VENICE, Italy — The historic lagoon city of Venice exists on the edge of a double threat: As it sinks, the seas rise.

That reality became more stark this week when Venice was hit with its worst flood in over 50 years, caused by a nearly 1.9 meter (6-foot) tide that sent waist-high water flowing through St. Mark’s Square, cast the city’s world-famous gondolas onto walkways, and threatened its medieval, Baroque and Renaissance art and architecture.

Damage to the City of Canals from the second-worst flood ever recorded was put at hundreds of millions of euros (dollars).

While the latest round of flooding has been attributed mostly to a combination of high tides from a full moon and high winds pushing water from the shallow Adriatic Sea into Venice, climate scientists note that exceptional tides — those over 1.4 meters — have become much more frequent in the past two decades.

Of the 20 exceptional tides recorded from 1936 through Tuesday’s, more than half have occurred since 2000.

“It is a long-term issue. It is not the issue of one flood, we restore, and we go back to normal,” Rossler said.

Climate scientist Stefan Rahmstorf of the University of Potsdam estimates that one-third of Venice’s increasing vulnerability is due to global warming, which has raised the sea level.

“The rest is mostly man-made,” he said.

The 1,600-year-old city is built on uncompacted settlement, which is sinking. Venice’s Tide Office said the net effect of the sinking and the rising sea has been a 30-centimeter (12-inch) drop since record-keeping began in 1873. About 10 to 11 centimeters of that took place since the last big flood, in 1966.

Venice is being monitored for inclusion on a list of World Heritage sites in danger, which serves as a call to action to the international community.

Other problems threatening the city include large numbers of tourists, which put stress on a city where even something as simple of trash collection must be done by boat, and the passage of cruise ships through St. Mark’s Basin.

The vessels release pollution, displace water into the city and carry other safety risks. Over the summer a cruise ship crashed into a boat and a dock.

The historic flooding only underscores the urgency to resolve Venice’s problems.