Air Pollution Drives Suicide Rates Even On A Weekly Basis

Researchers have found an innovative way to test a suspected connection between air pollution and suicide. Their results not only confirmed the relationship is real, they suggest it’s clearer than anyone expected. If all the other reasons to stop burning fossil fuels were not enough, here’s another one.

The link between atmospheric pollution and physical ill-health is very well established, but in recent years researchers have found evidence it’s bad for our mental health as well, including increasing the frequency of suicide. However, as Dr Tamma Carleton of the University of California, Santa Barbara, noted, this is a classic case of correlation not necessarily meaning causation. “One of the bigger challenges with prior work on this problem is that air pollution is correlated with a lot of things,” Carleton said in a statement. There is more pollution on weekdays than weekends for example, but it would hardly be safe to assume it is the pollution making people suicidal. 

“Our goal was to isolate just the role of pollution on suicide as opposed to all the other things that might be correlated,” Carleton said. With colleagues, Carleton explored the periods when pollution (measured via levels of particles of 2.5 microns in diameter or less, called PM2.5) rises without other factors changing, thanks to temperature inversions. These occur when a layer of warm air traps cold air beneath, preventing the dispersal of pollutants and causing local build up. Certain cities are particularly prone to these inversions because of the location of nearby hills.

To the extent any pollution-suicide relationship is chronic, reflecting long-term exposure, this test would not help. However, if there is also an acute connection, inversions represent a way of stripping out all the confounding factors.

Using data from 2000 to 2019, Carleton and co-authors have reported an increase of approximately 25 percent in suicide rates in Chinese counties in weeks where inversions sent pollution rates spiking. “Suicide rates increase substantially when air pollution rises,” they report. The effect is strongest among older women, whose rates increase 2.5 times as much as the general population. The authors offer several possible explanations for why older women are most vulnerable, without currently having a way to distinguish between them.

Crucially, suicide rates are not lower than normal in the weeks after an inversion, as would be expected if excess pollution was just bringing forward a tragedy that would have happened anyway. 

Carleton became interested in the question after having shown that hot weather increases suicides in India – a concerning finding in a warming world. However, she also noticed that suicide rates are falling globally, despite rising temperatures, and they’re falling faster in China than almost anywhere else. The decline in air pollution in Chinese cities, driven by the replacement of old coal-burners with cleaner technology, accounts for a significant proportion of this.

“Thirty years of warming in India led to about the same magnitude of suicide effects as about five years of air pollution control in China,” Carleton said, the latter saving around 46,000 lives. She noted, however, that 90 percent of suicides cannot be explained by pollution. The pandemic may well have scrambled things further.

It’s harder to measure broader mental ill-health, but it is plausible suicide represents the tip of a vast iceberg of suffering to which air pollution also contributes.

The finding is great news for China. Although air pollution has fallen a lot, it’s about to fall further as the spectacular increase in solar and wind generation will start to displace even relatively clean coal production, probably starting this year. Meanwhile, electric cars are now so popular in China that petrol and diesel vehicle numbers will be peaking soon as well.

It’s not such a positive finding for places where pollution is still rising, but it shows there are yet more benefits to be gained if countries can skip the coal and oil stage of industrialization and jump straight to renewables.

“We often think about suicide and mental health as a problem to be understood and solved at an individual level,” Carleton said. “This result points to the important role of public policy, of environmental policy, in mitigating mental health and suicide crises outside of individual-level intervention.”

The study is published in Nature Sustainability.

If you or someone you know is struggling, help and support are available in the US at the National Suicide Prevention Lifeline on1-800-273-8255. In the UK and Ireland, the Samaritans can be contacted on 116 123. International helplines can be found at SuicideStop.com.  

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