Australia said Monday it plans to cut its greenhouse gas emissions by as little as five per cent by 2020 — a reduction that critics say undermines international efforts to reach an effective global pact next year to avert dangerous climate change.

Prime Minister Kevin Rudd said the interim plan would not affect his commitment to slash the carbon emissions that are blamed for global warming by 60 per cent from 2000 levels by 2050.

But Rudd was rebuked by an environmental activist while announcing his 2020 targets at the National Press Club in the capital Canberra on Monday.

"No, that's not good enough," a woman in the audience yelled before she was restrained by officials.

Protesters calling for deeper cuts demonstrated outside Rudd's office in the east coast city of Brisbane and Climate Change Minister Penny Wong's office in the southern city of Adelaide.

Environmental groups have been lobbying for months for a 2020 reduction target to be set at a minimum of 25 per cent, as recommended for developed countries by the United Nation's expert Intergovernmental Panel on Climate Change. Rudd's plan calls for an interim reduction range of only five per cent to 15 per cent.

"The weak targets announced today will damage Australia's international reputation and hold back progress toward an effective international agreement," Australian Conservation Foundation executive director Don Henry said in a statement.

Frank Jotzo, an Australian National University economist who specializes in climate change policy, agreed that Australia had undermined the chances for an ambitious reduction target of more than 25 per cent at next year's United Nations climate conference.

"It's disappointing because it makes it very difficult, if not impossible, for Australia to come to the party of an ambitious international agreement," Jotzo said.

Australia's largest business group, the Australian Chamber of Commerce, said it remained apprehensive about being burdened with pollution reduction targets during the current economic slowdown.

But Rudd said the global economy could not excuse failing to act on global warming.

"Australia is today the biggest carbon polluter in the developed world on a per capita basis," Rudd said. "Yet we are the developed country with the most to lose from climate change."

The softest target of five per cent would apply if the United Nations fails to reach a binding agreement at Copenhagen next year committing developing and developed countries to making deep cuts in global emissions.

On a per capita basis, the Australian target is comparable to the European Union's commitment last week to reduce their greenhouse emissions by at least 20 per cent below 1990 levels by 2020, the government's climate change policy document said.

Australia also plans to introduce a carbon market on July 1, 2010, where polluters will have to bid against each other for government permits to emit carbon.