By Alister Doyle, Environment Correspondent
OSLO (Reuters) - Venice may be less at risk than feared from rising sea levels because damaging storm surges are likely to get less frequent this century as a side-effect of climate change, an expert said on Thursday.
Shifts in storm patterns in the Adriatic Sea could be a local impact of global warming, and this could offset higher sea levels in a city whose St Mark's Square and other historic areas are often flooded.
"Higher sea levels will be counteracted by less severe storm surges," Alberto Troccoli, of the Pye Laboratory of the Commonwealth Scientific and Industrial Research Organization in Australia, told Reuters.
"There's a balancing effect" between impacts of climate change, he said of a study he led with colleagues in Italy and Britain and published in the journal Climatic Change this month.
"Tidal flooding events might not be exacerbated over the current century, with potentially beneficial consequences for the conservation of the city," they wrote of Venice, one of the cities most exposed to a rise in sea levels.
They projected that the number of storm surges northwards through the Adriatic that cause floods in Venice would decrease by about 30 percent by 2100 because storms would tend to shift further north in Europe.
Under certain wind conditions, the Adriatic acts as a funnel along which waters build up toward Venice at the northern end. Italy is building flood barriers known as MOSE, Italian for Moses, to protect the city.
The most severe combination of storms and high tides of recent decades happened during the Great Flood of 1966 that pushed up water levels in Venice by 194 cms (76.38 inches) above normal.
If world sea levels rise by just 17 cms (7 inches) by 2100, matching the rise in the 20th century, the study suggested that "the frequency of extreme tides in Venice might largely remain unaltered" since the number of storm surges would decline.
The U.N. panel of climate scientists has projected that human emissions of greenhouse gases could cause sea levels to rise by as much as 59 cms by 2100.
Venice faces other problems however, such as subsidence caused by the drawing of water from aquifers beneath the city, especially from the 1950s to the 1970s.
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(Editing by Michel Rose)