Climate scientists dismiss Australian geologist's 'ridiculous' carbon dioxide claims

"Geologist, Professor Ian Plimer, utterly demolishes the human-induced 'climate emergency' fairy tale in three and a half minutes," reads a post shared on July 5 on Twitter, which is being rebranded as "X".

The post shares a clip of Plimer -- whose claims about carbon emissions had been previously debunked by AFP -- saying the Earth has just come out of an ice age so temperatures are bound to rise.

"I know this is going to surprise you but we've just come out of a little ice age. What do you think temperature's going to do, fall or rise?" he says in the clip. "If we go to our little ice age, we've warmed up since then."

He goes on to say carbon dioxide levels were once "over 20 percent" of the atmosphere compared to the current 0.04 percent and "halving those levels would cause all plant and animal life to die".

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A screenshot of the misleading post, captured on July 21.

The clip has been shared over 10,000 times on the social media site, as well as by Facebook users in Australia, New Zealand and the UK.

Plimer has also repeated similar misleading claims on conservative online shows including "Save the Nation", "Man in America" and "Zeee Media", with clips from these programmes being shared thousands of times.

'Ridiculous' claims

However, according to a 2021 report published by the Intergovernmental Panel on Climate Change: "It is unequivocal that human influence has warmed the atmosphere, ocean and land" (archived link).

The report represents the consensus among scientists on climate change.

AFP has repeatedly debunked misinformation around carbon dioxide emissions here, here, here, here and here.

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Graphs of temperature change since 1850 and simulations including and excluding human influence, and of CO2 concentrations in the atmosphere over the last 400,000 years. ( AFP / Eléonore HUGHES, Jean-Michel CORNU, Simon MALFATTO, Jonathan WALTER)

The Earth's current warming is "unrelated to post-ice age warming", James Renwick, a paleoclimate professor at the Victoria University of Wellington told AFP on July 21 (archived link).

"We know very well that the cause at present is human emissions of greenhouse gases. It is not a 'natural cycle' and it is happening much faster than any natural variation would," Renwick said.

Carbon dioxide levels have risen rapidly since the start of the Industrial Revolution in 1750, hitting 421 parts per million in June 2023, according to NASA (archived link).

This is about 50 percent higher than pre-industrial times, David Hutchinson, a paleoclimate researcher at Australia's University of New South Wales told AFP on July 19 (archived link).

Plimer was "trying to frame the current level of CO2 as being a tiny number", Hutchinson said.

Plimer's claims about climate change are "ridiculous and completely detached from scientific evidence", Australian National University paleoclimate professor Nerilie Abram told AFP on July 18 (archived link).

Carbon dioxide levels

Abram added: "I've no idea how Plimer can justify a claim that halving carbon dioxide levels in the atmosphere would cause all plant life and animals to die."

She said the Earth supported plant and animal life when carbon dioxide (CO2) levels were at 0.018 percent before the Industrial Revolution.

Ashleigh Hood of the University of Melbourne's School of Earth Sciences said it was possible that the planet had 20 percent atmospheric carbon dioxide concentration as Plimer claims (archived link).

But this would have been "several billion years ago".

"This early Earth had an atmosphere very different from today, and we think it was made up of a large part CO2 and methane, but no oxygen," Hood told AFP on July 24.

"At this time, Earth only had single celled life present."

Scientists agree the planet's recent speed of warming is "unprecedented" and is due to human-caused emissions.

"What Plimer doesn't mention is that even though CO2 has varied substantially though Earth's history, it has generally changed on relatively long timescales compared to the rate of our current warming," Hood added.

The IPCC warned in March that the world will cross the key 1.5C global warming limit in about a decade.

It said climate impacts sweeping the planet -- from devastating floods to blistering heatwaves -- are hitting faster than expected.