Benedict's plane landed in the northern city of Darwin in the morning after a more than 20-hour flight from the Vatican. His plane was making a brief refueling stop before flying to Sydney, where he will lead celebrations at the World Youth Day festival.
Benedict, 81, will spend three days resting at a retreat in Sydney before taking part in the festival, including a vigil service with thousands of young people and an outdoor Mass.
The pope met with reporters aboard his plane during the flight, and was asked about climate change following discussions on the environment during this month's Group of Eight summit in Japan.
There is a need to "wake up consciences," Benedict responded. "We have to give impulse to rediscovering our responsibility and to finding an ethical way to change our way of life."
Benedict said politicians and experts must be "capable of responding to the great ecological challenge and to be up to the task of this challenge."
"We have our responsibilities toward creation," Benedict said, stressing, however, that he had no intention of weighing in on technical or political questions swirling around climate change.
Benedict said he would also address the problem of sexual abuse by Catholic clergy. He reiterated his view that sexual abuse is "incompatible with the behavior" required of priests.
At the start of his U.S. pilgrimage, Benedict had said he was "deeply ashamed" of the abuse scandal and pledged to work to make sure pedophiles do not become priests.
Benedict said that during the 10-day visit to Australia he would work for "healing and reconciliation with the victims" of sexual abuse by Catholic clergy there "just as I did in the United States" earlier this year.
Clergy abuse support groups in Australia have demanded that Benedict apologize during his visit for the abuse they suffered. The exact number of victims of clergy abuse in Australia is not known, though activists say they number in thousands.
Benedict acknowledged that the Church in the West was "in crisis" but insisted it was not in decline. "I am an optimist" about its future, he said.
The Australia pilgrimage is the longest in his three-year-old papacy and will test the pontiff's stamina.
Although aides say the pope is in fine health, the Vatican appeared to be taking no chances to ensure Benedict is fit for World Youth Day, canceling a weekly public audience this past Wednesday and most other meetings to give him as much rest as possible.
After he succeeded John Paul three years ago, Benedict said he doubted he would make many long trips. But invitations keep coming in from world leaders and officials of his global 1-billion member flock.
He visited Brazil last year, made a pilgrimage to the United States in April and will travel to France in September.
Benedict will be greeted at Sydney Harbor Thursday by a group of Aborigines and other young people from the Pacific Basin and deliver what is expected to be an important address. In 2001, John Paul issued a formal apology to the indigenous peoples of Australia, New Zealand and the Pacific islands for injustices perpetrated by Catholic missionaries.
Australia's senior Catholic leader, Cardinal George Pell has been accused of badly handling a sexual abuse claim and this week agreed to reopen investigations into the 25-year-old case.