"Unfortunately, man-made phenomena have accelerated natural erosion to the point that we now have to take serious decisions to defend our coastline," Environment Minister Altero Matteoli told reporters this week.

"This is an economic as well as an environmental problem. If we lose beaches, we lose tourist resources, and if we lose land we lose agricultural potential."

Climate change - which many scientists say is caused by global warming - rapid coastal erosion and a fragile geological structure that means some areas are sinking, could combine to flood some 4,500 sq km (1,740 square miles) of Italian land, the ENEA report said.

Construction of a series of movable dams to shelter the Venice lagoon - long threatened by rising waters - is due to start next month, but the project, dubbed "Moses", is too costly to be copied in other areas at risk.

"Moses is great for Venice, but people in other areas have to accept that we can't build that kind of structure all over the place," said Paolo Ciani, head of environmental policy in the northeastern Friuli region.

"It seems like some areas will simply disappear."

LARGE INVESTMENTS NEEDED

Matteoli said efforts to shore up fragile beaches with sand taken from other parts of the coastline was only a temporary solution and large infrastructure investments were needed.

He said building dikes to protect certain areas was a possibility but no decisions had been made. Some land claimed from the sea in past generations should be allowed to return to the sea, he said.

"We human beings have to stop building where we were not meant to build," he added.

The ENEA report said the rise in sea levels was a global threat, but Italy was particularly fragile because geological activity was constantly shifting parts of its territory around and some parts were sinking.

Central Italy has been shaken by earth tremors several times in recent years, and some volcanoes in the south, such as Sicily's Mount Etna, are still active.

Higher temperatures are melting the world's great icecaps, raising sea levels and playing havoc with weather patterns. Torrential rain and parching drought greatly accelerate natural erosion, and building in vulnerable areas and man-made pollution often make the problem worse.

"In Italy's case, climate change does not create new risks but magnifies and worsens existing problems," the study said.

The largest loss of land would be in the south of the country, particularly along the Gulf of Taranto coast between the toe and the heel of Italy.