SYDNEY (AFP) - Pope Benedict XVI on Thursday warned Catholics of the perils of pop culture and pillaging the earth's resources after a rapturous welcome at the world's biggest Christian festival in Australia. Speaking against the spectacular backdrop of Sydney's famous harbour, the pontiff told hundreds of thousands of pilgrims in Australia's biggest and trendiest city that "something is amiss" in modern society. "Our world has grown weary of greed, exploitation and division, of the tedium of false idols and piecemeal responses, and the pain of false promises," the Pope said after a welcoming ceremony by Aborigines in tribal paint. Benedict told a vast sea of youths from around the world, gathered under a forest of national flags for World Youth Day, that humanity was squandering the earth's resources to satisfy its insatiable appetite for material goods. In one of his strongest-ever messages on the environment, the Pope spoke poetically of his 20-hour flight from Rome to Australia, saying the wondrous views from his plane evoked a profound sense of awe. But the 81-year-old pontiff told his youthful audience that the planet's problems were also easier to perceive from the sky. "Perhaps reluctantly, we come to acknowledge that there are 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 said. Earlier, shouts of "Viva, Papa" rang out over the harbour as a "boat-a-cade" of 13 vessels led by a water-spouting fire tug and flanked by bodyguards on jet skis glided past Sydney's iconic Opera House and Harbour Bridge en route to the Pope's World Youth Day debut. Benedict arrived in Sydney last Sunday, but took a four-day holiday before beginning his formal duties, which end with a papal mass expected to draw 500,000 people on Sunday. Ahead of his public appearance, he was welcomed by Governor-General Michael Jeffery, the representative of Australia's head of state, Britain's Queen Elizabeth II, and Prime Minister Kevin Rudd. In a brief speech at the ceremony at Sydney's Government House, the pontiff hailed Rudd's apology to Aborigines for past injustices in an historic address to parliament in February. "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," Benedict said. "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."  But there was some confusion over whether the pope would deliver an apology of his own - to Australian victims of sex abuse by Catholic clergymen, as the scandal cast a shadow over the festival.