Is climate change stressing you out? A new study linking weather and mental health in the United States suggests things could get much worse.

The study outlines three separate ways that hotter and more extreme weather stand to undermine the mental well-being of the people forced to experience it. The effects will be most pronounced for women and for low-income Americans, the findings indicate.

“Ultimately, if observed relationships from the recent past persist, added climate change may amplify the society-wide mental health burden,” the study authors wrote Monday in the Proceedings of the National Academy of Sciences.

The research team — led by Nick Obradovich, a data scientist at the MIT Media Lab who examines climate change and human behavior — was guided by the real-life experience of a diverse group of people from 263 cities across the country. All of them took part in the Behavioral Risk Factor Surveillance System, a health survey that’s been operated by the Centers for Disease Control and Prevention since 1984.


Between 2002 and 2012, nearly 2 million participants were asked this question: “Now thinking about your mental health, which includes stress, depression, and problems with emotions, for how many days during the past 30 days was your mental health not good?”

Obradovich and his colleagues used the responses to classify people into two groups: those who reported any recent days with poor mental health, and those who didn’t.

The study authors acknowledged that this was a far cry from assessing an individual’s true psychiatric state. But conducting individual assessments of so many people was simply not feasible. On the plus side, the survey participants were randomly selected to be representative of the nation as a whole. Also, the way the question was worded allowed the researchers to identify people who were experiencing mental distress even if they hadn’t sought professional health, they wrote.

The CDC data included a location for each participant, and the researchers used it to match each person’s mental health status to the weather where he or she lived. Over the 10-year study period, they found three distinct ways that climate change was associated with worse mental health.


The first was what the authors called “short-run weather exposure,” which they assessed in two ways.

For starters, they recorded the highest temperature for each day in each city, then calculated the average of those peaks over the course of each month. When the maximum daily temperature averaged 86 degrees Fahrenheit or above, the odds that people would experience poor mental health were 1 percentage point higher than in months when the average high temperature was between 50 and 59 degrees, and 0.5 percentage points higher than when the average high temperature was between 77 and 86 degrees.

Some people were more vulnerable than others, the researchers found. They sorted the participants into four groups according to their income and found that the effect of high temperatures on mental health was 60% greater for those at the bottom of the economic ladder than for those at the top.

The researchers also found that being a woman instead of a man was associated with an effect of the same magnitude. When these factors were combined, they calculated that the negative effect of high temperatures on mental health was twice as high for low-income women as it was for high-income men.


Rainy days took a toll as well. The odds of reporting mental health problems were 2 percentage points higher in extremely rainy months with more than 25 days of precipitation than they were in months with no precipitation at all.

Next, the researchers considered the effect of warming that occurred over the course of several years.

They divided their data into two time periods: 2002 through 2006, and 2007 through 2011. Among the 156 cities with data from both periods, they found that when the average maximum temperature increased by 1.8 degrees between the earlier and later years, the prevalence of mental health problems increased by 2 percentage points.

Obradovich and his colleagues tweaked their analysis in several ways to make sure that this result was not a fluke. For instance, when they focused on the 78 cities that had data for all 10 years, they found the effect was slightly larger.


The researchers noted that the effects of multiyear warming were most pronounced in the spring and summer.

Finally, the team considered the toll of hurricanes on mental health. They said they singled out this type of natural disaster because climate change is expected to make these storms more frequent and more intense.

The CDC data showed that after Hurricane Katrina struck the Gulf Coast region in August 2005, reports of mental health problems increased in places with declared disasters. Meanwhile, in places that weren’t affected by the hurricane, the mental health of study participants improved after the storm.

By comparing hurricane victims with other Americans, the researchers were able to estimate just how much the exposure to Katrina was associated with changes in mental health. Their result: The occurrence of mental health problems was 4 percentage points higher among those who were hit by the hurricane than among those who weren’t.


While all three factors were significantly associated with worse mental health, there was a clear hierarchy among them — hurricanes were the worst, followed by long-term warming and short-term temperature changes.

The CDC surveys used in this study did not provide the kind of detail researchers would need to explain exactly how climate change translates into worse mental health. But there are plenty of possibilities.

The researchers named a few, including the fact that rising temperatures may force some people to move, uprooting their entire lives. Others may work in industries threatened by climate change and wind up unemployed. Hot weather discourages people from exercising and makes it harder to get a good night’s sleep, and studies suggest that sleep deprivation increases the risk of depression.

“Given the vital role that sound mental health plays in personal, social, and economic well-being,” Obradovich and his coauthors concluded, “our findings provide added evidence that climatic changes pose substantial risks to human systems.”


karen.kaplan@latimes.com

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