One of the Government's key advisory bodies on climate change says Australia should triple its 2020 target for cutting carbon emissions.

A leaked report to the Government from the independent Climate Change Authority says Australia should aim to cut emissions by 15 per cent of 2000 levels by 2020.

That is up from the 5 per cent figure agreed to as a target by both sides of politics.

The report says the cuts should ramp up to 40 per cent cut by 2030, and 90 per cent by 2050.

The Gillard government set a 2050 target of 80 per cent.

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The report was obtained by the ABC's Radio National Breakfast, and is due to be handed to the Government in October.

The associate director of the Australian National University's Climate Law and Policy Centre, Andrew McIntosh, says a 15 per cent target is achievable.

"Economy-wide, an increase from 5 per cent to 15 per cent will result in only a marginal increase in the economic cost," he said.

"If you go to 40 per cent it will be significantly more, but not the sort of thing that's crushing, and we could do it without suffering a major loss in GDP growth and the other major macro-economic indicators."

The final recommendations and report from the Authority are due in April next year.

Mr McIntosh says if the world wants to aim to limit average temperature increases to just two degrees Celsius, governments will have to agree limit output of carbon to 300 billion tonnes over the next 90 years.

"Think of that as a big carbon cake," he said. "Every person on the earth should get an equal slice of that."

"If you adopt that approach, the 15 per cent by 2020 and 90 per cent by 2050 results in every person in Australia on average getting at least double what someone from the developing world gets.

"Assuming that all developing countries adopt a similar approach."

He says the Government must consider if it wants Australia to continue emitting much more carbon than fellow nations.

"How can you justify that the average Australian ends up with twice the allocation at least as the average Indian, or the average Chinese person?

"It's not enough and we need to go higher (than 15 per cent) if we want to reach that two degree target."

- Editor's note August 2, 2013: Earlier versions of this story incorrectly said the recommendation had come from the Climate Commission.