More from Australian idiot Ross Garnaut

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"If a sombre assessment of the risks changes what's possible in an agreement, I will be delighted," Professor Garnaut said, "but 550 would be a huge step forward."

He dismissed the so-called sceptics, who argue man-made climate change is not real or dangerous, or that temperatures are falling, not rising. "It's very understandable. You get crank religious movements that reinterpret the evidence around them whenever humanity faces a great challenge."