Sixty-cm submersion of Venice discovered thanks to Canaletto?s paintings.

Relative sea level (RSL) rise is a crucial issue for the safeguard of Venice and its historical buildings. The phenomenon over the last three centuries has been investigated by using a proxy of mean sea level: the height of the algae front on palaces. This indicator was accurately drawn by Canaletto and his pupils in their ‘photographic’ paintings made with an optical camera obscura. The positions of the fronts in the 18th Century and the present were compared. The RSL rise is due to a combination of natural and local anthropogenic factors which affected the land subsidence. An analysis was performed to establish the long-term trend and distinguish between natural and local man contributions. A prudent scenario for the future would suggest a rate between 1.9±0.4 mm yr-1 and 2.3±0.4 mm yr-1.