While Al Gore is likely to gain converts to the anti-global-warming cause thanks to the Cannes screening of docu “An Inconvenient Truth,” former Locarno Film Festival topper Irene Bignardi is on the Croisette to combat a related scourge of the earth: desertification.Bignardi will announce today the launch of UN-sponsored Desert Nights: Tales From the Desert, a one-off film fest raising awareness of how the earth is increasingly drying up. Bignardi will be artistic topper of the fest, which has recruited Italo helmer Bernardo Bertolucci, Afghan helmer Siddiq Barmak (“Osama”), Tunisian critic and filmmaker Ferid Boughedir (“A Summer in La Goulette”) and Indian novelist Amitav Ghosh as board members. This year is the Intl. Year of Deserts and Desertification under the Rio de Janeiro United Nations Convention to Combat Desertification, a problem that threatens the livelihood of more than 1 billion people in more than 110 countries. Weeklong fest will feature 30-35 titles including seven international preems, a retro, docus, shorts and non-conventional format films, Bignardi said. All pics will be presented by their helmers. In Cannes, Bignardi will begin selecting titles for the fest from filmmakers and distributors. Fest will take place Dec. 1-7 in Rome’s Casa Del Cinema near the Via Veneto.