(CNN) — Reading this on a smartphone? You might want to look away now -- especially if you're on a roller coaster.

Because, says theme park expert Stefan Zwanzger, that device in your hand is destroying the very thing you're supposed to be enjoying. And he claims to have the photos to prove it.

Zwanzger, AKA The Theme Park Guy , has spent the past decade exploring parks in more than 150 countries.

On a recent return journey to locations he visited in 2010 in the southern Chinese city of Shenzhen, he was struck by how once joyful places were now filled with unhappy-looking people unable to stop staring at their screens.

Photos taken in 2017 , when compared with similar shots from seven years earlier reveal, he says, the extent to which phones are causing the "zombification of the human spirit."

Glum faces

Zwangzer's 2010 images show smiles. In 2017 it's dull faces transfixed by devices. Courtesy Stefan Zwanzger

If smartphones are spoiling places where people are supposed to unplug themselves and embrace the fun, he argues, then they've already spoiled everything else.

"It's a warning," he tells CNN. "When you see people holding phones in front of their face even in theme parks, you can be sure they also do it on public transport, at dinner with their family, in bed, on the toilet and who knows maybe in the shower, too.

"A theme park is supposed to distract you from real life, grab your attention, enchant you, accelerate you, splash you... If you still can't let go of that thing, not even then, that probably means you use it for 10 or 12 hours per day."

Zwanzger's 2010 images show smiling park visitors enjoying the sights and interacting with each other. In 2017, glum faces are almost uniformly transfixed by their devices.

"The teenagers should be looking around, being curious. The boys and girls are supposed to be checking each other out, like they always did, but they're completely hypnotized," he says.

Depressing social implications

"It's not just Mainland China. There's a tendency to see this a little more in developed economies in Asia, because that part of the world has always been more techie and gadget-loving. But it really isn't an Asian phenomenon only, you also see it in Europe, America and elsewhere.

"Not so much in Africa. There are some really amazing places, such as small amusement parks in Ethiopia, where people are present and in a really good mood and you still feel like you're in the photos from 2010."

The images will do little to ease concerns over the impact our devices are having on some aspects of modern life -- from sleep patterns to child development

Zwanzger, who claims no regrets about being smartphone-free for more than a year, says these scenes have depressing social implications for today's kids.

Twenge says the years since 2010 have been marked by statistical rises in teen depression and suicide rates plus a decline in levels of happiness and life satisfaction, something possibly reflected in Zwanzger's photos.

"Obviously it's not researched, but it's a very interesting piece of anecdotal evidence, because it does do one thing that scientific studies try to do, which is control variables," she says. "It's the same situation, two different years."

'Sweet spot'

Twenge advocates limited use of smartphones. Youngsters without access to devices can be unhappy, she says, as can those overusing.

"Don't have it in your hand the entire time, limit your use to a few hours a day," she says. "That's the sweet spot for happiness, at least in the data on teens."

Zwanzger says theme parks should seize an opportunity to offer people an escape from an increasingly connected world.

"They should become offline parks where you hand over your phone and you and your family are forced to deal with each other and enjoy the here and now," he says. "It would be like a dive into the past, something special. Disneyland, too, offers visitors an escape into the past, with a romanticized American Main Street, German castles, car-free life... but in the end that's just buildings."

If theme parks were to focus now on virtual reality, augmented reality and media based attractions only, he adds, they could risk their own futures.