Former prime minister Malcolm Turnbull has labelled controversial carbon capture and storage technology championed by the Morrison government a scam and con.
The government wants to use so-called blue hydrogen, produced using fossil fuels before CO2 is captured and stored underground, to help reduce emissions.
"Blue hydrogen. This is a new buzzword," Mr Turnbull told the virtual Global Race to Zero Summit on Wednesday.
"This is the same old grey hydrogen, but using carbon capture and storage to put the carbon dioxide under the ground.
"Now this is a scam and a con. CCS (carbon capture and storage) is a proven failure."
Mr Turnbull thinks Australia's 2030 emissions reduction target should be lifted to well over 40 per cent.
His successor Scott Morrison has ruled out taking a stronger mid-term target to the looming COP26 summit in Glasgow in under two weeks.
Instead, Australia will rely on projections it will overshoot its 2015 Paris Agreement pledge to reduce emissions by between 26 and 28 per cent on 2005 levels.
Mr Turnbull thinks Australia has the ability to ditch coal by 2040 because of the rapidly falling cost of renewable energy, if it can also find the will.
He acknowledges the transition to net zero emissions by 2050 won't be a linear or smooth one.
"This is now being used as a way of justifying doing less now and waiting for when, perhaps the 2040s, for miracle new technologies to come along and save the day," the former prime minister said.
"Delay is the new denial."
Mr Turnbull chastised Nationals politicians for not being upfront about the inevitable end of the coal and gas sectors.
"It cuts both ways. Demand for coal and gas will not fade gracefully over 30 years. There will be sharp, fast disruptions as our major trading partners decarbonise," he said.
"If politicians really cared about regional communities and mining ones in particular, they would not be pretending coal goes on forever."
British high commissioner to Australia Victoria Treadell told the summit she was "delighted" Mr Morrison has confirmed his attendance at COP26.
"Right now, discussions are still underway. I don't want to get in the way of that," she said in reference to the coalition's internal battle to get a net zero target over the line.
"(The) main goal is to keep 1.5C alive. All of us, whether governments or business, need to bring commitments targets and policies that keep this goal within reach."
Australian Associated Press