A Simple Test of Nikolov's Alternative to Greenhouse Gases

This is a follow up to a post about Nikolov & Zeller here, updated on 4/14/2025.

In a recent manuscript[1] "published" on the so-called Science of Climate Change blog, Nikolov and Zeller (NZ) articulate how they believe that the Earth's temperature remains warmer than its effective temperature. Without getting into whether that amount should be considered 90K or 33K, it's clear that for them the long-term baseline temperature of earth is determined solely by total solar irradiance (TSI) and atmospheric pressure (P). Here it is in their words:

NASA planetary data indicate that the radiative “greenhouse effect” does not exist in reality. That’s because, across a wide range of planetary environments in the Solar System, the long-term (baseline) global surface temperature on rocky planets and moons is fully determined by the mean Total Solar Irradiance (i.e. distance from the Sun) and total surface atmospheric pressure.

Variability on this long-term baseline temperature is set by albedo (short-term) and changes in atmospheric mass (long term). Again, here it is in their words:

On time scales of thousands to millions of years, the Earth’s climate is driven by changes in total atmospheric mass & surface air pressure, which control the Earth’s baseline temperature.... On time scales of decades to centuries, the climate is modulated by cosmically forced variations of cloud albedo. Albedo changes only cause limited fluctuations of the global temperature around a baseline value set by TSI and total pressure (i.e. about ±1 K)

Since surface air pressure is determined by the Earth's gravity and mass of the atmosphere, this claim reduces to the need to explain all of Earth's variability in global mean surface temperature (GMST) in terms of atmospheric pressure (for long term fluctuations) and changes in cloud albedo (for short-term fluctuations). So to summarize, NZ claim that what scientists call greenhouse gases are irrelevant to global temperatures, and GMST is actually governed by only three factors: TSI, pressure (P) and albedo (α), with changes in pressure governing long-term fluctuations in temperature and albedo responsible for short-term fluctuations in temperature.

Now to evaluate this claim, we should begin by acknowledging that global temperature is governed by the balance of absorbed solar radiation (ASR) and outgoing longwave radiation (OLR). At equilibrium, the two are equal. We can express this with the following equation:  

ASR = OLR

TSI*(1-α)/4 = εσT^4

Of the three factors that NZ mention, only two (TSI and α) make an appearance in this equation; pressure is missing. In its place, there is a term for emissivity (ε), but NZ do not include ε as a factor in global temperatures (the emissivity of the Earth's surface is about 0.98). I'm going to argue that NZ are essentially assigning fictional properties to P so that it can take the place of GHGs (which affect the emissivity of the Earth's atmosphere). So I think it best to evaluate NZ's claims with a stepwise approach, beginning with the two known factors that we all agree influence temperature (TSI then albedo), and then seeing if NZ can successfully make a case that pressure can substitute for GHGs to bridge the gap between Earth's effective and observed surface temperature. 

TSI

NZ understand that the Earth's temperature history cannot be explained by changes in TSI alone. In fact, we know how TSI has changed on geologic time scales. The Sun increases in brightness predictably over time, and so TSI at any time in geologic history can be calculated as following:

TSI = TSIp/[1+0.4(1-T/To)], where

    TSI = the solar constant at T
    TSIp = the solar constant at present (1361 W/m^2)
    T = time in the past from the age of the earth
    To = the age of the earth (4567 million years)

Using this, we can reconstruct TSI since on geologic time scales. It was 1296 W/m^2 at the beginning of the Phanerozoic and increased to 1361 W/m^2 today in a roughly linear fashion. If we assume a constant albedo of 0.306, the Earth's temperature history would look like this.

If the Earth's temperature was governed only by TSI with a constant albedo, we would see a gradual, near linear warming effect in global temperatures, increasing from ~252K 500 million years ago to ~255K today. This is ~33K colder than what is actually observed today. Nikolov, at the very least, understands that we need more than just TSI to explain variability in GMST.

Albedo

NZ also seem to understand that adding albedo to the mix can't explain the actual temperature variability observed in geologic history. For now I'm going to take for granted that pressure has the magical ability to raise the Earth's temperature ~33K above its effective temperature. But since this claim is essentially an appeal to magic, there's nothing in our energy balance equation where pressure is relevant. So for this step, I set ε to 0.605. Doing so makes current temperature equal 288 K. Holding ε constant at 0.605, I calculated the changes in albedo (α) necessary to explain variability in GMST recorded in Emily Judd's reconstruction of global temperatures for the last 485 million years, and ε = 0.605 as a substitute for constant pressure. I came up with this. 

It should be easy to see that it's impossible for changes in albedo to explain changes in GMST on geologic time scales. If emissivity (our substitute for pressure) is constant, the Earth has been warm enough for large periods in geologic history to require an albedo lower than 0.2, and during warmest portions, even lower than the 0.1, the presumed albedo of the Earth with no clouds or ice. So we can't rely on albedo to explain changes in temperature on geologic time scales. And NZ also admit that this is the case: "albedo changes only cause limited fluctuations of the global temperature around a baseline value set by TSI and total pressure." So we can rule out changes in albedo in explaining Earth's geologic temperature history.

Pressure

So to explain this temperature variability on geologic time scales, NZ need for something beyond TSI and albedo to change. Scientists understand that greenhouse gases (GHGs) are responsible for this, but NZ substitute atmospheric pressure for GHGs. How is that accomplished? The ideal gas law (IGL) is often invoked by NZ (and their supporters) to explain this:

T = MP/(Rρ) where,

    T = atmospheric temperature in Kelvin
    M = atmospheric mean molar mass gm/mol⁻¹)
    P = atmospheric pressure in kPa
    R = gas constant (m³, kPa, kelvin⁻¹, mol⁻¹) = 8.314
    ρ = atmospheric density in kg/m³

In this equation, if you know the constants and values for all variables but one, you can solve for the one you're missing. If you know M, T and ρ, you could solve for P. But what does that tell you? Nothing at all about what changes T. In the real world, as T increases, ρ decreases with it (since the troposphere expands) leaving P essentially constant. P set by the Earth's gravity and the mass of the atmosphere.

It's also clear that P does not and cannot determine T, nor can changes in P drive changes in T. Take for instance a container filled with air at room temperature; if you compress the air, the temperature and pressure increases because of the work applied in compressing the container, reducing its volume. If you leave the container at that reduced volume, the temperature will return to room temperature (and pressure will decrease) because no additional work is being applied to the air in the container. In other words, pressure itself can't keep a gas hot or force temperatures to increase. The IGL just observes that relationships exist between T, P, and ρ; when temperature increases, at least one of the other variables in the equation must change in response. 

Nevertheless, for NZ to show that pressure can substitute for GHGS, they need to show that the above changes in GMST on geologic time scales are explained by changes in either atmospheric mass or gravity. On X, Nikolov has tried three ways to do this:

1. Gravity: If the force of gravity changes, P will change with changes in gravity.
2. Earth's Size: If the Earth changes is size then the amount of mass on top of any square meter of Earth will change, and atmospheric pressure will change.
3. Atmospheric Mass: If the atmosphere changes mass (that is, if the atmosphere contains more or less molecules) then P will change with changes in mass.

In fact, Nikolov is compelled to imagine that there have been large changes in the Earth's gravity, size and atmospheric mass. This leads to some rather bizarre and ludicrous notions about gravity and the size of the Earth. Let's look at his claims about each of these, noting that they are all inter-related.

Gravity

For changes in gravity, see here and here and here, where Nikolov suggests that the force of gravity was smaller in the past. His evidence? Dinosaurs with long necks couldn't hold up their heads if gravity then was as it is now.

It turns out that biologists have actually studied sauropods and evaluated how they may have held their heads. There's good evidence that sauropods did not in fact hold their necks up (as pictured above) but kept them in a horizontal position. Roger Seymour, who studies sauropods such as Apatosaurus , shows that there is strong evidence for ligament structures that would support their necks horizontally "at no energy cost to the animal," and their neck musculature was used to pull their necks down, not up (much like horses). This was published in 2009,[2] so there's no excuse for Nikolov to be unaware of this evidence. It appears that Nikolov invented a problem that was already solved so that he could devise a fictional solution having to do with gravity to support his fictional claims about pressure.

Earth's Size

Nikolov also subscribes to the "expanding earth" view as a replacement for plate tectonics, a pseudoscience position that suggests the earth's size is increasing, and this is what explains the motion of the continents. See here and here and here. The following post shows how his claims about both gravity and an expanding earth relate to each other.

Scientists are able to measure the movement of tectonic plates. They can see subduction zones and mid-ocean ridges. Scientists can also determine that the Earth's size is not expanding. So we can observe plate tectonics in operation without any need for Earth's expansion. There's no reason to propose an expanding earth, but this pseudoscience idea is a useful fiction that Nikolov can invoke to support the fictional properties he's assigning to pressure.

Atmospheric Mass

It should be acknowledged that changes in atmospheric composition has had an effect on atmospheric mass, and therefore atmospheric pressure. We know that atmospheric mass has changed somewhat over geologic history. The planet's atmosphere was likely denser in the Archean, and major changes in geologic history has had an impact on atmospheric composition that could affect total atmospheric mass, like the great oxidation event when photosynthesis began and turned the atmosphere into an oxygen rich atmosphere. These changes could have an impact atmospheric pressure. However, geologic evidence does not support large swings in atmospheric mass corresponding to changes in temperature in the Phanerozoic. In point of fact, his claims along these lines are again truly bizarre:

Notice that Nikolov has not found evidence for any of these changes in pressure. He developed a model that "predicts" how pressure would change if his "theory" is true, then calculated what those changes in pressure would be. In other words, all he's done is take a temperature reconstruction and, and using his model, calculated what mean surface atmospheric pressure would satisfy the IGL. And his model produces absurd results, making atmospheric pressure almost 4x larger during the PETM. Where did all that atmospheric mass come from? Where did it go at the end of the PETM? Nobody knows. If you make a model that produces absurd results, the rational conclusion is that the model is wrong. NZ appear to have concluded that the world is actually absurd. For any temperature, there is an atmospheric density value that will satisfy the IGL without having to change pressure at all; there is no physical reason to vary pressure with temperature as their model suggests. Now if Nikolov could actually show that pressure changed over the last 100 million years as described in this graph, well that would be interesting. But he hasn't done this. 

Here's another attempt by Nikolov to explain the variability of GMST during the glacial cycles of the Quaternary using pressure. Again, all he has done is the mean of two temperature reconstructions and feed them into his model to produce the supposed change in mean atmospheric pressure that would satisfy the IGL.

But Nikolov's model requires that atmospheric pressure be some 30-40% lower during glacial maxima than during thermal maxima. Given that the Earth's size hasn't changed and the force of gravity hasn't changed in the last 780,000 years, this means that Nikolov has to imagine that atmospheric mass experiences radical swings to cause these changes in surface pressure. Where does the extra mass come from to produce this increase in pressure? Where does it go when pressure decreases? Nobody knows. Scientists understand that these glacial cycles of the Quaternary sync with orbital cycles; over the last million years, they have synced with eccentricity. The Earth's orbit around the Sun becomes more or less elliptical (due to the gravitational pull of Jupiter) with a periodicity of 100,000 years. This causes changes in seasonal insolation on Earth and therefore variability in temperature. How does this also add to and subtract from the mass of Earth's atmosphere? Nobody knows. 

We also know that atmospheric composition has changed a little during this time frame, since CO2 varies by about 100 ppm between the glacial maxima and thermal maxima, and even Nikolov knows that this change can't produce meaningful changes in atmospheric mass. In one post on X, he makes this clear with regard to human emissions: "Human carbon emissions (currently at about 11 Gt/year) are like a 'fart in the wind' with respect to the mass of Earth's atmosphere, which is 5.148×10^6 Gt. So, we emit annually a gas mass that's 0.0002% of Earth's atmospheric mass." So how does atmospheric mass change across the Quaternary to produce these changes in temperature? Nobody knows.

Conclusion

I don't share these posts on X just to turn this post in to a hit piece for Nikolov. These are bizarre and hilariously ludicrous ideas, but that's not why I share them. I share them because Nikolov needs for these kinds of things to be true for his crank explanation for the GHE to be valid. You cannot explain long-term temperature variability of the Earth by TSI and albedo alone. Since NZ reject the overwhelming observational evidence regarding greenhouse gases, he needs something else to fill the void. To do this, he must assign magical properties to pressure and then invent ways to get pressure to change. It's his rejection observational data about GHGs that puts him into the position of needing to invent these bizarre and ludicrous ways to get atmospheric pressure to change.

If we accept that greenhouse gases and high altitude clouds are responsible for the greenhouse effect, we no longer need to assign magical properties to pressure, and we don't have to invent bizarre and ludicrous ways to get it to change just so to make the crank theory work. So it's baffling to me that anyone would buy into NZ's position unless they are either ideologically motivated to do so or blatantly unaware of how the IGL works, or both.

And to be clear, in the world we live in where greenhouse gases are responsible for the greenhouse effect, pressure is relevant to temperature. Perhaps the most significant way is what scientists call pressure broadening, which causes CO2 to absorb more along the "wings" around the central 15 μm band. But pressure itself simply does not have properties allowing it to either generate or trap energy on its own. If the Earth's atmosphere were completely transparent to LWR emitted from the surface, it would escape to space unimpeded regardless of the pressure of the transparent atmosphere.

References:

[1] Ned Nikolov, Karl Zeller. Toward a New Theoretical Paradigm of Climate Science. Proceedings of the International CLINTEL Prague Science Conference. https://doi.org/10.53234/scc202412/22

[2] Seymour Roger S (2009). Raising the sauropod neck: it costs more to get less. Biol. Lett. 5317–319. http://doi.org/10.1098/rsbl.2009.0096