Mike Cassidy

480 karmaJoined Working (6-15 years)


Associate Professor of Volcano and Earth Science at the University of Birmingham. Research affiliate at the Centre for the Study of Existential Risk, and Earth Sciences, University of Oxford. Interested in global catastrophic risks, EA and broad longtermism.


The Risk of Huge Volcanic Eruptions


Thanks for the reply- sorry not a lot of time to address all of these points.

I think in a simplistic world- one in which we react to such threats as you expect with resilience and preparedness, then yes the risk of Tambora sized eruption could be minimal* (*by this I mean raising food and energy prices and dramatically impacting/causing excess mortality of poorer/vulnerable nations). 

Yes the world is more resilient and famines are better etc (note that a VEI 5 eruption in 1982 led to the droughts and thus famine in Ethiopia in 1983-5 that led to half a million dying), but a more complex world has inherent weaknesses and new vulnerabilities, see here and here

But as mentioned, the world is unpredictable and multiple factors normally converge at the same time- e.g. the consequences of an eruption now, versus the consequences of an eruption where China has become politically isolated- could dramatically change the impacts, our response and cascading risk (e..g wars from resource shortages/export bans). 

You use a philsophical term to make that point that factors acting together is a conjuction fallacy, but I say this is exactly what has happened throughout history for smaller eruptions which have dramatically affected civilisations for centuries

Nonetheless, the greater the number of eruptions, the more time there would be to adapt, so the net effect of your point on extinction risk is not clear to me.

Yes you can guess this is right-and that's fine to have this opinion, but when speaking to agircultural professors and historical perspectives (see the Little Antique Ice age in 6th century), in fact the opposite is true, a short spike is something that can be absorbed if global trade is working, sustained periods of low growth is more impactful. 

Perhaps this is my scientific background, but how you put a number on such uncertain factors seems deeply unscientific/unrigourous to me. 

Hi there, Volcanologist here. Firstly, thanks for making the effort to look into this area and engage with it. 

TLDR: I agree that extinction risk from volcanic risk is extremely extremely low*… (*on its own). But this post comes up with a single probability number, based on one new (and not yet established) paper based on playing about with climate model parameters. You could do a dive into another volcano-climate paper and get a completely different view of impacts e.g. In fact, you could also see this same paper from a different side and say that it could increase the x-risk factor, by (depending on what aerosol size you pick and choose) heating the earth and driving rapid warming on top of Anthropogenic warming. Does this mean that we should not worry about volcanic eruptions as contributing to existential risk? My answer would be no. 

To suppose that you can predict (and put a probability value) on what the societal reactions and subsequent decisions made, the interaction between other risks (AI, wars, pandemics etc) and geo-political landscape and actions would be when faced with the impacts of a large volcanic eruption (note that I say large and not super-eruptions- cause we’re not just talking about super eruptions here), seems overly reductionist and simplistic to me. For instance,  When faced with the starvation of hundreds of millions of people (if not billions- though I think that study overestimates agricultural loss), as well as droughts and other extreme weather events (failure of monsoons etc), energy security, financial loss of tens of trillions etc, and knowing that often it’s the state of the world (e.g. vulnerability, inequality) and the geopolitical reactions to that risk, that really control whether the risk could be minimised through global governance cooperation and preparedness actions, or whether humanity’s reactions to such risks (e.g. banning exports) may worsen the initial risk considerably, as well as cascading risks. So for me, judging how volcanic eruptions contribute to civilisation collapse or x-risk needs to incorporate these factors, This post does not engage with this, and bases their numbers on one paper and has extrapolated using non-rigorous constriants. 

Point about the paper itself: 

I asked my climate science colleague about the paper and they had a lot of uncertainty on on how much trust we should place on this: “I would be wary about taking this 1.5C as ground truth...Lots of disagreement between our models, and lots of processes they don't account for yet (e.g. halogen, water, injection height, time of eruptions, eruption time frame). The proxy record is always tricky as it's a mix of forced response and natural variability, and not a full global picture. My understanding is also that if anything, tree ring underestimate peak cooling because they integrate the response a bit. So I don't think they reliably support or don't support this limit.”

 “Models with interactive stratospheric aerosols have been telling us for ~15 years that aerosol growth would strongly limit the cooling after very large events. There might be disagreement on maximum aerosol radius/cooling because there is still a large uncertainty in stratospheric aerosol modelling (Clyne et al 2021)”

A few of my own thoughts about the same paper Vasco cites:

- We really don’t understand aerosol size at all, let alone for smaller eruptions (For example, In smaller eruptions, aerosol size change throughout eruptions and we don’t know why this is yet (link:, and so we have an even poorer grasp on aerosol size for bigger eruptions (they say as much in the paper- and as much as anything-the paper advocates for more experiment studies- I totally agree). 

- Published proxy records record greater cooling than 1.5 degrees (mostly summer cooling and mostly based in Northern hemisphere- but that’s where the tree records are), e.g. the 540 eruption. So while it’s possible that 1.5 degrees is the limit, based on this smaller eruption exceeding that limit, it seems unlikely.

- Eruptions often do not erupt all their Sulfur in one go, and super eruptions especially likely last years and will be separated by breaks in activity, this periodicity mostly certainly affects the aerosol size- this doesn’t seem to be mentioned at all.


General points: 

 But your point about extinction risk being very low is mostly right, though you can do the same by diagnosing the statistics (super eruptions occur every 17,000 years or so, so it’s unlikely that humans would go extinct as we haven’t done previously 300,000 years). But there’s some more complicated caveats to this:

-        We’ve never experienced one since human civilisations started ~12,000 years ago, the last one was 26,000 ago in New Zealand, and let alone since modern interconnected, globalised society. 

-        Since then we’ve globalised the food trade, and its susceptible to harvest fails if all grown in certain breadbaskets, and hydroclimate extreme events following eruptions make this far more likely (see paper cited above), not to mention trade choke points. 

-        Saying this the conclusion that volcanic eruptions cannot lead to human extinction* (*on its own). This is where it get a bit more complicated, and often analyses like this and Toby Ord’s analyses feel too reductionist and simplistic. For instance, many societal collapses in previous history (many coincide with eruptions), but they are rarely due to one factor alone. However if you were to take out say catastrophic volcanic eruptions, then they would likely not happen at all. 

-        This is also apparent when we look at major collapses, which don’t always correlate with the largest climatic impacts, so the idea that you approximate existential threat based on the magnitude of the effects seems a bit of a strawman case for these reasons. This effect is accentuated by the regional impacts to breadbaskets or physical blocking of trade routes via direct volcanic material- this means that location of the eruption is super important too, not just the magnitude. Vulnerability, reactions and other compounding risks (wars, inequality etc) turn out to be much more important. The logic of Ord et al to assess one risk in isolation is not realistic and the numbers he generates have very little meaning in the real world.

In general, explosive volcanic eruptions will never be the sole cause for extinction, but they could be very meaningful in increasing existential risk factor, so that once another big risk(s) comes along they have increased the vulnerability to that threat, where we might have otherwise come through it without the eruption. 

 Finally this quote it makes it hard for me to relate with this wing of the Effective Altruism community:

"So I would argue interventions to decrease deaths from supervolcanoes can only be competitive under an alternative worldview, like ones where the goal is boosting economic growth or decreasing disease burden."

Irrespective of extinction risk - should we care (and do something) about that fact that large volcanic eruptions could threaten the lives and livelihoods of billions, and this is for a risk that has a 1 in 6 per century probability

Perhaps I'm in an alternative/more isolated worldview- but I would say yes. 

Hi Stan, thanks for your response. I understand your main thesis now -seems logical provided those ideal circumstances (high global co-operation and normal trade).

VEI 7 eruptions could lead to up to 2-3 degrees of global cooling for ~5-10 years (but more elevated in the northern hemisphere). See here: 

More likely is two VEI 6 eruptions close together, which may provide longer duration cooling of a similar amount ~2 degrees, like in the mid 6th century (Late antique ice age).

The Loughlin chapter didn't account for the incompletness of the geological record like papers published since have done with statistical methods (e.g. Rougier paper I cite in that post), or with ice cores that are better at preserving eruption signatures compared with the geological record. 

In the report a footnote 2 states:
"In mild agricultural shortfalls such as those that may be triggered by crop blight, VEI-7 volcanic eruption or extreme weather, adaptations like redirecting animal feed, rationing and crop relocation would in theory be sufficient to feed everyone".

How did you come to that conclusion? We're only aware of 1 academic study (Puma et al 2015) about food losses from a VEI 7 eruption and it estimates 1-3 billion people without food per year (I think this is a likely an overestimate, and I'm trying to do research to quantify this), so just trying to figure out what you're basing the above statement on, does this take into consideration food price increases and who would be able to pay for food (even if there is technically enough)?

Also note the use recurrence intervals of super eruptions is an order of magnitude off from Loughlin paper which has since been changed (see discussion here: ). Also note, VEI 7 eruptions can sometimes have the same/if not greater climatic impact as super-eruptions, as the magnitude scale is based on the quantity of ash erupted whilst the clmatic impact is based on the amount of sulfur emitted (which can be comparable for VEI 7 and 8 eruptions). I mention these as whilst nuclear war probabilities have huge uncertainties, our recurrence intervals from ice cores of large eruptions are now well constrained, so it might help with the calcs. 

Hi Christopher and Ewelina, thanks for this post, it's nice to see geoscientists in EA and advocating for the skillset that Geoscientists pose and you're right that it already plays a role in many of the EA causes. I may use this these examples to share with my undergrads!

I like the estimation calculation you do to equate the money proportional to planetary defense weighted to its odds. However you seem to use the Ord value of 1 in 8000 per century of a Supereruption. But Toby is talking here of a super eruption the size of Toba eruption which is 5000 km3 in volume. To be registered as a super eruption it's 1000km3 and the estimated probability of this supereruption volume is 1 in 170 per century (Rougier et al 2017). So it would be interesting to re-hash your model with this value instead- I would be interested to see how it compares with our expected value estimation in our paper here: "The financial losses resulting from a large-magnitude eruption are estimated to be in the multi-trillions8, roughly comparable to those of the pandemic. Given the estimated recurrence rate for a magnitude-7 event, this equates to more than US$1 billion per year." 

Another point to make here is the volume of the eruption is not necesarrily proportion to its impact, for the global climate-impacts sulfur content is a better metric, and sometimes there is an asymmetry between eruption volume (or VEI) and climatic impact (Schmidt and Black, 2022). This is where the ice-core record is a good proxy.

I should also add that we have been trying to attain funding from EA sources to conduct research on impacts from large eruptions on society for a few years (e.g. quantifying lives lost and mitigation strategies), but despite the neglectedness, tractability and importance of this risk, the funders have not been interested to date.

To end on a better note, I'd be happy to join your slack group- thanks for creating it.   

P.S. We have a paper on the Ethics of Volcano Geoengineering coming out next month

Just to follow up this post, we want to confirm  that (like many others)  we did not recieve the funds from the FTX foundation for our project before the FTX collapse. 

We want to thank the Clearer Thinking team for all their hard work on this competition (a great example of democratized funding) and for seeing the potential for quantifying the global risk from large magnitude volcanic eruptions. 

If anyone is able to help us find funding to ensure this project goes ahead (or put in touch with people who could help), it would be really apreciated. Thanks all, Mike and Lara

Really nice post- Thanks for writing this! Lot of thoughts- but just a few below for now:

From my experience in Natural hazard research in various countries (Mexico, Indonesia, Carbbean, S America) I can certainly confirm this statement:

One of the major issues with natural disaster prevention is that many believe that the necessary work is already in place, which I don’t think is the case in many countries.

The impacts are also strongly weighted by population exposure and vulnerability, especially for Earthquakes. For example, the magnitude 7 earthquake in Haiti (a strong but not unusual earthquake -occuring ~once a month somewhere in the world), killed 200,000-300,000 people. So targeted preparedness & research in some regions could be significantly more effective. 

Even if there is some organisation/preparedness in some areas/for some hazards, the low frequency, high impact natural disasters often catch orgs/charities out (e.g. we see this with recent Tsunami disasters in Japan and Indonesia), so again action in this area, might be most neglected and therefore effective. 

Thanks for writing this post and your efforts to address these issues! As someone who works in  scientific research I have frustrations about the framework/criteria by which science is funded- so I'm really glad someone connected to effective altruism is looking into this, and I agree that this a really important cause area!

Often the criteria used to judge proposals is based on things like how innovative, novel, timely the science is, if it uses cutting-edge methodology and how suited the candidate is to that study area. Also, as a reviewer of proposals I am asked to judge the proposal's 'excellence'- a quite ambiguous quality- that accounts for significant randomness and bias too.

I think this approach to judge proposals is a limited as it means that a) potentially more important or impactful work will not be funded as it may lack novelty. b) people coming from a problem from a different discipline with differing expertise-yet many scientific breakthroughs come from those from other fields. c) it can lead funding of niche fields of science, to the detriment of neglected areas of greater importance and wider scale tractability. 

Incorporation of the ITN framework would be beneficial, it may help fund more controversial or higher risk science and making decisions based on lotteries, after an initial sift, may also open up the field to more creativity and diversity, and counter some of the other biases that sadly occur. So I really agree with you here.

These issues above relate to the more open calls for proposals and how they are judged, but there are also many schemes one can apply to that are quite narrowly defined and have been decided by relatively few senior academics on a science board. It is not clear to many in the community how these grant calls are are decided, nor how rigorous and unbiased these are, making this process more transparent would be beneficial too. Your ideas based around cost-effectiveness and expected value might also provide more rigor to these decisions.

Anyway- really interested to see what you do with this, and let me know if I can be of help into the UK research council (UKRI) system. I'm currently part of the peer-review college for NERC and can find out more about specific protocols/decision making if useful.

Thanks Ken! Glad you appreciate the importance of this topic.

I'm afraid I've not come across much research about the potential correlation between grand solar minimums and volcanic activity, but let me know where you've come across this and I can look into it.

Thanks for this Toby. I like your suggestion about factoring the risk in this way, and we'll keep you informed about where this all leads. Regarding civilisation collapse & recovery, there's certainly a lot of parallels to abrupt cooling from nuclear and asteroid winters, though the nearer-field hazards (and resulting cascading impacts), may be significantly different. One major uncertainty in this seems to be the location of a super-eruption, which will strongly dictate its effects on society, e.g. similar magnitude super-eruption occurring in the Mediterranean versus New Zealand. So one of the things we hope to look into is identifying the regions & volcanoes where the next super eruptions are most likely to occur. Your book & the longtermism concepts have certainly made me reassess what the most important questions in our field are!

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