Rudd said naysayers were active in every country as the world approached the United Nations' climate summit in Copenhagen in December.

"They are a minority. They are powerful. And invariably they are driven by vested interests," he said.

Rudd said it was difficult to move towards a global agreement in the face of those who denied climate change was caused by human activity, those who refused to act on the evidence, or who wanted other countries to act first.

"As we approach Copenhagen, these three groups of climate skeptics are quite literally holding the world to ransom," he told policy think-tank the Lowy Institute in Sydney.

"Provoking fear campaigns in every country they can; blocking or delaying domestic legislation in every country they can; with the objective of slowing and if possible destroying the momentum towards a global deal on climate change," he said.

The centre-left Labor leader who campaigned strongly on the environment ahead of his 2007 election, said Australia was one of the hottest and driest countries on earth and would suffer more drought and higher temperatures if no action was taken.

"Climate change deniers are small in number, but they are too dangerous to be ignored. They are well resourced and well represented by political conservatives in many, many countries," Rudd said.

"And the danger they pose is this: by collapsing political momentum towards national and global action on climate change, they collapse global political will to act at all.

"They are the stick that gets stuck in the wheel, that despite its size may yet bring the train to a complete stop."

Rudd said Australia would push ahead with its Carbon Pollution Reduction Scheme which is aimed at cutting greenhouse gas emissions believed responsible for global warming by between five and 25 percent by 2020.

The scheme, which must be approved by parliament, would stipulate the higher figure if the rest of the world adopted "ambitious" reduction targets at Copenhagen.

Some 190 countries will meet in Copenhagen to thrash out a new climate treaty to replace the Kyoto Protocol, which expires in 2012.

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