2144) Google Scholar who showed that, by contrast with adults, young individuals were both more susceptible to environmental-related trauma and more likely to become depressed if their family members were injured. Taken together, these studies highlight the unique vulnerabilities and comorbidities of adolescents who have faced environmental disasters associated with climate change. Collectively, these findings indicate a significant and nuanced impact of climate on youth mental health across the world. In countries with large land masses, climate measures vary greatly across provinces and regions. Consequently, researchers aiming to characterise the link between climate change and youth depression should account for regional differences in surface temperatures and humidity. Moreover, delineation of possible mediators of climate-induced depression (ie, sex, prior traumatic exposure, and parental injury) could enhance disaster preparedness and lead to strategic deployment of therapeutic interventions. Youth depression is a burgeoning illness that may be uniquely sensitive to changes in global climate. Young people might be particularly vulnerable to climate-induced depression when faced with parental injury. Although the literature is still developing, several studies now suggest that fluctuations in climate affect both the onset and severity of depression at a population level. We believe that researchers and clinicians treating young people with mental illness should familiarise themselves with the potential ways in which climate change has already impacted mental health outcomes. Finally, researchers should identify ways to fortify the societal structures necessary for mental health that climate change threatens to erode. We declare no competing interests.

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