Guest post by Jim Steele,
Venice is composed of a hundred linked islands and sits in the center of the shallow Venice Lagoon. Island elevations are low and easily flooded during storms. The Great Flood of 1966 was the worst on record. Since then, Venice has been working to avert the next inevitable flood. But because its flood control projects were fraught with corruption and other difficulties, the government failed to prevent the 2019 flood. So, now experiencing its 2nd greatest flood, the mayor covered his political derriere and immediately blamed climate change. But that’s a tactic typical for politicians these days. In California, ex-governor Jerry Brown vetoed a bipartisan bill to secure the electrical grid. Shortly thereafter power-line sparks ignited some of California’s biggest wildfires, so of course Brown blamed climate change to disguise his policy failures.
As seen in Figure 1 above, sea level rise in the Venice Lagoon is modulated by how much water from the Adriatic Sea enters the lagoon via 3 inlets and how quickly it flushes out again. To prevent further flooding, Venice began designing the MOSE project, which would construct inflatable barriers that could be deployed when weather conditions predicted threatening inflows from the Adriatic Sea. High inflows from the Adriatic Sea are driven by the strength of the Sirocco and Bora winds that cause local sea level to surge.
Increasing Venice’s vulnerability, the land has been sinking. Dwarfing the 1.4 millimeters per year of estimated sea level rise, from 1930 to 1970 Venice sank at the rate of 2.3 millimeters per year, largely due to ground water extraction. After addressing that problem, the rate of sinking slowed, but Venice continues to sink at a rate of 1 millimeter per year. Furthermore, due to alterations of the lagoon’s basin, the amplitude of tides have been changing, which accounts for 20% of the rise in extreme sea level events. That tidal effect was largely due to alteration of flows through the inlets due to dredging for ship traffic, and alterations from the MOSE project.
As has become typical for every catastrophe, media outlets shamelessly and mindlessly blame climate change for Venice’s flooding. Others, like Dr. Marshall Shepherd writing for Forbes, attempted to appear more objective by acknowledging many factors had contributed to the flooding. But Shepherd’s real intent was to ensure that people would still blame climate change, at least a part, and that skeptics were biased by only focusing on Venice’s sinking land. But there is much more to the skeptics’ arguments. Furthermore Dr. Shepherd failed to provide any support for his climate change claims. But that is to be expected as the evidence provides very little support for Venice’s mayor or Shepherd.
If climate change had really played a significant role, then we would expect the flooding to be worse in 2019 when compared to the more “natural flooding” in 1966. But a comparison of floodwaters inundating Doge’s Palace (see below) suggests the flooding was slightly worse in 1966. Official measurements likewise determined flood levels in Venice Lagoon peaked at 74 inches, shy of the 1966 record of 76 inches. The climate change argument is weakened further when it is understood that the 1966 flood happened during a low tide, in contrast to the 2019 flood that happened during an extreme high tide. Furthermore, there is no correlation with global warming as the November 1966 flood happened when Venice experienced its coldest temperatures since 1924. Recent Venice temperatures are slightly less than the 1950s (Figure 2).
The Venice Lagoon is situated at the northernmost end of the Adriatic Sea. The Adriatic Sea is bordered by mountains on both its eastern and western boundaries. That geography creates a funnel effect. Each autumn the Sirocco Winds begin to intensify. These winds drive warm air from Africa northward, which in turn pushes Adriatic Sea water northward up the “funnel”. The end result is sea water piles up in front of the 3 inlets and begins flooding the shallow Venice Lagoon. Stronger winds drive greater flooding. And if the winds are strong enough, they temporarily prevent sea water from exiting the lagoons, causing sea level to rise even higher.
Naturally it would be natural to ask if climate change has caused an increasing trend in the Sirocco Winds. But there has been no trend.
We should also analyze how much has sea level rise affected Venice? It could certainly be argued that rising sea levels since 1900 contributed about 100 millimeters (4 inches) to the 1966 Great Flood as there was a steady rise in sea level between 1900 and 1970. But between 1970 and 2000 the Venezia (Venice) tide gauge shows sea level peaked around 7150 millimeters and then plateaued (Figure 3). Unfortunately, that tide gauge then moved to a new location designated Venezia II. There sea level began at a lower elevation and rose from 2001 to 2010, again plateauing just under 7150 millimeters (Figure 4).
Because various parts of Venice are sinking at different rates, it is difficult to know how much the new tide gauge location affected new estimates of sea level change. However, due to the uncertainty caused by Venice’s sinking land, researchers typically compare Venice sea level trends to neighboring Trieste in the far northeast corner of the Adriatic Sea. There the land appears to be more stable. Surprisingly, the Trieste sea level trend has been declining since 2000 (Figure 5). So, it would appear impossible to attribute sea level rise in the Adriatic Sea and climate change to the 2019 Venice flood.
However, there is another factor to consider. The winds in the northern Adriatic Sea cause sea levels to oscillate from east to west across the Adriatic’s northern basin. When sea levels fall around Trieste, they often surge around the Venice Lagoon. That sea level surge is associated with higher sea levels in the lagoon. Thus, at least in part, higher sea levels in the Venice Lagoon are driven by an ocean oscillation that creates higher sea level surges. And when that oscillation coincides with strong Sirocco Winds, a sinking Venice should expect more flooding.
In contrast, it’s unclear what effect is caused by global warming. Perhaps it’s negligible. Unfortunately for the public, that doesn’t stop media outlets from falsely hijacking the hardships in Venice to push a climate crisis. Alarmists continue to falsely suggest that every catastrophe has been partly driven by CO2 global warming. Sadly, as savvy propagandists know, if you tell a big enough lie often enough, people will start believing the lie.
Jim Steele is Director emeritus of San Francisco State’s Sierra Nevada Field Campus and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism