The Failed Predictions of Nikolov and Zeller from 2011

Nikolov and Zeller (NZ) published a "paper" (this link downloads a pdf) in 2011 that claims to be a "unified theory of climate" (UTC). In it they offer the nuts and bolts of what they think is an alternative explanation for the greenhouse effect (GHE). Instead of greenhouse gases (GHGs), they argue that long-term climate changes are caused by changes in atmospheric mass that change atmospheric pressure. The change in pressure changes global temperature via the ideal gas law (IGL). This concept has already been debunked; there's nothing resembling a working theory here. They seem very confused about the fact that it's work applied to compressing a gas that increases its temperature (and pressure); at hydrostatic equilibrium, pressure doesn't do work, and so pressure doesn't cause temperature to increase. If pressure could perform work to increase temperature, it would violate conservation of energy. Pressure changes as a result of the work that increases in the average kinetic energy of the molecules (temperature) in the gas. Gases will heat in response to the work of compressing it, but if left compressed, temperature will then return to thermal equilibrium with its surroundings, and pressure will change with it. Of course, on longer timescales, pressure does change, mostly with changes in atmospheric composition. However, in general a warming Earth correlates with an expanding troposphere (lower atmospheric density) while pressure remains roughly constant.

NZ's model predicts surface pressure must correlate with temperature long-term,
with albedo correlating with temperature short-term

But NZ created a model which allows them to "predict" what surface pressure must have been given GMST in the geologic past. For instance, their model in this paper predicts that mean surface pressure must have been double that of today during the PETM. In 2021, they altered this prediction to give the PETM four times current atmospheric pressure of today. This is from a post in 2024.

Of course, they do not bother to test these predictions against experiment. They never evaluate any evidence that the atmosphere gained mass to cause a fourfold increase in pressure during the PETM or how it lost mass later. Much of their UTC is appears to be untestable; or at least they are unwilling to test it. 

However, this paper does make some predictions that allow us to test their UTC against experiment using empirical data following 1998. Let me quote the relevant paragraph in full:

Earth’s climate is currently in one of the warmest periods of the Holocene (past 10K years). The Planet is unlikely to become any warmer over the next 100 years, because the cloud cover appears to have reached a minimum for the present level of solar irradiance and atmospheric pressure, while the solar magnetic activity began declining, which will likely lead to more clouds, higher planetary albedo, and cooler surface temperatures. The observed lack of global warming since 1998 and the presence of significant cooling trends in some regions such as the continental USA for the past 12 years may be the first signs of a climate reversal. According to the hereto proposed UTC, at present, only a sizable increase of total atmospheric mass can bring about a significant and sustained warming. However, human-induced gaseous emissions are extremely unlikely to produce such a mass increase. Hence, there is no anthropogenic forcing to global climate.

This paragraph makes claims that can be treated as theoretical predictions to test whether their "unified theory" is a useful replacement for climate science:

1. The so-called "pause" since 1998 will continue for the next 100 years, so we are unlikely to see any more warming until 2100.
2. Cloud cover has reached its minimum given current TSI and atmospheric pressure, and TSI has been declining.
3. We should see more clouds and higher albedo going forward, leading to a climate reversal; that is, he thinks there are already signs of cooling.
4. Only a sizable increase in atmospheric mass could bring about sustained warming. That is, more atmospheric mass would have to be added to increase atmospheric pressure and cause the planet to warm.

But since 2011, each and every one of these predictions have failed. Contrary to their predictions:

1. GMST has continued to warm since 2011 and since 1998. Warming has progressed at rates exceeding 0.2 C/decade, and 2023-2024 experienced a large warming spike likely associated with a decline in albedo, with some fraction having to do with reduced aerosols and decreased cloud cover.
2. Albedo and cloud cover have decreased, and this has been sustained for over 20 years.
3. We have not seen the increase in albedo or cloud cover he predicted in 2011; in fact, just the opposite.
4. There has been no "sizable increase in atmospheric mass." As a global average, atmospheric mass and pressure have been essentially constant since 1850.

What has changed since 1998? The concentrations of GHGs have continued to increase, and aerosol pollution has decreased, unmasking a portion of the warming effect of those GHGs. So what can we conclude from this? Quite clearly that Nikolov and Zeller do not have any working "unified theory." Not only does it falsely assume pressure does work (and therefore adds energy to the climate system), it also failed multiple theoretical predictions from almost 15 years ago. Changes in GMST have had nothing to do with changes in atmospheric mass or pressure, as they claim. Neither TSI nor pressure offer a lower limit to albedo or cloud cover. Albedo can decrease and GMST can warm, and these things happen with no change in atmospheric mass and pressure.

I thought about showing all the graphs with the data that demonstrate these failed predictions, but I don't think even NZ dispute the observations since 1998; I think NZ are just hoping nobody remembers they actually said these things. But above l linked to other posts of mine that do show the data supporting these observations, so if you're interested, you can check those out. This link contains all my posts about Nikolov and Zeller.

Reference

[1] Nikolov, Ned S. and Karl Zeller. “Unified Theory of Climate Expanding the Concept of Atmospheric Greenhouse Effect Using Thermodynamic Principles : Implications for Predicting Future Climate Change.” (2011).