Sydney, Australia —- Pope Benedict XVI said Thursday mankind's "insatiable consumption" has scarred the Earth and squandered its resources, telling followers that taking care of the planet is vital to humanity.

The 81-year-old pontiff gave his first major speech for Roman Catholicism's World Youth Day before adoring crowds who had traveled from 168 countries to see him in Australia's largest city.

As the sun set in the mild chill of the Australian winter, Benedict struck a theme that has earned him a reputation as the "green pope."

"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.

The crowd, some 200,000 young pilgrims gathered on a disused wharf on Sydney's harbor, waved their national flags and frequently applauded.

"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, who arrived Sunday on the longest pilgrimage of his just-over three-year-old papacy, today will meet with non-Catholics and eat lunch with 12 young Catholics. He is to fly back to Rome on Monday.