The official reason for the actor's presence in town is to appear at tonight's Italian premiere of Martin Scorsese's The Departed, one of the highlights of the first Rome Film Festival, which opened this weekend. But DiCaprio will also be appearing this afternoon outside the festival at the Tor della Monaca Theatre to present his short films Global Warning and Water Planet.

Each film is a brief piece narrated by Di Caprio over still images and slogans, offering a simple primer in environmental awareness. In Water Planet, the actor explains water shortage and urges the UN to instigate a global treaty on the right to water. In Global Warning, he highlights the depletion of natural fuel resources, attacks the oil industry, insisting, "We must demand a separation between oil and state", and urges viewers: "Get educated . . . join the fight to save this unique planet".

The films are roughly five minutes long and pose no threat to this year's big green cinema hit, Al Gore's An Inconvenient Truth, which has grossed over $23m in the US. However, the Leonardo DiCaprio Foundation, which he founded in 1998 to promote environmental awareness, will release a feature-length documentary, 11th Hour, early next year. Also next year, DiCaprio can be seen starring in Blood Diamond, a drama that attacks the trade in African 'conflict diamonds' . . . gems used to support dictatorships and fund wars.

The actor has long identified himself as an environmentalist, but found himself in an embarrassing position in 1999 when filming The Beach. The shoot, on the Thai island of Phi Phi Le, involved bulldozing sand and planting palm trees, and came under attack from local government and residents. Di Caprio said the production actually cleaned up the island, saying, "I don't want a bad reputation as somebody who endorses something hostile to the environment."

The following year, DiCaprio visited Washington to interview then president Bill Clinton for ABC television on global warming and ways of making the White House more eco-friendly. He recently announced his plans to turn Blackadore Caye, a 104-acre island off the coast of Belize, into an eco-friendly, self-sustaining holiday resort. The actor has commented: "Money is very important to me. I want to accumulate enough so that one day I can do something really great for other people, for the environment or for children."

DiCaprio's environmental website (leonardodicaprio. org) features sections on global warming and biodiversity, and criticises US president Bush's record on the environment. His activities highlight the fact that being green is increasingly a measure of a credibility in Hollywood. Brad Pitt recently sponsored a competition for energy-efficient housing to rebuild New Orleans. And last year, the makers of George Clooney film Syriana stressed that it was a 'climate-neutral' production, with 'green credits' equal to 2,040 tons of carbon dioxide bought to offset pollutants generated in making it.

You don't need to go to Rome to see DiCaprio's short films . . . they are on his website. But his Italian fans today may be more excited to see him in traditional Hollywood pursuits, blowing away low-lifes in The Departed.