According to one study, as global temperatures rise, mental health problems will increase.

For the study, Obradovich and colleagues combined data from the US Center for Disease Prevention and Control's behavioral risk factor surveillance system, which includes personal mental health data from nearly 2 million US residents. randomly selected, with daily weather data from 2002 to 2002. 2012.

The surveillance survey of behavioral risk factors could be the largest public health surveillance survey in the world, Obradovich said. "We have collected data from about ten years in this survey, about 2 million people answering the same question.The question is essentially: how, during the recent period, your was mental health status? "

Interviewees indicated that "everything in the range of stress, anxiety, depression and emotional problems"; it "basically means things that are less extreme than hospitalization and suicide but that are more meaningful than being grumpy or emotional day-to-day. [agitation]. "

Then he and his colleagues linked the mental health reports to the meteorological data of the city where each respondent lived. "We had this beautiful decade of information on the relationships between environmental conditions and people's mental health status," Obradovich said.

The research team analyzed the data in three ways.

First, they examined temperatures and precipitation over a 30-day period and compared them to mental health. "Exposure to warmer temperatures and higher precipitation rates over this period has increased the likelihood of people reporting a mental health problem during this period," Obradovich said.

Specifically, the change from monthly average temperatures between 25 ° C (77 ° F) and 30 ° C (86 ° F) to temperatures above 30% corresponds to a 0.5 percentage point increase in the probability of mental health problems. If this exact temperature change was generalized across the country, "it would produce an estimated 2 million more people reporting mental health problems," Obradovich said.

The team then analyzed reports on long-term warming and mental health in different cities. Here, they discovered that five-year warming of only one degree Celsius was associated with an increased prevalence of mental health problems of 2%.

Finally, the team examined reports on the mental health of people affected by Hurricane Katrina and compared them with those living in areas of comparable size that had not been affected by the catastrophic hurricane. Katrina's experience was linked to a 4 percentage point increase in the prevalence of mental health problems.

Overall, research has indicated that people most vulnerable to the effects of climate change studied include low – income people, people with existing mental health problems, and women.

So, why do not people living in warmer places generally have worse mental health than those living in colder places? Obradovich said it was one of the "outstanding issues in identifying the social impacts of climate change". Because some factors, such as adaptations of life to climate, can not be taken into account, the new study only allows researchers to say that on average, "warming over time is associated with a deterioration of mental health over time ". "There are many other place-specific factors that can lessen the effect."

"Stress and despair"

Patz, who did not participate in the new research, said the strength of the study encompassed the large number of participants, but said that the data rested "on a single question regarding the mental health of the person and only at the monthly level ".

"The most important point of this [new] The study shows that climate change is actually affecting mental health and that some populations (women and the poor) are disproportionately affected, "said Patz, who called for more research on climate change, in an e-mail.

He also said that the study might underestimate the negative effects of climate change and that there could be "stress and desperation" because governments and the industry do not react at the pace recommended by many scientific assessments. "

Obradovich, who said some people living near the coast may be worried that their homes might be damaged by a hurricane, said: "This concern could have additional effects on climate change concerns."