While Australian federal government is struggling to sell its proposed carbon tax, head of one of Australia's biggest banks, National Australian Bank on Tuesday threw his support behind the plan.

There is bipartisan agreement that carbon levels in Australia need to be cut by five percent by 2020. National Australia Bank chief executive Cameron Clyne said he is not a climate scientist so he cannot say which of the two policies between federal government and the Opposition would cut to achieve the five percent target.

However, he said from an economic perspective, the federal government's climate action plan is better than the Opposition's.

"If you're asking for an economic assessment of the two, the carbon price followed by an ETS (emissions trading scheme) is economically superior to the direct action policy," he told ABC News in Melbourne on Tuesday.

"It will drive certainty, it will drive investment, so as a straight comparison between the two, that's the choice."

The commends came following a latest poll showed 41 percent of people prefer Opposition Leader Tony Abbott, compared to 39 percent for Julia Gillard as prime minister.

Gillard's satisfaction rating is down two points to 28 percent, her lowest since becoming leader. Her dissatisfaction with her has jumped to a high of 62 percent, or seven points up in the past two weeks.

Despite the glooming poll, Gillard said she is determined to push on with the plan to put a price on carbon, "because it is the right thing to do for the country's future."