[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.
rlms said:
I don’t think an existential risk has to kill literally everything, the usual standard seems to be billions of deaths and the centuries-scale-irreversible destruction of civilisation as we know it. If you use the literally-everyone standard, I don’t see how you could reasonably class nuclear war and pandemics as X-risks (there’ll always be a few thousand uncontacted tribespeople in the Amazon/people hiding in bunkers).
By that standard, it’s definitely true that the likely outcomes of climate change (e.g. 5 degrees warming with no nasty surprises) aren’t X-risks, even though uninformed people often suggest they are. But tail risks could be, or at least EAs who are better informed than me and working on general X-risk such as CSER seem to think so. For instance, see here https://www.pnas.org/content/107/21/9552 — the extremely buried lede (last sentence) says double digit warming would lead to halving of inhabitable land. It’s difficult to imagine that happening without billions of deaths, even discounting the other effects of that level of warming.
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Lambert said:
How do you expect climate change to irreversibly destroy civilisation?
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rlms said:
I don’t expect it to, but in the worst cases where you have to relocate New York, San Francisco, most of England because of sea level rises; deal with hundreds of millions of refugees; and reorganise most of the world’s food supply there isn’t going to be much money left for things like healthcare and education.
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Lambert said:
That’s still only a transient issue, in the general scheme of things.
The fall of rome and the late bronze age collapse both destroyed a lot of civilisation, but civilisation recovered from both within 500-1000 years.
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rlms said:
Sure, I did say “centuries-scale-irreversible”.
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Fisher said:
Wait, you’re saying that the atmospheric pressure won’t increase by a factor of 90 and torrential downpours of sulfuric acid aren’t going to appear?
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PatrickM said:
I know, what a disappointment.
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Cerastes said:
Honestly, if we’re talking about true extinction, as in zero human population, I’m not sure there are any known existential risks of any significant estimable chance. Remember, 500 people can rebuild the species with a bit of planned mating, and 5000 don’t even need that. If we have genetic tools to deal with inbreeding depression, even fewer survivors are needed.
Nuclear wars, chemical weapons etc may kill of 99.99% of humans, but will they really kill *everyone*? Plagues (whether man-made or natural) have a virulence/transmissibility tradeoff that guarantees no total extinction. Any self-replicating nano-tech that uses rare materials won’t be a threat, and if it uses common ones, bacteria will rapidly evolve to eat it (seriously, find me a common material that some bacteria somewhere *can’t* eat, I’ll wait). AI risk is frankly just speculation at this point,with no actual data of what could happen of whether it really is a risk at all. There’s no truly colossal asteroids or comets with any appreciable risk of collision within the next 1000 years, and we’ve found all the big ones. And there’s no compelling evidence that volcanism alone is sufficient for mass extinctions (no, contrary to that Atlantic article, the Deccan traps were not the primary cause of the KT event).
Predicting the future is hard, especially for events we’ve never seen, but that goes in both directions – it could be worse than we think, but it could also be better. There’s been a fair amount of research, discussed in hushed tones, that the whole “nuclear winter” thing may have been totally overblown and based on poor estimates.
And we’re persistent little fuckers. Looking at the history of life, aside from large body size and k-selected life history, we have EVERY trait associated with surviving a mass extinction – wide range of tolerable environments, massive geographic range, massive dispersal ability, adaptability like nothing ever before, omnivorous, high levels of genetic diversity, etc.
And there’s never been a species like us, either, not that we know of. If we had explored the universe and found the ruins of 10,000 extinct alien species, we should be justifiably alarmed, but right now Fermi’s paradox can be explained by either life or intelligence being rare. For all we know, civilization-level intelligence is some sort of “game breaker” once you reach a certain tech level. We literally have no idea.
I think the focus on X-risk distorts the thinking, by hyper-valuing extremely unlikely, purely speculative, or even borderline impossible scenarios. If the moral weight of prevention is the probability of occurrence times cumulative cost, X-risk gets to wave away the first term entirely by setting the last term to infinity. Consider a list of “things that could kill more than a billion people”, versus only a list of true X-risks. The latter only includes a few items, none of which have ever happened, and most of which are purely speculative. The former includes all of the X-risks, but also lots of things which have happened (global plagues, asteroid strikes, famines) or are currently happening (global climate change, morons with nuclear weapons), all with much, much higher probabilities of causing the billion deaths. The only benefit to focusing on X-risk is that it gives way for people to “bypass” the tiny or unknowable probabilities of their pet highly speculative scenarios and prioritize them over genuinely pressing issues which affect literally billions of people.
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Doug S. said:
The unlikely climate change nightmare that scares me is the one where the ocean loses too much oxygen and anaerobic bacteria produce enough hydrogen sulfide to make the atmosphere toxic. Something like that seemed to be involved in the Great Permian Extinction, but the aftermath of the Siberian Traps eruption supposedly caused about ten degrees C of warming, which is way more than any climate change projection, and that link with the criticism of the New Yorker article suggests it would take millennia for the existing anoxic patches in the ocean to grow into something dangerous.
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Thomas Jones said:
People advocating for reducing x-risks generally also think they are large – I think most see it as like 0.1*(big number), not epsilon*(big number).
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kechpaja said:
>Remember, 500 people can rebuild the species with a bit of planned mating, and 5000 don’t even need that. If we have genetic tools to deal with inbreeding depression, even fewer survivors are needed.
That’s 5000 people who can contact one another, get themselves into more or less the same spot, and who know all of the skills necessary to survive and raise children in a post-apocalyptic world. 5000 people scattered randomly across Siberia and northern Canada aren’t going to have such an easy time.
For what it’s worth, I also basically agree with the premise that the extinction of %100 of the human population is extremely unlikely. But let’s not assume that the existence of 5000 survivors entails a community of 5000 people capable of working together and reproducing.
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Cerastes said:
Except they don’t all need to contact each other, not right away, anyhow. One person marrying someone from the next village over every generation or two would be fine. And our species is REALLY good at walking (it takes less than a year to walk across the US) and has a very long lifespan. If that 5000 people are split into groups of 50, that means there’s probably another village within 1000 miles at the start. Inbreeding effects take some time to really show up – a few generations of first-cousin marriage will have relatively minor effects. And we breed fast – assuming we retain some old tech (even just antibiotics and knowing what germs are), a village of 50 could be a village of 500 in 3-4 generations. And with 500 people for over a century, *someone* will leave to explore, be cast out, leave in a huff because nobody likes their music, etc. If they have cars, that 1000 miles is a few days’ drive, so a few weeks of exploration will land you on their doorstep. And that’s assume nobody is nomadic, which makes finding other groups easier, and somehow all the radios stopped working. Those other villages are essentially genetic resevoirs of diversity, capable of severely mitigating the genetic effects of mass population loss once they’re re-united.
Plus, what’s the likelihood that mortality will be evenly distributed? More than likely you’d have areas with total or near-total eradication, but other areas may have much lower mortality or even be spared entirely, depending on the nature of the event (isolated tribes in the Amazon, Pacific islands, Arctic/Siberia, etc., Oil platforms, Ships at sea, Antarctic research stations, etc). Shit, something that only spares planes in mid-flight would still leave enough humans to repopulate. That clustering will make the distance between settlements longer, but more self-sustaining (resource-wise and genetically).
And bear in mind that’s literally the most extreme scenario. Something which wipes out 99% of humanity still leaves 77 million people. 99.99% mortality still leaves 770k. You’d need >99.9999% mortality to be in that danger zone.
My central point was that humanity can recover from extremely small population levels, so anything less than almost 100% mortality (which is extremely implausible) is still not and extinction, just a setback. If the Toba volcano theory is right, we’ve already recovered from populations of less than 10,000 once, and that was before we moved out of the Stone Age.
We’re not as easy to kill off as you think.
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sauliussimcikas said:
Also see https://docs.google.com/document/d/1qmHh-cshTCMT8LX0Y5wSQm8FMBhaxhQ8OlOeRLkXIF0/edit# which analyses the same topic
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adrianmholmes said:
You are absolutely right. It’s what makes it a hard sell for climate scientists in current U.S. politics. Trump and his GOP supporters, if they do give climate change any consideration, believe that it’s more a problem for the “Other Guy” than it is for us in America and that we’ll be just fine in the “land of plenty and prosperity”. This, in part, is why they see “America First” and isolationism as the correct path to take. They see “nasty things” like wars, trade conflicts, natural disasters, drought, famine and civil unrest -all consequences of climate change, as caused by poor decision making by foreign governments and it doesn’t involve the U. S. They believe that by raising the ramparts, manning the bastions, and sealing the entryway the U. S. will be safe and secure from all that goes on outside.
Nice dream.
The truth is that climate change everybody on this planet and unless you have some sort of self-sustaining, underground bunker where you can seal yourself off for a few centuries (or millennium) you won’t escape it.
End of the world? Humanity? Sorry, apocalypticists, there won’t be a Second Coming but there will be a lot of war, disease, famine, disease, and death.
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PandaBox said:
I am not as versed in risk calculation, so forgive if this is level-1 reasoning, but I see the problem in the way a substantial change of climate would mess with our ability to focus on other issues. Lets take Malaria/ Aging as an example – the research centers/ charities dedicated to solving these issues would probably experiece a lack in resources, would the climate change that drastically, would it not? Also, looking at solving malaria or other issues like food supply – would climate change not make it harder to fix these issues and render current solution strateies worthless? Since it interacts with a lot of known top issues in a way that maximized their impact, is it not worth focussing on climate change?
However, I agree that the climate-change horror scenarios have not helped in any shape to focus on solutions.
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Hivewired said:
I’ll make a longer post about this later because that’s apparently necessary, goddamnit, but here is in brief, Some of the X-Risks in climate change are:
1) If you displace several billion people there is a good chance of simply collapsing global civilization in the ensuing wars, famines, and human migration patterns. “But this won’t kill everyone!” you say predicting that humanity would be able to bounce back to high tech industrialization after being knocked into a dark age and we haven’t already consumed so much of the world’s resources that we fail to reindustrialize. A lot of people are concerned if we destroy the current iteration of civilization that there are not enough things like low hanging hydrocarbon fuels and rare earth metals to successfully make another go at getting off the rock, and if humanity doesn’t become multi-planetary, we eventually go extinct with the Earth, even if we do manage to cling to existence for a long time after civilization fails.
2) There’s a possibility of much greater and more catastrophic sea level rise by 2100 then 1 meter of nuisance flooding, recent theories of the breakup of the Laurentide ice sheet and observations of the West Antarctic ice sheet indicate a possibility that the melting rate is closer to exponential than linear, and the entirety of the ice sheets could end up going unexpectedly quickly and causing 6-10 meters of sea level rise over a few year period. Again, this stands a good chance of just collapsing global civilization on its own.
3) The threat of Ecocide is rarely talked about, but there have been major die-offs of insect biomass and there’s a growing concern that we may be seeing the beginnings of the biosphere unzipping itself from the bottom up. If we kill the biosphere then our food supply will collapse and with it civilization.
4) Ocean acidification/deoxygenation could cause a bloom of toxic microorganisms that release clouds of poison gas into low-lying areas and turn the atmosphere toxic.
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dolphinwrite said:
I’m just little old me: nothing more than anyone else. I was fortunate to have an understanding mind, though I’m imperfect as others. I simply know when something is real and something isn’t.
Taking trips across the oceans, driving across states, reading up and researching, then pondering why I was told pollution was destroying the world when everything I saw and understood told the complete opposite. This Earth is far too big for us to put a dent in it much less destroy the planet and have to move to the moon or Mars. As I grew up, thinking for myself, listening to those in my family that believed in man-made climate change, I really listened. No one told me not to believe. The understanding I was born with told me. Like when I realized the swinging pail of water explained gravity, I knew man can’t change the climate. It’s a theory, but that’s all it is, the data showing no provable evidence.
Why is so much effort being put into getting our youth to believe this stuff? We know that using “climate change”, then saying naysayers are deniers, are simply tools to control people’s rights to see for themselves. That alone caused a lot of suspicions. When I’ve listened to people’s arguments, I saw only emotions, verbal attacks, and an intensity not born of understanding. In other words, most people don’t know what they’re talking about, but due to their supportive friends, the media, and the education system that has not effectively allowed children to think for themselves, they feel they are on the right path, never willing to think for themselves. Most people don’t understand what that means, and that is scary in an of itself, but it also explains why so many have bought into the dogma.
No one’s going to Mars to live. No one’s going to the moon to live. Just on the face of it, we already live on a planet with an incredible amount of life. Much easier to fix some pollution problems, fix microcosm problems, then try to create life on lifeless celestial objects that aren’t designed to support. That told me something. Also, the fact that the media and political movements have effectively silenced those scientists, which are many, from disproving man-made global anything, tells me something else. And as a teacher, realizing that “truth” seems to fall on too many deaf ears tells me another. We are being trained not to hear and differentiate. We’ve been trained to go along with popular, or apparently popular, media supported, thinking without question so as to keep our jobs and status. I guess, I just can’t do that. Why? Because I really want to know.
Spend some time driving across America. Drive south to north through Utah. Take an ocean voyage. Take a few lessons on small planes. Calculate the waters. Calculate the air. Read about how the sun moves through cycles, the Earth too, and the changes that occurred long before we got here. Then, consider that any real study on Earth’s temperatures are short. 100 years ago, no one was guaging temperature changes accurately. The data is so pidly. It will take a thousand more years or so of evidence for any real conversation to take place. The Earth is just too big.
However, I know I will probably never convince anyone, but simply support those who need supportive thinking. And that’s okay.
The difficulty in disproving what is obvious to me is when people believe something, they emotionally bond to their thinking, then they can no longer hear evidence.
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