Malcolm Turnbull’s son, Alex Turnbull, has joined former Liberal leader John Hewson in calling on constituents of the blue ribbon seat of Wentworth to vote anything but Liberal in the coming by-election, to “send a signal” to the Party on climate change.

In a Facebook video posted Thursday – less than two months after his father was ousted as PM for the extraordinary two-sided crime of being ‘too strong’ on climate, and yet doing absolutely nothing to combat it – Alex Turnbull said he was making the statement as a form of intervention.

“We’re going to have an election in 12 months anyway, so if you want to send a signal as to which way the Liberal Party is going, and your displeasure with where it is going, then this is your opportunity,” he said.

“Don’t vote for the Liberal Party at the Wentworth by-election. If you want to pull the Liberal party back from the brink, it’s the one clear signal you can send.

“Consider it an intervention, for Australia, the Party and for Wentworth. This time, don’t give the Liberals your vote.”

The call to arms comes as the LNP continues to astound with what has been a breathtakingly stupid response to the much anticipated – and multi-government commissioned – report from the Intergovernmental Panel on Climate Change.

The Singapore-based investment banker said the Liberal Party’s response to the IPCC’s findings – a report he described as “frankly … terrifying” – proved the party had been “taken over … by extremists on the hard right” intent on pursuing a “crazy” fossil fuel agenda.

“As an investor in energy, I’ve seen that … there’s no way coal can compete any more,” the junior Turnbull said.

“Renewables have gotten too cheap, firming costs are reasonable, and really there’s no trade-off anymore between lowering your power bills and reducing emissions.

“And yet still, some would like to prosecute a culture war over this issue, for whatever their reasons may be.”

Forget for a minute that this is what his dad should have, but could not – or would not – say, when he had the Prime Minister’s podium.

These are really important points – not least because they are the sort of irrefutable, economic-based arguments that should be the Liberal Party’s bread and butter.

Certainly, Hewson – who is an economist (although, so is current federal energy minister Angus Taylor) – knows this, and he believes that voters understand it, too.

Which makes the Party’s inaction and obfuscation on the issue even more frustrating for the ex-leader.

“It is very odd, indeed, to ignore such a strong electoral sentiment,” Hewson wrote in the Fairfax newspapers this week.

Alex Turnbull puts it another way.

“It’s seemingly insane not to do anything about this,” he said in his video.

“To me, this particular event seems to show the Liberal party has been taken over, frankly, by extremists on the hard right who aren’t particularly motivated to win an election and aren’t particularly motivated to serve the general public. They just want to pursue a crazy agenda.”

New PM Scott Morrison, who has deflected all talk of climate action with slogans about electricity prices, responded to the comments thus:

“I disagree with Alex. His father disagrees with him too.”

He also noted that “if an independent is elected at the Wentworth by-election, that will throw us into a hung parliament and a lot of uncertainty at a time when the country doesn’t need it.”