London: Former prime minister John Howard has poured scorn on the "alarmist" scientific consensus on global warming in a speech to a gathering of British climate sceptics, comparing those calling for action on climate change to religious zealots.

Mr Howard said he was an "agnostic" on climate science and he preferred to rely on his instinct, which told him that predictions of doom were exaggerated.

He also relied on a book written by a prominent climate sceptic, which scientists have attacked as ignorant and misleading.

And he called on politicians not to be browbeaten into surrendering their role in determining economic policy.

Nuclear power – a "very clean source of energy" - shale oil and fracking were solutions to the world's energy needs, Mr Howard said.

Mr Howard's speech in London on Tuesday night was to the Global Warming Policy Foundation, a think tank established by Nigel Lawson, one of Britain's most prominent climate change sceptics, former chancellor in the Thatcher government and father of TV chef Nigella.

Mr Howard revealed before the speech that the only book he had read on climate change was Lawson's An Appeal to Reason: a Cool Look at Global Warming, published in 2008.

Mr Howard said he read it twice, once when he was writing his autobiography, when he used it to counter advice for stronger action on climate change given to him by government departments when he had been prime minister.

But the book has been attacked by climate experts.

Mr Howard quoted as "compelling" one of Mr Lawson's claims in the book: that unmitigated warming would leave future generations 8.4 times better off, compared with 9.4 times richer in the absence of climate change (the book in fact uses the numbers 8.5 and 9.5).

That calculation is based on "sleight of hand and faulty logic", said Bob Ward, policy director at the London School of Economics Grantham Research Institute on Climate Change and the Environment, and it ignores the possibility of warming at the higher end of estimates by the Intergovernmental Panel on Climate Change.

Sir John Loughton, lead editor of the first three reports by the IPCC, the UN's climate panel, called the book "neither cool nor rational", saying it showed a "surprising ignorance of elementary statistical analysis" and ignored the impact of more frequent floods and droughts.

When told of Mr Howard's comments, climate scientist Tim Flannery said it was unclear which particular aspects of the science the former prime minister was doubtful about.

Contrary to Mr Howard’s assertions, Professor Flannery said climate scientists had established a direct link between global warming and an increased risk of extreme weather and events such as bushfires.

Professor Flannery recommended some additional reading material for Mr Howard, when told that the only book the former prime minister had read on climate change was Mr Lawson's tome.

''Particularly prime ministers should be reading the science and should be familiarising themselves with what the experts are saying rather than what some commentator happens to be saying,'' Professor Flannery said.

''I would just say [to Mr Howard], go to the IPCC report summaries, go to the Climate Commission reports that explain those things in simple language.''

A spokesman for Environment Minister Greg Hunt said about Mr Howard's speech: ''Government accepts the science that climate change is real. We will take action to reduce domestic emissions by 5 per cent by 2020, but we'll do it without a carbon tax which hurts households and business.''

Tuesday night's speech was titled "One religion is enough".

In notes for the speech distributed beforehand, Mr Howard said he chose the title "in reaction to the sanctimonious tone employed by so many of those who advocate … costly responses to what they see as irrefutable evidence that the world's climate faces catastrophe".

He said policy makers were faced with attempts to "intimidate" them with the mantras of 'follow the science' and 'the science is truly settled'."

However, it was the job of politicians to make public policy, and they should not surrender that role, Mr Howard said.

"The ground is thick with rent-seekers. There are plenty of people around who want access to public money in the name of saving the planet.

"Politicians who bemoan the loss of respect for their calling should remember that every time they allow themselves to be browbeaten by the alleged views of experts they contribute further to that lack of respect."

Economic growth in developing countries was much more important than countering global warming, Mr Howard said, and the West had no right to deny economic development to the rest of the world in the name of climate change.

He accused the IPCC of including "nakedly political agendas" in its advice.

Mr Howard said he had always been an agnostic on global warming.

He had not "totally" rejected the conclusions of scientists, although he recalled the "apocalyptic warnings of the Club of Rome" – a think tank that in 1972 mistakenly predicted population growth would lead to a major economic and food supply crisis in the early 1990s.

Mr Howard said his government proposed a carbon emissions trading scheme in 2006 in the face of a political "perfect storm" on the issue.

Now the "high-tide of public support for over-zealous action on global warming has passed", he said.

He said it was unlikely there would ever be a global agreement on climate change action.

"I don't see a real prospect of that happening," he said.

Mr Howard also criticised "zealous advocates of action of global warming" and "alarmists" for attempting to exploit the NSW bushfires in October.

He pointed out that a big bushfire in Victoria took place 163 years ago, "when the planet was not experiencing any global warming. You might well describe all of this as an inconvenient truth."

Renewable energy sources should be used when it makes economic sense, but nuclear energy should be used in the long term, and the ‘shale revolution' would be a game-changer in the energy debate, Mr Howard said.

Speaking in London before the speech, Mr Howard said climate change activists saw the issue as a substitute religion. "It's the latest progressive cause," he said.

But the global financial crisis had caused the general population to become more sceptical.

"I don't know whether all of the warnings about global warming are true or not," he said. "You can never be absolutely certain that all the science is in.

"I am unconvinced that catastrophe is around the corner. I don't disregard what scientists say. I just don't accept all of the alarmist conclusions.

"I instinctively feel that some of the claims are exaggerated."

He was sceptical about science that linked climate change to the increased likelihood of extreme weather events or bushfires.

"Australia has always had extreme weather events," he said. "The first Australians knew how to deal with [the risk of bushfires] through regular backburning. It's something that's worth contemplating."

He said renewable energy should be used only when it was affordable and would not hurt poorer families or developing countries.

He predicted that shale oil and gas had opened up a "tantalising prospect" of an energy independent US, which would dominate energy policy in that country and would "dwarf" consideration of a carbon trading scheme.

In Australia, nuclear power should be "kept on the table" and used as it became better value for money.

With Jonathan Swan