Is there enough fossil carbon in the atmosphere to create global warming? Lessons from mistakes, misinterpretations, and propaganda

 

The great holobiont called the "biosphere" continuously exchanges carbon with other parts of the Earth system: the hydrosphere and the geosphere. It is a fascinating section of the science of the atmosphere that, just like all other sections, is subjected to misinterpretations, mistakes, and sheer propaganda,   

Earth's climate is one of the most fascinating fields of study nowadays and if you are interest you can learn something new every time you stumble into a new report. Even the so called "debate," biased as it is, may be useful to learn something not just about climate science, but about human psychology as well. Let see an example starting from a comment that recently appeared on twitter,

"Goggle Bob" defines himself as "Engineer that likes technical financial charting (energy, precious metals, commodities, cryptos); as well, a student of the fiat money system." 

First lesson learned: people will think that something they don't understand is "very good science" if it agrees with their personal biases. 

Now, let's go to the paper by Skrable et al that Google Bob cites. It is not an easy paper to digest, but it is an attempt to quantify the fraction of atmospheric CO2 that's the result of the burning of fossil fuels. It is all wrong, as we'll see in a moment, but it is a good occasion to learn something about atmospheric physics and hydrocarbon dating.

It is all about the "Suess Curve;" proposed by Hans Suess in 1967. The curve is about the fraction of the 14C isotope contained in the atmosphere as a function of time. 14C is an unstable isotope, but it is continuously created in the atmosphere by a reaction of carbon nuclei with cosmic rays, and its concentration can be taken as approximately constant, apart from human perturbations. One of these perturbations is the burning of fossil fuels. Since 14C gradually decays with time, those carbon materials which are not continuously exchanged with the atmosphere tend to lose it. So, fossil hydrocarbons contain essentially zero 14C, and burning them is expected to reduce the fraction of 14C. 

Quantifying this amount is not easy, but the final result is that fossil fuels generated about 75% of the extra 145 ppm (from ca. 280 to 425 ppm) of CO2 relative to pre-industrial times. The rest was generated mainly from deforestation and cement production. Another conclusion is that just about 45% of the carbon generated by fossil fuels remains in the atmosphere right now; the rest is stored somewhere in various reservoirs in the ocean and in the biosphere. This is a story I already knew in its main lines, but the discussion about the paper by Skrable et al. led me to go deeper into the matter. 

Second lesson learned: bad science can lead you to learn some good science. 

Now, let's go into the details. At a first read, the paper by Skrable et al. looks legitimate. For someone like me, not an expert in atmospheric radiochemistry, the way the paper is written seems to make sense: there are estimates, equations, and conclusions, all written in the standard jargon of scientific papers. But the  problem, a big one, is their statements that "the quantity of anthropogenic fossil CO2 in the atmosphere in 2018 represents about 23%  of the total amount of anthropogenic fossil-derived CO2 that had been released to the atmosphere since 1750." They also say that ""the atmospheric concentration, <CF(t)>, of anthropogenic fossil derived CO2 in 2018 is 46.84 ppm." And that "the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming."  (boldface mine)

You only need to know the basic elements of climate science to understand that the final statement is a flag for something badly wrong. Today, we have about 425 ppm of CO2 in the atmosphere, which is about 145 ppm more than the pre-industrial concentration of 280 ppm. Let's assume that the authors are right in their estimate (47 ppm of CO2 resulting from fossil fuels). It means that there are about 100 ppm of extra CO2 in the atmosphere that are NOT the result of fossil fuel burning. And where does this huge amount of carbon come from? 

You would have to think that the total ca. 300 ppm of CO2 emitted by the burning of fossil fuels was almost wholly absorbed by the reservoirs. And not only that: this CO2 must have triggered a huge release of carbon that had been stored in some surface reservoirs for a short time. Otherwise, it would be depleted in 14C and indistinguishable from fossil carbon. Difficult to believe, but even if it were true, the current CO2 excess would still be an indirect result of hydrocarbon burning. No matter how you see it, the statement that "the total CO2 due to the use of fossil fuels ... is much too low to be the cause of global warming." simply makes no sense. It is not a specific isotope of carbon that generates warming; it is the total amount. 

From this, the authors do much worse when they state that "unsupported conclusions of the dominance of the anthropogenic fossil component of CO2 and concerns of its effect on climate change and global warming have severe potential societal implications that press the need for very costly remedial actions that may be misdirected, presently unnecessary, and ineffective in curbing global warming." In Italy we have a way of defining this kind of statements as "peeing outside the pot," and I think you understand what it means. 

Third lesson learned: bad scientific papers can often be identified by their politically-oriented statements.

So, what was actually wrong with Skrab's paper? Examining in detail a scientific paper dense with equations, numbers, and tables is a lot of work (and, in Italian, we have a principle describing how unrewarding it is, but I won't report it here because it uses scatologic terms). In this case, though, there is a crystal clear explanation provided by Andrews and Tans that highlights the trivial mistakes that Skrab et al. made. 

Without going into the details, the main mistake in Skrab's paper was to neglect the effect of nuclear explosions in creating an extra amount 14C, thus giving the impression that the fraction of fossil carbon in the atmosphere is lower than what it actually is. It is more complicated than that, but it is enough to pinpoint the most glaring mistake in the story. 

Fourth lesson learned: a good rebuttal to a bad paper can teach you a lot!

Now, how can it be that a group of scientists with a good reputation in their field choose to deal with a subject they are not familiar with and end up making fools of themselves? It may happen that a scientific revolution comes from newcomers in the field; for instance, when Galileo showed that planets couldn't possibly move because they were pushed by angels, he made a fundamental contribution to a field that wasn't his; theology. But that's rare. Making a fool of oneself is much more common. It could be easily avoided with a minimum of humility: before publishing your paper, why don't you submit it first to the experts in the field? That doesn't mean that the experts are always right, but they can point at the mistakes that you may well make if you are an amateur. Nevertheless, it happens all the time.

Fifth lesson learned: scientists can be blinded by their preconceived ideas just like everyone else. 

To conclude, as you may have imagined, the statement that "the total CO2 due to the use of fossil fuels ... is much too low to be the cause of global warming." is making the rounds on Social Media, being reported by people who made no effort to understand why it was uttered, nor why it is wrong. And so it goes

Sixth (and final) lesson learned: Politics always trumps science in the debate.