WHAT WAS CLAIMED
In order for human carbon emissions to warm the planet by 1C, every CO2 molecule emitted would have to reach a temperature of 10,000C.
OUR VERDICT
False. The claim misunderstands the mechanism by which CO2 warms the planet.
AAP FACTCHECK - An outgoing Queensland senator incorrectly claims to have debunked climate science in a Facebook video viewed by more than half a million people.
Gerard Rennick, who lost his re-election bid in May, has made a series of claims which he says are based on his understanding of the laws of physics.
However, experts told AAP FactCheck his assertions are "muddled" and "nonsense".
His claims include:
1. Every atmospheric carbon dioxide (CO2) molecule would have to reach a temperature of 10,000C to warm the planet by 1C.
2. Solar energy absorbed by atmospheric CO2 is five times stronger than the thermal energy it absorbs as it makes its way back from earth into space.
3. Atmospheric CO2 only emits heat when at -80C.
4. The greenhouse effect is incompatible with the first law of thermodynamics.
5. Albert Einstein said that radiation is so small that it is insignificant.
The claims, which particularly take aim at the greenhouse effect, feature in an April 2025 Facebook post that also includes a video of him addressing the Senate during the second reading of the Climate Change Bill 2022.
False: CO2 must reach 10,000C to warm planet by 1C
"The idea that one CO2 molecule can heat up 10,000 N2 [nitrogen] and O2 [oxygen] molecules by 1 degree and then maintain that increase in temperature is false," Mr Rennick wrote in reference to the first claim.
"Assuming equal molecule weights that would require that the CO2 molecule is 10,000 degrees in order to confirm with Newton's third law of motion or the 1st law of thermodynamics.
"This is clearly impossible. The temperature of the Sun is 5,700 degrees and the heat inside an internal combustion engine of a space ship is 3,000 degrees."
In an email to AAP FactCheck, Mr Rennick said he based this claim on the fact that 99 per cent of the atmosphere is nitrogen and oxygen, while CO2 accounts for 0.043 per cent, or 430 parts per million (ppm).
He stated that atmospheric CO2 levels had increased by 100ppm, or one part per 10,000, since the Industrial Revolution.
If that extra CO2 has increased the global temperature by 1C, he said, each individual CO2 molecule would've had to have warmed 10,000 other gas molecules in the atmosphere by 1C.
Atmospheric CO2 levels have actually risen by close to 150ppm, not 100ppm, while global average temperatures have risen by 1.3C since pre-industrial times, according to NASA.
Experts also say Mr Rennick has misunderstood the mechanism by which CO2 warms the planet and the underlying claim is incorrect.
Martin Jucker, a climate physicist at the University of NSW, told AAP FactCheck Mr Rennick's claim is based on CO2 warming the planet via conduction - the direct transfer of heat from one object to another.
In reality, CO2 primarily warms the planet via radiation, which transfers heat via electromagnetic waves, and this makes Mr Rennick's argument incorrect.
"It is wrong that the CO2 molecules need to heat the surrounding air," Dr Jucker said. "The atmosphere is heated from the ground via radiation, convection and latent heat (moisture), not conduction. So this entire argument is void."
Atmospheric CO2 is also not the source of additional heat, as Mr Rennick implies, but prevents the earth from losing the heat, like a layer of insulation.
Michael Brown, an astronomer with an interest in climate change physics, told AAP FactCheck that Mr Rennick's claim was akin to suggesting a sleeping bag would need to reach roasting temperatures to warm you.
"Using his logic, if I were to use a 4kg sleeping bag to increase my temperature by 10C then the sleeping bag's temperature would need to increase by roughly 200C," Associate Professor Brown said.
"Fortunately for me this does not happen. And neither the greenhouse effect nor my sleeping bag break the laws of physics."
This also addresses Mr Rennick's claim that gases are poor conductors of heat. While this claim is true, Dr Jucker says conduction is not the mechanism by which atmospheric CO2 warms the planet, so it's irrelevant.
"Yes, he's right, but it's not conduction so it doesn't matter," Dr Jucker said.
False: CO2 absorbs five times more energy from the sun than heat leaving earth
A further claim, which features in the post's video, again questions the greenhouse effect.
Mr Rennick claims the radiation that atmospheric CO2 absorbs from direct sunlight has five times more energy than the thermal radiation it absorbs as this energy is radiated back from earth and into space.
His assertion suggests CO2 is blocking far more radiation energy from reaching earth than it is trapping and preventing from leaving the earth's atmosphere.
However, the fact that atmospheric CO2 allows sunlight to pass through the atmosphere and warm the earth, but then absorbs the heat that earth radiates back towards space, is fundamental to the greenhouse effect.
The basis of Mr Rennick's claim relates to the fact CO2 only absorbs radiation at specific wavelengths, measured in microns.
"One of those frequencies [that CO2 absorbs radiation at] happens to be 2.8 microns, which is incoming radiation," Mr Rennick said (timestamp 10 minutes 37 seconds). "Another frequency it absorbs at is 14.8 microns, which just happens to be outgoing long-wave radiation."
He then references Planck's Law, a law of physics that states a photon with a shorter wavelength will always have more energy than a photon with a longer wavelength.
Based on Planck's Law, it is correct that a single photon (or particle of radiation) at 2.8 microns will have about five times more energy than a single photon at 14.8 microns.
However, experts say his claim does not account for the fact that there is simply far more thermal radiation leaving earth at 14.8 microns than there is solar radiation going towards earth at 2.8 microns.
Dr Jucker explained that atmospheric gases only absorb radiation at discrete wavelengths and CO2 absorbs in bands peaking around 2.8, 4.3, and 15 microns.
The sun, meanwhile, emits radiation, or sunlight, mostly in wavelengths between 0.3 and 3 microns, with a peak near 0.5 microns.
Because the sun emits very little radiation at 2.8 or 4.3 microns - and almost none at 15 microns - only a small portion of sunlight is absorbed by CO2.
Some sunlight is absorbed by water vapour and ozone and about a third is reflected by clouds and ice, but about half of the energy passes through the atmosphere and is absorbed by the earth's surface.
Dr Jucker said this sunlight is then emitted back towards space as thermal radiation (heat) in longer wavelengths between 5.0 and 30 microns, peaking at about 10 microns.
One of CO2's primary absorption bands is 14.8 microns, which is close to the peak wavelength of the heat re-emitted from earth, meaning it absorbs more of this available radiation.
Dr Jucker said this and other factors - including that water vapour also absorbs radiation near 2.8 microns and that CO2 absorbs radiation in a wide band centred on 14.8 microns - mean atmospheric CO2 absorbs at least 10 times more outgoing radiation from the earth than incoming radiation from the sun, not five times less as Mr Rennick implies.
False: CO2 only emits heat at -80C
In his speech, Mr Rennick also claims that CO2 only emits heat at extremely cold temperatures (-80C), citing Wien's Law of physics.
"You'll need to go either to the bottom of Antarctica or about 10 kilometres up into the troposphere to start getting carbon dioxide to emit heat," he said.
Under Wien's Law, an object's temperature determines the peak wavelength of the radiation it emits, Dr Jucker said.
For example, the sun's radiation peaks at 0.5 microns and, based on Wien's Law, its temperature is around 5700C.
Scientists can therefore use Wien's Law to estimate the temperature of far-off planets by measuring the wavelengths of the radiation emitted.
However, Dr Jucker said Mr Rennick has inverted Wien's Law, erroneously calculating CO2's temperature based on the wavelengths it absorbs at, rather than the wavelengths at which it re-emits energy.
"CO2 absorbing at 14.8 microns or 2.8 microns does not mean it emits at those wavelengths," he said. "It will emit according to its temperature, which is set by its surrounding atmosphere."
False: climate science is incompatible with thermodynamics
Dr Jucker said a further claim by Mr Rennick, relating to the first law of thermodynamics, is another misunderstanding of the greenhouse effect.
The first law states energy cannot be created or destroyed, only converted from one form to another.
"With a photon that is absorbed by carbon dioxide, it only absorbs an existing photon. It doesn't increase the overall energy intake that's in the atmosphere," Mr Rennick said.
Dr Jucker explained that rather than destroying or creating energy, CO2 prevents a portion of energy from leaving earth's atmosphere, and re-radiates some of this back towards earth as heat.
"You're not creating heat, you're just not letting it out any more," he said.
False: Einstein said radiation is so small it is insignificant
In his speech, Mr Rennick also quotes Albert Einstein in an attempt to debunk the greenhouse effect.
He quotes from the final paragraph of his 1917 paper, Quantum Theory of Radiation, in which the physicist says (page 14): "... momentum transferred by radiation is so small that it always drops out as compared to that from other dynamical processes."
"Albert Einstein," Mr Rennick adds. "The great man himself, the greatest scientist that ever lived, said that radiation is so small that it is insignificant. Just remember that."
However, Dr Jucker said the passage - and the paper in general - have been misinterpreted.
In the quote, Einstein states it is the momentum transferred by radiation that is small (the physical momentum caused by a photon hitting a molecule), not the energy transferred by radiation.
"He's not saying radiation is so small that it is insignificant," Dr Jucker said.
"This entire paper is about the interaction between radiation and molecules and that it's significant."
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