Thoughts on Climate Change - part 2

As I stated in my response on the RealClimate blog, the apparently very reasonable argument presented by CCHolley (see my previous post) raises epistemological issues that call for additional discussion  and analysis. Epistemology, of course, is the philosophy of knowledge and the means by which we may attain  it. While it is sometimes contrasted with metaphysics, if we take the literal meaning of metaphysics, i.e., that which is "prior to physics," into account then  epistemology can be seen as a branch of metaphysics. It's not difficult to see that science must be grounded in certain basic principles that cannot themselves be subject to the usual sort of scientific testing, but must be accepted as "prior" to any type of scientific investigation. Among these, for example, is the employment of simple two-valued logic in the evaluation of any claim. Another example would be Occam's Razor, to which I'll be referring presently.


Holley's argument is based on the drawing of an analogy between a basic principle of modern physics, Newton's laws of motion, and certain claims of contemporary mainstream climate science. Specifically, Holley claims that the cooling and/or leveling off of global temperatures during a roughly 40 year segment of the twentieth century can legitimately be explained by the cooling effect of aerosol emissions emanating from the same burning fossil fuels typically held responsible for warming the Earth via the emission of large amounts of Carbon Dioxide, known to be a warming greenhouse gas. When I questioned this notion as a "saving hypothesis" in violation of Occam's Razor, Holley countered by reminding me that Newton's laws could have been questioned in a very similar manner by someone testing them without accounting for the effects of drag produced by atmospheric resistance. In both instances, according to his argument, it's necessary to add a complicating factor to the mix, since "in a complex world, if observations seemly conflict with . . . scientific certainty, then looking for explanations is absolutely the right thing to do."

Holley's rejoinder does seem reasonable on its face. However, if we were to accept it uncritically then what of Occam's Razor, which forbids us from complicating an hypothesis that seems to be failing by shoring it up with the introduction of additional elements? Is this fundamental epistemological principle to be shunted aside so easily? Occam is not as easy to ignore as he might seem. According to an excellent online explication by F. Heylighen,

Though the principle may seem rather trivial, it is essential for model building because of what is known as the "underdetermination of theories by data". For a given set of observations or data, there is always an infinite number of possible models explaining those same data. . . . For example, through two data points in a diagram you can always draw a straight line, and induce that all further observations will lie on that line. However, you could also draw an infinite variety of the most complicated curves passing through those same two points, and these curves would fit the empirical data just as well. Only Occam's razor would in this case guide you in choosing the "straight" (i.e. linear) relation as best candidate model. A similar reasoning can be made for n data points lying in any kind of distribution. (http://pespmc1.vub.ac.be/OCCAMRAZ.html)

An article in Wikipedia makes the same argument more straightforwardly:

[F]or each accepted explanation of a phenomenon, there is always an infinite number of possible and more complex alternatives, because one can always burden failing explanations with ad hoc hypotheses to prevent them from being falsified . . . (https://en.wikipedia.org/wiki/Occam%27s_razor#Ockham)

The analogy drawn by Holley would seem to pose a problem for epistemology therefore, by calling into question our ability to distinguish legitimate complications, necessary to scientific understanding, from  questionable ad hoc hypotheses whose sole purpose is to shore up a failing theory. How does one tell  the difference?

For Holley, the claim that the AGW (Anthropogenic Global Warming) theory requires the addition of cooling aerosols

is NOT simply collecting evidence to support a pre-conceived view, it is attempting to explain the world based on known physical laws. We don’t just throw out physical laws because of any little bump in the road, that would be an extraordinary claim that requires extraordinary evidence. CO2 is a greenhouse gas that prevents heat from escaping to space. That is a scientific certainty. . . . Aerosols like drag have an effect and cannot be ignored.

Unfortunately, this sort of explanation could be offered for a great many attempts to account for an evidentiary gap by invoking what might seem to be sound scientific principles. It is not enough to claim that some complicating factor is based on solid scientific evidence but also to demonstrate that the insertion  of this factor is not simply an ad hoc patch, but, to quote Occam, "necessary" -- thus capable of holding up under careful scrutiny in a variety of different circumstances. The accepted way to demonstrate that is to conduct experiments. The laws of motion were tested on the basis of carefully controlled experiments, conducted in a vacuum, which demonstrated their validity rather dramatically when a feather was found to fall at the same speed as a heavy weight as soon as the effects of atmospheric drag were eliminated. Unfortunately, there would not seem to be any way of conducting a similar experiment to test the effects of aerosol pollution in the very complicated real-world circumstances affecting climate change. The effect must be inferred from  consideration of a variety of different so-called "forcings," which are, in many cases, not at all easy to measure or assess. Complication piled upon complication.

However. It IS  possible to conduct a thought experiment which might shed some light on the matter. Let us assume that we are in fact able to very precisely measure both the amount of sulphur dioxide aerosols and the amount of CO2 in the atmosphere at some given place and time, and let us assume as well that the aerosols are indeed consistently found, after several strictly controlled experiments, to have a cooling effect sufficient to cancel the warming effect being claimed for CO2, which could indeed account for the cooling tendency we see for the period in question (ca. 1940-ca. 1979). As far as I can tell, such a result would conform quite closely to what most climate scientists now seem to accept more or less as a given.

Would such a result satisfy Holley and his colleagues at RealClimate? I wonder. As I've already noted on the RealClimate blog, once it's established that industrial aerosols produced from the same fossil fuel emissions as anthropogenically generated CO2 will either cancel out the warming effects produced by the latter or produce a net cooling effect, then it is no longer possible to claim the existence of a long term warming trend over most of the 20th century due to industrial CO2 emissions. If CO2 produced through the burning of fossil fuels does indeed have a significant warming effect on the atmosphere and if aerosols produced through the same process have a comparable cooling effect capable of cancelling the warming effect of the  CO2, then no instances of fossil fuel burning at any time prior to the introduction of anti-pollution laws in the United States and Europe, during the 1960's and 70's, could be seen as producing any net warming at all.

I presented this argument at the RealClimate blog and it was greeted with various attempts to demonstrate that fossil fuel emissions did indeed function as warming greenhouse gases since the onset of the industrial revolution, based on what they considered solid evidence. Well, if this could in fact be demonstrated, well and good.  But that would effectively nullify the claim that aerosols were largely responsible for the cooling effects seen from 1940 to 1979. You can't have it both ways. Either the greenhouse effects of CO2 emissions are strong enough to overcome the cooling effects of sulfate aerosols or not. If they are, then the explanation offered by Holley and so many others for the lack of warming over a period of roughly 40 years is clearly ad hoc and cannot be applied across the board (as can the effects of atmospheric drag). And if not, then a long term period of CO2 induced warming from the advent of the industrial revolution until the adoption of strict anti-pollution laws cannot be claimed.

There are other reasons for skepticism regarding this claim. According to Holley, the physics behind the AGW hypothesis are as solid as the physics behind Newton's laws of motion, so whenever the evidence seems to point in another direction it should go without saying that, as in the case of Newton's laws, the problem lies with the evidence, not the theory. This claim is easily refuted, since Newton's laws have been confirmed by controlled experiments of a sort not possible in the highly complex and often chaotic realm of real world climate, where results must be inferred on the basis of numerous sets of measurements, so tenuous as to require continual adjusting as new factors are discovered. Regardless, if we want to take Holley's claim seriously, it becomes evident that it is based on a circular argument. There is in fact NO evidence whatsoever of any temperature forcing stemming from the burning of fossil fuels during the entirety of the 40 year period in question. Certainly the existence of sulfate aerosols in the atmosphere cannot in itself be seen as evidence that CO2 produces a warming effect of any significance. Climate scientists assume the existence of CO2 forcing on the basis of their certainties regarding "the physics" behind our understanding of greenhouse gases. So ALL the evidence for CO2 forcing during this period is based solely on "the physics." Yet at the same time, the claim of a long-term warming trend during the 20th century is seen as evidence that "the physics" is indeed correct. But such a trend can only be established if the standard interpretation of "the physics" is accepted ahead of time -- otherwise the 40 years of cooling and/or leveling must be seen as going counter to the so-called trend.

More evidence that Holley's explanation is strictly ad hoc stems from a source I've never before seen referenced in regard to this particular issue. It is claimed that the cooling effects of industrial aerosols were ultimately neutralized by the institution of pollution controls in the US and Europe from the 1960's on, which would explain the sudden turnaround beginning in the late 70's, when global temperatures soared, in what looked like a strong correlation with soaring CO2 levels. The warming after the 1940-1979 hiatus is indeed currently attributed to the relative lack of cooling aerosols in the atmosphere from then to now. Can this hypothesis be tested? Well, yes it can.

Thanks to a helpful link provided by someone commenting at RealClimate I was able to find some very interesting data relating to the worldwide distribution of sulfate aerosols. The paper to which I'll be referring, authored by Hannah Ritchie and Max Roser, is titled simply Air Pollution. If you scroll down a bit you'll find a chart titled "SO2 emissions by world  region":

As is evident from this chart, SO2 emissions from the Americas and Europe peaked around 1979, which would be consistent with the theory defended by Holley. But the graph for Asia is totally different, as it shows a continual rise in SO2 emissions beginning in the 1940's and persisting till the graph's upper limit, 2010. Now it's important to realize that the scope of industrial aerosols is very different from that of atmospheric CO2. The latter is long lived and spread out in roughly equal portions throughout Earth's atmosphere, while the former is short lived (only a year or so) and highly localized. If SO2 aerosols indeed have a cooling effect strong enough to counter the greenhouse warming alleged for CO2 during the years 1940-1979, then we would expect the growing volume of such aerosols in Asia to continue the same cooling trend well into the late 20th and early 21st centuries. Is that in fact the case? Let's look:

The graph presented above is taken from a paper titled Comparative Analysis of China Surface Air Temperature Series for the Past 100 Years, by Guoli Tang et al. It is labeled Figure 1 and depicts temperature anomalies for 5 different data sets measuring Chinese surface air temperatures. What we see looks very similar to the worldwide data that's been so widely disseminated. Clearly, temperatures in China have not abated due to the increasingly high levels of SO2 pollution produced by their many coal burning plants during this entire period.

[Added Friday, Mar. 30: When I completed the above post, I felt that what I'd written would be sufficient to make my point for anyone who'd been following my argument with any care. Reading over it again, however, I feel the need for a summary and also some sort of concluding statement. So here goes.

1. First of all, let's take a look at the data to which I've been referring:

The graph reproduced above is taken from a 2016 article at the NASA website and represents average temperature anomalies from 1880 through 2016. It was intended to demonstrate a recent spate of extreme warming, but the segment that concerns us here dates from the 40 year period from  roughly 1940 through roughly 1979, where, as should be evident, no warming trend can be seen. The lack of a warming trend during this period has never been contested, but the cause is thought, by orthodox climate scientists, to be due to the cooling effect of pollutant aerosols due to the industrial burning of fossil fuels, the principal topic of discussion here.

2. Assuming that such aerosols actually neutralized or even overcame the warming that otherwise would have occurred due to steadily rising CO2 emissions during this period, there is no reason to assume that the same neutralizing effect would not have been present at all prior times, as pollution controls did not come into effect until the latter part of the century, meaning that CO2 emissions and aerosol emissions, created in tandem from the same fossil fuel burning process, could not have produced any net warming effect at all, not only from 1940 on, but from the beginning of the industrial revolution until the adoption of the clean air acts during the 60's and 70's. But this contradicts the long-held claim of so many climate scientists that there has been a significant long-term warming trend throughout the 20th century due principally to the burning of fossil fuels. The only alternative would be to drop the aerosol-cooling hypothesis -- but how could one then claim a correlation between global warming and steadily rising CO2 emissions in the face of a 40 year period during which CO2 emissions were soaring and temperatures either fell or leveled off for no known reason?

3. If "the physics" is sufficient to fully support the AGW (Anthropogenic Global Warming) hypothesis, as has so often been claimed, then no further evidence is needed, apparently. Yet gaps in the evidence that tend to undermine any correlation between warming and CO2 levels strongly suggest that there may well be something wrong with "the physics" -- which given the complexity of the worldwide climate system is not at all surprising. When attempting to account for such gaps, AGW supporters nevertheless use assumptions based on their understanding of "the physics" to develop theories, such as the aerosol cooling theory, intended to explain away these gaps. Since such theories are intended to produce evidence supporting the assumptions on which they are based, it's not difficult to see circular reasoning at work.

4. The abrupt and rather steep rise in global temperatures from ca. 1979 through 1998 (see the NASA graph above) has typically been attributed to the imposition of pollution control laws in the United States and Europe a decade or so prior. In the lessening of sulfate aerosol emissions from that time on, the "lid" was removed, and, as far as the climate orthodoxy is concerned, the warming effects of CO2 emissions were unleashed without any significant constraints. As I've demonstrated, however, the situation was very different in Asia, where pollution controls were not widely implemented during this same period, aerosol levels continued to rise at the same rate as before, and yet temperatures also soared, in tandem with temperature rises worldwide. Since pollution-based aerosols, unlike CO2 molecules, are short-lived and localized, it's very hard to see how the same cooling effect claimed for them during the 40 year "hiatus" we've been examining would not also have cooled Chinese temperatures during the last 20 years of the previous century, just as they had cooled worldwide temperatures during the earlier period.

The laws of motion referenced by Mr. Holley were corroborated by controlled experiments that supported them very convincingly. However, the notion that some underlying warming trend produced by CO2 emissions was masked by aerosol cooling has never been subject to experiment, least of all controlled experiments. But the evidence from Asia would appear to serve very well as a control, and the results are negative. Aerosols produced from industrial pollution are known to have a cooling effect, yes, but their failure to cool Asian temperatures in a manner analogous to the mid-century temperature dip tells us there is something wrong with the "science" behind the climate change orthodoxy. If no explanation  can be found for what happened during that 40 year period, then no fossil fuel generated long-term warming trend can be claimed and the fabric of AGW becomes very thin indeed.]