World leaders who descended on the United Nations annual climate summit in Brazil on Thursday only needed to look out their airplane windows to sense the unfathomable stakes.

Surrounding the coastal city of Belém is an emerald green carpet festooned with winding rivers.

But the view also reveals barren plains: Some 17 per cent of the Amazon's forest cover has vanished in the past 50 years, swallowed up for farmland, logging and mining.

Known as the "lungs of the world" for its capacity to absorb vast quantities of carbon dioxide, a greenhouse gas that warms the planet, the biodiverse Amazon rainforest has been choked by wildfires and cleared by cattle ranching.

Here on the edge of the world's largest remaining rainforest, Brazilian President Luiz Inácio Lula da Silva hopes to convince

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