The Pope is to make climate change one of his key concerns during his trip to Australia for World Youth Day.  The pontiff has said that politicians and scientists must respond to what he calls the "great ecological challenge" of global warming.  Australia's highest ranking Catholic, Cardinal George Pell, has welcomed the statement, but says he remains a climate-change skeptic.  From Sydney, Phil Mercer reports.

Picture released by the Vatican newspaper L'Osservatore Romano shows Pope Benedict XVI (L) and Monsignor Alfred Xuereb at the Kenthurst Study Centre, in Sydney, 14 Jul 2008

Pope Benedict says society has to meet the challenges posed by climate change and it has a responsibility to find "an ethical way to change our way of life."  He made the comments during his trip to World Youth Day in Australia.

The pontiff's views are at odds with those of Australia's most-senior Catholic leader, Sydney Catholic Archbishop George Pell. He is a climate change skeptic, but insists his attitudes are not incompatible with the Pope's decision to set the issue as a theme for his visit to Australia.

"I'm well aware that, over the hundreds of years, there have been great changes in the climates," he said.  "And, whether we are going through one of those cha nges or whether we are contributing to that, I don't know.  And, whether we're heading slowly toward an ice age, or whether we're heading towards significant warming, I don't know.  But I'm pretty certain if you look at the figures, the temperature dropped, worldwide, in the last 12 months."

Some climate change proponents in Australia believe that the Pope's opinions on the environment do not carry much practical relevance.

Stephen Douglas, from the Australian National University, says Benedict's views on climate change should not be taken too seriously.

"There's a growing body of what you could call symbolic policy;  so these are things that are somewhat unfortunately referred to as 'motherhood statements.'  So they're essentially warm and fuzzy statements about how we should be seeing things, how we should be caring for creation in Christian terms; but what we're not seeing is meaningful operational policy," said Douglas.  "You're not seeing a restructure of the Catholic Church, or any other religious organizations, that would bring them up to speed with how they need to operate to address things like climate change."

The Vatican has declared itself a carbon neutral state, although critics argue that its environmental credentials are compromised by fuel consumption an airline for pilgrims that it operates.

The Pope continues to rest in a Catholic retreat outside Sydney ahead of his official World Youth Day commitments that start with a trip across Sydney Harbor on Thursday.

The highlight of his 10-day visit to Australia will be a giant papal mass in Sydney on Sunday in front of an estimated 250,000 pilgrims.