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Canaletto rides to Venice's rescue
( 2001-10-18 10:19 ) (7 )

More than 230 years after he died, the great Venetian painter Canaletto is helping climate scientists in their study of global warming, one of the greatest threats to his beloved city.

Experts are using highly accurate paintings made by Canaletto in the 18th century to draw up a detailed picture of sea levels which are rising as a result of higher temperatures, the British weekly New Scientist reports in this Saturday's issue.

Needing a quick and easy way to turn out his paintings, Canaletto used a version of the pinhole camera, the camera obscura, to project the outlines of the cityscape onto his canvas.

He then traced the outlines of the buildings and canals on the canvas, and painted them in.

A team led by Dario Camuffo of the Institute of Atmospheric Science and Climate in Padua, Italy, has find these "photographic" paintings to be so precise that they can be used as a source of data.

The canvases notably show a line of brownish algae growing on the sides of buildings, which marked the average high-tide level at the time.

Comparing this line with the modern-day level, Camuffo found that the relative sea level in Venice has risen by up to 80 centimetres (32 inches) since Canaletto's day.

The finding is an invaluable contribution to the fight to save Venice from the rising waves.

Global warming, in which the sea levels rise through the thermal expansion of the oceans, is not the only cause of Venice's problems.

The city, built on a lagoon in the Adriatic Sea, is subsiding and the digging of channels in the last century to let big ships enter its port also enabled high tides and sea surges to flood the city, helping to rot the porous limestone buildings.