Global warming will increase suicides, researchers say

SAN FRANCISCO -- More people are likely to take their own lives as the planet warms, say researchers at Stanford University and the University of California at Berkeley in a study published Monday that suggests yet another worrisome impact of climate change.

The multidisciplinary research team looked at nearly 1 million suicides in North America and found that hotter temperatures correlate with higher suicide rates. The warming projected through 2050, the group figures, could increase suicide rates by 1.4 percent in the U.S. and 2.3 percent in Mexico over that time, resulting in 21,000 additional deaths in the two nations.

The role of heat, the authors said, may be just as significant as other, more well-known drivers of suicide, like economic hardship, which also pushes rates up, and suicide prevention programs and gun control legislation, which tend to push rates down.

``The overall health burden of suicides and poor mental health is already large in this country and it's going to grow,'' said Marshall Burke, the study's lead author and an assistant professor of earth system science at Stanford.

While earlier research has suggested a link between climate change and suicide, specifically climate-related disasters like drought, the driver was generally thought to be something deeper, like anguish over a financial loss.

Burke and his colleagues, however, said warm weather itself probably has a direct effect on a person's mental well-being.

The researchers said they evaluated such a large number of suicides over such a long period of time -- 866,000 in the U.S. and 74,000 in Mexico as far back as 1968 -- that they concluded that other factors couldn't account for all of the incidents and trends.

``The only explanation is that it's some sort of underlying biological response to hotter temperatures,'' Burke said, noting that some had long suspected the contrary, that cooler temperatures were more problematic. ``We had typically thought of people being unhappy in the cold and dark.''

The study indicates that the link between heat and suicides was equally discernible in warm and cold climates.

Since the group's statistical analysis doesn't prove the presence of a physiological factor, merely suggests one, the researchers turned to social media to test whether the hotter temperatures are truly driving a person's mental state.

``We wanted to be as sure as we could about what we were saying,'' said Solomon Hsiang, study co-author and associate professor of public policy at UC Berkeley.

The researchers observed more than 600 million Twitter posts to evaluate moods in different kinds of weather. They found that every 1.8-degree Fahrenheit increase in temperature, or 1 degree Celsius, raises the likelihood of a depressive tweet, one that contains such words as ``lonely'' or ``suicide,'' by as much as 1 percent.

The correlation between temperature rise and the pattern researchers saw in tweets is almost exactly the same as that between hot weather and suicide rates, Hsiang said.

``It looks very much like it's something that's mental and less contextual,'' he said.

The researchers also found that the link between temperature and both depressive tweets and suicide risk is uniform for rich and poor and for men and women.

``Often when you hear climate change discussed in the media or even in the academic literature, you hear that there's going to be winners and losers,'' Burke said. ``In suicide, that's not what we find at all. Everyone is losing.''

Nationwide, 45,000 suicides occurred in 2016, making it one of the top 10 causes of death in the U.S., according to the Centers for Disease Control and Prevention. And it's a problem that's on the rise.

In California, suicides have increased 14.8 percent between 1999 and 2016, according to the CDC.

San Francisco Suicide Prevention, which provides counseling and outreach in the city and runs a hotline for those struggling emotionally, reports an uptick in the number of calls over the past year.

Fletcher Johnson, outreach coordinator for the organization, said the bottom line is that people's emotional needs aren't being met, with higher temperatures or no higher temperatures.

``There might be a relationship between climate change and suicide,'' he surmised, ``but it might be simpler than that.''

The new study on suicides is published in the science journal Nature Climate Change.