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New study shows how depression rises with the temperature

New research published in Proceedings of the National Academy of Sciences used survey data from 2 million Americans to examine the links between climate change and mental health issues.

New study shows how depression rises with the temperature
Pixabay Commons
  • The study examined survey data reported by 2 million Americans between 2002 and 2012.
  • The results showed that hotter and wetter months were associated with increases in mental health issues like stress and depression.
  • Women and low-income Americans seem to have been most affected by the weather changes.

The United Nations' top climate science panel recently warned that the world would see "rapid, far-reaching and unprecedented changes" if global temperatures rise 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial averages in coming years. Such an increase would likely be catastrophic for millions of people, particularly those who live in island nations or along the world's coasts.

Now, new research suggests rising temperatures could also have similarly disastrous effects on mental health.

The link between weather and mental health

A paper published in the journal Proceedings of the National Academy of Sciences found that exposure to hotter temperatures, increased precipitation and tropical cyclones was associated with an increase in mental health issues. These effects will likely hit women and low-income Americans the hardest, according to the research team led by Nick Obradovich, a data scientist at the MIT Media Lab.

"If we push global temperature rise into the 2 degrees-plus Celsius range, the impacts on human well-being, including mental health, may be catastrophic," Obradovich told Inverse.

The team analyzed self-reported data of 2 million Americans who responded to the US Centers for Disease Control and Prevention's Behavioral Risk Factor Surveillance System, a health survey, between 2002 and 2012. This survey, which included a location for each respondent, asked people to rate how stress, depression, and "problems with emotions" had affected their mental health over the past 30 days. The researchers then cross-referenced respondents' answers with their location and weather records.

They found that, on average, people were slightly more likely to experience mental health problems during months in which the average temperature exceeded 86 degrees compared to months when average temperatures hovered between 50 and 59 degrees. The results showed less of a contrast in months when the average temperatures ranged from 77 to 86 degrees, suggesting that mental health issues increase as temperatures rise.

The results also showed that months in which there were more than 25 days of precipitation were linked to a 2-percent increase in the probability of mental health issues. What does more rain have to do with climate change? Rising temperatures leads to more evaporation, which puts more water vapor in the atmosphere where it'll eventually come back to Earth as precipitation. The evaporation of more and hotter water also leads to an increase in tropical storms.

Image: Climate Central

Women and low-income Americans affected most

Perhaps unsurprisingly, the survey data showed that people hit by hurricanes between 2002 and 2012 were 4 percent more likely to experience mental health issues compared to Americans not affected by tropical storms.

Lastly, the team compared the links between weather and mental health along lines of gender and wealth, finding that females and low-income Americans were both 60 percent more likely to experience mental health issues during the hottest months compared to males and high-income Americans, respectively.

Still, the team cautioned that the study results revealed correlations and not necessarily causes.

"We can't be sure," Obradovich told Inverse. "It could be via the impacts of heat on sleep, on daily mood, on physical activity rates, on heat-related illness, on cognitive performance, or any complex combination of the above. Unfortunately, these processes are so complex that we can't easily identify precisely which mechanism is driving our results."

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A clever new study definitively measures how long it takes for quantum particles to pass through a barrier.

Image source: carlos castilla/Shutterstock
  • Quantum particles can tunnel through seemingly impassable barriers, popping up on the other side.
  • Quantum tunneling is not a new discovery, but there's a lot that's unknown about it.
  • By super-cooling rubidium particles, researchers use their spinning as a magnetic timer.

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Exactly why or even how quantum tunneling happens is unknown: Do particles just pop over to the other side instantaneously in the same way entangled particles interact? Or do they progressively tunnel through? Previous research has been conflicting.

That quantum tunneling occurs has not been a matter of debate since it was discovered in the 1920s. When IBM famously wrote their name on a nickel substrate using 35 xenon atoms, they used a scanning tunneling microscope to see what they were doing. And tunnel diodes are fast-switching semiconductors that derive their negative resistance from quantum tunneling.

Nonetheless, "Quantum tunneling is one of the most puzzling of quantum phenomena," says Aephraim Steinberg of the Quantum Information Science Program at Canadian Institute for Advanced Research in Toronto to Live Science. Speaking with Scientific American he explains, "It's as though the particle dug a tunnel under the hill and appeared on the other."

Steinberg is a co-author of a study just published in the journal Nature that presents a series of clever experiments that allowed researchers to measure the amount of time it takes tunneling particles to find their way through a barrier. "And it is fantastic that we're now able to actually study it in this way."

Frozen rubidium atoms

Image source: Viktoriia Debopre/Shutterstock/Big Think

One of the difficulties in ascertaining the time it takes for tunneling to occur is knowing precisely when it's begun and when it's finished. The authors of the new study solved this by devising a system based on particles' precession.

Subatomic particles all have magnetic qualities, and they spin, or "precess," like a top when they encounter an external magnetic field. With this in mind, the authors of the study decided to construct a barrier with a magnetic field, causing any particles passing through it to precess as they did so. They wouldn't precess before entering the field or after, so by observing and timing the duration of the particles' precession, the researchers could definitively identify the length of time it took them to tunnel through the barrier.

To construct their barrier, the scientists cooled about 8,000 rubidium atoms to a billionth of a degree above absolute zero. In this state, they form a Bose-Einstein condensate, AKA the fifth-known form of matter. When in this state, atoms slow down and can be clumped together rather than flying around independently at high speeds. (We've written before about a Bose-Einstein experiment in space.)

Using a laser, the researchers pusehd about 2,000 rubidium atoms together in a barrier about 1.3 micrometers thick, endowing it with a pseudo-magnetic field. Compared to a single rubidium atom, this is a very thick wall, comparable to a half a mile deep if you yourself were a foot thick.

With the wall prepared, a second laser nudged individual rubidium atoms toward it. Most of the atoms simply bounced off the barrier, but about 3% of them went right through as hoped. Precise measurement of their precession produced the result: It took them 0.61 milliseconds to get through.

Reactions to the study

Scientists not involved in the research find its results compelling.

"This is a beautiful experiment," according to Igor Litvinyuk of Griffith University in Australia. "Just to do it is a heroic effort." Drew Alton of Augustana University, in South Dakota tells Live Science, "The experiment is a breathtaking technical achievement."

What makes the researchers' results so exceptional is their unambiguity. Says Chad Orzel at Union College in New York, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say." He calls the research, "one of the best examples you'll see of a thought experiment made real." Litvinyuk agrees: "I see no holes in this."

As for the researchers themselves, enhancements to their experimental apparatus are underway to help them learn more. "We're working on a new measurement where we make the barrier thicker," Steinberg said. In addition, there's also the interesting question of whether or not that 0.61-millisecond trip occurs at a steady rate: "It will be very interesting to see if the atoms' speed is constant or not."

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