A guest post by Tallis
The very worst case scenarios are rarely considered for disasters and for usually a good reason. They are either so unlikely or so boring that there is no point in worrying or thinking about it. The worst case impact event is one that would completely destroy the Earth and make another asteroid belt or planet entirely. The worst case tornado would be one that would produce Jarrell level damage while moving at 70 plus mph through the downtown area of a large city (Not likely at all!). Flood basalts and gamma ray bursts are similar events. However volcanic winter through explosive eruption are not like that, since we don’t even know the climate effects of upper end VEI 7 eruptions let alone VEI 8s. We can’t just sit here and say “We don’t know so forget about it.” so I have done some brainstorming and I have conceptualized a potential worst case scenario for Explosive Volcanic winter.
First let’s address the best case scenario; lately some scientists have come forward saying that VEI 8 eruptions produce limited climate effects, producing a drop in temperatures of less then 1 C. It would seem that there is cold war when it comes to the effects of these eruptions between skeptics and supporters of apocalyptic volcanic winter. Personally I think a VEI 8 eruption would likely produce a temperature drop of 5-8 C. Pretty nasty but not crazy, the mere fact that an argument could be made for a drop of 10+ C or 1> C shows how little we know.
The central battle of this cold war is the Toba eruption, various arguments have been put forth on both sides but the physical evidence leans towards the skeptics. The two biggest arguments put forward by the skeptics is that as the mass of SO2 is released increases, the aerosols will become larger and will be flushed out quicker and higher concentrations of aerosols cannot be sustained because the aerosol microphysics will lead to higher removal rates. Supporters have argued with skeptics concerning how much these factors would limit volcanic winter but there is not a lot of arguments on other ways that the Toba eruption’s climate effects could be neutered.
Some have argued that the sulfur load from Samalas eruption is the point where the aerosols become too large and are flushed out quicker. For reference, this eruption released around 120-240 megatons of SO2, if this mass would be the limit of sustainable volcanic winter, then it would be safe to say that we wouldn’t really have to worry about larger eruptions. Thankfully we have a prehistoric event that disproves this: 7,600 years ago Mt Mazama produced an eruption similar in size to the Samalas eruption also with similar SO2 amounts for the northern hemisphere. An analysis of ice cores following this eruption has shown that the SO2 was flushed out over a period of 6 years! So I am sure that means the Samalas eruption didn’t exceed the perfect mass threshold. Whatever this ”Magic Mass” is, I don’t think any historic eruption has surpassed it, for all we know it could be a pretty small number or it could be the most massive numeral.
The first limit to explosive volcanic winter is time, the aerosols usually have a lifetime of 2-3 years at the most. The worst effects will usually be gone after the second year and there is no reason to assume the rules would change with larger eruptions. Finding concrete physical data concerning an event so brief will be extremely difficult, the longer term effects are likely mild compared to other cooling events so that may not be reliable either. The Toba eruption took place during the Ice Age and I believe the Ice Age neutered the eruption.
There are two fundamental ingredients for sulfuric aerosols, SO2 and water. If there isn’t enough of one then it doesn’t matter how much of the other you have, you are not going to see much. I think the SO2 released by the Toba eruption didn’t have a lot of water to work with because of the Ice Age. This may sound like stupid argument at a glance considering the most abundant gas released by volcanic eruptions is water vapor so surely this shouldn’t be an issue. Stratospheric volcanic water vapor injections have been studied and shockingly they found that while there was an increase, it only lasted a few days, not enough time to form all of the aerosols. Other studies of the stratospheric injection of other volcanic gases, have argued that not all of them can make it to the stratosphere. In fact only limited amounts of some volcanic gases take a lasting residence in the stratosphere. Effusive eruptions likely don’t have this issue due to the fact that the plume dynamics are completely different.
During an Ice Age, natural water vapor would not be enough to react with all of the SO2, I do believe that some of volcanic H2O could make a longer residence within the stratosphere but ultimately not enough. This could actually explain why a lot of large eruptions in the past 2 million years don’t seem to produce extreme climate effects. The evidence for the basic idea of limited water vapor injections are supported with real results. So I am pretty confident this is the likely cause for the neutered climate response of Toba.
With this idea, the dynamics of large amounts of sulfuric aerosols may be even more mysterious and hard to understand. We don’t know these dynamics and until something grants us the understanding and knowledge, neither the supporters or the skeptics can declare victory. The magnetism of an incredible disaster or the fear of it can cloud someone’s mind, after all no matter how unbiased one claims they are, they’ll always be inclined to one side. I am sure you can guess which side I am inclined for.
Can we even concretely discern the worst case scenario without this crucial knowledge? No. Can we get a picture? Yes. I believe there is the perfect level of SO2 mass that balances aerosol lifetime and intensity, I don’t know what the exact value of the “Perfect mass” would be but I am sure it exists. The eruption’s size would be an important factor for the worst case scenario but it is not the most important part. What is the other part? Younger Dryas shows the answer.
The cause for Younger Dryas has been debated ranging from an impact event to a supernova but the most accepted cause is a melt water pulse shutting down the Atlantic meridional overturning circulation. The AMOC as we’ll call it in this article, is responsible for the transport of warm water into the northern Atlantic. This is what keeps the climate of Western Europe and Eastern America warm. It is part of the Global thermohaline circulation.
There is a hypothesis that the eruption of Laacher See coinciding with the melt water pulse that triggered this event. (Note:The Laacher see volcano is in Germany and is part of a still kicking system and if you want some more information read this article https://www.volcanocafe.org/unrest-at-laacher-see-is-it-us-or-the-volcano/) This hypothesis hasn’t been confirmed, but there has been no significant evidence against it. Younger Dryas did take place very shortly after this eruption and sea ice-ocean circulation positive feedback could sustain the cooling from the eruption. The dynamics of such a process are not settled and this is what keeps this idea getting more support.
In order for this hypothesis to work, we need to find out how the melt water pulse would intensify and sustain the cooling from the aerosols. As previously mentioned the pulse would slow down the Atlantic meridional overturning circulation and we already have current data on what that would look like because the AMOC is weakening quickly now. Whether one believes in apocalyptic anthropogenic climate change (I am pretty skeptical myself) doesn’t change the fact that the AMOC is weakening pretty quickly now and in fact, this is the weakest it’s been in 1600 years. (The data goes to 450; it was stable from that time to the 19h century.) I believe this could be what has been driving the recent active Atlantic hurricane seasons and some of the recent powerful European windstorms as well. We can see clearly the results of this change in the ocean, as a growing blob of cold water exists in the northern Atlantic. This slowdown would lead to a decrease in salinity as well as temperature.
The first thing that would enhance the volcanic winter is the fact that freshwater freezes quicker than saltwater, with a sudden influx of cold freshwater with the reduced transport of warm saltwater. A significant amount of sea ice could develop, how much though, would depend on the scale of the cooling. Due to the nature of volcanic winter, the most intense cooling would take place during the summer, and as such for a year or 2, sea ice melt would be weak and could actually build. Once the aerosols are removed, this sea ice would melt and would disrupt the circulation even more so.
If enough sea ice develops, then the ice could increase the Earth albedo, and give the volcanic winter a decent boost as well. With the weakening of the AMOC, there would be an increase in baroclinicity, which would lead to more powerful extra-tropical cyclones. Which means there would be more significant snowfall which could also give the winter a boost.
It has been said that large volcanic eruptions are perfectly capable of decreasing heat flow to the arctic all on their own after all the AMOC isn’t the only circulation on this Planet! The AMOC is connected to other major currents across the world, including the Kurishio and East Australian currents, they all make up the global thermohaline circulation so if you mess with one then you mess with it all. So the volcanic eruption and meltwater pulse would mess with the other circulations as well, likely to a lesser extent.
Just simply with the nature of large scale volcanic winter already messing this circulation, we have some issues, with a meltwater pulse, that makes it even more nasty! However, even though the current disruption to the AMOC is related to the warming of the Planet, global cooling is perfectly capable of disrupting the circulation as well. In fact I just explained how that would work earlier! So with the sudden disruptions to climate through the aerosols the weakening of the circulation would actually begin to intensify and get worse.
This wouldn’t be a quick event, with the cooling lasting for decades and the circulation on life support, smaller volcanic eruptions would make things worse and could sustain the trend for a longer time. This wouldn’t last forever though as other variables to the climate exist and if we are to assume that the water vapor in the stratosphere has a big role on the scale of volcanic winter then it would be safe to assume that after a while there wouldn’t be enough to sustain any more large scale volcanic winter but the question is…was the Laacher see eruption big enough to affect the circulation like this? At a glance, it may seem a little outlandish. The eruption was only the size of the 1912 Novarupta eruption and the SO2 load was similar to the Tambora eruption, this eruption produced around 120 megatons of SO2.
But let’s investigate this proposition a little further, was there any eruption like this historic times? Any eruption with real and well studied effects? Yes! In fact, it has around the same SO2 load and took place firmly in the same hemisphere. Her name was Laki.
Starting June 8 1783, this massive fissure would release 14.7 cubic km3 of liquid magma with 0.8 km DRE of tephra as well over 9 months but mostly within the first 6 months covering the Europe haze laced with volcanic gases that killed tens of thousands and produced one of the most severe volcanic winter known in history. While it is unknown, it is possible that the volcanic winter killed or helped kill millions worldwide. This eruption also produced around 120-150 megatons of SO2, however the plume dynamics of this eruption ensured that not all of that gas would make a lasting residence in the stratosphere. Looking at this table we can see the total drop in solar irradiance from this eruption is around 15.5 W m-2. It is important to note that all of that only goes for the northern hemisphere and once you factor that in Laki can stand with top 3 eruptions on this list.
The eruption of Laki caused a drop of temperatures of around 1.3 C for the northern hemisphere, a very bad volcanic winter to say the least. I think this gives us a picture on the potential climate impacts of the Laacher see eruption. I am sure the climate impacts would be far more significant then the Laki eruption due to the fact that most of the SO2 would make it to the stratosphere and be converted to longer lasting aerosols. An abrupt drop of 1.3+ C should be enough to produce some significant sea ice and snow. Whether the Laacher see eruption caused Younger Dryas or not, an eruption could enhance the effects of a meltwater pulse and slowdown of thermohaline circulation and vice versa. (Once the eruption is large enough!)
The worst case scenario, would be a large eruption with this hypothetical perfect SO2 mass taking place with a meltwater pulse with a neutral or negative ENSO. I am not qualified to give any specific numbers but I am sure this would drop global temperatures by at least 9 C Once again, I can’t actually prove my hypothesis but someone else can! If there are any climatologists and volcanologists reading this, please give the idea a whirl!
It wouldn’t be one of my articles if I don’t somehow try to connect this to the present! So are the conditions currently suitable for a Younger Dryas scenario? That’s a resounding NO but I do believe current conditions are suitable for good volcanic winter. We already have the issues with the AMOC but are there any other supportive variables? Currently in the southern hemisphere we have significant icebergs breaking off and the West Antarctic ice shelf is unstable, if we can get more ice to break off we might be able to see some disruptions to the circulations in the south.
Another issue is that the Beaufort Gyre, an Arctic sea current, has been accumulating fresh water for years and it will ultimately release this water back into the Atlantic. This isn’t anything compared to the Freshwater released during Younger Dryas but it is still significant. This wouldn’t be enough to take the volcanic winter to Super Saiyan but it could be enough for Kaio-ken. We have seen the stratospheric water vapor increase over the past years as well. This has been a problem for the Ozone layer, as water vapor helps in the destruction of the ozone. Now I couldn’t find the exact number but we can find out with the information we have. Currently there are 4-10 ppmv of water vapor in the stratosphere, now the stratosphere contains around 20% of the atmosphere’s mass and the total amount of particles in the atmosphere is 1.09×1044 so let’s divide that by
20%, Um I mean 5! Which leads to 2.18×1043 let’s kill 6 zeros and multiply value by 4 which gives us 8.72×1037 . The molar mass for H2O is 18.01528(33) g/mol so let’s divide again by 6.02214076×1023 which gives us 61,772,053,298,867 lets multiply that 18 and divide that by a million, which gives us 1,111,896,959 tonnes. On the lower end, on the other end we get 2,779,742,398 tonnes.
With this we find that even if the Toba eruption took place now, there still wouldn’t be enough water vapor for all of that SO2 and this is after the current climate trends supporting excess H20 within the stratosphere! Still it’s enough to support a large eruption to say the least, so if we get a nice billion ton SO2 emitting eruption, we have enough water to turn all that to aerosols. Not accounting for potential water vapor from the eruption. Ultimately, the aerosol microphysics will decide the strength of the volcanic winter in the absence of external variables and as smart as I am, that is something I couldn’t possibly figure. The dynamics of the aerosols from larger eruptions need some more research and with an open mind, this can’t be approached with the wrong deposition. I do believe the current conditions are suitable for a large-scale volcanic winter but before I conclude, I must address the elephant in the room.
The Pinatubo eruption took place recently and produced a volcanic winter, however it didn’t seem enhanced in any way despite taking place during a pretty favorable period according to my hypothesis. I know it was a pretty small eruption in terms of SO2 load compared to historic events and it doesn’t even show up in the top 25 eruptions in the past 2500 years. So that could be the answer but I believe since there was an El Nino that took place shortly before and continued a few years after the eruption, the cooling wasn’t as intense. Depending on how much El ninos reduce the cooling from volcanoes, the mere fact that there was a substantial cooling event could mean the Pinatubo eruption was enhanced.
Whatever, the reality is, I am sure we can figure it out. This cold war between skeptics and supporters must come to an end and we must find the facts concerning volcanic winter. I could be dead wrong in everything I have put forth here, but on the journey to truth we have to expect some falls. We might be able to test this idea out in real life so let’s keep an eye on the actual volcanoes too!
The Die has been cast, the trumpet has been blown
The warm light is dead, Blue skies gone,
Night is now eternal and it will never falter
The Sun has fallen and the heavens quiver,
Stars have fled, and the moon weeps
God’s wrath has come and hell awaits
The babes cry no more, they are hushed
The children look to their parents, confused
The men and women cannot answer they cannot speak.
Every beast knows what is coming, The truth is bleak
Death smiles. It will feast this hour
The angels frown. They will protect no more
Gone is the sustaining rain, the skies bring only fear and pain
Gone is the nurturing earth, the ground brings only famine
There is no love, there is no happiness, there will be no reprieve
There will only be hate, despair and tears on this eternal eve