King's College London
Whilst public awareness surrounding the health implications of climate change is growing, the effects of climate change on mental and cognitive health are often overlooked, reflecting a global dialogue which regularly neglects mental health. A recent study from the International Journal of Mental Health Systems emphasised that while it can be challenging to directly attribute outcomes to climate change, there is growing literature linking specific outcomes to the detriment of mental health.
Ignoring the mental health aspect of climate change is delusional–the psychological impacts from any form of natural disaster far outweigh physical injuries by 40 to 1, and climate change-related weather disasters have increased by almost 50% since 2000. The impact of natural disasters on mental health is well documented to cause elevated rates of anxiety and mood disorders. The statistics are striking, and those of a lower socioeconomic status are most at risk. Six months following Hurricane Maria in 2017, over half the residents of Punta Santiago, a low-income community in Puerto Rico, were found to be suffering from major depression, generalised anxiety disorder and PTSD.
Scientific literature shows that rising temperatures could have a dramatic effect on global mental health rates, and for every 1°C of global warming there is an associated 2% increase in mental health disorders. Whilst 2% sounds insignificant, this would equate to over 140 million more people experiencing mental health issues globally. Current projections predict a 2.4–5.8°C rise in average global temperatures by the end of the century. In other words, in the best-case scenario nearly half a billion more people globally will experience mental health issues as a result of climate change. The worst-case scenario is frightening to consider.
This begs the question: how could global warming have this effect? Recent literature suggests that rising temperatures affect mental health in multiple ways, including hypothyroidism, sleep loss, and interference with psychotropic medication. Heat waves, in particular, are known to exacerbate underlying mental disorders, contributing to significantly higher rates of hospitalisation and suicide. This is especially true of individuals whose bodies are less able to thermoregulate as a result of ingesting alcohol, opiates or psychotropic medications (e.g. antidepressants and antipsychotics) – namely, people suffering from substance-abuse disorders and other psychoses.
"...in the best-case scenario nearly half a billion more people globally will experience mental health issues as a result of climate change."
Additionally, heat can alter hormone levels, with higher temperatures stimulating growth hormones and causing functional hypothyroidism, which in turn causes lethargy, low mood and cognitive impairment. Temperature is integral to quality of sleep and signalling its onset. Increasing ambient temperatures are predicted to disrupt normal sleep patterns, which could exacerbate susceptibility to health problems such as depression as well as affect cognitive performance by reducing memory and attention through sleep deprivation.
Perhaps unexpectedly, higher temperatures are associated with increasing rates of aggressive and criminal behaviour which in turn results in higher rates of physical assault and homicide. One study in the United States found a causal relationship between heat and violence, showing that for every 2°F rise in the average annual temperature, there was a corresponding increase of around 24,000 assaults or murders a year. Numerous cross-sectional studies (after controlling for sociocultural factors such as age, race and poverty) have shown that cities with higher temperatures consistently experience higher rates of violent crime. Lab-based manipulations of temperature also show that heat can have an immediate effect on violent tendencies. One experiment indicated that police officers undertaking a firearms training simulation in a warmer room were significantly more likely to perceive the suspect as being aggressive and draw their firearm.
Rising sea temperatures may also impact human cognitive health. A recent study by the University of Toronto anticipates that global warming will significantly reduce human consumption of Docosahexaenoic acid (DHA): an essential omega-3 which plays a critical role in brain function. Humans have a limited capacity to synthesise their own DHA despite its vital role in neurological development and health, and currently we obtain the chemical from eating fish.
"...cities with higher temperatures consistently experience higher rates of violent crime."
As our seas heat up, algal DHA production will be disrupted and the subsequent impact on fish and their DHA concentrations will affect human neurological health. The potential shortage will disproportionately affect foetuses and infants as DHA intake is critical for the developing brain. Developing nations in tropical regions where human nutrition depends most on wild fish are also at greater risk.
Future potential sources of DHA for humans could involve production of DHA by genetically engineered seeds or consumption of transgenic mammals bred to accumulate DHA in their tissues. However, there are obvious social and ethical considerations regarding the production and consumption of genetically modified food, and these makeshift solutions fail to address the cause of the problems in the first place. Whilst high income countries may be able to meet a reduced DHA supply by compensating with new advances in production, lower income countries lack the technological infrastructure to do so. This would exacerbate the differential accessibility of DHA, leaving the most vulnerable nations at risk and mirroring the wider problem whereby developing countries are the most impacted by climate change and the least able to afford its consequences.
At present, 93% of children in the world are exposed to levels of pollution higher than the World Health Organisation air quality recommendations, the vast majority of whom are living in low or medium-income countries.
Children’s developing brains are more vulnerable to the effects of air pollution. Exposure to urban air pollution in children has been associated with slower brain maturation and poorer cognitive performance. In megacities such as Mexico City, children display early hallmarks for Alzheimer’s and Parkinson’s diseases, decreased brain volume and cognitive dysfunction. By obstinately persisting with the use of fossil fuels for the majority of our energy production, we continue to increase air pollution levels and put more children at risk of dire health consequences.
Even if we were to cease all human activity contributing to climate change tomorrow, it would be too late mitigate the effects on future generations. Climate change has the capacity to impair the mental health of future generations before they are even born. Maternal exposure to factors such as air pollution, heat extremes and extreme weather events can shape a developing foetus, mediated by epigenetic modulation. Associated health problems include neurodevelopmental disorders such as Autism Spectrum Disorders (ASD), schizophrenia and mood disorders amongst many others.
This has been observable in various studies such as that of Hurricane Katrina in 2005 and the Iowa flood in 2008, in which maternal stress was associated with low foetal body weight, ASD, ADHD, and mood disorders. Children are the least responsible for climate change but will bear the greatest burden of its effects. It is impossible to comprehend the full scope and impact that climate change will have on the mental health of future generations, but we can’t afford to treat the psychological impacts of climate change as an afterthought. As we allocate public health resources and develop strategies to mitigate the effects of climate change, mental health needs to be an integral part of the discussion. The impacts of climate change on mental health are real, and demand to be taken seriously.