Sydney - Despite Pope Benedict XVI putting global warming on the agenda for his visit to Sydney for an international youth gathering, the leader of Australia's 5 million Catholics came out Monday as a climate change sceptic.

Speaking to reporters Sunday during his 23-hour flight from Rome, the pontiff said, "We have to give impulse to rediscovering our responsibility and to finding an ethical way to change our way of life."

"I have no intention of entering into technical or political questions, but the church has to give fundamental impulses in order to help politics tackle these challenges," said the Holy Father, who, after his arrival, was resting in Sydney before beginning his official duties Thursday.

The pope's call for Catholics to help heal the planet was rebuffed by Cardinal George Pell, who, as archbishop of Sydney, is his host.

"I'm a bit of a sceptic about the claim that human activity is likely to produce a manmade catastrophe," Pell said. "It's very difficult to predict what will happen tomorrow. It's even more difficult when you're trying to predict what will happen in five or 10 or 15 or 20 or 100 years."

The Oxford-educated Pell, a close friend of the pope, identified a low birth rate and declining religious observances as the real challenges in Australia.

"No Western country is producing enough babies to keep the population stable," Pell said. He also blamed "ruthless commercial forces" for driving people away from God.

Pell was criticized by top scientist Graeme Pearman, a former head of the government's CSIRO climate research division.

With 225,000 young Catholics from 170 countries gathering in Sydney this week for the World Youth Day celebrations, Pearman said Pell's comments might be seen as undermining the pope's call for action on global warming.

He welcomed the pope's acceptance that the church had a "responsibility for reacting to a threat to the Earth." (dpa)