SYDNEY, September 5, 2008 (AFP) - Australia's chief climate advisor Friday urged a 10 percent reduction in greenhouse gas emissions by 2020 but conceded this may not save the country's natural assets such as the Great Barrier Reef.

In an assessment of the targets required to manage the harmful effects of air pollution on climate, Professor Ross Garnaut said Australia should cut its emissions by 10 percent of 2000 levels by 2020 and by 80 percent by 2050.

This would be Australia's share of the burden if international agreement was reached to limit carbon emissions in the atmosphere to a concentration of no more than 550 parts per million molecules, Garnaut said.

He said while a global objective of 450 parts per million would suit Australia better, his review's targets and trajectories 'are the best available to us now' as emissions rise rapidly due to global economic growth.

Garnaut said natural assets at risk at the level he had recommended were the Great Barrier Reef, the world's largest coral ecosystem, and the Murray-Darling River system which irrigates Australia's biggest farming zone.

'I have to say the odds are not great for the Great Barrier Reef... if the world gets no further than 550 parts per million,' the esteemed economist and former diplomat told the National Press Club.

'There are lots of important environmental values in Australia that will be at risk at 550 parts per million. Where they will be without mitigation of climate change -- they are not at risk, there's certain death.'

Garnaut said he accepted that the only progress on the issue would be global and that if the international goal was set at 450 parts per million 'the odds are we might not get there.'

'So I say that 550 (ppm) is the realistic, immediate objective but that should not be the end of the game,' he said.

Prime Minister Kevin Rudd, elected in November in part on the strength of his campaign to combat climate change on the world's driest inhabited continent, has committed to a target of a 60 percent cut in emissions by 2050.

Rudd has long maintained he would use Garnaut's review, the final report of which is due in September, to guide his thinking on cuts to emissions in the short-term.

Garnaut's emissions trajectories are based on the 'per capita' allocation of emissions rights -- which he said provided the only possible basis for an international agreement including developing countries.

He said the 10 percent cut by 2010 was a 30 percent cut per capita and amounted to a 'major task of structural adjustment.'

He said modelling indicated that the cost to Australia of the 550ppm scenario would be 1.1 percent Gross Domestic Product by 2020.