Gaia's Forge: when you are the hammer, hit. When you are the anvil, sit.

How CO2 concentrations and temperatures are correlated

“When you are the hammer, hit. When you are the anvil, sit” is the literal translation of a saying in Italian, here demonstrated by the Goddess Gaia in her forge. It is a good illustration of how dynamic systems function: sometimes you are a forcing (hammer), sometimes you are a feedback (anvil). Note the low neckline of Gaia’s dress in this image created by Dall-E. It doesn’t look like the kind of dress that a female blacksmith would wear, but maybe the AI knows more than it seems. If you ever tried to use an old-style forge, you noticed that the red-hot smithereens will fizzle out and do no damage when reaching your sweat-covered skin — and you sweat a lot when hammering iron! The Goddess seems to be adopting a hammering strategy based on naked skin but, for obvious reasons, not completely.

The great wave of skepticism that’s engulfing science risks to submerge it and drown it forever. It may happen, and if it happens, it means that there were reasons for it to happen. One is the fact that decades of heated political discussions have left a trace of misunderstandings and incomprehension all over the debate. Another is that the PR campaign against climate science and its consequences continues unabated, and taking always new and different forms. In this post, I would like to discuss an old misunderstanding that recently became fashionable again.

You surely saw the data showing the oscillations in Earth’s temperatures and CO2 concentration over the past 500-800 thousand years ago. These data have been known since the early 2000s and were shown in Al Gore’s “An inconvenient truth” film in 2006. The plot below is taken from Euan Mearns’s blog, published in 2017,

I know Euan Mearns personally, and he is a smart guy in all respects. However, when commenting on this diagram, he made a typical mistake: he thought he had discovered something new, not realizing that it had been known for a long time. Noting that CO2 trends trail those of temperatures, Mearns comments, “The climate Science community continues to ignore the fairly profound implications of what the data actually shows.”

Unfortunately, Mearns arrived at least 10 years too late. This trend had already been noted and discussed in 2003. The idea that the time lag disproves global warming was already defined as a “myth” in 2007.” For details, you can see the “paleoclimate” section of the IPCC reports. The interpretation of the Vostok data in the latest version (6th report) has not significantly changed from that of earlier reports.

Yet, several intelligent persons recently told me that they can’t believe a word of what climate scientists say because “CO2 lags warming in the ice core records.” Some of them added that this was a recent discovery that the climate science community had completely missed.

It is likely to be the result of the new tack of the ongoing PR campaign against climate science. Up to recent times, it was mostly based on demonizing climate scientists (do you remember “Climategate”?). Now, it is aiming at “un-demonizing” carbon dioxide. How can this friendly molecule do all the damage attributed to it? No, it is a good thing; it is plant food, and it helps us fight world hunger. Such small amounts of it could never have any effect on temperature,

In part, this new campaign pivots on the papers published by Demetris Koutsoyiannis, a geologist. A prolific (to say the least) scientist, he has already published 38 papers in scientific journals in 2024 (!!) (more than three papers/month and counting). Several of his articles are dedicated to what he calls the “hen and egg” question, that is, to the CO2/temperature relationship in climate science (that he calls a “doctrine.”).

Just as several others, Koutsoyannis keeps beating the same dead horse, demonstrating over and over that CO2 trails temperatures and not the reverse. He comments, “These results contradict the conventional wisdom, according to which the temperature rise is caused by CO2 increase.” Too bad that there is no such “conventional wisdom” in climate science.

It is the usual problem. Climate is a complex system, but people tend to reason in linear terms, that is, in terms of cause and effect. So, they expect that if CO2 can cause atmospheric warming, then it must always be the cause of warmig. But no, it doesn’t work that way. In complex systems, there are no causes and effects; there are only forcings and feedback. In the climate system, CO2 and atmospheric warming go together in a reciprocal feedback relationship.

Therefore, there is nothing especially profound or unexpected in the fact that CO2 lags temperatures in the record of the Pleistocene, the epoch that preceded the current Holocene. It would be weird if it were the opposite; if CO2 were the forcing, where would it come from? During this period, there have been no large volcanic eruptions of the kind that can modify climate. Nor were hominins indulging in hobbies involving SUVs and jet planes.

So, during the Pleistocene, CO2 was not a forcing; it was a feedback (*). The initial forcing that caused the Pleistocene oscillations was the variation in the solar irradiation caused by oscillation in Earth’s orbital parameters. This small forcing triggered a cascade of effects: colder temperatures caused the replacement of forests with grasslands, but grasslands have a higher albedo (solar reflection ratio) than forests and are associated with large amounts of carbon stored in soils. That generated more cooling. Lower temperatures caused the expansion of the icecaps, which also had a higher albedo and caused more cooling. The whole process was reversed by a switch in solar triggering, and oscillations went on for a few million years. Complex systems are just that: they are complex, and there are always several factors that affect their homeostasis.

Ultimately, the story of CO2 and climate is just an example of the wise idea that systems adapt to changes. We can express it as “When you are the hammer, hit. When you are the anvil, sit.” (in the original Italian version: “se sei martello batti, se sei incudine, statti). Sometimes, CO2 is the hammer; sometimes, it is the anvil. It is the way the universe works.

Incidentally, the proverb about the hammer and the anvil is popular among poker players. All human-created games reflect reality in various ways, and the Goddess Gaia masters them all.

(*) Note that, during the last deglaciation, the trend was the opposite: CO2 growth preceded the temperature rise. Complexity, complexity, complexity….