A new study from researchers at the University of Vermont adds to the body of evidence suggesting that better mental health is right out your front door. [Schwartz, AJ, et al, “Visitors to urban greenspace have higher sentiment and lower negativity”, People and Nature, 2019; published by the British Ecological Society]

According to Christopher Danforth, one of the study’s co-authors,

Being in nature offers restorative benefits on dimensions not available for purchase in a store or downloadable on a screen.

That’s bad news for the wellness-industrial complex.

Noting “a growing interest in understanding the connection between mental health and exposure to biodiversity”, the researchers, funded by the National Science Foundation, turned to Twitter and geolocation technology to assess the association between park visits and changes in happiness, as expressed in tweets. In 2016, they collected all tweets (about 70,000 per day) geotagged with latitude and longitude in San Francisco, CA, for three months. San Francisco was selected because over 98% of its population live within walking distance of its top-ranked park system, which spans more than 220 sites and 3,400 acres. Parks were categorized based on vegetation cover in order to better understand how park type relates to the benefits of park visits. In other words, is bigger and greener better?

Using a complex process to collect and analyze Twitter user location and tweet content, the researchers compared user sentiment before, during, and after park visits. Lest you think “sentiment” too squishy a measure for science, you’ll be relieved to learn the researchers used the Hedonometer,

a word analysis tool that quantifies the sentiment of text based on the happiness values attributed to English words. The Hedonometer has been demonstrated to correlate with traditional survey metrics of subjective well-being at the city and state level, including Gallup’s well-being index and United Health Foundation’s America’s health ranking. The Hedonometer has also been deployed to analyse the discourse around climate change following hurricanes. [Citations omitted.]

How does this work?

The Hedonometer includes a sentiment dictionary for 10,022 of the most commonly used English words, merged from four distinct corpora . . . [and] performs favourably compared the other sentiment dictionaries . . . .The words were rated on a scale from 1 (least happy) to 9 (most happy). For example, “sunshine” has a score of 7.9 and “traffic” has a score of 3.3. [Citations omitted.]

To give context to their study, the authors catalogue some of the existing research on the mental health benefits of exposure to nature, including associations between

  • Subjective well-being and nearby natural areas,
  • Neighborhood greenness and lower levels of depression,
  • High levels of childhood exposure to greenspace and lower risk of developing psychiatric disorders,
  • Improved affect and cognition and walking through natural areas (as opposed to urban environments),
  • Walking in areas with greater biodiversity and subjective well-being,
  • Nature exposure and prosocial behavior,
  • At least 120 minutes of weekly nature exposure and enhanced self-reported health and well-being.

They note that “complementary theories from psychology and neurobiology suggest several mechanisms connecting nature exposure with mental state.” These include the “Biophilia hypothesis”, the idea that humans have an innate affinity for the natural environments like those in which we evolved, and “Attention Restoration Theory”, which predicts that time spent in nature gives us the opportunity to restore “directed attention capacity”, improving cognition. “Stress reduction theory” predicts a decrease in stress after contact with nature, “resulting in a variety of positive health outcomes”.

And the results are

In their research, the authors asked three questions.

What is the magnitude and duration of the change in sentiment (or, “happiness values”) from visiting urban parks?

Tweets posted within parks have a higher “happiness value” than tweets posted before or after park visits, and this elevated sentiment lasts from one to four hours. The mean change in sentiment for all parks was 0.229, which the authors compared to that of Christmas Day, 2016, the “happiest day” of that year, at least according to Twitter. They found that

tweets during visits to urban parks exhibited a similar increase in sentiment as the jump on Christmas Day for Twitter users as a whole.

What is the association of park type and vegetative cover with the change in sentiment from park visitation?

The bigger and greener the park, the greater the mean change in sentiment. Regional Parks have the highest mean change, followed by neighborhood parks and playgrounds (moderate mean change), then Plazas and Squares (lowest mean change).

What do word frequency patterns indicate about the mechanisms driving the change in sentiment from park visitation?

Park visits mean happy tweets.

Tweets in parks have higher sentiment than tweets prior to park visitation due to positive words with higher frequency, such as “beach”, “beautiful”, “festival”, “happy”, “young”, “fun”, and negative words with lower frequency, such as “not”, “no”, “don’t”, “can’t”, and “wait”. Of specific interest, negation words such as “not” and “don’t” fluctuate before and after park exposure but exhibit a marked drop (45% and 47%) in and around the park exposure. The word “beautiful” exhibits the opposite pattern, fluctuating around a baseline and then roughly doubling in frequency during park exposure. Finally, we examine the first person word “me” which has a neutral sentiment . . . . Use of “me” drops 38% from its mean use level during park visits. [Intra-article references omitted.]

That last stat leads me to infer that golf courses are no substitute for parks.

The authors note several limitations of their study: the difficulty of separating the roles of exercise and socialization from the contributions of nature to well-being and the inability to look at how age, gender, education levels, culture, socioeconomic status, and climate type may affect one’s response to nature.

On a policy level, they suggest that

Research further linking health with urban greenspace and biodiversity protection can help planners and public health officials build new strategies that support both goals. We suggest building or expanding parks near populations with limited access to greenspace and targeting funds towards the most effective types of parks for mental health benefits.

But, volcanoes

Despite the capacity for happy tweets, research tells us there are downsides to park visits. For example, you might want to think twice about making Yellowstone National Park your destination. Or, for that matter, any park in Colorado, Wyoming or Utah. According to a recent opinion piece in the New York Times, while it is “very, very, very unlikely” that the supervolcano beneath Yellowstone will erupt while you’re there, nevertheless, it has done exactly that three times over the past 2.1 million years, most recently 640,000 years ago.

First would come increasingly intense earthquakes, a sign that magma beneath Yellowstone was rushing toward the surface. The magma would burst through the ground in a titanic eruption, discharging the toxic innards of the earth to the air. It would continue for days, burying Yellowstone in lava within a 40-mile radius.

This would start a cascade of devastating events, which volcanologists estimate would bury large portions of Colorado, Wyoming and Utah in up to three feet toxic ash and, depending on the weather, dump a few inches on the Midwest and sprinkle the coasts. This supervolcano eruption would destroy crops, contaminate pastureland, and ruin power lines and transformers. Global temperatures might plummet due to blocked sunlight, rainfall would decline, perhaps killing off tropical forests, and farming could collapse, all making for what a 2015 European Science Foundation report on extreme geohazards called “the greatest catastrophe since the dawn of civilization”.


But there is some good news. Although Bryan Walsh, the author of this op-ed, cheerfully titled “A Giant Volcano Could End Human Life on Earth as We Know It”, thinks we pay insufficient attention to existential risks like supervolcanos, the probability of a supereruption at Yellowstone in any given year is 1 in 730,000.

There are 20 of these supervolcanoes on earth. Mr. Walsh doesn’t say where the others are, something you may want to look up before choosing which park you might visit to improve your mental health. Whatever you decide, if you feel the earth trembling, be sure to tweet about it.

Posted by Jann Bellamy

Jann J. Bellamy is a Florida attorney and lives in Tallahassee. She is one of the founders and Board members of the Society for Science-Based Medicine (SfSBM) dedicated to providing accurate information about CAM and advocating for state and federal laws that incorporate a science-based standard for all health care practitioners. She tracks state and federal bills that would allow pseudoscience in health care for the SfSBM website.  Her posts are archived here.