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Prof. Murry Salby: Atmospheric carbon is not a pollutant and humans cannot regulate it

In 2016 atmospheric scientist Professor Murry Salby delivered a lecture at University College London.  The purpose of his lecture was to provide proof of why atmospheric carbon is not a pollutant and why humans cannot regulate it.

The effect of fossil fuel on CO2 emissions is minute, Prof. Salby said.  “The fossil fuel perturbation is too small to even be detectable … [It] is presently not detectable.  It will not be detectable, ever.”

Science has been taken over by “government bureaucracy under the aegis of the UN.”  Its objective, he said in 2016, “has become an exercise in social engineering to predict and control the undetectable.”

Who is Murry Salby?

Murry Salby was critical of anthropogenic global warming. His last position in academia was as a professor at Macquarie University, Sydney, Australia. 

According to Wikipedia, in 2013 the university dismissed Prof. Salby on grounds of refusal to teach and misuse of university resources.  DeSmog highlighted on Prof. Salby’s profile page that “between 1988 and 2013, Salby committed financial and other offences that led to his departures from faculty positions at two major universities.” 

Regarding Macquarie University it appears DeSmog used an in-house report that could not have been accessed without requesting it under the Freedom of Information Act (“FoI”). “DeSmog vaguely suggest there ‘must have been an FoI’, but there are no links to support that. In the end, a confidential, low standard, internal document with legalistic sounding words, may have been ‘leaked’ to those in search of a character attack,” Jo Nova noted.

Prof. Salby’s dismissal from Macquarie University followed a series of unfulfilled commitments by the university, deliberate attempts by the university to sabotage and silence him and a misconduct hearing held by the university while Prof. Salby was in France. As Jo Nova noted at the time: “Is his research is so dangerous to the cash cow that is ‘global warming’ that it had to be stopped at any cost?” 

Prof. Salby died in 2022.

Despite the persecution he suffered for going against the climate change narrative, Prof. Salby did not stop speaking out about what he knew to be the truth, as demonstrated by the lecture he gave at University College London in 2016.

During this lecture, Prof. Salby demonstrated why carbon dioxide is not a pollutant as climate change catastrophists claim.

Carbon Dioxide is Not a Pollutant

Almost all of the carbon in the atmosphere is in the form of carbon dioxide, Prof. Salby explained.  Carbon dioxide cannot be a pollutant, he said, because the combustion of hydrocarbons is a form of oxidation. 

Combustion is a type of oxidation reaction because it involves the addition of oxygen to a substance, resulting in the loss of electrons and an increase in oxidation state. In combustion, the fuel reacts with oxygen to produce heat, light and oxidised products, such as carbon dioxide and water.

The plumes of “smoke” you see coming out of towers that are used as the poster child for “climate change” is water vapour, not CO2, Prof. Salby said.

It is also water vapour that you see coming out of car exhausts on a cold morning. And the same process of oxidation powers the human body.  In this process, CO2 cannot be produced without simultaneously producing water vapour. CO2 and water are the products of perfect combustion.

Methane, for example, is a simple fuel.  In the combustion of methane, for every molecule of CO2 produced, two molecules of water vapour are produced.

Appalachian coal is an example of a more complex fuel.  In its combustion, for every three CO2 molecules produced, two molecules of water vapour are produced.

“In regard to climate, whether the ratio of water vapour to CO2 is two to one or two to three really doesn’t matter,” Prof. Salby said.  He explained why it doesn’t matter using the opacity of infrared radiation.

Opacity of Infrared Radiation

In his lecture, Prof Salby presented the graph below labelled ‘Greenhouse Heat Trapping Capacity’. It shows the atmosphere’s opacity for the wavelengths of infrared radiation (“IR”) collected over all greenhouse gases. 

Opacity refers to the measure of impenetrability to electromagnetic or other kinds of radiation. IR is a type of electromagnetic radiation with wavelengths longer than that of visible light but shorter than microwaves.

In the context of IR radiation, opacity describes the absorption and scattering of IR radiation.  The opacity of IR radiation in the atmosphere is influenced by various factors including water vapour, CO2, other gases (such as methane, ozone and nitrous oxide) and temperature.

As Prof. Salby explained, the opacity of IR radiation is “what traps radiant heat at the Earth’s surface.  It’s also the premise for the EPA’s finding of ‘endangerment’ by CO2.” The EPA is an acronym for the US Environmental Protection Agency.

In the image above, notice that over almost all wavelengths (horizontal axis) the opacity (vertical axis) is already at the maximum possible of 100% absorption,  Prof. Salby pointed out.  This is indicated by the area shaded in grey. 

The question then is: What atmospheric gases are contributing to the almost 100% opacity of IR radiation?

Prof. Salby placed the contribution CO2 makes to opacity below the total opacity graph, shown in green in the image below.  CO2 represents less than 10% of the overall opacity of IR radiation, Prof. Salby said.

He then explained that almost all of the remaining opacity of IR radiation comes from water vapour, as shown in blue in the image below.

“Notice, even at those wavelengths where CO2 absorbs radiation, water vapour absorbs over half of the maximum that’s possible,” Prof. Salby said.  “Only what remains – less than half – is influenced by changes of CO2 …  [Therefore], the heat-trapping capacity [of water vapour] vastly exceeds the heat-trapping capacity of CO2.”

As stated earlier, in the combustion of hydrocarbons water vapour is produced at the same time as CO2. In other words, water vapour is emitted along with CO2.  Add the fact that the heat-trapping capacity of water vapour vastly exceeds the heat-trapping capacity of CO2 (as seen the in image above) and the conclusion can only be as Prof. Salby said: “CO2 will be a pollutant the day that water vapour is a pollutant.”

“It follows that energy sources which circumvent CO2 emission are neither cleaner nor greener, they’re just different,” he added.

What Role Does Fossil Fuel Emission of CO2 Play in Atmospheric CO2

The United Nations Intergovernmental Panel on Climate Change (“IPCC”) takes the simplistic view that all anthropogenic atmospheric CO2 comes from fossil fuels.

What is the reality?

Sharing the graphs in the image below, Prof. Salby explained: “During the decade before the turn of the century, fossil fuel emissions increased almost linearly. During the subsequent decade, it also increased linearly but three times faster.”  This increase can be seen in the steepness of the lines in the top graph.

The area under the curve represents the CO2 that was emitted into the atmosphere.  “Far more was emitted during the second decade than during the first decade – 200% more,” he said.

“During the same period, atmospheric CO2 also increased linearly,” he said. This can be seen in the second graph.

In the first decade, atmospheric CO2 increased by about 20 parts per million by volume (“ppmv”). During the second decade, unlike fossil fuel emissions, the increase of atmospheric CO2 was virtually identical to the first decade.

“Fossil fuel emission during the second decade was three times that during the first decade. Yet, its impact on the increase of atmospheric CO2 was virtually zero,” Prof. Salby said.

“Where the additional anthropogenic CO2 ended up cannot be said. Where it did not end up [i.e., in the atmosphere] is unambiguous,” he added.

“The premise of the IPCC that increased atmospheric CO2 results principally from fossil fuel emission is impossible,” Prof Salby said. Why?

Because “if fossil fuel emission represented as little as 10% of the increase in atmospheric CO2 the atmospheric increase during the second decade would have been 30% greater than during the first decade – it wasn’t even close,” he explained.

The graphic below of an estimate of the CO2 budget originates from the IPCC. “Of total emission, human emission accounts for only a couple of per cent.  The rest – over 95 per cent – comes from natural emission. Even a minor change of natural mission would overshadow human emission,” Prof. Salby said.

IPCC Climate Change Models

Prof. Salby then talked through, in detail, the assumptions and mathematical equations used in climate models to determine the contribution of anthropogenic CO2 to atmospheric CO2.

The principle that underpins it all is conservation law.  Conservation law, in physics, is a principle that states that a certain physical property (that is, a measurable quantity) does not change over time within an isolated physical system.  In short, what goes in must come out.

The conservation law is closely related to equilibrium.  While conservation law ensures that certain physical quantities remain constant over time, equilibrium is a state where the net external force acting on an object or system is zero. In the case of atmospheric CO2, equilibrium is reached when emission equals absorption. If the equilibrium is perturbed by an external force, a new equilibrium will be established.

The problem with global CO2 emissions is we don’t know the global absorption to be able to calculate the rate of emission. However, the IPCC thinks it does, Prof. Salby said.


As seen in the image above, the IPCC believes the global absorption is 150 gigatonnes of carbon.  “In truth [the 150 gigatonnes] is a little more than a guestimate. Observations of global absorption do not exist,” he said.

“It should therefore come as no surprise that IPCC estimates of major contributions change by as much as a hundred per cent,” he added.

There is a Way of Determining CO2 Absorption

During the 1950s and 1960s, nuclear bomb tests elevated carbon-14 (“C14”).  C14 is a radioactive isotope of carbon that is naturally produced in the upper atmosphere by the interaction of cosmic rays with nitrogen-14 atoms. This process is known as cosmic ray spallation. The produced C14 atoms combine with oxygen to form CO2. 

“The nuclear source was removed in 1963 by the nuclear test ban treaty.  C14 then decayed through unbalanced absorption,” Prof. Salby explained.  By “unbalanced,” Prof. Salby is referring to a perturbance in the equilibrium. “The decay was almost perfectly exponential with an absorption time of just under a decade,” he said.

Comparing this to the absorption of CO2 in the IPCC climate models, “even after 200 years almost 30 per cent of CO2 present initially, remains,” Prof. Salby said and presented the graph below.  The blue/green line represents the absorption from nuclear test C14 (decaying to produce CO2) and the pink line represents the absorption according to the IPCC climate models.

Another perturbation, or introduction of unbalanced absorption, is fossil fuels which introduce an anthropogenic component of CO2.  “With fossil fuel emission [it is] known … the conservation law completely determines the anthropogenic component,” Prof. Salby said.

The slowest absorption determines the “upper bound.”  This slowest absorption is the decay of C14 which is 10 years.

Observation of CO2 in the free atmosphere began in 1960.“ An upper bound follows by presuming that for all years before 1960, fossil fuel emission was equal to its maximum – namely, the fossil fuel emission in 1960. Recall, the perturbation never exceeds its equilibrium level.”

From this Prof. Salby was able to calculate the upper limit of anthropogenic CO2 in 1960 (10 ppmv) and its proportion of the total atmospheric CO2 (24%).  Using this as a baseline, Prof. Salby calculated that the upper limit of anthropogenic CO2 over the last 50 years increased by approximately 20 ppmv, 28% of the total increase in atmospheric CO2.

What Effect Does the Increase in Anthropogenic CO2 Have on Temperature?

Prof. Salby then used this upper limit of 28% to estimate the increase in temperature due to anthropogenic CO2. This is where the opacity of IR radiation becomes relevant. 

The opacity at most wavelengths is already saturated, at 100%, and the collective opacity has plateaued at 75%, Prof. Salby explained. Increasing CO2 to 280 ppmv adds only 6% to opacity and increasing CO2 further to 400 ppmv adds only another half a per cent, he said. “As we’ve seen, less than 30% [28%] of that increase is the fossil fuel perturbation.  It introduces a temperature perturbation of less than a tenth of a degree [Celsius].”

“The projected life for fossil fuel reserves is about 100 years. At the current growth of CO2, the opacity then will have increased by another 1%. Even then, the fossil fuel perturbation represents less than 40 per cent of the increase – it introduces an additional temperature perturbation of less than three-tenths of a degree,” he said. “The cumulative fossil fuel perturbation [over the 100 years] is less than half a degree.”

“The range of natural variability [in temperature] is half a degree to one degree. That’s considerably larger than the fossil fuel perturbation,” Prof. Salby said. “Without major amplification through feedback, the fossil-fuel perturbation is not even detectable. It’s smaller than the noise of natural variability.”

All of the above is an upper bound, the upper limit, which means the effects of fossil fuel cannot be greater.  It can, however, be smaller.  And as it turns out, it is, said Prof. Salby.

A More Definitive Treatment of CO2 Absorption

A disturbance or perturbation to CO2 emission is temporarily introduced and then removed from a system. This temporary nature of perturbations allows for a more definitive calculation of CO2 absorption.

CO2 is perturbed by changes in temperature which modulates CO2’s emission.  Perturbation in emission is proportional to the perturbation in temperature. And so, changes in temperature will produce proportional changes in CO2.  Although, there is a time lag between CO2 changes and the temperature change.  Changes in CO2 lag behind temperature changes.

Nature provides perturbations that allow scientists to study this lag and the effect temperature has on CO2 emission. Annual disturbances such as El Niño, La Niña and volcanic eruptions perturb global temperature, which perturbs CO2 emission.  Using these events to establish the lag of CO2 emission behind temperature, the absorption time of CO2 can be determined.  Using observation of these events, the absorption time has been calculated as 9 months.

“That’s 10 times faster than what’s apparent in the decay of carbon-14,” Prof. Salby said.  How can that be?

The short answer, he said, is that “carbon-14 lied, but not intentionally.”  It is presumed that when elevated C14 was taken out of the atmosphere, it stayed out of the atmosphere. “That is impossible,” he said and, although we haven’t noted the details here, explained why it was impossible.

“With an absorption time of less than a year [9 months], the anthropogenic fraction of increased CO2 isn’t just smaller than 30% – it’s smaller than 3%,” he said.

Natural Fluctuations in CO2

“During an interval of eight months from September to May, CO2 increases by 7.5 ppmv.  During the subsequent interval of four months, CO2 then decreases by about 6 ppmv,” Prof. Salby explained.  Noting that the sole reason CO2 decreases in those four months is due to unbalanced absorption. 

“Each year CO2 goes up five steps of 1.5 ppmv, then down four steps. Five steps up, four steps down … notice the residual after each cycle is 1.6 ppmv.  Ring a bell? It’s identical to the trend of CO2,” he said.

This annual step-up-step-down CO2 cycle, where 80% of the CO2 perturbation is absorbed in four months, shows that the absorption time of CO2 is less than the 9 months as calculated using the CO2 lag behind temperature method.  Using the annual CO2 cycle, the annual mean absorption time for CO2 is calculated as 7.5 months.

How Much of the Annual Increase in CO2 is Due to Fossil Fuels?

Each year, total CO2 increases by 1.6 ppmv.  Of that, 0.1 ppmv is due to anthropogenic emission.  “At only 0.1 ppmv per year, additional anthropogenic emission is eclipsed by additional total emission,” Prof. Salby said. 

He used various methods to calculate the proportion of anthropogenic CO2 emissions in the total increase in CO2 emission since 1960.  They all came out at less than 3% (between 1.3% and 2.8%).  The IPCC assumes that all anthropogenic CO2 emissions come from fossil fuels. Based on this assumption, it means that fossil fuel emission contributes less than 3% to the increase in CO2 emission.

“The fossil fuel perturbation is minute,” Prof. Salby said.  “The fossil fuel perturbation is too small to even be detectable … [It] is presently not detectable.  It will not be detectable, ever.”

Speaking of the dramatic language relating to fossil fuel emissions used by advocates of the climate change agenda Prof Salby said: “Never has so much been claimed on the premise of so little.”

Below, we have embedded Prof. Salby’s presentation to begin at the final 10 minutes where he starts his conclusion.  If you are unable to watch his full presentation, these 10 minutes are well worth hearing.  He speaks about the subversion of science by “government bureaucracy under the aegis of the UN.”  Its objective, he said in 2016, “has become an exercise in social engineering to predict and control the undetectable.”

Prof Murry Salby Lecture: ‘Atmospheric Carbon’, 18 July 2016 (85 mins)


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