Guest post: The growing problem of how extreme heat damages mental health

§ How heat can affect mental health

Being in the midst of a heatwave can feel all encompassing. Generally, being hot and uncomfortable can affect a person’s mood, leading some to feel more irritable and stressed. This can have a knock-on effect on behaviour. For example, research shows that people are more likely to tweet negative comments during a heatwave.

Extreme heat can have even more significant implications for sleep. Research shows that warming nights are eroding human sleep globally – and the effect is three times larger for residents of lower-income countries. 

While lost sleep in hot and humid conditions is unpleasant for anyone, for those with mental health problems, poor sleep carries a real risk of making them worse.

Nonetheless, not all heat is bad for mental health. Many people believe that they are happier on sunny days and some research agrees. 

For example, a 2023 study in Switzerland found that, in the general population, mood tends to improve as temperatures get warmer. However, the study also found that the opposite is true for people with anxiety, depression and psychosis, who were more likely to experience low mood.

§ Impacts of extreme heat

The impact of extreme heat on an individual’s mood has implications for social behaviours and interactions. 

There is a growing body of research linking extreme heat with an increase in violent behaviour, such as homicides, sexual violence and assaults, which – in turn – can negatively impact mental health.

For example, a study conducted in India, Nepal and Pakistan found that with each 1C increase in the annual temperature there was a 4.5% increase in violent acts. This finding alone is an indicator that heat affects a person’s psychology, but there are so many other factors that need to be considered.

There are other possible social drivers that may explain this link. People living with pre-existing mental-health problems may be more vulnerable to the impact of extreme heat due to societal factors that put them at increased risk. 

Due to the relationship between mental-health problems and poverty, people living with mental-health conditions may be more likely to live in less energy-efficient housing, have less access to adaptation mechanisms such as air conditioning, be more socially isolated, or work in occupations that increase their exposure to extreme heat.

Finally, certain medications for mental-health problems – such as some antidepressants or antipsychotics – may disrupt the body’s ability to regulate temperature, meaning that people taking these medications may be more vulnerable in high temperatures. This may explain why people taking these medications have been found to be at higher risk of being hospitalised or dying during heatwaves.

One patient in the UK taking antipsychotics – medication for mental-health problems where symptoms include psychotic experiences – was quoted last year in the BMJ explaining how they were affected by extreme heat. They said:

“[F]or many summers I had also noticed that I struggled to tolerate the heat as the UK weather grew more extreme. I would sweat profusely, my skin would feel clammy, and I would feel very tired, irritable and would struggle to think…I had no idea this was related to my medication.”

Prescribing appropriate medications for certain mental-health conditions and ensuring people taking them are protected from the potential negative impacts of heat represents an important clinical and policy priority.

§ Research gaps

To date, most studies on climate change and mental health have been conducted in Europe, North America and Australia. This means that there are huge gaps in research for the global south, which is facing some of the most severe impacts of climate change.

A new project called Connecting Climate Minds, which Wellcome funds, aims to develop a research and action agenda on climate change and mental health. As part of this project, 900 people shared their experiences on the impact that climate change is having on mental health around the world. 

One of them is Laila, a teacher working in Jordan. She has been suffering from stress, anxiety and depression. At its worst, she confesses that she struggles to teach and finds communicating with the children very difficult.

Over the past few years, these episodes have become more frequent and severe. Her psychologist noticed that Laila’s mental health seemed to worsen during the country’s extreme heatwaves – something that is becoming more and more common in the region.

Watch her interview in full below.

Wellcome is also set to launch a funding call later this year focusing on uncovering the mechanisms underpinning the association between heat and mental health among the most affected communities worldwide. 

The aim is to help build global understanding of the biological, psychological, environmental and social links around extreme heat, which will in turn inform better climate resilient solutions and mental health interventions.

§ Policymaking lagging behind

As with research, there are gaps in policymaking on mental health and climate change.

Most countries do not currently consider mental health within climate change policies, such as heat action plans. At present, only 3% of the climate pledges submitted by national governments under the Paris Agreement mention mental health.

South Australia is among the few states already doing this. The South Australian warning system incorporates public heat warnings, health advisories and targeted support for at-risk groups including those with mental-health conditions, ensuring that they can access help if needed. In Athens, a city exposed to more frequent and severe heatwaves, psychologists are being deployed to support older adults experiencing loneliness in the heat.

Nature-based policies that improve access to green and blue spaces and transport policies that encourage active modes of transport have also been shown to have co benefits for mental health and the environment.

However, for now, climate change represents one of the biggest threats to physical and mental health globally. Extreme heat is deadlier than hurricanes, floods and tornadoes combined. Heat stress can exacerbate underlying illnesses – such as cardiovascular disease, diabetes, asthma – and can increase the risk of accidents and transmission of some infectious diseases. And this is not considering the huge hidden cost of increasing cases of poor mental health.

Research on how climate change is impacting mental health remains limited and disconnected. A better understanding of how and why extreme heat is negatively impacting mental health will be essential to achieve a world where no one is held back by mental health problems, even in the context of a changing climate.