A project using more than 100 paintings by the Venetian painter Canaletto has shown precisely how much the sea has risen around the city in the 200 years since his death.
Canaletto's realistic paintings of the city include features such as tide marks on buildings beside canals. The paintings are as accurate as photographs because Canaletto used a camera obscura, a device using a lens to project images on to sketchpads or canvases, to produce them.
His works offer a record of where the high tide marks lay during his life, from 1697 to 1768. Those show that the sea has since risen by 80cm (31in) – an average of 2.8mm (just over an inch) every year.
The figures agree closely with those produced over a shorter time series, from 1872, when tidal readings were first taken. Those suggest that the sea has risen on average by 2.4mm annually.
The paintings "fill gaps in our knowledge", said Dr Dario Camuffo, a climatologist at the Institute of Atmospheric Science and Climate in Padua. "Canaletto is absolutely reliable," he told New Scientist magazine.
Venice lies in a lagoon in the Adriatic Sea, which leaves it at the mercy of rising sea levels – a problem made worse by the fact that the city itself suffers from subsidence. The findings are being used to help to decide what measures to take against flooding, such as in St Mark's Square, which is under water 50 times a year.
Dr Camuffo began comparing the pictures with the reality earlier this year, and produced his results separately from the tidal measurements that began in 1872. "I was surprised that these two kinds of data fitted so well," said Dr Camuffo, who studied more than 100 Canaletto paintings in his research. "Knowing the earlier rate could help to predict sea-level change."
Climatologists noted, though, that the predictions, and the findings, would only be applicable to sea-level rises locally, rather than globally.Reuse content