Pope Benedict today called for the earth to be protected for future generations, saying the world had been "scarred" with erosion and deforestation and its oceans squandered to fuel an insatiable consumption.
Addressing some 150,000 young Catholic pilgrims in Sydney, the pope said that protecting the environment was "of vital importance to humanity".
Some attending the event had come from island homes whose very existence was threatened by rising sea levels and others from drought-hit nations such as Australia, the pontiff told the World Youth Day gathering on the shores of Sydney Harbour.
On his flight from Rome to Sydney, the pope said he witnessed the sparkle of the Mediterranean, the grandeur of the north Africa desert, the lushness of Asia's forests and the vastness of the Pacific Ocean.
"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 said.
The pope said the "social world" also had scars, highlighting alcohol and drug abuse, violence and sexual degradation. He questioned how the media's portrayal of violence and sexual exploitation can be considered "entertainment".
The Catholic Church hopes World Youth Day, the brainchild of the late Pope John Paul II, will revitalise the world's young Catholics at a time when the cult of the individual and consumerism has become big distractions in their daily lives.
The pontiff also praised Australia for apologising for past injustices to Aborigines, saying it was a courageous move to repair race relations and offered hope to the rest of the world.
Australian Prime Minister Kevin Rudd officially apologised to Aborigines in February.
Pope Benedict acknowledged Aborigines are the first people of Australia. "I am deeply moved to stand on your land, knowing the suffering and injustices it has borne, but aware too of the healing and hope that are now at work."
Australia's 460,000 Aborigines make up about 2 per cent of the country's 21 million population and have consistently higher rates of unemployment, substance abuse and domestic violence, as well as a life expectancy 17 years less than other Australians.
The leader of the Catholic Church has said he will apologise to Australian victims of sexual abuse in the church during his visit.