Simple Physics and Complex Climate

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See German summary at the bottom of the post.

This is exactly my reaction, when I was first confronted with Global Warming as a relatively simple linear function of CO2 concentrations, way back in the early 1990s: 

I refused to believe that a single factor could dominate something as complex as the world's climate.

Incidentally, at the time, I met a German Professor of Chemistry in a wine bar in Frankfurt. He just happened to sit next to me at the counter, eating a bowl of chilli con carne, occasionally sipping at a glass of red wine. A well-clad gentleman, he was in a foul mood, complaining with disgust about the climate models that had come into use even then.

He said that the models were basically haystacks whose purpose it was to hide the convenient manipulations that it took to let the climate look like the horror scenarios intended by the alarmist camp. It was easy to get any result from them that you might care for.

And despite the disguise of mathematical complexity, the climate models are based on a very simple fundamental relationship - temperatures being conceptualised as a linear function of CO2-mediated solar forcing - which epitomises their basic inadequacy in the face of a hugely intricate interconnectedness of factors contributing to climate change.

Willis Eschenbach puts his finger on it when he argues that simple physics just is not good enough to come to grips with climate change. The subject matter is far more complex than the phenomena dealt with by "simple physics".

Eschenbach notes that putting a block of iron (or steel or copper or glass) at one end of it into hot water while measuring temperature change on the other end confronts us with a phenomenon of the type that can be dealt with successfully by simple physics. It will yield useful regularities and provide us with explanations that can be beneficially relied upon.

But put your feet in a tub of hot water and measure the outcome of this on the other end of the "object" (your head with a thermometer in your mouth), and the result will be complicated by complex influencing factors.

I sit with my feet in the bucket of hot water, put the thermometer in my mouth, and wait for my head to heat up. This experimental setup is shown in Figure 1 above.

After all, simple physics is my guideline, I know what’s going to happen, I just have to wait.

And wait … and wait …

As our thought experiment shows, simple physics may simply not work when applied to a complex system. The problem is that there are feedback mechanisms that negate the effect of the hot water on my cold toes. My body has a preferential temperature which is not set by the external forcings.

Writes Eschenbach:

I keep reading statements in various places about how it is indisputable “simple physics” that if we increase amount of atmospheric CO2, it will inevitably warm the planet.

But Eschenbach warns:

Unfortunately, while the physics is simple, the climate is far from simple. It is one of the more complex systems that we have ever studied. The climate is a tera-watt scale planetary sized heat engine. It is driven by both terrestrial and extra-terrestrial forcings, a number of which are unknown, and many of which are poorly understood and/or difficult to measure. It is inherently chaotic and turbulent, two conditions for which we have few mathematical tools.

The climate is comprised of five major subsystems — atmosphere, ocean, cryosphere, lithosphere, and biosphere. All of these subsystems are imperfectly understood. Each of these subsystems has its own known and unknown internal and external forcings, feedbacks, resonances, and cyclical variations. In addition, each subsystem affects all of the other subsystems through a variety of known and unknown forcings and feedbacks.

Then there is the problem of scale. Climate has crucially important processes at physical scales from the molecular to the planetary, and at temporal scales from milliseconds to millennia.

As a result of this almost unimaginable complexity, simple physics is simply inadequate to predict the effect of a change in one of the hundreds and hundreds of things that affect the climate. 

The way a river constantly evolves provides an example of a flow system that is too complex to be well described by simple physics: 

[J]ust as in our experiment with the steel block, simple physics simply doesn’t work in this situation. Simple physics says that things roll straight downhill, and clearly, that ain’t happening here … it is obvious we need better tools to analyze the flow of the river.

Are there mathematical tools that we can use to understand this system? Yes, but they are not simple. The breakthrough came in the 1990’s, with the discovery by Adrian Bejan of the Constructal Law. The Constructal Law applies to all flow systems which are far from equilibrium, like a river or the climate.

It turns out that these types of flow systems are not passive systems which can take up any configuration. Instead, they actively strive to maximize some aspect of the system. For the river, as for the climate, the system strives to maximize the sum of the energy moved and the energy lost through turbulence. See the discussion of these principles here, here, here, and here. There is also a website devoted to various applications of the Constructal Law here.

There are several conclusions that we can make from the application of the Constructal Law to flow systems:

1. Any flow system far from equilibrium is not free to take up any form as the climate models assume. Instead, it has a preferential state which it works actively to achieve.

2. This preferential state, however, is never achieved. Instead, the system constantly overshoots and undershoots that state, and does not settle down to one final form. The system never stops modifying its internal aspects to move towards the preferential state.

3. The results of changes in such a flow system are often counterintuitive. For example, suppose we want to shorten the river. Simple physics says it should be easy. So we cut through an oxbow bend, and it makes the river shorter … but only for a little while. Soon the river readjusts, and some other part of the river becomes longer. The length of the river is actively maintained by the system. Contrary to our simplistic assumptions, the length of the river is not changed by our actions.

So that’s the problem with “simple physics” and the climate. For example, simple physics predicts a simple linear relationship between the climate forcings and the temperature. People seriously believe that a change of X in the forcings will lead inevitably to a chance of A * X in the temperature. This is called the “climate sensitivity”, and is a fundamental assumption in the climate models. The IPCC says that if CO2 doubles, we will get a rise of around 3C in the global temperature. However, there is absolutely no evidence to support that claim, only computer models. But the models assume this relationship, so they cannot be used to establish the relationship.

However, as rivers clearly show, there is no such simple relationship in a flow system far from equilibrium. We can’t cut through an oxbow to shorten the river, it just lengthens elsewhere to maintain the same total length. Instead of being affected by a change in the forcings, the system sets its own preferential operating conditions (e.g. length, temperature, etc.) based on the natural constraints and flow possibilities and other parameters of the system.

Final conclusion? Because climate is a flow system far from equilibrium, it is ruled by the Constructal Law. As a result, there is no physics-based reason to assume that increasing CO2 will make any difference to the global temperature, and the Constructal Law gives us reason to think that it may make no difference at all. In any case, regardless of Arrhenius, the “simple physics” relationship between CO2 and global temperature is something that we cannot simply assume to be true.

 And Eschenbach, therefore, concludes here:

I hold [...] that the temperature of the [climate] system is relatively insensitive to changes in forcing. This, of course, is rank heresy to the current scientific climate paradigm, which holds that ceteris paribus, changes in temperature are a linear function of changes in forcing. I disagree. I say that the temperature of the planet is set by a dynamic thermoregulatory system composed of emergent phenomena that only appear when the surface gets hotter than a certain temperature threshold. These emergent phenomena maintain the temperature of the globe within narrow bounds (e.g. ± 0.3°C over the 20th Century), despite changes in volcanoes, despite changes in aerosols, despite changes in GHGs, despite changes in forcing of all kinds. The regulatory system responds to temperature, not to forcing.

Deutsche Zusammenfassung: 

Ein Kernproblem der zeitgenössischen Klimaforschung besteht darin, dass sie methodisch so aufgestellt ist, als ließe sich das Klima der Erde mit der Physik einfacher Erscheinungen ("simple physics") erfassen. 

Obwohl die vorherrschenden Klima-Modelle außerordentlich kompliziert sind, ist der grundlegende Erklärungszusammenhang, auf den sie festgelegt sind, sehr einfach: 

Sie erklären die Durchschnittstemperatur auf der Erde als eine lineare Funktion der durch CO2 "eingefangenen" Sonneneinstrahlung. 

Es wird also behauptet, die Welttemperatur werde durch einen Sensitivitätsfaktor geregelt, und zwar so, dass eine Verdoppelung der CO2-Konzentration in der Atmosphäre einen Wärmeanstieg um das x-fache verursache.

(Beiläufig: es gibt laut IPCC nicht genügend fossile Brennstoffe, um eine Verdoppelung der CO2-Konzentration in den betrachteten Zeiträumen zu ermöglichen, so dass selbst die höchsten Sensitivitätswerte nicht zu einem Katastrophenszenario führen können.)

Das Klima gehört jedoch nicht dem Universum der einfachen physikalischen Phänomene an. 

Es ist nicht vergleichbar mit einem Stab aus Stahl, Kupfer oder Glas, dessen Reaktion auf Erwärmung durch einen einfachen Funktionszusammenhang abgebildet werden kann. 

Eher ähnelt es dem sehr viel komplexeren "Objekt" Mensch, der in der Lage ist mit Hilfe seines Körpers und durch sein Verhalten, die Auswirkungen von Temperatureinflüssen variabel auszusteuern.

Das Weltklima stellt eine komplexe selbstregulierende spontane Ordnung dar, die bei Auftreten von bestimmten Schwellentemperaturen, und nur dann, also unabhängig von der Stärke aufheizender Wirkkräfte ("forcing" möglicherweise verursacht durch CO2, Vulkane, Wolkenbildung etc.), dafür sorgt, dass die Temperatur innerhalb einer bestimmten Spanne verharrt.

Solche spontanen selbstregulierenden Abläufe sind mit den Mitteln einer Physik, die auf einfache Wirkzusammenhänge geeicht ist, nicht zu erfassen. 

Klimaforscher, die einfache lineare Funktionszusammenhänge mit komplizierten Modellen zu beglaubigen suchen, forschen unweigerlich am Klima - wie es sich tatsächlich entwickelt - vorbei.