A general view shows people walking across the flooded St. Mark's Square, at St. Mark's Basilica on November 15, 2019, in Venice, two days after the city suffered its highest tide in 50 years.
Filippo Monteforte | AFP | Getty Images
For Venetians, water is a way of life. It surrounds the city, ebbs and flows, and at certain times of the year – usually in the fall – the tide swells, spills water into the narrow streets and swamps the large piazzas.
But Alberto Canestrelli, who was born and raised in Venice and spent two years working on flood forecasts for it, said the intense flood this week in the lagoon city was unlike anything he has seen in his life.
"I am 39 years old and have never seen this," said Canestrelli, who works as an associate professor of environmental engineering at the University of Florida. "I've never seen boats broken or gondolas stranded at the top of the bridge. It was shocking. These things don't usually happen. "
He is not the only native Venetian working in climate science who has seen the past week's events. With a mix of personal pain and professional horror.
With worldwide attention focusing on images of People who tread through deep deep water and gondolas rendered in the city streets, carried there by the tide, say scientists ̵
"Venice is like a canary in a coal mine," said Sergio Fagherazzi, a coastal geomorphologist at Boston University who also grew up in the northern Italian city. "It is possible to apply the same concept in the United States, and it is very relevant now for any low-lying area. "
Read more from NBC News
The most dangerous part of California's wildfires: Pollution
Tree planting campaigns are pop unlearned, but do they make a difference?
How to cut holiday waste and help the planet
As climate change causes sea levels in Venice – and across the planet – to regularly inch higher, scientists say catastrophic floods can become more severe and frequent, with some parts of the city being flooded weekday.
This week's flooding stemmed from unusually high tides exacerbated by the full-moon gravitational effects of strong 62 mph winds that whipped up a higher-than-expected storm surge. On Tuesday, the water levels reached 6 feet 2 inches – the highest in 53 years and only 2 inches shy of matching the 6 foot 4 inch record set in November 1966.
The government declared the state of emergency Wednesday, and the water level remained high for the rest of the week .
Some floods are common during the so-called astronomical high tide, when the Earth, moon and sun are aligned, and the gravitational attraction of these celestial bodies generates strong tidal forces. But rising sea levels make catastrophic events more frequent.
"During normal tides, only a few parts of Venice go underwater," Fagherazzi said. "Now, because the sea level is higher and higher, what used to be an event every 100 years, an event every 20 years."
Since the 1966 flood line, Venice's sea level has risen more than 5 inches. And according to a recent report by the UN Climate Panel, sea levels around the world could rise by 1 meter, or more than 3 feet, by the end of the century.
"That means the sea levels will be so high that the lagoon will flood the city regularly," said Marco Marani, professor of civil, environmental and architectural studies at the University of Padua in Italy. "What we refer to as tides will be more than just a nuisance. It will be potentially twice a day. Floods twice a day are not lively."
But Venice is also struggling with what researchers refer to as subsidence. In the main, the city is slowly sinking.
From the 1950s, Italy underwent a period of rapid industrial development, with the government pumping huge quantities of groundwater from beneath the lagoon city.
"They were not very sensitive to environmental problems, and they extracted a lot of fresh water from the aquifers," said Sonia Silvestri, a senior researcher at the University of Bologna who has done extensive work on sea level rise in Venice. "When you pump out water, you let the sediment go together. So what happens is that the land and the islands will lose altitude."
Groundwater pumping has stopped, but the city is still sinking at a rate of about 2 millimeters a year. – a relatively small effect, but one that has important consequences as the sea level continues to rise.
But Venice is not alone in confronting how to hold back the invading sea.
"You have to consider that most of the global population lives within 250 kilometers of the coast, so this is something that is relevant, not just for a place like Venice," Marani said. "With so many people living near the coast, this is a much broader issue. This is by no means a local problem."
Silvestri said she hopes the shocking images of a water-filled Venice that has circulated on social media this week will galvanize people and government to seize.
"All the pictures and movies that were posted were very scary," she said. "In 1966, it was difficult to follow what happened, but this time social media was a very powerful way of spreading information around."
In Venice, where residents are used to dealing with periodic flooding, this time feels different, according to Fagherazzi, whose brother owns a store in the city that was flooded with water.
"For the first time I saw them save," he said of the residents' attitude. "Before, they would be upset or annoyed at losing goods or damaging their house, but this time I saw more and more people were scared to death."
This week's events, which will probably cost hundreds of millions of euros in damages, also show that climate change is not a future problem, but one that affects people's lives now, said Georg Umgiesser, senior scientist at the Italian National Research Council's Institute for Marine science in Venice.
No feelings about sea level rise, but they can see what happens during a storm surge, Umgiesser says. "People can't believe you if you say sea levels are rising, but they can see that their house has flooded three times this year already."
Subscribe to CNBC on YouTube.