Prince Charles and Camilla also had an audience with Pope Benedict XVI
Prince Charles has called for "inspired leadership" in tackling global warming to save the environment for future generations, during a speech in Italy.
The prince and the Duchess of Cornwall have also met Pope Benedict XVI at the Vatican, during a two-day tour.
Speaking earlier to lawmakers in Rome, he said he feared the current recession would be "nothing" compared with the horrors brought by global warming.
Prince Charles has attracted criticism for hiring a private jet for the trip.
The royal couple are spending two days in Italy before travelling to Germany.
The prince addressed politicians and business leaders at the Chamber of Deputies in the morning, ahead of the couple's audience with the Pope.
Speaking in Italian, Charles said that if the world did not win the battle to save the environment, "our grandchildren will never forgive us".
Chamber of Deputies President Gianfranco Fini praised the Prince of Wales for his commitment to the environmental cause.
Charles also made room for a reference to footballer David Beckham's spell with AC Milan in the speech.
Highlighting the inspiration Britain has taken from Italy since the Renaissance, he cited the record of England's football team under Italian manager Fabio Capello.
It "might be one of the most successful collaborations yet", suggested Prince Charles.
"To prove trade is a two-way relationship, I understand that one of our own footballers has been making quite a good impression in Milan this year," he added.
Following the meeting Prince Charles and Camilla - his second wife - were granted a private audience with the pontiff.
It was Charles's first audience at the Vatican since his divorce from the late Princess Diana.
They were greeted at the Vatican by an honour guard of the Swiss Guards and a Vatican nobleman.
The royal couple finished the visit by exchanging gifts. The Prince said he was "touched" after the Pope presented them with an honorary medal and drawing of the St Peter's Basilica.
Prince Charles and Diana, Princess of Wales, met Pope John Paul II in 1985
In return, they gave the Pope a set of plates, with paintings of plants from the Prince's Highgrove Estate.
Charles met Pope John Paul II in 1985 when he visited Rome with Diana, Princess of Wales.
Vatican protocol dictates that the prince had to meet the pontiff alone before being joined by the duchess and then other members of the Royal Household.
Camilla was required to wear black and a matching veil.
Prince Charles has attracted some criticism for hiring a private jet for the duration of the tour, which is mainly focused on environmental issues.
As well as making a speech on climate change, he will attend a meeting of Italian business leaders and a reception to promote the "slow food" movement of local sourcing and organic production.
Liberal Democrat transport spokesman Norman Baker MP said the prince's travel arrangements would emit so much carbon it would "weaken his case" for tackling climate change.
He said the couple should have travelled by rail, or at least by scheduled flights.
He said for longer - non-European - destinations it was "perfectly proper" people travel by air, but added: "Each us has a duty to minimise our carbon footprint".
A Clarence House spokesperson confirmed the couple had hired a private jet.
She said they had originally intended to fly by RAF plane, but on Friday it had become unserviceable outside the UK, leaving them with "no other viable option" at short notice.