World leaders have kicked off a three-day UN summit in Rio, where they are set to back a blueprint on tackling poverty and protecting the environment.
Prime Minister Julia Gillard arrived in Rio to a military honour guard before travelling in a six-car motorcade accompanied by motorcycle police amid a heavy security presence.
Yet other Western leaders decided not to show, including US President Barack Obama, British Prime Minister David Cameron and Angela Merkel of Germany, CNN reported.
UN chief Ban Ki-moon formally opened the Rio+20 summit on sustainable development, which brings together 191 UN members, including 86 presidents and heads of government.
The high-profile event comes 20 years after Rio's First Earth Summit when nations vowed to roll back climate change, desertification and species loss.
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The summit was launched to a three-minute movie, Welcome to the Anthropocene, which gave a visual trip through the dramatic changes in the environment since the Industrial Revolution.
The Anthropocene is the name given by many scientists for a new era in Earth's history. It derives from Greek words to indicate the era of humans.
Summit participants then heard a moving appeal by Brittany Trilford, a 17-year-old student from New Zealand, challenging leaders to lay the foundation for a more sustainable world.
"I stand here with fire in my heart. I'm confused and angry at the state of the world. We are here to solve the problems that we have caused as a collective, to ensure that we have a future," Trilford, winner of the "Date with History" youth video speech contest, said.
"I am here to fight for my future ... I would like to end by asking you to consider why you are here and what you can do here. I would like you to ask yourselves: Are you here to save face? Or are you here to save us?"
Some 191 speakers are expected to take the floor until Friday when the summit leaders are to give their seal of approval to a 53-page draft document agreed by negotiators on Tuesday.
As the summit got under way, eight multilateral development banks announced they would set aside $US175 billion to finance sustainable transport systems over the next decade.
The pledge was made jointly by the World Bank, Asian Development Bank, African Development Bank, Inter-American Development Bank, CAF-Development Bank of Latin America, European Bank for Reconstruction and Development, European Investment Bank and Islamic Development Bank.
Transport is one of the fastest-growing source of greenhouse gases, driven especially by urban growth in giant emerging economies.
Around a billion people are likely to move to cities over the next 20 years, which means traffic congestion, air pollution and road accidents will become major urban challenges.
