This post is a translation of a post on my blog in Italian. It originates from a post published by “The Skeptical Chemist,” an Italian expatriate in Europe whose real name is unknown but who clearly has a deep knowledge of chemistry, in particular pharmaceutical chemistry. His blog and his pages on social media were very successful during the pandemic when he criticized the various manipulations of the truth by the powers that be. As you may have expected, the PTBs took their revenge by making his blog disappear from search engines and social media and also directing against him the wrath of a crowd of clowns in search of a circus. The Skeptical Chemist abandoned social media; he still publishes his blog, but has closed the comments. In this post, you find references to the “grillini,” members of the Italian “five star” populist party created by Beppe Grillo. The post also mentions Franco Prodi, an Italian atmospheric scientist who criticized the current climate change interpretation.
The “Skeptical Chemist” brings up an interesting and little-known graph on his blog. It is the "power spectrum" of the natural variability of temperatures on a time scale ranging from tens of millions of years to a few minutes. The peaks you see represent the intensity of cycles of a certain frequency. You see the daily cycle of night and day, and the yearly cycle of the seasons. You may note the “100 kyr” peak that corresponds to the cycles of ice ages and interglacials of the last million years or so.
One look is enough to hear voices screaming, “Climate has always changed!!! So what does man have to do with it??” The implication is that the climate is chaotic, so we can't make predictions. Wrong. Completely wrong. If we talk about cycles, it means that the system is periodic, that is, it is NOT chaotic; at least as far as these cycles are concerned. Which means that it is predictable, at least within certain limits.
Correctly, at this point, the skeptical chemist notes about the populist 5-star movement (the “grillini”) that “the grillini could conclude that this is all stuff to throw away” but that is “a bad grillino conclusion, wrong as always.” Unfortunately, the grillini are not the only ones who arrive at this conclusion; there are a lot of people out there who seem to think that saying "the climate has always changed" is something smart, and they love to say that while solemnly shaking their head. The Skeptical Chemist also cites the atmospheric scientist Franco Prodi; a more serious and prepared person, but who also says more or less the same thing: since the climate changes all the time, no conclusion is possible. But that’s not what the graphic shows.
The matter needs to be explained, and the post makes several correct points, but it is a long comment that may be confusing at times. Let me explain where that graph comes from and how it should be interpreted without going into the details.
The first version of that graph dates back to 1976 (!!) and should be taken with great caution, considering that the author of the graph (Mitchell, JM (1976). An overview of climatic variability and its causal mechanisms. Quaternary Research, 6(4), 481–493) says it is the result of an "educated guess" (!!). A subsequent version dates back to 2002 and can be found at this link, where the graph is defined as "artistic". It's the one linked by the skeptical chemist.
So, the graph should be taken with great caution. You find an in-depth but complicated discussion in this recent article by Franzke et al., where the graph is cited, but we don't find an updated version simply because we don't have enough data to make a reliable quantitative version. Overall, however, we can say that the graph is qualitatively valid.
So, what can we say from it? Well, nothing that wasn't known, even without graphs. Like other complex systems, the Earth's climate is subject to cycles of varying periodicity. These cycles are typical of complex adaptive systems (CAS), which include biological, social, economic, and other systems. A simple example is the Lotka-Volterra system, the one about foxes and rabbits, which is the basis of the concept of biological cycles.
The essence of the story is that if the climate changes, there is something that makes it change - we can call this "something" as "forcing," but the term used is not a crucial point. Complex systems tend to react like a guitar string, oscillating at natural frequencies that depend on its physical characteristics. Depending on how you adjust it, the string will oscillate at different frequencies, therefore producing different notes. The ecosystem will also produce climate oscillations at different frequencies.
To explain with an example, consider the 100,000-year cycle of ice ages. This is usually related to Milankovitch cycles, that is, oscillations in the solar irradiation that the Earth receives. But the intensity of these variations is not sufficient to generate glacial cycles; it is the whole system that resonates with a series of physical and biological effects. It's a fascinating and complex story, and also a little-known one. It would be worth telling in detail, but this is just a blog, not a treatise on climate science (maybe I'll try one of these days).
To return to the discussion about the grillini and others, the fact that there are detectable climate cycles does not mean that human activity cannot change the climate. In some cases, the interplay of forcings and feedback generates cycles that appear in the spectrum shown in the figure. However, the spectral analysis “sees” only periodic phenomena within the time limits examined. The recent human forcing could not fit in it, simply because there have been no humans on this planet for the last 4 billion years. To see cycles generated by intelligent species (so to speak), we would need — at the very least — to extend the scale of the graph to several tens of billions of years into the future. But the planet is only 4 billion years old or so, and it won't last that long. Thus, the graph does not demonstrate, and could never demonstrate, that humans do not affect the climate.
Another example to explain the concept: a single human being has a "power spectrum" that shows peaks created by various metabolic cycles: heartbeat, breathing, sleep/wake, and many others. But if someone hits you on the head, this is a forcing that you won’t see in the power spectrum because it happened once and, after the hit, there will be no power spectrum unless it was a near miss. I think you understand what I mean.
The climate has always changed, and we are late to the party, but hell, it's our turn now!
:-o