"We've got to stop this false debate, this misleading debate about whether getting to net zero emissions by 2050 ... is something that's optional," he said in Sydney on Tuesday. "Well, I suppose it is optional but it's an option you don't want to miss because if we do miss it we know what the consequences are. "The fires of this last summer will seem like a very, very mild experience compared to what a 3 degrees Celsius [warmer] world will look like." Loading Replay Replay video Play video Play video Mr Turnbull cited the Paris Agreement on climate change and the advice of the United Nation's Intergovernmental Panel on Climate Change to warn that anyone who rejected the net-zero target by 2050 was, in effect, supporting an increase in global temperatures of 3 degrees, which would make much of the world "uninhabitable".

"It is an absolutely unthinkable, catastrophic, apocalyptic scenario," he said. Loading "This challenge is real. The objective of net zero emissions by 2050 is not a 'nice to have' or an 'interesting' target, a 'would be nice to do if we can' or 'if we can afford it'. "The alternative is unthinkable – apparently except in the bubble down to the south of us in Canberra." While Mr Turnbull has taken issue with Mr Morrison in the past, the speech represented a significant and forceful attack when the government is fomenting political alarm over Labor's policy of net zero emissions by 2050.

Mr Turnbull said the facts showed Australia could achieve net zero in a way that lowered energy prices. He said while the Howard government confronted a cost barrier to reducing emissions when it advocated an emissions trading scheme, the dramatic fall in the cost of renewable energy meant it was now cheaper to reduce emissions than to use coal. "We have the means, with the engineering and economics, as opposed to the ideology and idiocy … to move to a zero-emission energy sector which will deliver cheaper and cleaner and reliable energy," he said. The arguments in favour of coal are just sheer ideological claptrap. Malcolm Turnbull "The reality is the cheapest form of new generation in Australia right now is solar supported by firming – by pumped hydro or other forms of firming depending on the location.

"The cost of batteries, in particular, continues to come down." Mr Turnbull said the cost per watt of a photovoltaic cell has fallen by 90 per cent over the last eight years, a point echoed by experts in the audience who noted it had gone from more than $2 to about 20 cents per watt. Loading "We've got the means to get there and we can be a cheap energy economy if we choose to be." The speech did not criticise Mr Morrison by name and did not explicitly endorse Opposition Leader Anthony Albanese for setting a net-zero target for Labor in recent days.

Mr Turnbull's position was in line with the support for net-zero by the Business Council of Australia, the Australian Industry Group, agricultural groups and leading scientists. Loading Replay Replay video Play video Play video NSW Energy and Environment Minister Matt Kean conspicuously praised Mr Turnbull at the conference, using his speech to thank the former prime minister. Mr Kean said the politics in Canberra were "challenging" but said he was working with his state counterparts in Victoria, South Australia and elsewhere to reduce emissions. "Let me make it very clear to my friends in Canberra: we should and we must move towards zero net emissions," Mr Kean said.

The government has not ruled out having a net-zero target of its own for 2050 but has mounted an attack on Mr Albanese on the grounds that he could not say how he would achieve the target. While Nationals MPs such as Barnaby Joyce and Matt Canavan argued for coal-fired power, Mr Turnbull said the party was letting down its rural constituency when coal was no longer economic. Loading "The trend is absolutely clear – the arguments in favour of coal are just sheer ideological claptrap," he said. "There is no economic case for building a new coal-fired power station in Australia anymore, regardless of what you think about carbon policy – and everyone in the energy sector knows that.