Former PM John Howard thinks there’ll never be a worldwide climate change agreement and admits he only backed emissions trading before the 2007 election because he faced a “perfect storm” on the issue.

Mr Howard delivered the Global Warming Policy Foundation’s annual lecture in London on Tuesday night.

The foundation was established by former Thatcher minister Nigel Lawson, who is sceptical about the impact of rising temperatures.

“I’ve always been agnostic about it (climate change),” Mr Howard told reporters in London before his address.

“I don’t completely dismiss the more dire warnings but I instinctively feel that some of the claims are exaggerated.

“I don’t accept all of the alarmist conclusions.”

Mr Howard said he’d grown up being told ulcers were caused by stress but it was later revealed a virus was to blame.

“You can never be absolutely certain that all the science is in.”

Before the 2007 federal election then prime minister Howard pledged a re-elected conservative government would introduce an emissions trading scheme (ETS).

But he now says that was because by late 2006 his government hit a “perfect storm” with on-going drought, severe water restrictions, bushfires and the release of the Stern Review and Al Gore’s film An Inconvenient Truth.

“To put it bluntly, ‘doing something’ about global warming gathered strong political momentum in Australia,” Mr Howard said in his written lecture.

Regardless, Labor won the 2007 poll.

Mr Howard says that was partly because the party had even “more fashionable” views on climate change.

But six years on, Australia’s second-longest serving prime minister insists the high tide of public support for “over-zealous action” on global warming has passed.

“I am very sceptical about the possibility of a global agreement ever being reached when you look at what happened in Copenhagen,” he said, adding there was no real prospect of a deal between the major emitters Europe, the US and north Asia.

Mr Howard believes anti-global warming policies should never stand in the way of economic growth in developing countries.

Most economists believe current Prime Minister Tony Abbott’s direct action approach to curbing carbon emissions will be more expensive than an ETS.

But Mr Howard on Tuesday refused to be drawn on his protegee’s policy.

“It’s better for the government that’s proposing the direct action plan to engage in the debate,” he said.

The former Liberal leader was forced to defend his decision to read Lord Lawson’s book An Appeal to Reason twice despite not having picked up any other book on global warming.

Asked if that was unbalanced, the ex-PM said he re-read the work as a courtesy after being invited by Lord Lawson to deliver the lecture.

Mr Howard said it was a “counterbalance” to advice previously received from government departments and stressed he’d read “numerous articles” on climate change.

The 74-year-old also used the lecture to argue nuclear power “must be part of the long term response” to global warming.

“It is a very clean source of energy.”

Mr Howard later criticised the ABC for being captured by climate change “alarmists”.

“The group-think at the ABC on this issue is quite clear,” he said during the question and answer session after his lecture.

“On this issue it’s signed up – there’s no doubt about that.”

The former prime minister said the Murdoch press, particularly The Australian newspaper, was more sceptical.

“(But) talkback radio commentators in Australia have more political influence than they do in this country (and) they are ferociously sceptical.

“So we have had, for some time, a more balanced debate.”