Rising temperatures have been linked to an increase in mental health problems.

In a study published in the Proceedings of the National Academy of Sciences, more than two million responses to an annual government survey that asked people about their mental health over the last 30 days collected over a 12-year period, were analysed.

Researchers found that people were more likely to report issues like stress, anxiety and depression during months when average temperatures were above 30 degrees Celsius, compared to months when temperature averaged between 25 and 30 degrees.

Mental health problems also increased in cities that reported a one-degree increase in average temperatures over five years.

However, the report acknowledged that an increase in average temperatures is likely just one variable that has changed over time, and that the study can only show an association between rising temperatures and mental health, rather than cause and effect. While the team did control for factors such as the demographic makeup of cities, the association remained.

Relationship

"The finding isn’t definite, but it certainly suggests we should look further into that relationship,” said lead author Nick Obradovich.

There are several reasons why warmer weather could lead to worse mental health. In a previous study, Obradovich and his colleagues found that people tend to post negative emotions more frequently on social media when temperatures are at their highest.

"It could be a direct relationship between temperature and mood,” he said. It is also possible that people have more trouble sleeping when its warmer; that temperature has an effect on cognition; or that people are simply more anxious about other consequences of climate change. Figuring out exactly what is going on is one of the more important things scientists in this area are working on.”

Also, warmer temperatures likely mean more events like severe hurricanes and floods, and living through a natural disaster can affect mental health.

Overall, the link between warmer temperatures and mental health problems was strongest in women, people with lower incomes, and those with existing mental health problems.

With temperatures set to rise above the recommended limit if nothing drastic is done to prevent that, public health systems might need to prepare to deal with more mental health problems due to warmer climate.

Science journal