The city of Venice is being held in limbo by two conflicting forces of nature, both consequences of climate change, writes Steve Farrar.
An increase in the number of surges caused by higher sea levels in the Adriatic has been balanced out by a decrease in the frequency of the severe storms that cause the flooding in the first place, a study has found.
As a result, the Italian city has not suffered as much flood damage as might be expected.
The research, published in the International Journal of Climatology , illustrates the complexity of climate change.
Isabel Trigo and Trevor Davies, dean of the school of environmental sciences at the University of East Anglia, reached their conclusions after examining 40 years of meteorological records from the region.
Individual severe floods are triggered by storms in the western Mediterranean whose strong winds pile up water in the northern Adriatic while lowering the atmospheric pressure, causing sea levels to surge suddenly.
The fact that underlying sea levels have been gradually rising as a result of global warming, compounded by subsidence of the land around Venice, has meant Venetians find themselves knee-deep in water more often today than they did at the start of the 20th century.
This is because the higher seas slop back and forth in the Adriatic in the wake of the disturbance caused by storms, leading to secondary surges.
Nevertheless, the records show that the amount of flooding in the city has plateaued since 1960.
Professor Davies said this was because the storms responsible for the most severe surges were becoming less frequent.
"The weakening of the storms is a local response to global warming and shows how careful we have to be when trying to identify the consequences of such warming," he said.
"If the strongest Mediterranean storms had not weakened, Venice would have suffered even more damage than it has already."