Professor Garnaut offered two main scenarios for cutting the greenhouse gas emissions which scientists believe are causing climate change.

Achieving a level of 450 parts carbon dioxide per million in the Earth's atmosphere would require Australia to reduce its emissions by a quarter by the year 2020 and 90 per cent by 2050.

Aiming for 550 parts per million, which Professor Garnaut says will be simpler to achieve although it does put the world at a greater risk of very dangerous climate change, would require Australian emissions cuts of 10 per cent by 2020 and 80 per cent by the middle of the century.

"There is a path to Australia being a low-emissions economy by the middle of the 21st century, consistent with continuing strong growth in material living standards," the report says.

The international climate change meeting in Denmark next year is a key element, and a realistic and binding target that includes developing nations like China is at the centre of Professor Garnaut's thinking.

"If things go well, very well, Copenhagen will be the end of one process, and the beginning of others that will lead, over time, to effective global mitigation at a level that reduces risks of dangerous kind to an extent that seems acceptable to most informed people," Professor Garnaut writes in the conclusion to his report.

But the failure of negotiations on a new global agreement to cut carbon emissions would be devastating, he warned.

"If things go badly, they could go very badly. When human society receives a large shock to its established patterns of life, the outcome is unpredictable in detail but generally problematic. Things fall apart."

The report accepts that there is a slim possibility scientific predictions about impending global warming are wrong, but says the safe option is to prepare for the most likely scenarios.

"That formulation allows the possibility that the views on climate change of the IPCC and the learned academies in all of the main countries of scientific achievement are wrong," the report states.

"There is a chance that they are wrong. Just a chance. But to heed instead the views of the minority of genuine sceptics in the relevant scientific communities would be to hide from reality. It would be imprudent beyond the normal limits of human irrationality. It is prudent to give the major weight to the mainstream science."