The Pope has failed to apologise or even tackle the issue of paedophile priests as he welcomes pilgrims to Sydney for World Youth Day celebrations.

Pope Benedict XVI instead used his speech, in front of 150,000 flag-wavers in Sydney Harbour, to throw his weight behind the urgency of tackling global warming, linking the world’s “insatiable hunger” for consumption to rising sea levels and droughts.

The 81-year-old pontiff dispensed with his cap as he stood on the top deck of a motor launch during his 45-minute “boat-a-cade” trip around the harbour. With the wind whipping back his hair and red cloak, he grinned broadly as he waved to the thousands who gathered to watch from parks and wharves on a bright and mild winter afternoon.

After receiving a traditional welcome by Aborigines with didgeridoos and eucalyptus leaves, the Pope donned gold reading glasses and told the cheering, chanting crowd that after his long journey from Europe he almost felt like “we have come to the end of the world”.

In welcoming the influx of pilgrims to Sydney for World Youth Day celebrations, the Pope delivered a strong message urging his young audience to realise life was not a series of experiences, but a search for truth, goodness and beauty. While he decried the sexual exploitation of people for “entertainment”, he did not tackle the controversy of abuse by priests, instead returning to a theme he vowed to raise during the visit - the impact of human behaviour on the climate and environment, and the “vital importance” of sustainable development.

“Perhaps reluctantly we come to acknowledge that there are also scars which mark the surface of our earth, erosion, deforestation, the squandering of the world’s mineral and ocean resources in order to fuel an insatiable consumption,” he told the crowd from more than 170 nations, many hoisting their national flags.

“Many of you come from island nations whose very existence is threatened by rising water levels; others from nations suffering the effect of devastating drought.

“When God is eclipsed our ability to recognise the natural order, purpose and the ‘good’ begins to wane. What was ostensibly promoted as human ingenuity soon manifests itself as folly, greed and selfish exploitation.”

Earlier, in a speech at Government House, the Pope said it was appropriate to “reflect upon the kind of world we are handing on to future generations”, and to protect the environment.

In an apparent reference to Canberra’s new plan to cut the carbon emissions blamed for global warming, he praised Australia’s “serious commitment to address its responsibility to care for the natural environment”.

The Pope earlier prayed at the chapel of Sister Mary MacKillop, the Australian nun who is likely to become the nation’s first saint. With fresh evidence being presented to the Vatican of her contribution to a second miracle – the final step for sainthood – the Pope is likely to boost her case.

Benedict had said she would become a saint, one sister told reporters after the visit. “He said: 'She will be canonised, we're waiting for the miracle'” said Sister Anne Derwin.

An apology to aborigines for mistreatment by whites, made earlier this year by Kevin Rudd , the Australian Prime Minister, won papal endorsement.

“Thanks to the Australian Government's courageous decision to acknowledge the injustices committed against the indigenous peoples in the past, concrete steps are now being taken to achieve reconciliation based on mutual respect,”' he said at the official welcome at Government House.

“This example of reconciliation offers hope to peoples all over the world who long to see their rights affirmed and their contribution to society acknowledged and promoted.”