The world's natural resources are being squandered in the pursuit of "insatiable consumption," Pope Benedict XVI said Thursday in a speech urging followers to care more for the environment and reconnect with the principle of peace.

Benedict, speaking to more than 200,000 pilgrims gathered for the Roman Catholic church's youth festival, expanded on a theme that has led him to be dubbed "the green pope."

The crowd, massed on a disused wharf in Australia's largest city, regularly erupted in cheers that gave the event the feel of a sporting event.

"Some of you come from island nations whose very existence is threatened by rising water levels; others from nations suffering the effects of devastating drought," the pope said, referring to global warming.

He noted that during his more than 20-hour flight from Rome to Sydney he had a bird's eye view of a vast swath of the world that inspired awe and introspection.

"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 said.

Types of "poison" are afflicting the world's social environment, he said, such as substance abuse, along with the exaltation of violence and sexual degradation, for which he blamed television and the Internet.

"The concerns for nonviolence, sustainable development, justice and peace, and care for our environment are of vital importance for humanity," Benedict told the crowd.

Benedict's speech Thursday was his first major appearance at the festival and one of the set piece events of his 10-day trip.

The pontiff emerged from three days at a secluded vacation spot to engage in a busy round of events for World Youth Day, an inaccurately-named six-day festival held every few years that is designed to inspire a new generation of Roman Catholics.

He received a series of welcomes: an official one from Prime Minister Kevin Rudd, a traditional one from pelt-clad Aboriginal dancers, and finally a rapturous one from pilgrims who journeyed to Sydney from more than 160 countries to attend.

The pope toured Sydney's famous harbor by boat, cruising past the city's twin landmarks — the white-shelled opera house and the bridge nicknamed "the coathanger" because of its shape.

At the ceremony with Rudd, Benedict praised the Australian government for its "courageous" apology to the country's indigenous Aborigines for past injustices, saying it offered hope to all disadvantaged peoples who are seeking reconciliation.

Aborigines are an often-marginalized minority of about 450,000 in Australia's population of 21 million. They are the country's poorest group, with the highest rates of unemployment, illiteracy, incarceration and alcohol abuse, and a life expectancy 17 years shorter than other Australians.

In February, Rudd formally apologized to Aborigines as one of his first official acts after taking power, and made closing the gap between indigenous and non-indigenous Australians a priority of his government.

Benedict's comments about Aborigines were not the first time a pope has recognized indigenous peoples.

In 2001, John Paul II issued a formal apology to the indigenous peoples of Australia, New Zealand and the Pacific islands for injustices perpetrated by Catholic missionaries.

Crowds of people thronged Sydney streets Thursday evening, shutting down a large part of downtown during rush hour, as Benedict drove in the popemobile through the city.

Security was tight, with thousands of police deployed and dark-suited security guards walking alongside the pope's vehicle.