"In most cases, the technical solutions exist and the know-how is available to help the greatest number," Hama Arba Diallo, the executive secretary of the UN Convention to Combat Desertification (UNCCD), said at the opening of the conference in the Tunisian capital.

However, he lamented that 10 years after the UN convention on desertification the world's leaders still had not learned to deal with the global advance of arid land.

Some 300 international experts have gathered for the three-day conference in north Africa, organized by UNESCO, as the "first demonstration" in the UN's year of focus on deserts and desertification, according to the UNESCO undersecretary general for science, Walter Erdelen.

Desertification threatens 1.2 billion people in 110 countries, according to the UN, while two billion - or a third of the world's population - live in arid and semi-arid regions.

With crop losses from the problem at an estimated 42 billion dollars (33 billion euros) a year, the advance of desert land causes famine, insecurity, social tension and mass migration from southern countries to the north, the organisation says.

The most endangered region is Africa, especially in the south and in the Sahel countries bordering the Sahara Desert, followed by central Asia and China, said UNESCO environment expert, Thomas Schaff.

"But desertification affects all the continents," he added, noting in the Americas, the deserts in Chile, the southwest of the United States and the north of Mexico.

"Europe too is not spared, especially in its southern region" - the south of Spain, Italy and Portugal, he said.

UNESCO presented the conference with a "teaching kit" in nine languages designed for teachers in countries dealing with advancing desert land.

Schaff also pointed to another constituency that needs to join the battle - tourists.

"The effort must also address the tourism sector which can bring financial benefit to the local people if it is managed in a responsible and adequate way," he said.

Tourists should be made aware of the life of the local population and they should be shown how "to economise water and share it," he said.

The conference also attracted a glamorous UNESCO goodwill ambassador promoting ecology: Italian actress Claudia Cardinale.

She called attention to the critical need for water in the ecological balance.

"Water must become an element of peace and exchange rather than of conflict," Cardinale said, pointing for example to the deforestation of the Amazon region of Latin America.

Man-made global warming is set to accelerate desertification - some experts say this is probably already the case - yet paradoxically it also threatens deserts themselves, placing unique wildlife and cultures in peril.

Drylands, areas with low rainfall and high evaporation that are on the fringes of the desert, account for 41 percent of Earth's land area, 43 percent of its cultivated surface.

The conference will come up with recommendations and proposals for the future of the world's drylands, which then will be presented to a summit of government leaders in October in Algeria.

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UN Convention to Combat Desertification