Scientists analysed data from nearly two million US residents who reported the state of their mental health for 30 days with the US Centres for Disease Control and Prevention between 2002 and 2012, coupling this with climate data.
On average, months with temperatures above 30C or more than 25 days of rainfall saw increased reports of stress, depression and “problems with emotions”, scientists said in the journal Proceedings of the National Academy of Sciences.
Nick Obradovich, the study’s co-author and Massachusetts Institute of Technology research scientist, said: “It’s really important to consider this as yet another piece in the puzzle of understanding how climate change will influence society, and the conclusion here is that it’s not likely to be good.”
The sheer scale of the study adds important weight to the growing body of evidence that shows exposure to climate change-related heat worsens mental health and increases suicide rates.
Alarmingly, Dr Obradovich’s team also found that women and those on low incomes were 60 per cent more likely to report mental health problems as a result of weather than the highest earners.
The study also noted a 4 per cent rise in reports of poor mental health linked to Hurricane Katrina, which struck the US Gulf Coast in August 2005 and affected millions of people.
Delving deeper into the findings, Dr Obradovich said: “One of our theories is it’s possibly being driven through the effects of higher temperatures upon sleep. However, there’s a lot of other ways it could be happening.”
He believed other possible factors could include the negative effects of heat upon an individual’s productivity and cognitive function, or its impact upon the brain’s ability to regulate emotion.
“We don’t know for sure and a big part of the work that we as climate change social scientists and impact scientists have to do is figure out what is driving the effects – largely because if you’re a policymaker you want to know what you should target to reduce these effects,” he said.
Dr Obradovich also pointed out the study did not take into account the impact that the existential risk of climate change could be having upon our collective mental health, or harder to quantify symptoms of climate change such as rising sea levels.
He called for all countries to improve their mental healthcare services so if people “face stressors that are produced by climate change, they may have a better baseline level of mental healthcare and availability”.
However, the study stated that the correlation between rising heat levels and worsened mental health “may not persist into the future”, as humans could find a way to adapt either technologically or physiologically to the effects observed.
On the day of the study’s publication, the UN Intergovernmental Panel on Climate Change warned there are only 12 years left to limit global temperature increases to below 1.5C.
The UN report argued urgent and unprecedented policy changes are necessary to avoid the worst effects of global warming.
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