Climate change and mental disorders

Climate change, the reality of which is fully accepted by the present authors, will inevitably have an impact on mental health in the affected communities. But does this justify the anxious anticipation of a major threat to the mental health of nations? One way in which epidemiology can contribute to this issue is to clarify the magnitude of the expected morbidity and its administrative significance for services. Such information can provide a basis for action. Here, we consider three categories of variable. First are the environmental events that climate change is believed to promote. Floods, tsunamis, droughts, heat waves, cyclones and wildfire must each carry substantial threat to the mental health of those exposed. Some events will be acute, a few long-lasting, while there is the additional likelihood of multiple exposures to one or more event in the same population. Second are those groups who will be particularly at risk since the health impact is likely to be non-random. The third category is the nature of the psychopathology likely to be induced and its expected course, short- and long-term. In considering this, it is important to bear in mind that the need to adapt to extreme adversity is not new in the history of human evolution.

A sizeable literature has already accumulated on climate change and mental health, but only some of it carries quantitative data. More common are calls to action without clear evidence for an increase in prevalence in the general population. Clearly, adverse climatic events will be followed by an increase, within the affected communities, in distress, grief reactions, depression and anxiety disorders including post-traumatic stress disorder (PTSD) and a small rise in suicide rates. In a comprehensive review of the psychological impacts of global climate change, Doherty and Clayton (2011) add evidence for increased violence with increased ambient temperature, inter-group conflict in the face of diminished resources and emotional reactions to forced relocation. Many authors point to the particular vulnerability of groups living in poverty or already in impaired health including mental disorders. So far, little has been written about effects on infants and children or the very elderly. However, McDermott et al. (2014) reported that 1 in 5 children and 1 in 12 adolescents endorsed cyclone-related PTSD symptoms 18 months after the Queensland cyclone. Spittlehouse et al. (2014) noted that 18 months after the Christchurch earthquake, rates of major depression were higher and social functioning scores significantly lower in middle-aged persons than similar population norms.

What are the implications of the available information for mental health at the national level? The magnitude of the overall impact, expressed as an increase in annual prevalence for a nation, is unlikely to be great. Administratively, in those countries with developed mental health services, only a proportion of those who develop symptoms will seek or obtain psychotherapy and on occasion medication. Such a peak in service demand is likely to be transient. The impact on mental health and social distress will not be as bad as that caused by, for example, the mass movement of refugees in Europe, the current and ubiquitous Ice (methylamphetamine) epidemic, domestic violence or abuse in childhood. Indeed, there is so far little evidence to justify climate change being given priority above other threats to mental health. That apart, one hypothesis not yet proposed is that an increase in global temperature might have neurobiological sequelae, including an influence on the foetal brain.

There are some counter-intuitive consequences of disasters or other extreme environmental adversity. They can be associated with an increase in social capital through the emergence of previously absent mutual support. This was seen in the London Blitz and more recently in the Christchurch earthquake, where some study participants reported a strengthening of social and family relationships with increased resilience (Fergusson et al., 2015). Remarkably, a dose–response association was also found, with increasing exposure being followed by increased resilience. While the relative risk of suicide increased in men during drought in New South Wales (NSW) during 1970–2007, it decreased in women. One interpretation was that women particularly benefit from increased community supports. In his magisterial examination of the place of social capital in relation to climate change, Adger (2001) points out that in the past 10,000 years of human history, it may have been climate changes which provided the impetus for altering the way resources are managed.

In summary, when it is proposed that climate change presents a potential threat to world mental health, we recommend that data be acquired to support this, thereby allowing an appropriate response to be formulated.

See Research by Ferguson et al., 49(4): 351–359.