(CNN) -- Pope Benedict XVI recalled the natural beauty he observed during his 20-hour flight to Sydney, saying he felt "a profound sense of awe," and denounced "insatiable consumption" as a threat to the world's environment.
Pope Benedict XVI is joined by young people in a flotilla of vessels at Sydney Harbour on Thursday.
The pope made his first major appearance on his Australia tour Thursday before an estimated crowd of 150,000 people at World Youth Day.
The event is believed to be the world's largest Christian gathering and dubbed "the Catholic Woodstock."
He delivered his homily in several languages to people representing 70 countries, lamenting "erosion, deforestation, the squandering of the world's mineral and ocean resources in order to fuel an insatiable consumption."
"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. God's wondrous creation is sometimes experienced as almost hostile to its stewards, even something dangerous. How can what is 'good' appear so threatening?"
Earlier, the pope held a private early-morning mass at St. Mary's Cathedral and toured Sydney Harbour on the city's most luxurious cruise ship. Watch the Harbour serve as a "cathedral aisle" »
He was greeted at World Youth Day by a traditional aboriginal welcoming ceremony. In his address, the pope thanked aboriginal elders and noted the decades of hardship native people faced throughout Australia's history.
"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, rightly bringing pride to all Australian citizens," the pope said. "To the young indigenous -- aboriginal and Torres Strait Islanders -- and the Tokelauans, I express my thanks for your stirring welcome."
At a meeting with top government officials, including Australian Prime Minister Kevin Rudd, the pope praised his official apology in February on behalf of the nation to its aboriginal people.
Thursday's events were the pope's first public appearances since arriving in Australia on Sunday and spending several days resting. Watch the pope visit Government House »