The question of when Venice will sink is less about a single catastrophic date and more about a continuous, accelerating process of relative sea-level rise. This historic city, built on a dense collection of low-lying islands, has battled the Adriatic Sea for a thousand years. Its vulnerability results from the combination of rising global waters and the steady descent of the land itself. The future of Venice is a gradual submergence that scientists track in millimetres per year, threatening its architectural heritage.
The Dual Drivers of Vulnerability
Venice faces a double threat because its foundation is sinking while the sea around it is simultaneously rising. The sinking of the land, known as subsidence, is driven by natural geological forces and historical human activity. The city rests on layers of soft sediment that have naturally compacted over millennia, a process accelerated by the pressure of the city’s dense buildings.
The underlying tectonic situation also contributes, as the Adriatic plate is slowly subducting beneath the Apennine Mountains, causing the region to tilt and drop. This natural subsidence was amplified in the 20th century by the large-scale extraction of groundwater from aquifers beneath the city and the nearby industrial area of Marghera. Pumping water caused the deep sediment layers to compress and settle more rapidly, a practice halted in the 1970s to mitigate the effect.
The second, and now more dominant, factor is eustatic sea level rise, the overall increase in global ocean volumes due to climate change. This rise is caused primarily by the thermal expansion of seawater as it warms and the influx of meltwater from glaciers and ice sheets. While geological sinking has slowed since groundwater extraction stopped, the acceleration of global sea level rise means the city is losing elevation relative to the sea faster than before.
Quantifying the Current Rate of Submergence
Translating these forces into measurable data quantifies how quickly Venice is losing ground. The combined effect of land subsidence and sea level rise is known as relative sea-level rise, the true measure of the city’s vulnerability. Over the 20th century, the city sank and the sea rose by a cumulative total of approximately 240 millimetres.
Current scientific consensus indicates that the city continues to subside at an average rate of between 1 and 2 millimetres per year due to natural processes. When this is added to the accelerating rate of eustatic sea level rise, recent data shows the relative sea level is increasing at a mean rate of around 4 to 6 millimetres per year in the Venetian lagoon area. This combined rate means the city is sinking relative to the sea by about half a centimetre annually.
Scientists track these minute movements using sophisticated geodetic techniques, including specialized GPS networks and satellite-based radar interferometry (InSAR). These methods allow researchers to map the absolute vertical movement of the city and its surrounding islands with millimetre accuracy. This data confirms that the vulnerability is not uniform, with some parts of the surrounding lagoon subsiding at slightly different rates than the historic center.
The Impact of Extreme Weather and Acqua Alta
Beyond the slow, continuous submergence, the most immediate threat to Venice comes from acute flooding events known locally as acqua alta, or “high water.” These events occur when astronomical tides, low atmospheric pressure, and strong southerly winds push the Adriatic Sea into the shallow lagoon. The increased frequency and severity of acqua alta are directly linked to the already elevated sea level.
As the baseline water level rises, even minor storm surges are enough to breach the city’s defenses and flood low-lying areas. The frequency of high-water events has increased dramatically, causing disruption and damage to infrastructure. St. Mark’s Square, the city’s lowest point, is one of the first areas to flood, often becoming inundated when the tide reaches just 80 centimetres above the reference datum.
An extreme example occurred during the 2019 flood, when water levels peaked at 187 centimetres, the highest recorded since the 1966 flood. Such events accelerate the decay of the city’s foundations, as saltwater intrusion erodes the brickwork and weakens the structures. The increasing intensity of storm surges, a predicted outcome of climate change, adds a further layer of threat.
The MOSE System and Future Projections
The primary response to Venice’s predicament is the MOSE (Modulo Sperimentale Elettromeccanico) project, a massive system of mobile flood barriers. This system consists of 78 submerged gates installed across the three inlets connecting the Venetian lagoon to the Adriatic Sea. When an exceptionally high tide is forecast, compressed air is pumped into the hollow gates, causing them to rotate and rise to block the flow of water.
Since becoming operational, MOSE has successfully protected the city from numerous high tides, keeping St. Mark’s Square dry during events that would have previously caused severe flooding. However, the system’s long-term viability is dependent on future sea level rise scenarios. MOSE was originally designed to be effective for a sea level rise of up to 60 centimetres.
Future projections indicate that the system’s limits may be tested sooner than expected, with some pessimistic models for the late 21st century showing a sea level rise exceeding 100 centimetres. If the sea level rises by 50 centimetres, the barriers would need to be closed daily for prolonged periods. Such frequent and lengthy closures would severely disrupt the delicate lagoon ecosystem, affecting tidal exchange, water quality, and the port industry, turning MOSE into a permanent wall rather than a mobile defense.