Aerosols in “Climate Science”
Honestly, writing this “blog”, I tend have some problems with structuring. Usually that would not be an issue. I mean you just pick a chapter, a topic, a certain perspective, you know roughly what you will need to tell, and then you just execute. With climate science I find this simple, outright procedure is not quite working, and there is a reason for it. Despite having the article almost written in the head so to say, there are always some things to look up and reflect on. And as I do so, I tend to run into new problems with “the science”. Just when you think you know about all the mistakes in it, you discover even more. They are just as abundant as holes in Swiss cheese. And then the question is what to do with it. It certainly needs to be sorted out and so I tend to incorporate it into the article I was actually intending to write. But doing so will bloat up the article and provide a lot of vital information, not to be expected given the headline. So probably it is better to outsource such issues into separate articles, even if it means I’ll have to rewrite the original one. This here is one of these "sideshows".
Aerosols, although poorly understood, play a vital role in climate models. If you ask why global warming only really started in the 1970s, aerosols are the answer. If you wonder how the only moderate warming witnessed so far shall support high climate sensitivity, again aerosols are the answer. So it is about time we take a closer look at them.
Aerosols and Volcanos
It is true, aerosols can cool the planet. In fact declining (surface-) temperatures have been observed many times over after volcanic eruptions. In the course of an eruption, lots of hot gases, most importantly sulfur, get ejected. Because of the heat, these gases are less dense than the surrounding air, making them ascend. Sure, there is also an initial thrust from the ejection, but that would not carry it all too far. As any gas ascends, it will cool adiabatically and it can only continue to ascend, as a long as it is warmer than the surrounding atmosphere. Within the troposphere that is not much of a problem, as itself becomes colder with altitude. From there on it will take about 10K for every single kilometer.
At some hundred degrees Celsius (massive) Plinian eruptions have all it takes to go right into the stratosphere, and once they approach their equilibrium temperature, they will start to spread horizontally. They provide a layer of gases, aerosols (sulfur, CO2, H2O..) and ash that will continue to spread out, eventually globally. The ash, as it is heavier (or denser respectively) than air, will follow gravity and soon disappear. Those gases and aerosols however can and will remain for months or even years.
Now other than CO2 und H2O, both GHGs, sulfur is a bit specific. It tends to react with hydrogen and oxygen to sulfuric acid (SA), a liquid aerosol which is highly opaque, and toxic btw. In many instances it is claimed SA would then reflect sun light and cool the planet, but that is only partially true and gives the wrong idea. Rather SA absorbs sun light, so that the stratosphere warms as a consequence. And as the stratosphere warms, while containing more emitting stuff, it releases a lot more radiation right back into space. In this way solar energy is so to say short-cut, and there is less energy for both surface and troposphere underneath.
This pattern is quite specific and it does not need to be this way. Early 2022 we had another powerful Plinian eruption, this time it was the Hunga-Tonga volcano. Since it is actually an underwater volcano, it emitted an extraordinary large share of H2O. Because of this it seems, as H2O (or vapor) is a GHG hardly absorbing sun light, but emitting well in the infrared range, the stratosphere actually cooled.12 Whether it does anything to surface temperature, be it warming or cooling, remains to be seen. The orthodoxy assumes surface and stratosphere temperatures would always go in opposite directions in the course of such perturbations, but I doubt it. At least no specific global heat wave has been identified in 2022.
Moreover such volcanic events typically lead to “years without summer” and poor harvests. The latter is likely more due to a lack of sunshine, which plants need for photosynthesis, rather than a slight decline in temperature btw. Winters however may actually turn out warmer3. All in all the climatic outcome of volcanic eruptions is highly circumstantial, depending on the specific quantities of what is emitted. Also the “where” is important, because certainly there will be different effects in the stratosphere, than in the troposphere.
Aerosols and “the Science”
Anthropogenic aerosols are essentially limited to the troposphere, as they lack the intense heat required to lift them above it. Accordingly “stratospheric aerosols mostly stem from volcanic eruptions.”4 So the question is how these aerosols, mainly sulfur again, behave within the troposphere. To my knowledge there is not even much of a theoretic framework to it. Neither hitran nor modtran feature it. The materials I checked are a) relating the aerosols from pollution to the experience from volcanic eruptions, thereby equating tropospheric and stratospheric aerosols, or b) simply stating aerosols are reflecting and scattering light.
Both arguments are pointless. The location is pivotal. In fact most of the time it is less the “what”, but the “where” that determines the radiative effect. On the other side, within the troposphere whatever reflects sun light, or SW radiation, will also interact with LW radiation thereby adding to the GHE. It is hard to imagine how sulfuric acid in the troposphere would have a net cooling, rather than a warming effect.
Apart from any direct radiative effects, aerosols also serve as cloud condensation nuclei (CCN). It would appear logical that aerosols thus promote the formation of clouds, and if clouds were cooling, then indeed there might be a substantial negative climate impact. The problem I have with this idea is about “climate science” not understanding clouds, and falsely assuming they were cooling. You may want to check the articles hereto.
The beast under the bed part 1
The beast under the bed part 2
The cloud mess part 1: Something simple to start with
The cloud mess part 2: Something spooky
The cloud mess part 3: data, data, data..
The doubt and the criticism
IPCC’s AR5 features a nice chart of all the respective forcings, with error bars. I would like to draw your attention to the negative forcings in the lower half of the chart, these are “Aerosols and precursors” and “Cloud adjustments due to aerosols”. The error bars there are huge.
If you add up both positions, total aerosol forcing could be somewhere between about -2W/m2 cooling and a slight +0.17W/m2 of warming. The “science” has not even figured out if aerosols are actually cooling, but despite all the uncertainty, prefers to assume they do. Also, going with the orthodoxy, this uncertainty over aerosols carries directly into the assessment of overall climate sensitivity. We will deal with it in a moment.
Naturally this has provoked some criticism. Richard Lindzen for instance names the way the IPCC treats aerosols a “fudge factor”.5
“As I and others have noted, many of these fudges involved more sulphate aerosols than are now regarded as possible.“6
Also Lindzen references the work of Prof. Bjorn Stevens7, working at the Max Planck Institute for Meteorology. The paper itself is certainly a worthwhile read, if you want to learn about some of the issues with assumed aerosol forcing. Essentially he points out, that aerosol forcing must have outpaced GHG related forcings before 1950. Bear in mind that aerosols are short lived, while GHGs tend to accumulate over long periods. By 1950 sulfur emissions had reached about 50% of their present level, while anthropogenic GHG concentrations were yet in their infancy. Accordingly, if aerosols had such a strong cooling effect, there should barely have been any warming by then.
And the problem only gets worse if we consider the IPCC states global forcings, while anthropogenic aerosol forcing is naturally concentrated in the northern hemisphere. The NH thus should rather have been cooling till 1950, which it did not. It is a little hint, pointing out reality does not match the theory. Also it is a dangerous notion, as in “climate science” the orthodox theory needs to be guarded from reality, and anyone endangering it by siding with reality, will be called a “denier”. Unsurprisingly Prof. Stevens then attenuates his criticism towards arguing just a low end aerosol forcing, within the wide range of uncertainty.
“For a hammer everything is a nail”
Working within the orthodox framework you only have a limited number of tools, and plenty of restrictions you must not break. Explaining global warming trends you are largely left with positive GHG-, and negative aerosol forcing. If for a hammer everything is a nail, the for “climate science” all climate trends over the last 150 years must be either due to the one, or the other. And guess what, it does not quite work.
What is at stake
I would like to explain what this is all about and what is at stake here. If you look up the table below you will find surprisingly high figures for anthropogenic forcings. That is 2.16W/m2 (CO2) + 0.54 (methane) + 0.21 (N2O) + 0.41 (halogens) + 0.47 (O3) + 0.05 (strat. WV) + 0.06 (contrails) = 3.79W/m2. If we ignore other parameters like land use and so on, mankind then has increased the GHE by 3.79W/m2, which is more than you would expect from a sheer doubling of CO2 (3.7W/m2).
Here is data given in annex III of AR6 WG1 for ERFs (effective radiative forcings) of all respective “forcers” (in W/m2).4
Since these are all forcings, it really does not matter what agent causes them, and climate sensitivity applies to the sum of them. In other words, whatever you assume to happen with a doubling of CO2, it already happens. If ECS for instance was 4K, well within consensus estimate btw., then this 4K warming is already under way. It only just takes some time for the planet to warm up and get back into equilibrium at this higher temperature.
Depending on actual climate sensitivity, about 50% of this warming should have happened already. It will be a lower percentage with high sensitivity, and a higher percentage with low sensitivity (with the latter being true, as there factually only is a 1.2K warming). That is because temperature adaptation takes the longer the larger it is. But then we only have about 1.2K warming since preindustrial, that is if we assume temperature records are right, not biased by urban heat island (UHI) effects, and all the warming was man made, or caused by anthropogenic GHGs respectively. If other causes added significantly, like the sun or aviation induced cirrus, only a part of the 1.2K warming could be attributed to GHGs. And then of course there is no definite “preindustrial” temperature, as global climate was never stable and always fluctuated by a couple tenths of a degree at least.
The same issue applies when we take the current warming trend, which is somewhere between 0.13 and 0.18K per decade. Again this is well below what models predict(ed). They typically (but not exclusively) range between 0.25 – 0.3K per decade with the given emission pathway. And there is no real fix for that, except for raising the error bar. Yet that is a different story.
In the long run however, if we consider all the warming since preindustrial, there is. As you may guess, it is aerosols. If you seek to argue high climate sensitivity, you have to explain why it failed to materialize so far. The answer is because aerosols were masking GHG driving warming. They were cooling the planet all along and once we started to care about pollution, enacting clean air acts, the true warming trend was unmasked.
As with the data above, aerosols would cancel out about one third of GHG forcing. Applying this relation to the 1.2K warming we have so far, then saying the warming would be 1.8K without aerosols and applying the 50% ratio named above, it would mean an ECS of about 3.6K, plus/minus whatsoever. Sure this is simplified, and there is uncertainty all over, but it roughly places us in the high climate sensitivity range. For this to work however, aerosols need to be cooling substantially, just as the IPCC claims.
A cringy falsification
As named above, Dr. Stevens already pointed out some of the issues with the idea aerosol forcing. In reality I fear things are much worse. First of all let us have a look on where aerosol pollution is located, with the example of sulfur. Unsurprisingly it is mainly North America, Europe & East Asia. Notably sulfur is also emitted naturally, from volcanoes, wildfires and bacteria8 (DMS). The fact that most of the planet is colored in light green, meaning very low concentrations, is related to these natural emissions. It does not mean anthropogenic emissions, at least at a low level, would spread globally.
(Vet et al. 2014, “A global assessment of precipitation chemistry and deposition of sulfur, nitrogen, sea salt, base cations, organic acids, acidity and pH, and phosphorus”)9
Similar patterns are true for other aerosols. Btw. I should add the term aerosols is a bit simplified because many of them start actually as gases, like SO2, and only later on, due chemical reactions in the atmosphere, turn into aerosols. Anyhow, despite fruitful efforts to reduce these pollutants, the US and Europe are still main hubs. China on the other hand has already put much effort into improving the situation, but likely has still a long way to go. You may recall the horror stories around the 2008 Olympic Games and how industries had to be shut down to make them even possible. Peak emissions were in the 1970s in the USA, the 1980s in Europe, and the 2000s in China.
The negative aerosol forcing logically has to be where the aerosols are. The GISTEMP v4 record gives us the warming by latitude, split up into eight segments. If we simply compare the first vs. the last 20 years of the record, we get the chart below. Obviously there is a strong north-south divide. By far the strongest warming is in the northern polar region, which can be explained by polar amplification. And although the strong Arctic warming may have some repercussions to the second most northern segment, it would still seem the source of this “global” warming is somewhere in the mid northern latitudes. That is where it is most intense, apart from the amplified Arctic.
Unsurprisingly there are a couple of problems related to this pattern.
1. The amazing, totally absurd thing here is, that we have most warming where there should be the most aerosols forced cooling. It is exactly the opposite of what we would expect. GHG shall be warming globally, while aerosols shall cancel about 1/3 of that global warming(!) just locally in the mid NH latitudes. The cooling momentum there should be huge, exceeding GHG warming, but instead it does not seem to exist. If reality does the opposite of the theory, in science we call this a falsification.
2. Then there is another logical problem here, and in case it is not obvious enough, let me explain it. Imagine you would heat the NH only to raise the temperature there by 1K for instance. Would you then expect the SH not to change at all? Hopefully not. Rather it would be inevitable for some of that extra heat to spill over and dissipate into the SH. After all we have convection. Bearing this in mind, a good part of the SH warming must have been inherited from the NH, which itself would have warmed even more, if it was a closed system and did not lose heat towards the south. So whatever causes the warming, it will be more strictly located in the NH than the chart above suggests.
3. What if we simply subtract alleged aerosol cooling from the equation? Then again the NH would have had to warm substantially more than it did anyway. This multiplies with point 2, meaning an even more north bound positive forcing.
4. This brings up an inconvenient choice to the consensus narrative. If you hold on to the aerosol cooling story you will have to explain why the GHG forcing is so strictly linked to the north, and avoids the south. This is conflicting with a GHG related forcing that should be global. If you give up on aerosol cooling on the other side, this would mitigate forementioned problem, but then you will not be able to argue high climate sensitivity. Anything above an ECS of 2.5K will become implausible. Also you would need to find a new explanation as to why the cooling between the 1940s and 1970s occurred.
Theory or Dogma?
Do not get me wrong, I am not trying to argue low climate sensitivity based on this perspective, since we are far past that. ECS is only in the 0.5K region, so that we do not need to discuss it here anyway. Rather this is about another appalling inconsistency within “the settled science”. These are tiny little details, most people, even the critical ones, might not take notice of, or consider to be relevant, but any Sherlock Holmes would pay ultimate attention to.
It is like solving a jigsaw puzzle by force, with a cutter, a hammer and some paint. These are tells “climate science” gives away for free, letting us see behind the curtain. With the few tools they have, or are allowed to use rather, they try to squeeze everything into the confined narrative. But that only goes so far and at some points the contradictions just become unbearable. There and then only distraction remains as an option. And that is another interesting thing.
Whenever such inconsistencies occur “climate science” is ready to provide an explanation. Why does the southern ocean refuse to warm? It is because deep ocean currents transporting heat from cold to warm, and from south to north!10 Ok?! Do not ask any questions here. Rather place any arbitrary theory as a joker, a theory that does not need to be confirmed, let alone it would to be exposed to falsification (that would make you a climate denier), and already there is a fix. And although it is totally normal to have many different theories up for scientific discussion, the problem is “climate science” needs these add-ons to stay plausible. These are alibis to guard the core theory of GHG related warming from falsification. But in actual science theories must be allowed to be falsified, and if not, they are just dogmas.
At least you get this from Gavin Schmidt:11
"There are systematic differences in the Southern Ocean in recent decades between the observed and modeled SST trends.. Are there processes missing in all these CMIP6 models that can explain the southern ocean discrepancy? Probably"
Sure, you can not get it all right, and who cares about Southern Ocean anyway, where no one lives? But I am afraid it is a little bit worse. Models have been parameterized for decades to roughly fit in hindcast. Then there are many model runs, with different assumptions, so that some of them should always fit. And eventually uncertainty is already factored in, so that no one even expects a good, let alone perfect fit. Sure the NH warming then is somewhat in line with model predictions, or hindcasting respectively. On the other side however, it is not just the Southern Ocean, but the whole north-south divide with it, that they fail to explain. And this is far more than just insufficient parameterization (ie. “add-ons”), rather it affects the core theory itself.
Meanwhile Schmidt and colleagues suggest melting ice could do the trick12. Essentially they argue the south refuses to warm because of melting ice from Antarctic glaciers. Please do not ask why it is melting in the absence of warming, and that would explain the absence of warming!? There is research suggesting the opposite anyhow13. Rather there is a more pressing problem. The Greenland ice sheet is producing substantially more melt water than the whole of Antarctica, while the North Pole is heating more than anything else. There must be some nuanced differences we do not yet understand, maybe something like the butterfly effect. I mean why not include chaos theory to fix the chaos in a theory? At least they have not hard-patched their models by latitude – yet.
Always look on the bright side of “science”
“The science” runs into plenty of problems over the north-south divide and the suggested negative aerosol forcing is only worsening it. It gets over it (partially) by ignoring the long run temperature record, and focusing on the trend over the last decades. With this perspective, aerosol forcing actually helps in explaining the rapid warming in the mid NH latitudes. But even that comes with a twist. China, despite some recent improvements, has definitely seen a massive increase in air pollution over the last 40 years. Yet it is one of the “hot spots” in the warming trend.
Shut your eyes, ignore it, take on the right “mindset” and look on the bright side. Got it, but no! Rather we will have to reject the idea of some negative aerosol forcing. There are just too many things speaking against it.
- There is most warming where aerosol forcing should dominate GHG forcing.
- It aggravates the already highly troublesome north-south divide
- Equating aerosols within the troposphere with those in the stratosphere (from volcanoes) is just pointless
- Even by the IPCC’s own admission, they do not know if aerosols are cooling at all
- The largest share of aerosol forcing is derived from their impact on clouds. The role of clouds in the climate system however is totally misrepresented by “the science”, as they are rather warming than cooling
If anything, it seems more likely aerosol pollution would add to AGW, not counter it. Ironically this might help to explain why models overestimated recent warming trends, as the reduction in air pollution provided an erroneous positive forcing. This remedy however is short lived. Not that it would matter anyway, but in a wider context it instead rules out high climate sensitivity.
The more significant find is, that there is no working model to explain the warming pattern within the orthodoxy. Something is heating the NH at an impressive rate since the 1970s. If we rule out a side effect of clean air acts, then GHG forcing is equally unsuited, as it would not produce one sided NH warming. This insight is not so revolutionary given we already know about the fundamental mistakes in calculating ECS and that they can not account for the bulk of given warming.
With GHGs and aerosols being insufficient, there needs to be an expansion of the toolbox, which is overdue anyhow. Whenever “the science” says the warming can only be due anthropogenic GHGs, it is a dogmatic, a political statement. You may rule out the sun as being the driver of the past 5 decadal warming, but that will not falsify the previously well established theory that it played a significant role otherwise. Nor would it rule out ALL possible factors. And I can tell you I am not the only one to have identified something “much, much, much larger than the projected increase due to greenhouse warming”14
14Charles Long 2015, Senior Researcher NOAA
amazing article and lots of questions as feedbacks. I am going to start with only one.
"[..] The answer is because aerosols were masking GHG driving warming. They were cooling the planet all along and once we started to care about pollution, enacting clean air acts, the true warming trend was unmasked. [..]"
As far as i understand, the official AGW explanation is that after 80's anthro aerosols started to decrease in the NH, so cloud dimming started as a result of less direct interacton between them.
... the consequence is not only less clouds (less cooling), but an increasing absorved solar radiation as a positive feedback (more short wave radiation heating earth).
GHGs radiative forcing 1980-2019 was about 1.6 w/m2 (from your table), around 0.4 w/m2/decade. I have read peer review papers that calculate similar watts in the same period caused by more ASR, no GHGs.
There is something odd i don't understand about all of this. We are not talking Aerosol & Cloud interaction act like a cold blanket on your forehead when you have fever (cools the fever), but a mechanism where if you release the blanket from your forehead, yes, your temperature increase (fever), but you also receive more heat from a radiator.
How can we know how much of those 1.6 w/m2 are coming from GHGs, from Aerosol cooling, and from more ASR?
your article is gold, seriously.
I was just pointing out to ASR because you didn't mention in your present article. There is evidence that more ASR is heating Europe and EEUU since 80s, and there is some kind of correlation with Aerosols decreasing trend since the same decade. But if decreasing aerosols are the cause of more ASR at the NH, then somebody should explain why SH is not heating at higher rate, since its troposphere is cleaner and there should be even higher absorved solar radiation :-)
Maybe i will not get the answer i am looking for, but at least, i am happy to have a better comprehension of the AGW toolbox contradictions.
Well again, it is a matter of the time frame. Anthropogenic aerosols decreased somewhat since 1980. Restricting the view onto the time since then it helps to explain why the NH warmed faster. Since the late 19th century however aerosols are only sharply up, so it will not work in the long run. It only worsens the problem. Also the absence of warming in the SH is completely unaddressed by the orthodoxy.
the only thing i don't understand is this whole thing about
"[..] The answer is because aerosols were masking GHG driving warming. They were cooling the planet all along and once we started to care about pollution, enacting clean air acts, the true warming trend was unmasked. [..]"
If you read, for instance, Loeb et al. 2021, absorved solar radiation (ASR) was around +1.17 W/m2 period 2002-2020:
If you calculate the GHG forcing from your table for 2000-2019 period, it was around 0.72 W/m2. So, what is this "masking" thing that i don't understand? if you eliminate the GHG forcing for equation for a sec, we pretend extra GHG forcing doesn't exist, those 1.17 W/m2 would be enough to increase EEI in the system, warm oceans, increase temps and all the stuf. What is this "true warming trend was unmasked"?
I hope you can help.
in fact, if we read more bibliography, like the following ...
... we can see LW forcing (clouds, WV, CO2) has been decreasing since 80s (mainly as a result of less clouds), while SW radiation trends have been rising also since the 1980s. In fact, according to Fig. 2 b, ASR increased by 3 W/m2 1985-1999 period. If numbers are correct, and we add up Loeb numbers, since 1985 SW forcing was about 1.17 + 3 = 4.17 W/m2.
It coincides with a human SO2 decreasing trend since 80s, but then we can say modern temperature trends is SO2 driven, not GHG driven.
But if we see the bigger picture, does it mean this SW values are the "normal" values without human SO2, like when earth was at pre industrial levels? Is the "normal" state of climate having less clouds?
As you can see, and after reading your post, there is something odd i don't get.
GHD2 weeks ago