The mainstream scientific community believes much deeper cuts are needed more quickly and that yesterday's announcement all but locks Australia into a hot and rather bleak future.

The modest cuts for 2020 are seen as marking a fork in the road in Australia's approach to climate change, with the Government proceeding down one route and the research that underpins the need for emissions cuts heading down another.

"There's now a disconnect between what politicians are doing and what the science requires," Professor Barry Brook, director of the Research Institute for Climate Change and Sustainability at the University of Adelaide, said.

"Targets in that range [5-15pc] are politically realistic but not scientifically realistic.

"Just talking about emissions cuts at these small levels is avoiding the main point, which is that we're already over the limit.

"Let's have a bit of scientific honesty in the debate."

The Prime Minister, Kevin Rudd, attempted to claim the middle ground in his speech to the National Press Club yesterday, saying that people on the "extreme" ends of public debate would be unhappy with the Government's position.

Carbon cuts from 25-40pc on 1990 levels are required by 2020, along with an international agreement that ties major polluting nations to similar cutbacks, are needed to ward off the worst effects of climate change, according to the Government's Garnaut climate change review.

That report concluded that allowing the concentration of greenhouse gases in the atmosphere to rise to 550 parts per million, which is what the Government's cuts will mean if other nations make similar modest moves, would be disastrous for Australia.

It would mean the disappearance of the Great Barrier Reef "as we know it, with high impact to reef-based tourism", collapsing biodiversity in many districts, major changes to the tropics and Kakadu National Park and a cut of 20pc to food production along the Murray-Darling system.

Dr Barrie Pittock, a lead author of the Intergovernmental Panel on Climate Change's fourth assessment report, said the targets announced would fall short of the safer level of 450 parts per million.