Rome- Pope Benedict XVI headed off to Australia on Saturday for a 10-day visit on the occasion of the 23rd annual Catholic World Youth Day, with the environment set to be a major theme.

Politicians have to "be in the position to provide answers to ecological challenges," the pontiff said, in reference to the results of the recent summit of Group of Eight (G8) rich nations in Japan.

Ecological issues are to pay a central role at the Youth Day celebrations in Sydney, Benedict said, "because we have a stewardship over creation."

"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."

Also the issue of sexual abuse by priests is to play an important role in Australia, the pope said, adding that "being a priest is inconsistent with sexual abuse. This behaviour contradicts holiness."

Following a 20-hour flight from Rome - including a brief refuelling stop in Australia's remote northern city of Darwin - the papal plane will land at a Sydney air force base.

His ninth trip abroad since his papal election in 2005, Benedict is to begin his public engagements in earnest on July 17. The occasion is to culminate with Sunday Mass on July 20 before tens of thousands expected to attend the Youth Day celebrations, dubbed the "Catholic Woodstock," a reference to the famous 1969 rock concert in the United States that attracted a massive turnout. (dpa)