[Everything in this post is true to the best of my knowledge, but I am not a climatologist and my last science class was in high school. It is very likely I have misunderstood something. I welcome corrections. Dedicated to Annie.]
I often see people say that climate change is going to kill us all, or that human extinction is inevitable due to climate change, or that if effective altruists were really concerned about existential risk we would put lots of effort into fighting climate change because all scientists agree that is the biggest existential risk.
As far as I can tell, absolutely none of this is true.
Climate Feedback, a nonpartisan website educating people about the scientific consensus on climate change, has written about human extinction from climate change. Christopher Colose, a postdoctoral research fellow at NASA GISS, puts it clearly:
Actual numbers are important here. The global temperature increase could indeed reach 4-5 degrees by 2100, if humans don’t do anything to our emissions, and beyond this patches of uninhabitable areas (for humans) could start to open up in the tropics, due to heat stress limits imposed by the evaporative limits of our body. Indeed, a world 5+ degrees warmer is a big cause for alarm, even if the world takes a linear path to that mark. The world also does not end in 2100, and while it is tempting to think of later dates as “very far off,” it is worth reminding ourselves that we would live on a different planet had people of the Viking era industrialized and emitted carbon uncontrollably.
Nonetheless, the near future climatic fate of New York probably looks more like the climate of South Carolina or Georgia than something from a Mad Max movie. This is still an important basis for concern given that the socio-political infrastructure that exists around the world is biased toward the modern climate.
Many of the nightmare scenarios in this article, such as no more food, unbreathable air, poisoned oceans, perpetual warfare, etc. are simply ridiculous, although food security is indeed an issue at stake (see David Battisti’s comments). A “business-as-usual” climate in 1-2 centuries still looks markedly different than the current one, but there’s no reason yet to think much of the world will become uninhabitable or look like a science fiction novel.
The IPCC, the world’s leading experts on climate change, publish regular reports about climate change which explain what the expert consensus about climate change is. The most recent report about the impacts of climate change was published in 2014. (The fifth assessment report is in drafts but has not been officially published.) It lists five reasons for concern about climate change:
- Unique and threatened systems— Climate change will destroy certain vulnerable cultures and ecosystems.
- Extreme weather events— Climate change increases the risk of some natural disasters, such as heat waves, coastal flooding, and extreme amounts of rain.
- Distribution of impacts— Climate change will disproportionately harm the global poor.
- Global aggregate impacts— Due to climate change, we’ll have a harder time getting the things we usually get from nature– pollination, flood control, bushmeat, and so on– which will harm the economy.
- Large-scale singular events— Some physical systems and ecosystems are at risk of abrupt and irreversible changes, such as the loss of the Greenland ice sheet.
Key risks are the potentially severe adverse consequences for humans resulting from climate change. The list of key risks is as follows:
i) Risk of death, injury, ill-health, or disrupted livelihoods in low-lying coastal zones and small island developing states and other small islands, due to storm surges, coastal flooding, and sea level rise. [RFC 1-5]
ii) Risk of severe ill-health and disrupted livelihoods for large urban populations due to inland flooding in some regions. [RFC 2 and 3]
iii) Systemic risks due to extreme weather events leading to breakdown of infrastructure networks and critical services such as electricity, water supply, and health and emergency services. [RFC 2-4]
iv) Risk of mortality and morbidity during periods of extreme heat, particularly for vulnerable urban populations and those working outdoors in urban or rural areas. [RFC 2 and 3]
v) Risk of food insecurity and the breakdown of food systems linked to warming, drought, flooding, and precipitation variability and extremes, particularly for poorer populations in urban and rural settings. [RFC 2-4]
vi) Risk of loss of rural livelihoods and income due to insufficient access to drinking and irrigation water and reduced agricultural productivity, particularly for farmers and pastoralists with minimal capital in semi-arid regions. [RFC 2 and 3]
vii) Risk of loss of marine and coastal ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for coastal livelihoods, especially for fishing communities in the tropics and the Arctic. [RFC 1, 2, and 4]
viii) Risk of loss of terrestrial and inland water ecosystems, biodiversity, and the ecosystem goods, functions, and services they provide for livelihoods. [RFC 1, 3, and 4]
To be clear, all of this is really bad. People are going to die. “Economic damage” sounds dry and abstract, but it means people going hungry and children dying of preventable diseases. The effects will fall substantially on the global poor, who have limited resources to help them cope. We can expect a climate refugee crisis.
It is also, notably, not human extinction.
Human extinction, if it were a likely outcome of climate change, would probably fall under reasons for concern #4 or #5 (although it’s still weird it didn’t get its own headlining concern). For this reason I will discuss #4 and #5 in more depth.
There is a low level of consensus about concern #4. If global warming is kept below 3 degrees Celsius, 20 to 30% of species are at risk of extinction– mostly specialist species who would have a far more difficult time adapting to climate change than humans would. Below 2.5 degrees Celsius, climate change will only cause a small reduction in gross world product; there is no consensus about the effects about 2.5 degrees Celsius, but they are expected to accelerate with increasing temperature. Human extinction is nowhere listed as a potential consequence of extreme levels of warming.
Concern #5 includes the following large-scale singular events:
- Over centuries or millennia, the Greenland ice sheet and possibly the West Antartic ice sheet may deglaciate, leading to a five to ten meter rise in sea level.
- The disappearance of the Arctic summer sea ice, which is likely reversible, although loss of biodiversity is not.
- Irreversible changes in coral reef, Arctic, and Amazon ecosystems.
- Two events described as “unlikely” or “very unlikely,” which include:
- Accelerated carbon emissions from wetlands, permafrost, or ocean hydrates, which could cause a higher-than-predicted rate of global warming. I have not been able to find an estimate of how high the warming would be or what the effects would be.
- Shutdown of the Atlantic meridional overturning circulation (AMOC), which would cause cooling in North America and Europe, increased extreme weather events, and (no matter what the Day After Tomorrow tells you) not human extinction
One concern I’ve often seen is an accelerated greenhouse effect turning us into Venus. However, Climate Feedback quotes Ken Caldeira, senior scientist at the Carnegie Institution for Science:
The Earth is not at risk of becoming like Venus. We have done climate model simulations in which all available fossil fuels were burned and the resulting CO2 released into the atmosphere. The planet warmed up about 10 °C in these simulations. This was enough to melt all of the ice sheets and produce 60 meters of sea-level rise, but in no such simulation does the Earth become anything like Venus.
Most of our climate models only extend to the relatively near future, such as 2100. There is a high degree of uncertainty about what will happen in the more distant future, with some exceptions, such as the melting of the Greenland ice sheet. It’s difficult to model things that are that far away. No one really knows what the world would look like in 2500 with three degrees of warming. But there’s also a lot of time in the next five hundred years to deploy other mitigation and adaptation solutions.
In conclusion, climate change will be very very bad. Lots of people will die. Many people– disproportionately the global poor– will go hungry, get sick or injured, not have access to clean water, or suffer from treatable or preventable illnesses. There will be many natural disasters. There will be global geopolitical instability, perhaps including wars and refugee crises. We will damage or lose many ecosystems that people value, such as coral reefs. The Amazon may become a grassland. But scientific consensus is that it will not result in human extinction or Earth becoming Venus.
Also see Is climate change an existential risk? by John Halstead. He gave a talk about it at EAG London 2018 as well.
I really like the writing and material in this post. :) Have you considered the possibility that global warming may introduce instability that could exacerbate other potential conflicts, leading to potential existential crises from nuclear war? Perhaps this is too indirect and unlikely, but my understanding is that EAs that worry about climate change as an x-risk envision this kind of two-step x-risk scenario.
One terminology for this is introduced in "Governing Boring Apocalypses", a recent x-risk paper. They call direct bad things like nuclear war an "existential harm", but note that two other key ingredients are necessary for existential risk: existential vulnerability (reasons we are vulnerable to a harm) and existential exposure (ways those vulnerabilities get exposed). I don't fully understand the vulnerability/exposure split, but I think e.g. nuclear posturing, decentralized nuclear command structures, and launch-on-warning systems constitute a vulnerability, while global-warming-caused conflicts could lead to an exposure of this vulnerability.
(I think this kind of distinction is useful, so we don't get bogged down in debates or motte/baileys over whether X is an x-risk because of indirect effects, but I'm not 100% behind this particular typology.)
I'm told that CSER is writing something on the indirect risks. My observation is that climate change is a very indirect stressor of the risk of nuclear winter. The causal path would be: extreme climate change => tension between nuclear powers => nuclear war => nuclear winter => existential catastrophe. Given that the risk of nuclear war conditional on climate change seems considerably lower than the unconditional risk of nuclear war, working on nuclear war directly looks a much better bet, assuming that working on nuclear war directly is in the slightest bit tractable.
We are indeed writing something on this (sorry it is taking so long!). I would dispute your characterization of the principle contributor of climate change to nuclear war though. Working on Barrett and Baum’s recent model of how nuclear war’s might occure I would argue that the greatest threat from climate change is that it creates conditions under which a prec[ititating event such as a regional war might escalate into a nuclear conflict are more likely - i.e. it increases our vulnerability to such threats. This is probably more significant than its direct impact on the number of precipitating events. Since such events are not actually that uncommon (Barret and Baum find over 60 I seem to remember whilst a Chatham House survey found around 20) I think that any increase in our vulnerability to these events would not be insignificant.
What is certainly correct is that the nature of the threat posed by climate change is very different in many ways to that posed by AI. Indeed the pathways from threat to catastrophe for anything other than AI (including pandemics, nuclear weapons, asteroids and so on) are generally complex and circuitous. On the one hand that does make these threats less of a concern because it offers multiple opportunities for mitigation and prevention. However, on the other hand, it makes them harder to study and assess, especially by the generally small research teams of generalists and philosophers who undertake the majority of x-risk research (I am not patronising anyone here, that is my background as well).
What would be the mechanism whereby it increases the risk of nuclear war? The main one I can think of is mass migration, but I'm not sure what the proposed mechanism is. Are there analogues in the past for comparably large mass migrations causing wars or increased nuclear tensions? We've had quite large refugee flows recently, but this seems to have had basically no impact on nuclear tensions. Given that the main worry for nuclear winter is US-Russia conflict, how could climate change exacerbate tensions there?
I also think it would be surprising if there had been 60 genuine near misses in the past, but that is another debate. That suggests surprising levels of luck. The Tertrais et al paper questions some claims about nuclear near misses
I think we might disagree about what constitutes a near miss or precipitating event. I certainly think that we should worry about such events even if their probability of leading to a nuclear exchange are pretty low (0.001 lets say) and that it would not be merely a matter of luck to have had 60 such events and no nuclear conflict, it is just that given the damage such a conflict would do they still reprasent an unaceptable threat.
The precise role played by climate change in increasing our vulnerability to such threats depends on the nature of the event. I certainly think that just limiting yourself to a single narrative like migration —> instability —> conflict is far to restrictive.
One of the big issues here is that climate change is percieved as posing an existential threat both to humanity generally (we can argue about the rights and wrongs of that, but the perception is real) and to specific groups and communities (I think that is a less contraversial claim). As such I think it is quite a dangerous element in international relations - especially when it is combined with narratives about individual and national reponsibility, free riding and so on. Of course you are right to point out that climate change is probably not an existential threat to either the USA or Russia but it will be a much bigger problem for India and Pakistan and for client states of global superpowers.
What do you make to the argument that the probability of nuclear winter caused by climate change is considerably lower than the probability of nuclear winter, so focusing more directly on nuclear winter looks a better bet?
Of course it will be smaller, however that does mean that tackelling climate change will not make a sizeable contribution towards reducing the risk of nuclear winter. The question for me is whether nuclear winters that relate to climate change are more or less tractable than nuclear winter as a whole. My view would be that trying to reduce the risk of nuclear winter by tackelling climate change and its consequences may be a more tractable problem then doing so by trying to get nuclear weapons states to disarm or otherwise making nuclear war less likely in general, but that efforts to make nuclear winter more survivable are probably more efficient than either of these policies from a purely x-risk reduction perspective.
However, I also do not think that nuclear winter is the only way in which climate change may lead to an existential threat (at least reading existential threat to include the prospect for an unrecoverable from civilisational collapse) as there are some interesting feedback loops between environmental and social collapse that have the potential to cause non-linear and self-perpetuating shifts in the structure of global civilisation. Admittedly these are hard to study, but from a value maximisation perspective I would say that in the face of uncertainty we will do better if we assume that global civilisation is relatively fragile to such changes than if we assume that it is more robust to them.
I don't agree that working on climate change is plausibly a better way to reduce the risk of nuclear war than working directly on nuclear war. Firstly, climate change is a very intractable problem in the first place for philanthropists and for national governments, given that action is opposed by entrenched interests across all society and requires cooperation pretty much of all nations. Nuclear peace is opposed by some entrenched interested in the military industrial complex, but these do not reach anywhere near as far into society as a whole. Major results could be achieved just by getting cooperation between Russia and US, which is not true of climate change.
Secondly, climate change is much less neglected than reducing the risk of nuclear war. Thirdly, there have been lots of apparently successful treaties that have e.g. limited the size of US and Russian arsenals. It just seems much easier to make progress on things that foster peace and reduce arsenals than on nuclear war caused by climate change. The path for the latter is extremely indirect.
Do you really mean that P(nuclear war | climate change) is less than P(nuclear war)? Or is this supposed to say that the risk of nuclear war and climate change is less than the unconditional probability of nuclear war? Or something else?
Yes sorry I meant the probability of a nuclear war caused by climate change is lower than the probability of a nuclear war.
Having looked at warhead stocks, nuclear winter research, etc, I think nuclear war isn't an x-risk either.
I'm also rather doubtful that climate change significantly increases the probability of nuclear war. Regional conflicts and insurgencies in certain places, sure. But the pathway from there to nuclear war is very unclear. You can point to the Indo-Pakistani dyad as a possible flashpoint, but both of them have few nuclear weapons. And their historical conventional conflicts did not escalate to involve other countries.
But remember, X-risk is not just extinction - there are many routes to long term future impacts from nuclear war - some are mentioned here.
But it is outcomes that are morally close to extinction, the loss of most of humanity's capacity and potential. Nuclear winter of a few degrees would not impact agriculture so adversely to cause this to happen. At this point you are multiplying so many small probabilities in series that you cannot call climate change a real x-risk without doing the same for so many other things that are equally likely to set a chain of bad events in motion.
I think it is useful to discuss qualifies as an X-risk. Asteroid/comet impact is widely regarded as an X-risk, but a big one that could cause human extinction might only have a one in a million probability in the next 100 years. This is a 0.0001% reduction in humanity's long term value. However, if you believe 80,000 Hours that nuclear war might have a ~3% chance in the next 100 years and this could reduce the long term future potential of humanity ~30%, that is a ~1% reduction in the future of humanity this century. So practically speaking, it is much more of an X-risk than asteroids are. Similarly, if you believe 80k that extreme climate change has a ~3% chance in the next 100 years and it reduces the long run potential by ~20%, that is a 0.6% reduction in the long term future of humanity. This again is much larger than asteroids. I personally think the nuclear risk is higher and the climate risk is lower than these numbers. It is true that some of the long-term impact could be classified as trajectory changes rather than traditional X risk. But I think most people are interested in trajectory changes as well.
I don't think the 80k estimate on climate change is based on a thorough investigation of the science. I just don't see how from the impacts estimated in the next 100 years, extreme climate change could be thought to be a greater than 0.1% ex risk. The heat stress of >4 degrees would be bad but if things started going that badly, I think the world would take action. In a few decades it will be much cheaper to abate GHGs and everyone will have an interest in doing so
I generally agree. The question is whether we should call something an X-risk by the impact if it happens alone or by the impact*probability. If the latter, and if comets are an X-risk, then we should call extreme climate change (and definitely nuclear war) an X-risk.
I see, yes good point.
By that logic you are turning the idea of an x-risk into anything that really matters in the long run. So poverty is an x-risk too in this definition. That makes it not a useful definition and is also very different from how most people think about the term.
Extinction (or something just as bad): x-risk. I go by that.
"Normal" nuclear war could be only only a first stage of multistage collapse. However, there are some ideas, how to use exiting nuclear stockpiles to cause more damage and trigger a larger global catastrophe - one is most discussed is nuking a supervolcano, but there are others. In Russian sources is a common place that retaliation attack on US may include attack on the Yellowstone, but I don't know if it is a part of the official doctrine.
Future nuclear war could be using even more destructive weapons (which may exist secretly now). Teller has been working on 10 gigaton bomb. Russians now making Poseidon large torpedo system which will be probably equipped with 100 Mt cobalt bombs.
Absurd. Why would anyone do that?
I'm sure it isn't. Also, scientifically speaking it doesn't even seem possible to ignite a supervolcano with nukes: https://www.iflscience.com/environment/what-would-happen-if-a-nuclear-bomb-was-dropped-on-yellowstone-supervolcano/
Even the most destructive historical weapons (e.g. Tsar Bomba) have not been deployed. Warheads have gotten smaller over recent decades. No reason for this trend to reverse.
Theoretical reasons for Doomsday weapon was laid by Herman Khan in "On Thermonuclear war". I scanned related chapter here: https://www.scribd.com/document/16563514/Herman-Khan-On-Doomsday-machine
The main idea is that it is ideal defence weapon, as no body will ever attack a country owning such a device.
The idea of attacking the Yellowstone is discussed very often in Russian blogosphere (like here https://izborskiy-club.livejournal.com/310579.html), and interest to the geophysical weapons was strong in the Soviet Union (details here: http://nvo.ng.ru/armament/2006-04-21/6_weapontheyfear.html) - this interest ended up in creating Poseidon artificial tsunami system which is now under testing.
I've read that US has an instrument to attack hardened underground facilities by multiple heavy nuclear strike in one place, which allows creating much deeper crate than a single nuclear explosion and destroy targets around 1 km deep. The same way an volcanic caldera cover could be attacked, and such multiple strikes could weaken its strength until it blow up by internal pressure - so you don't need to go through the whole caldera's cover. no new weapons for it is needed - just special targeting of already exiting.
Russian Poseidon system has 100-200 Mt bombs delivered by a very large torpedo and is in final stages of construction. https://en.wikipedia.org/wiki/Status-6_Oceanic_Multipurpose_System
I don't think this is indirect and unlikely at all; in fact, I think we are seeing this effect already. In particular, some of the 2nd-order effects of climate change (such as natural catastrophe-->famine-->war/refugees) are already warping politics in the developed world in ways that will make it more difficult to fight climate change (e.g. strengthening politicians who believe climate change is a myth). As the effects of climate change intensify, so will the dangers to other x-risks.
In particular, a plausible path is climate change immiserates poor/working class + elite attempts to stop climate change hurting working class (eg war on coal) --> even higher inequality --> broad-based resentment against elite initiatives. X-risk reduction is likely to be one of those elite initiatives simply because most X-risks are uninutitive and require time/energy/specialized knowledge to evaluate, which few non-elites have
Beware brittle arguments.
That's a good point, but I don't think my argument was brittle in this sense (perhaps it was poorly phrased). In general, my point is that climate change amplifies the probabilities of each step in many potential chains of catastrophic events. Crucially, these chains have promoted war/political instability in the past and are likely to in the future. That's not the same as saying that each link in a single untested causal chain is likely to happen, leading to a certain conclusion, which is my understanding of a "brittle argument"
On the other hand, I think it's fair to say that e.g. "Climate change was for sure the primary cause of the Syrian civil war" is a brittle argument
AFAIK this is not how the current refugee crisis occurred. The wars in the Middle East / Afghanistan were not caused by climate change.
If climate change increases, that will convince people to stop voting for politicians who think it is a myth.
You're also relying on the assumption that leaders who oppose immigration will also be leaders who doubt climate change. That may be true in the US right now but as a sweeping argument across decades and continents it is unsubstantiated. It's also unclear if such politicians will increase or decrease x-risks.
I'd previously read that there was substantial evidence linking climate change-->extreme weather-->famine--> Syrian civil war (a major source of refugees). One example: https://journals.ametsoc.org/doi/10.1175/WCAS-D-13-00059.1 This paper claims the opposite though: https://www.sciencedirect.com/science/article/pii/S0962629816301822.
"The Syria case, the article finds, does not support ‘threat multiplier’ views of the impacts of climate change; to the contrary, we conclude, policymakers, commentators and scholars alike should exercise far greater caution when drawing such linkages or when securitising climate change."
I'll have to investigate more since I was highly confident of such a 'threat multiplier' view.
On your other two points, I expect the idea of anthropogenic global warming to continue to be associated with the elite; direct evidence of the climate changing is likely to convince people that climate change is real, but not necessarily that humans caused it. Concern over AGW is currently tied with various beliefs (including openness to immigration) and cultural markers predominantly shared by a subsection of the educated and affluent. I expect increasing inequality to calcify tribal barriers, which would make it very difficult to create widespread support for commonly proposed solutions to AGW.
PS: how do I create hyperlinks?
Highlight your text and then select the hyperlink icon in the pop-up bar.
One comment - "Two events described as “unlikely” or “very unlikely,” which include:..."
In the IPCC reports, 'unlikely' means 0-33% probability, and 'very unlikely' means 0-10% probability. "Very unlikely" therefore doesn't mean negligible. This is a pretty woeful choice of terminology by the IPCC, but important to be clear on.
It's clear that climate change has at best a small probability (well under 10%) of causing human extinction, but many proponents of working on other x-risks like nuclear war and AI safety would probably give low probabilities of human extinction for those risks as well. I think the positive feedback scenarios you mention (permafrost, wetlands, and ocean hydrates) deserve some attention from an x-risk perspective because they seem to be poorly understood, so the upper bound on how severe they might be may be very high. You cite one simulation that burning all available fossil fuels would increase temperatures by 10 °C, but that isn't necessarily an upper bound because there are non-fossil fuel sources carbon on Earth that could be released to the atmosphere. It would of course also be necessary to estimate how high the extinction risk conditional on various levels of extreme warming (8°C, 10°C, 15°C, 20°C?) would be.
Regardless, it's a good idea to have a clear view of how big the risk is. You're right that the casual claims about extinction or planetary uninhabitability I hear from many people who are concerned about climate change are not justified, and they seem a bit irresponsible.
I would be curious about any views or research you may have done into geoengineering risk?
My understanding is that climate change is not itself an existential risk but that it may lead to other risks (such war which as Peter Hurford mentions). One other risk is geoengineering where humanity starts thinking it can control planetary temperatures and makes a mistake (or the technology is used maliciously) and that presents a risk.
It's really not clear how any geoengineering plan would cause extinction (they only aim to make modest changes to temperatures and precipitation, e.g. to counteract climate change), and there is such popular antipathy towards geoengineering that we can assume polities to err on the side of too little geoengineering rather than too much.
One way in which geoengineering increases societal fragility is if we pump particles into the atmosphere and then find ourselves obliged to keep pumping particles into the atmosphere in order to maintain the effects, and then suffer a significant collapse of infrastructure that makes us not capable of this any longer. This could result in extremely sudden warming and a rapid, unpredictable change in weather patterns. Something would have to go very wrong first, of course, but it could compound an existing catastrophe and take it from recoverable to irrecoverable.
See the recent paper by Parker and Irvine on termination shock. The catastrophe required to terminate solar geoengineering efforts would be extraordinarily specific, making the use of planes or hot air balloons impossible for months or making the production of aerosols such as sulphates impossible for months. While this is possible, it doesn't seem like a big enough risk to make solar geoengineering a significant concern - how exactly could this happen? Other parts of our infrastructure, such as the production of fertiliser, could also be interrupted by some incredibly specific catastrophe, but these aren't usually thought to be among the top risks we should consider.
As I argue in a recent paper on solar geoengineering, many of the alleged risks of solar geoengineering are overblown. The main problem is getting governance of it over an extended period, which looks extremely difficult, but would presumably also be a disincentive to use it in the first place.
Another thing to consider is that, given climate modeling is so imprecise and regularly flawed, that our models are wrong and the risk is significantly different than predicted.
(Similar to some of Toby's stuff on the Large Hadron Collider risks: http://blog.practicalethics.ox.ac.uk/2008/04/these-are-not-the-probabilities-you-are-looking-for/)
This could go both ways.
"Normal" global warming is not x-risk, but possible heavy tail connected with something unknown could be. For example, the observed stability of our climate may be just an "anthropic shadow", and, in fact, climate transition to the next hotter meta-stable condition is long overdue, and could be triggered by small human actions.
The next meta-stable state may be with median temperature 57C according to the article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4748134/ ("The climate instability is caused by a positive cloud feedback and leads to a new steady state with global-mean sea-surface temperatures above 330 K")
Because of rising solar luminosity the extinction level global warming is a question of "when", not "if", but typically it is estimated to happen hundreds millions years from now.