Addressing some 150,000 young Catholic pilgrims in Sydney, the pope said some 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 that protecting the environment was "of vital importance to humanity".
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.
"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.
"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."
In an earlier welcoming speech to Australian Prime Minister Kevin Rudd, the pope said: "It is appropriate to reflect upon the kind of world we are handing on to future generations".
He said there was a "need to protect the environment and to exercise responsible stewardship of the goods of the earth".
The pope said Australia was "making a serious commitment" to saving the environment. The Rudd government is in the throws of preparing a carbon trading system aimed at cutting greenhouse gases by 60 percent of 2000 levels by 2050.
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.
