Kevin Rudd has mounted a scathing attack on Cardinal George Pell for being a “radical climate change sceptic” who is “muddying the ethical waters” ahead of the critical Paris climate change conference, in direct contradiction to the views of Pope Francis.

Rudd says the ethical imperatives of strong climate action and the fact that Pell is now a “global figure”, means it is time to confront “head on” the views of the cleric, who was a strident critic of the Labor government’s climate policies as archbishop of Sydney and who is now a senior Vatican cardinal.

“After many years of silence in response to Cardinal Pell’s public critique of my government’s policy on climate change, the reason I have chosen to enter the debate now is, on the eve of the Paris conference, we once again enter into a critical time both for Australia and the world,” Rudd says in a lecture to be delivered at Melbourne University’s Trinity College on Tuesday night.

“It is, therefore, no small matter, at this most critical of times, for the ethical waters, at least in the community of faith, to be so deeply muddied, by such radical climate change sceptics as Cardinal Pell, and for his commentary to go without challenge. Of course he is free to contribute to the public policy debate in any manner he wishes. But it is equally important, particularly now that Cardinal Pell has become a global figure, to have his ... statements on climate change challenged by others in the public space. It is high time his views were confronted head on. The stakes are now far too high for us all,” Rudd says in the Rowan Williams lecture.

The prime minister, Malcolm Turnbull, said recently no energy source could have a “moral characteristic” and Australia just needed to make rational choices between the various abundant energy sources it had available.

But Rudd insists that “anyone who claims in making policy judgments they are doing so oblivious to ethical considerations, and instead are simply acting on a simple ‘value free’ premise of ‘common sense’, is engaged in deep self-delusion”.

And he strongly defends the right, and even obligation, of churches to engage in public debate as one of a number of “ethical voices”.

“Unless there is at least one institution seeking to construct, maintain and argue the continuing ethical parameters within which the stated purposes and unintended consequences of government action should be considered, then there is a greater risk that public policy simply becomes ‘interest group politics’ or, even worse, retail politics by another name,” he says.

Pope Francis signs a cricket bat he received from Cardinal George Pell at the Vatican in October. Photograph: AP

Contrasting Pell’s views (including the statement that “in the past pagans sacrificed animals and even humans in vain attempts to placate capricious and cruel gods, while today they demand reductions in carbon emissions”) with Pope Francis’s encyclical, Rudd remarks: “The pope says the science on climate change is sufficiently clear. Cardinal Pell says it is not, and further that the purported science is without foundation. The pope says all of humanity faces a common ethical challenge to protect the planet from climate change. Because Cardinal Pell disputes the science, he says there is little if any ethical imperative at all. And on the question of the policy imperative, the pope speaks with urgency. Cardinal Pell describes policy measures as an unnecessary fad and an unacceptable cost to both companies and consumers.”

He says he is not arguing that Pell should not be free to express a view even though “his position happened to mirror precisely that of ... Tony Abbott”, but Rudd strongly argues that governments should instead listen to the “ethical guidance” of the pope.

Rudd also addresses frequent criticisms that after declaring climate change “the greatest moral challenge of our time” he shelved his emissions trading scheme after it failed to pass the parliament.

“Those who attacked this particular formulation were not only the usual legion of climate change sceptics and deniers. It included those corporations who concluded that policy change would be financially injurious to their bottom line, and who therefore found it convenient to join forces with the deniers,” he says.

“But it also included those who accused me of not living up to my word by accepting the advice of my most senior ministers that following the second defeat of the government’s emissions trading scheme legislation, we should defer its implementation for two years until the conclusion of the Kyoto Protocol’s commitment period until 2012. As I was prime minister at the time, I accept responsibility for this decision and for the poor communication of it to the Australian public.

“As for the related attack that my stated belief in the moral significance of climate change should have resulted in a double dissolution, I would draw attention to the fact that as of June 2010 [when Rudd was replaced as Labor leader by Julia Gillard] the window for calling a double dissolution was still open and remained open until August of that year.”

Rudd points out Australia’s emissions declined by 7% over Labor’s time in office, and according to modelling firm Reputex will rise by 8.5% between 2014 and 2020.