Imagine, if you will, a government board to champion Australian arts without any artists on it, or an agency to advise on medical research without any medical researchers.

Or perhaps even, imagine a government authority set up to provide expertise on climate policy without any actual climate scientists.

Well you don’t have to imagine that last one, because that’s what we now have – the government’s Climate Change Authority is now sans climate scientist.

Prof David Karoly, of the University of Melbourne, has just finished his term on the authority’s board – the only member to stick it out for the full five years.

Karoly says without someone to replace him, the authority will struggle to fulfil its legal mandate. He told me:

I think that it is critically important that at least one member of the Climate Change Authority is an expert and experienced climate change scientist. Such a member is needed to provide information and interpretation on the latest climate change science publications and data.

In my view, it can only do that with a climate change scientist as a member, to provide expert assessment of the effectiveness of proposed greenhouse gas emission reductions nationally and globally, and the projected impacts on Australia from current and future climate change. The Climate Change Authority Act 2011 states that, in conducting a review, the authority must have regard to environmental effectiveness among a number of other matters.

I asked the Department of the Environment and Energy if there were any plans to replace Karoly with another climate scientist. The department said:

Government appointments to the CCA are a matter for the Government under the CCA’s legislation. The Chief Scientist is an ex officio Member of the Authority and can assist on scientific matters and in providing access to the scientific community, including climate scientists.

So in other words, it won’t replace Karoly and will instead just rely on the chief scientist, Alan Finkel, to act as a go-between, which of course is much more efficient and logical than actually having a climate scientist right there in the room. That would be silly, right?

Remembering too that the CCA has always had the serving chief scientist on its board so, by this logic, Karoly was always a spare part.

In reality, the makeup and character of the CCA was fundamentally altered after Malcolm Turnbull made changes to the board in 2015.

So why did Karoly decide to stick it out this long, when colleagues including Prof Clive Hamilton, Prof John Quiggin and Danny Price were throwing in the towel out of frustration that the government was listening to rightwing anti-science advocates instead of actual expertise? Says Karoly:

I decided to stay on because I believe that the CCA was established by the Australian Parliament.

I believe that it is important that the Parliament and the Australian people are provided with the best possible independent science-based advice on Australia’s climate change policy. Unfortunately, after six new members were appointed by the Government to the CCA in 2015, I do not think this continued to be the case, despite my efforts. That is why Clive Hamilton and I published our Minority Report in 2016. I did not resign at the same time as Clive Hamilton as I still wanted to provide the best possible science-based advice to the members of the CCA and to the Government.

Karoly’s account of a shift in the authority under the Turnbull government matches that of Hamilton, who told me this year that “the whole character of the authority changed”.

In its earlier years, the CCA had been forthright in its advice to the government. Simply put, the authority’s detailed reports showed targets to cut emissions were well short of what was needed if Australia wanted to mount any sort of claim to be doing its fair share globally.

Under the former Liberal leader Tony Abbott, the government vowed to axe the authority entirely – but couldn’t get enough support in parliament. So instead, if you believe its former insiders, the authority was carefully manipulated and undermined.

As Hamilton put it, the CCA became “dominated by people who want action, but not too much action”.