Former prime minister John Howard has defended his previous commitment to an emissions trading scheme despite the federal opposition slamming Labor's ETS proposal.
The global context has changed since the Howard government announced in 2007 it would roll out a $627 million cap and trade emissions trading system that would be up and running by 2011, he said.
But speaking at an Australia-Israel Chamber of Commerce lunch in Sydney on Tuesday, Mr Howard said he now supports the coalition's Direct Action policy.
"I think what's happened over the last few years ... there's more questioning of the science," he said.
"There was an absolute total failure of international will at the (2009) Copenhagen (climate change conference), and I think people have to understand that.
"When we looked at emissions trading system ... in 2006 it was within the context of a moving of the rest of the world towards that type of arrangement."
And his policy also preceded the global financial downturn and a slowing economy, he said.
The government has been dogged by coalition attacks around the carbon tax and Prime Minister Kevin Rudd's decision to shift to a European market-based ETS in July, 2014.
In July opposition leader Tony Abbott criticised the ETS as a "so-called market in the non-delivery of an invisible substance to no-one".
Mr Abbott has promised to spend $3.2 billion over four years funding activities to reduce emissions, like revegetation and improving soil carbon.
The coalition's Direct Action plan uses a carbon buyback approach.
