That would leave Abbott two choices. He could roll over and concede defeat or, far more likely, use a Senate block to trigger a double-dissolution election.
This would send Australians back to the polls to vote not only for a new House of Representatives, but for an entirely new Senate. Only half the Senate's seats are contested in a normal election. With all seats in both Houses up for grabs, Abbott could gamble on winning control of both.
He seems prepared to take the plunge. He has promised that on the new Parliament's first sitting day he will introduce legislation to repeal the carbon tax. It will then pass to the Senate - and there it could crash if Labor and the Greens combine to block it.
Regardless of the outcome of the Upper House election, new Senators will not take their seats for another nine months, leaving the Greens' present nine Senators holding the whip hand.
Abbott is playing down the prospect, counting on Labor to avoid the prospect of further retribution from voters furious to be recalled for another election. He has declared Saturday's vote a referendum on the carbon tax, and claims a Coalition victory would give him a mandate to repeal it.
"We will do whatever is necessary to abolish the carbon tax, but I tell you this, if we win the election ... the last thing the Labor Party will do is commit political suicide twice by continuing to support this absolutely toxic tax," Abbott said.
For the moment at least, Labor is standing firm. While careful not to appear to be conceding defeat, Rudd said the party's policy remained carbon pricing through an emissions trading scheme.
Climate Change Minister Mark Butler added: "Labor has a very clear position on this and ... it is not the position that Tony Abbott takes."
The Greens are hard-line. Milne told the National Press Club in Canberra yesterday: "As long as the Greens hold the balance of power it will not be repealed."
Abbott has played very clever politics. Until he zeroed in on the carbon tax this week climate change had been all but ignored in the campaign. He has sidestepped the planned transfer to emissions trading, declaring both a tax and fuelling wide voter dislike of it. Watch this space.
Australian Election 2013
2 days to go