"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 cheering crowd.

The 81-year-old pope appeared in good form as he started the official part of his trip after three days of rest. He chatted with young people on the ferry and stepped off sprightly to receive a bear hug welcome by an Aboriginal on the dock.

He told the young people, some of whom had come from island nations threatened by rising sea levels or drought-hit nations such as Australia, that protecting the environment was "of vital importance to humanity".

The pope recalled how his long flight from Rome last weekend, he marvelled at 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.

"It is as though one catches glimpses of the Genesis creation story -- light and darkness, the sun and the moon, the waters, the earth and living creatures," he said.

In a welcoming speech to Prime Minister Kevin Rudd on Thursday morning, the pope said: "It is appropriate to reflect upon the kind of world we are handing on to future generations".

Australia, one of the world's highest per capita greenhouse emitters due to coal-fired power stations, is in the grip of the worst drought in 100 years and is struggling to save its major river system that feeds the nation's food belt.

APOLOGY TO ABORIGINES PRAISED

The pope 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.

Rudd officially apologised to Aborigines in February.

Australia's 460,000 Aborigines make up about 2 percent 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 pope thanked Aborigines for a traditional welcoming ceremony and 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...," he said.

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 lives.

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".

He warned young pilgrims "do not be fooled by those who see you as just another consumer". (Additional reporting by Michael Perry; Editing by Alex Richardson)