The study provides longitudinal and country scale evidence that local suicide rates in both a developed and a middle-income country are robustly associated with local temperatures
A new study found that for a 1°C increase in monthly average temperature, suicide rates rise 0.7% in US counties and 2.1% in Mexican municipalities. The study looked at the effect of local ambient temperature on the rates of suicide across the US and Mexico—two countries that, based on current estimates, account for roughly 7% of all global suicides.
Climate affects many dimensions of human health, ranging from vector-borne disease mortality to rates of cardiac arrest. But linkages between climate and mental health are often theorised and are poorly quantified. This study quantified the effects of climate change induced warming on mental health.
According to the study, the relationship between temperature and suicide was analysed by using monthly vital statistics data for thousands of US counties between 1968–2004 and Mexican municipalities between 1990–2010. The study provided longitudinal and country-scale evidence that local suicide rates in both a developed and a middle-income country are robustly associated with local temperatures, findings that are consistent with recent work in both developed and developing countries.
Use of depressive language on social media
The study also analysed use of depressive language in more than 600 million social media updates on X (Twitter), which suggested that mental well-being deteriorates during warmer periods.
According to the researchers, the estimates of temperature effects were driven from comparing suicide rates or depressive tweets between an average January in a given county to a warmer-than-average January in the same county, after having accounted for any changes common to all counties in a given state in that year.
It was then assessed how responses differ across decades, by income level, sex, population level, and both air conditioning and gun ownership rates, as well as across regions with different long-run average temperatures.
No improvement despite rising income and air conditioning
The study suggested that the mechanism through which temperature affects suicide is likely to be distinct from temperature’s effects on many other causes of mortality. In contrast to all-cause mortality (death rate from all causes of death for a population in a given time period), suicide increases at hot temperatures and decreases at cold temperatures. Also, unlike all-cause mortality, the effect of temperature on suicide has not decreased over time and does not appear to decrease with rising income or the adoption of air conditioning.
The researchers projected that unmitigated climate change could result in a combined 9,000-40,000 additional suicides (95% confidence interval) across the US and Mexico by 2050, representing a change in suicide rates comparable to the estimated impact of economic recessions, suicide prevention programmes or gun restriction laws.
In absolute value, the study found, the effect of climate change on the suicide rate in the US and Mexico by 2050 is roughly two to four times the estimated effect of a 1% increase in the unemployment rate in the European Union, half as large as the immediate effect of a celebrity suicide in Japan, and roughly one-third as large in absolute magnitude (with opposite sign) as the estimated effect of gun restriction laws in the United States or the effect of national suicide prevention programmes in Organisation for Economic Co-operation and Development (OECD) countries.
Calculations from the study suggested that projected changes in suicide rates under future climate change could be as important as other well-studied societal or policy determinants of suicide rates. Therefore, it must be looked into for further understanding and also to form effective suicide prevention policies.