If European cities fail to address overtourism, protests will definitely spread, warns UNESCO official.

If European officials do not address the negative impact of mass tourism on residents' lives, protests in Spain will spread, UNESCO's Peter Debrine stated on "Squawk Box Asia" on Monday.

"The UNESCO senior project officer for sustainable tourism stated that the situation is becoming increasingly volatile as civil society tries to bring about change. However, it is crucial for elected officials to listen to the needs of their city's residents and respond accordingly."

As an illustration, he pointed to the prohibition of big cruise vessels in Venice, Italy, in 2021.

"On that issue, people gathered in the streets," he stated. "The Grand Canal is no longer being traversed by cruise ships."

Measures that work?

The structural and environmental integrity of Venice is preserved by having cruise ships dock farther from the city.

The North Adriatic Sea Port Authority predicts that Venice will receive 540,000 cruise ship passengers this year, a 9% increase from 2023.

Venice's 5-euro ($5.45) tourism tax on peak days has not been effective in thinning crowds, according to Euronews.

The popularity of Barcelona has long been a source of frustration for its residents, with the number of people who feel tourism benefits the city decreasing each year, while the number who feel it is detrimental continues to rise, according to a 2023 survey by the city council.

"Debrine stated that in Barcelona, they exceeded a limit, but there are answers."

'Quality over quantity' tourism

The interests of locals and travelers need to be rebalanced, said Debrine.

Prioritizing big-spending travelers over mass tourists is a strategy that a city facing an overload of tourists can adopt, according to him.

During the Covid-19 pandemic, destinations worldwide announced a push for fewer luxury travelers due to safety and staffing concerns, rather than many budget ones.

Travelers who exhibit high-quality behavior can also address the issue of tourists who misbehave.

Debrine told CNBC that it's not just the numbers of residents, but their behavior that's a concern, as Spaniards have long complained about tourists' excessive drinking, littering, brawling, and running naked through the streets.

Debrine said Amsterdam is exploring policies to change behaviors like those.

The Dutch capital launched a travel campaign in 2023, urging some visitors, specifically young, male British tourists, to avoid the city if their purpose is to purchase drugs or attend parties.

Calls for 'tourism degrowth'

Barcelona officials are being urged by civil groups to implement policies that promote "tourism degrowth," including higher taxes on tourism, restrictions on cruise ships, and limits on short-term housing rentals.

But travelers also play a role in curbing mass tourism, said Debrine.

He suggested the idea of "mirror cities" as a way to be more mindful in our travel choices.

"Tarragona, a city located south of Barcelona, boasts a stunning coastline and numerous cultural attractions, just like Barcelona."

Unlike Barcelona, he said, it "could benefit from less tourism."