Kevin Rudd once described climate change as "the greatest moral challenge of our generation", but on Tuesday afternoon he gave up the fight to enact the centrepiece of his government's environmental strategy, the emissions trading scheme - or the Carbon Pollution Reduction Scheme (CPRS), as he prefers to call it.
The scheme has now been shelved until 2013 at the earliest, well after the next election, which will come before the end of the year.
The Rudd government has now made two unsuccessful attempts to get the measure passed in the upper house of parliament, the Senate. But it does not command a Senate majority, and the deal negotiated with the opposition ahead of Copenhagen came unstuck, of course, when Malcolm Turnbull was ousted by the new Liberal leader, Tony Abbott. Mr Abbott won the leadership by vowing to block the ETS, and has now effectively delivered on that pledge.
Mr Rudd has blamed the obstructionism of the opposition, reminding everyone that Tony Abbott once famously described climate change as "absolute crap". He also placed part of the fault on the slow progress made by other countries in the aftermath of Copenhagen.
We have spoken before of how the politics of global warming changed quite abruptly following the failure of Copenhagen to produce a more comprehensive agreement. In the BC phase - Before Copenhagen - of his prime ministership, Mr Rudd was supremely confident that battling for the ETS would not only win him a second term in a "climate change" election, but obliterate the opposition.
But public support for the ETS showed signs of erosion fairly quickly after the inconclusive end to the climate change conference. Leading sceptics, like Professor Ian Plimer of the University of Adelaide, started getting more air time, the "Climategate" scandal started to generate more headlines, and large swathes of Australia started getting significantly more rain.
Prior to Copenhagen, support for the ETS was steady at more than 60%. Afterwards, it dropped by 10%. The proportion of Australians who fear there's a risk of catastrophic climate change also slipped to below 50%. A more recent poll for the Climate Institute and Conservation Foundation showed that voter concern about climate change had slipped by 9% since May 2009 - although it is still strong at 68%.
An oft-heard argument leveled against the ETS was why should Australia press ahead with such a major structural reform of its resources-based economy when the rest of the world hasn't yet signed up to binding cuts in emissions. The government has failed to provide a convincing rebuttal.
Environmentalists would claim that it has not even tried to mould the public debate. Since January, as he watched his personal approval ratings slide, Mr Rudd has not delivered much of a counter-argument, and has effectively retreated from the battlefield of climate change. He has not made a major speech on climate change, and has been largely reticent on the issue ever since he returned from Copenhagen.
His critics will say that this exposes a familiar characteristic of his leadership: his reluctance to fight for causes when the polls suggest he might be in danger of ending up on the wrong side of public opinion. His predecessor John Howard won a lot of respect, sometimes even from his detractors, for fighting for unpopular causes, like the introduction of a sales tax, the GST. But Kevin Rudd tends only to fight battles when public opinion is emphatically on his side. He is reluctant to squander his personal popularity, his main selling in a party which always respected his abilities but never really taken him to its heart.
Partly because of its heavy reliance on cheap coal, Australia has some of the highest per capita emissions of any industrialised nation, and Mr Rudd came into office vowing to exercise global leadership on the question of climate change. By shelving the centrepiece of his environmental strategy, has he shirked from that pledge?