The man Julia Gillard wanted to become her successor as prime minister, Greg Combet, says Labor must again go to war with Tony Abbott on carbon - but this time win the politics.
Speaking at the launch of his book The Fights of My Life, the former climate change minister said Mr Abbott's abolition of the carbon tax was only a temporary setback.
"Ultimately, all of the work that we did will return because if you are making a reform of that nature, you've got to find the most economically efficient, environmentally effective and socially fair way of enacting it - and that is the reform that we made," he said.
Mr Combet noted that new data from the US National Oceanic and Atmospheric Administration reported that June was the 352nd consecutive month where the global temperature was above average and that the last below-average month was in February 1985.
He commended Opposition Leader Bill Shorten for re-embracing an emissions trading scheme as Labor policy and urged the party and its supporters to take up the fight against the coalition on carbon.
Speaking earlier at the launch, Ms Gillard confirmed she had urged Mr Combet to run as Labor leader in June last year when it became clear to her that her prime ministership was critical.
"My belief that the nation and my political party should be led by a person of good values and a clear sense of purpose remains strong . . . my view was that the best person at that time was Greg Combet," she said.
Mr Combet declined to run, partly on health grounds but also because he believed voters would not tolerate another change of leaders.