Niel Bowerman: Could climate change make Earth uninhabitable for humans?

How likely is hu­man ex­tinc­tion due to cli­mate change? Neil Bow­er­man, a former cli­mate physi­cist who is now at 80,000 Hours, ad­dresses one com­po­nent of this ques­tion — the fu­ture phys­i­cal hab­it­a­bil­ity of Earth — by sur­vey­ing pos­si­ble routes to ex­treme lev­els of warm­ing and ways in which ex­treme warm­ing could lead to un­in­hab­it­a­bil­ity.

We’ve lightly ed­ited Niel’s talk for clar­ity. You can also watch it on YouTube or read it on effec­tivealtru­

The Talk


I’m go­ing to be talk­ing about whether cli­mate change could make Earth un­in­hab­it­able for hu­mans.

We already know that cli­mate change is caus­ing in the bal­l­park of hun­dreds of thou­sands of pre­ma­ture deaths. This is likely to in­crease to as many as hun­dreds of mil­lions over the com­ing decades. Cli­mate change is already hav­ing sub­stan­tial im­pacts on a wide range of ar­eas from Arc­tic sea ice melt to flood­ing and other ar­eas. We have a sound eco­nomic case for ad­dress­ing cli­mate change, and it is harm­ing the poor­est peo­ple the most. And yet these are also the peo­ple that have least con­tributed to cli­mate change, cre­at­ing a cli­mate jus­tice is­sue. Over­all, as we look at the pic­ture, it doesn’t look good.

But I’m talk­ing here only about the medium-case sce­nario. As a longter­mist in­ter­ested in ex­is­ten­tial risk, I want to ad­dress the tail risk is­sues on cli­mate change. And so that’s what I’m go­ing to be talk­ing about for the rest of this talk: look­ing at how cli­mate change con­tributes to ex­is­ten­tial risk.

The re­la­tion­ship be­tween cli­mate change and ex­is­ten­tial risk

Let’s start by defin­ing ex­is­ten­tial risk. It means hu­man ex­tinc­tion or the per­ma­nent and dras­tic cur­tail­ment of hu­man­ity’s long-term po­ten­tial. So how might cli­mate change con­tribute to ex­is­ten­tial risk?

As I see it, there are three main ways. (There’s a bunch of ways that you can slice the cake here, but I found the fol­low­ing frame­work use­ful as I think about this is­sue.)

  1. Mak­ing Earth un­in­hab­it­able for hu­mans.

  2. In­creas­ing the risk of other ex­is­ten­tial risks.

  3. Con­tribut­ing to the like­li­hood of so­cietal col­lapse.

Now, if I had to guess, I would guess that the sec­ond and third risks here — the con­tri­bu­tion to other ex­is­ten­tial risks and to so­cietal col­lapse — are prob­a­bly larger than the first, but they’re also less tractable to study.

And so I’m go­ing to do the thing that aca­demics of­ten do: ig­nore the big im­por­tant things and ad­dress the thing that I know about as a cli­mate physi­cist. We’re go­ing to be set­ting the sec­ond and third risks aside and fo­cus­ing pri­mar­ily on this ques­tion of mak­ing Earth un­in­hab­it­able…

The risk of so­cietal collapse

...ex­cept for the next slide, where I want to talk briefly about so­cietal col­lapse. So what do I mean when I talk about the chance of so­cietal col­lapse? What I’m talk­ing about here is that I’m ges­tur­ing at some­thing in the vicinity of a com­plete break­down of poli­ti­cal in­sti­tu­tions, a col­lapse of in­ter­na­tional trade, and re­ally a break­down of the fabric of so­ciety. To make this re­ally con­crete, I’m talk­ing about a re­duc­tion in global GDP of more than 80% in less than a decade.

This would be dras­tic and very dra­matic, but I have no idea how likely it is to oc­cur. I also have no idea how likely it is that so­cietal col­lapse would con­tribute to ex­is­ten­tial risk. And I don’t know [how cli­mate change might in­fluence the in­ter­ac­tion be­tween so­cietal col­lapse and ex­is­ten­tial risk]. But I would guess that [col­lapse] is one of the biggest av­enues for cli­mate change to con­tribute to ex­is­ten­tial risk. And so I’m ex­cited to see fur­ther study of this.

For­tu­nately, the folks at the Cam­bridge Cen­ter for the Study of Ex­is­ten­tial Risk are start­ing to think about this. They’ve got a cou­ple of pa­pers in drafts that I’ve put down in the bot­tom of the slides where they’re start­ing to use a sys­tems per­spec­tive to think about some of these ques­tions. But I’m now go­ing to set aside so­cietal col­lapse and con­tri­bu­tion to other risks and fo­cus on the thing that I can ac­tu­ally give a talk on, which is the chance of Earth be­ing made un­in­hab­it­able for hu­mans due to cli­mate change.

What does it mean for Earth to be “un­in­hab­it­able”?

I want to start by say­ing that this is a re­ally high bar. For Earth to be­come un­in­hab­it­able to hu­mans, that means that hu­mans have to be able to sur­vive nowhere on Earth, in any of its wide-rang­ing cli­mates [even af­ter the Earth be­comes much warmer and cold cli­mates be­come more hab­it­able]. This is a re­ally high bar to meet.

But it’s worth say­ing that hab­it­a­bil­ity is re­ally a func­tion of two things. One is the en­vi­ron­ment of Earth, and the other is the set of so­cial, tech­nolog­i­cal, and eco­nomic fac­tors and tools that we have available to us. And so if I had to put my finger in the air and guess, I would guess that if our eco­nomic and tech­nolog­i­cal tra­jec­tory con­tinues on as it is, it’s pretty un­likely that Earth will be­come un­in­hab­it­able, sim­ply be­cause we have the tools and the tech­nol­ogy to sur­vive in such varied cli­mates. We [are work­ing to cre­ate] habitats on the moon or on Mars, and liv­ing on Earth un­der dras­tic cli­mate change is prob­a­bly go­ing to be a lot eas­ier than that.

But if we were to ex­pe­rience some form of dras­tic and dra­matic so­cietal col­lapse and some­how knock our­selves back to the stone age, then I think there’s a much more in­ter­est­ing ques­tion here: could you imag­ine a sce­nario where, un­der ex­treme warm­ing and ex­treme cli­mate change, Earth does be­come un­in­hab­it­able to [hu­mans with Stone Age tech­nol­ogy]? That’s what I’m go­ing to be ad­dress­ing for the rest of this talk.

The his­tor­i­cal effects of cli­mate change

I want to start by look­ing at some pa­le­o­cli­mate ev­i­dence and think­ing about what we can say about the hab­it­a­bil­ity of Earth un­der some his­tor­i­cal cli­mates and some his­tor­i­cal cli­mate changes. First, I’m go­ing to talk about the Pa­le­ocene-Eocene Ther­mal Max­i­mum. This hap­pened about 55 and a half mil­lion years ago. We saw warm­ing of about 12 de­grees above what we cur­rently see to­day, and yet we didn’t see a mass ex­tinc­tion. We didn’t see vast species die-off in the way that you would ex­pect if Earth were be­com­ing un­in­hab­it­able. Now, this may be some ev­i­dence that dra­matic warm­ing could be hab­it­able for hu­mans, but the rate of warm­ing was re­ally a lot slower than it is to­day. So it’s not a perfect anal­ogy.

What about a time with much faster rates of change? Well, about 11,000 years ago, hu­man­ity emerged out of the end of the re­cent ice age into what’s known as the Younger Dryas. Snow and dust ac­cu­mu­la­tion sam­ples tell us that the Earth warmed by about seven de­grees in cer­tain parts in less than a decade. And hu­man­ity also sur­vived that, though it was mov­ing from a much colder cli­mate to the cli­mate we en­joy to­day. So again, not a perfect anal­ogy, but it’s maybe some ev­i­dence that hu­man­ity is able to sur­vive rapid rates of change.

The fi­nal ex­am­ple I want to give in this space is just look­ing at the range of con­di­tions that hu­mans en­joy liv­ing in to­day. Hu­mans thrive in cli­mates as di­verse as Bahrain and St. Peters­burg — cli­mates that vary in av­er­age over 16 de­grees centi­grade. So this is maybe some ev­i­dence that even [on a warmer planet], pro­vided that ev­ery­thing else didn’t fall apart around us, we would be able to sur­vive in a range of differ­ent cli­mates pro­vided that the en­vi­ron­ment and ecosys­tems adapted. But again, re­ally not a perfect anal­ogy be­cause these are static con­di­tions as op­posed to mov­ing ones.

Is there a causal chain lead­ing to po­ten­tial hu­man ex­tinc­tion?

There is [ad­di­tional] ev­i­dence that we can bring to play here. Dur­ing my PhD, I would talk about this ques­tion a fair bit with my old su­per­vi­sor. He would always say that in or­der to ad­dress cli­mate change as a con­tri­bu­tion to X-risk, you need a story you can tell about what events oc­cur that get us from now to a point where Earth is un­in­hab­it­able or where hu­mans have gone ex­tinct. And so what I want to do for the rest of this talk is to try and sketch out a story that I find [vaguely] plau­si­ble for how we could get there.

I’m not say­ing this is likely. I’m not say­ing this is go­ing to hap­pen. I think this is in­cred­ibly un­likely. But the challenge I gave my­self was: could I tell a story where we get to a world like that? So that’s what I’m go­ing to do here.

The long-term po­ten­tial of global car­bon emissions

This is not the first time that this graph has been shown in this con­fer­ence. I think Good­win showed it in her talk ear­lier, but I want to briefly talk us through this. So along the ver­ti­cal axis here, you’ve got the amount of warm­ing go­ing from zero to five de­grees. For con­text, in­ter­na­tional cli­mate ne­go­ti­a­tions are aimed at keep­ing us be­low two de­grees. Five de­grees would be a dra­mat­i­cally and dras­ti­cally differ­ent world from the one that we en­joy to­day, with mass loss of species, [many risky] tip­ping points, and all sorts of things that have been cov­ered el­se­where in the con­fer­ence over the course of the last cou­ple of days. [The slide also shows] how much car­bon hu­man­ity is burn­ing. The black line [rep­re­sents the pre­sent year]. To­day, we have burnt about half a trillion tons of car­bon diox­ide; by the year 2100, if we carry on burn­ing CO2 un­der busi­ness as usual sce­nar­ios, we’ll get up to about 2 trillion tons of car­bon burnt.

And that’s burn­ing the amount of car­bon that we would un­der busi­ness as usual. What if we some­how got re­ally car­bon-hun­gry and [even­tu­ally] ended up burn­ing all the po­ten­tially eco­nom­i­cally vi­able car­bon [in fos­sil fuel re­serves]?.To [un­der­stand the re­sults], we need to zoom out a lit­tle bit and con­tinue the axis along here.

This is the range of the graph that we would be look­ing at if hu­man­ity were to burn all of the po­ten­tially eco­nom­i­cally vi­able fos­sil fuel re­serves that [we cur­rently know of].

If you look at the red band com­ing up here, this is the one you want to be think­ing of, and the ques­tion is: where will this red band go to if we end up burn­ing this much fos­sil fuel? And the an­swer is, I don’t know. There’s a whole bunch of com­pli­cated cli­mate sci­ence that would go into an­swer­ing this ques­tion. Peo­ple have made ca­reers out of point­ing out that this is roughly a straight line so far, but it’s prob­a­bly not go­ing to be a straight line for­ever. There’s a bunch of fac­tors that are go­ing to go into this. But this is more to prime your in­tu­itions that our burn­ing that much fuel would prob­a­bly lead to a very bad world.

Cloud-based tip­ping points

So that’s the first pillar of the story that I want to tell. The sec­ond pillar of this story is look­ing at cloud-based tip­ping points and ask­ing the ques­tion: could there even be cloud-based tip­ping points? Those of you who are in­ter­ested in the so­lar sys­tem (like I was as a kid) prob­a­bly know that Venus is ac­tu­ally warmer than Mer­cury, de­spite the fact that Venus is fur­ther away from the sun. And this is be­cause Venus has a run­away green­house effect. Now, it hap­pened differ­ently there than the way it would hap­pen on Earth, but if it were to hap­pen on Earth, it would go some­thing like this:

  • Some forc­ing would heat up the ocean — say, in­creased car­bon emis­sions or in­creased en­ergy from the sun.

  • The oceans would get a lit­tle warmer; they would evap­o­rate a bit more, and that evap­o­ra­tion would put more wa­ter va­por into the at­mo­sphere.

  • Water va­por traps out­go­ing ther­mal ra­di­a­tion (heat). That heats up the at­mo­sphere, which in turn heats up the ocean.

  • And so your cy­cle con­tinues.

On Venus, that just kept go­ing and kept go­ing and kept go­ing un­til… I think Venus is about 700 de­grees centi­grade. On Earth, if this were to oc­cur in a very im­pos­si­ble worst-case sce­nario, you could imag­ine boiling all the oceans or some­thing like this if the effect didn’t stop.

Peo­ple have looked into this and they’ve said, “Ac­tu­ally, this isn’t re­ally very plau­si­ble. You’d need a lot more in­com­ing so­lar ra­di­a­tion than is ever re­ally go­ing to oc­cur, be­cause we know how the Earth or­bits the sun and we know the range of so­lar ra­di­a­tion that tends to reach Earth and we know this is re­ally not go­ing to hap­pen any­time soon.” I think we can rule out this run­away green­house effect. But is there some­thing like this that could hap­pen?

Re­cent de­vel­op­ments in cli­mate modelling

Back when I was start­ing my PhD, which I finished in 2013, there wasn’t re­ally a story I could tell like this. But in 2016, an in­ter­est­ing pa­per came out by Pop et al (2016), which had a very sim­ple cli­mate model with a strange effect: cloud feed­back kicked the tem­per­a­tures up to sta­bi­liz­ing at about 20 de­grees [centi­grade above cur­rent tem­per­a­tures]. So you ba­si­cally saw this run­away af­fect that I’ve been talk­ing about.

Pop et al.’s model wasn’t very plau­si­ble; it was in­cred­ibly sim­plis­tic and it made enough as­sump­tions that no one re­ally be­lieved it. But it started to get peo­ple scratch­ing their heads and won­der­ing: Is this a thing that could hap­pen? Is there a fea­si­ble mechanism here?

Fast-for­ward to 2019. As I was read­ing the liter­a­ture ahead of writ­ing this talk, I was amazed to find this pa­per by Sch­nei­der et al (2019), which is ac­tu­ally kind of a big deal. It uses an­other sim­plis­tic model of the at­mo­sphere. And what hap­pens in this model is they triple car­bon diox­ide con­cen­tra­tion (the amount of CO2 in the at­mo­sphere). And what they find is that the stra­tocu­mu­lus cloud layer in the trop­ics would burn away.

Clouds have this lovely white fluffy prop­erty that makes them re­ally re­flec­tive to in­com­ing sun­light. And so that stops the Earth from warm­ing too much. But when the clouds dis­ap­pear, the dark ocean un­der­neath of them ab­sorbs a lot of sun­light. And that in turn heats up the ocean. And you re­mem­ber our story be­fore about heat­ing up the ocean, wa­ter into the at­mo­sphere, blah blah blah. And so what hap­pens in the Sch­nei­der et al (2019) sim­ple model is that you see eight ex­tra de­grees of warm­ing on top of the tripling of CO2 con­cen­tra­tions that hap­pened sim­ply from what they did in the model.

This model, [like Pop et al’s], had a mixed re­cep­tion from sci­en­tists. Some peo­ple said, “Hmm, that’s re­ally in­ter­est­ing.” Others said, “No, it’s a sim­ple column model. It’s not go­ing to ap­ply globally. We shouldn’t kid our­selves enough about this.”

But I think it is fair to say that we now at least have a phys­i­cally plau­si­ble mechanism here. Some­thing worth in­ves­ti­gat­ing fur­ther. And so if we take this sim­ple model and put it in differ­ent places on the planet, you’re go­ing to see this feed­back effect kick­ing in at differ­ent times. And so you’re not go­ing to see a rapid jump in the way that you do here, but you might end up see­ing an in­crease in the rate of warm­ing that we get for each ton of car­bon diox­ide emit­ted. In cli­mate par­lance, you might see cli­mate sen­si­tivity in­creas­ing at higher tem­per­a­tures. And in the lat­est mod­els that are go­ing into the IPCC [In­ter­na­tional Panel on Cli­mate Change] re­port — the sixth one that’s com­ing out in 2021 — they do start to see some of this effect where at higher tem­per­a­tures you see more warm­ing per unit of car­bon diox­ide con­cen­tra­tions than you do at lower car­bon diox­ide con­cen­tra­tions.

We don’t re­ally know how big a deal this is. We don’t know if this is go­ing to be a big deal or a small deal, but at least there’s some ev­i­dence that maybe this is the thing we should be wor­ry­ing about. And so what I’ve been do­ing here is scratch­ing my head and ask­ing my­self: can I tell a plau­si­ble story about how Earth be­comes un­in­hab­it­able due to cli­mate change? Th­ese are the two main pillars that I’m look­ing at.

How does that lead to un­in­hab­it­a­bil­ity? Well, mainly I’m go­ing to ask you to use your imag­i­na­tion re­gard­ing a world with 20 to 30 de­grees [centi­grade] of warm­ing. But these are some of the things that would be kick­ing in. I gave a longer ver­sion of this talk where I go into the de­tails on some of this, which we don’t have time for now, but maybe we can get some of the de­tails through the Q&A.


To sum up here, we’ve asked the ques­tion of how cli­mate change might con­tribute to the prob­a­bil­ity of ex­is­ten­tial risk. I high­lighted these three things: the chance of mak­ing Earth un­in­hab­it­able, the con­tri­bu­tion to other ex­is­ten­tial risks, and [the effect on the prob­a­bil­ity] of so­cietal col­lapse. And I ruled out the sec­ond and third be­cause they weren’t things I know much about, even though they’re prob­a­bly the big­ger terms go­ing on here, and fo­cused on the un­in­hab­it­a­bil­ity point.

We then saw what it would look like to burn a lot of fos­sil fuels, and how that could lead us to a re­ally warm cli­mate. And then we hy­poth­e­sized and spit­balled about cloud-based tip­ping points, and how maybe that’s a thing that we should pay at­ten­tion to. Maybe, I don’t know. And to­gether, these things ges­ture in the di­rec­tion of a story of how Earth might be­come un­in­hab­it­able.

So as you can tell, this was a pretty shaky line of ar­gu­ment. But for me, at least, it ges­tures in the di­rec­tion of this idea de­serv­ing fur­ther study. And I’d love for peo­ple to go away and think about each of these differ­ent parts — un­in­hab­it­a­bil­ity, con­tri­bu­tion to other X-risks, and so­cietal col­lapse — and maybe in­ves­ti­gate some of these un­cer­tain­ties, with a par­tic­u­lar fo­cus on think­ing about the chance of cli­mate change re­ally con­tribut­ing to hu­man­ity go­ing ex­tinct al­to­gether.

Thank you all for mak­ing it through this late on a Sun­day af­ter­noon. I’ll now open this up to Q&A. Thanks.

Q&A session

The epistemic sta­tus of cli­mate change science

Nathan Labenz: I wanted to start with the epistemic sta­tus of cli­mate sci­ence in gen­eral. I think this is an au­di­ence [that ex­am­ines some top­ics with] a tremen­dous amount of rigor. In the ses­sion be­fore this, we looked at ques­tions as (seem­ingly) tractable as: “If you give peo­ple more money, will they be bet­ter off?” And the an­swer is yes, but it’s a lot harder to prove that than you might think. And then on the far end of the spec­trum, you’ve got ques­tions like: “Do in­sects suffer? And if so, what might we be able to do about it?”

Cli­mate sci­ence is prob­a­bly some­where in the mid­dle, but it seems to be hotly de­bated. And I find that this is an area where it’s hard to get clar­ity as an out­sider on just how solid all of the sci­ence is. So maybe you could give us your per­spec­tive on all of that.

Niel Bow­er­man: Yeah, I would love to. So what do we know? We know for cer­tain that the world is warm­ing, we know for cer­tain that car­bon diox­ide con­cen­tra­tions are go­ing up, and there’s a lot of con­sen­sus on the phys­i­cal mechanisms whereby those car­bon diox­ide con­cen­tra­tions would lead to warmer tem­per­a­tures. I think that 97% of sci­en­tists agree that cli­mate change is most likely caused by hu­mans.

When we zoom out and talk about cli­mate change as a con­tri­bu­tion to ex­is­ten­tial risk, now we’re just con­duct­ing pure spec­u­la­tion. This talk isn’t re­ally a talk about rigor­ous sci­ence. This is talk about Neil stand­ing up on stage and spit­bal­ling for half an hour. And so this talk isn’t re­ally sup­posed to try to con­vince you of any­thing. This is more of a prompt to en­courage peo­ple to go and work on this ques­tion a bit more and try and pin down some of these an­swers. Be­cause I think that other than maybe my first slide, ev­ery­thing I’ve said to­day is largely spec­u­la­tion — but it’s spec­u­la­tion try­ing to get at the ques­tion of where this chance of ex­tinc­tion might lie, which is very im­por­tant from a longter­mist per­spec­tive. If we come at the prob­lem from this per­spec­tive, then I think there are a bunch of re­ally in­ter­est­ing ques­tions to ask that I’d love to see the broader com­mu­nity ad­dress­ing.

The ex­pected sever­ity of cli­mate change

Nathan: Stick­ing with more main­line ques­tions just for a sec­ond: Some of your ear­lier com­ments to­ward the be­gin­ning of the talk sug­gest that your out­look would be: “Hu­man­ity will be pretty adapt­able. Yes, there will be costs to cli­mate change, but in the ab­sence of a story where other things hap­pen as knock-on effects, the main­line ex­pec­ta­tion is not so bad.” Is that a fair read­ing of your view?

Niel: Yeah. It de­pends on what you mean by “not so bad”. I ex­pect tens of mil­lions, maybe even hun­dreds of mil­lions of peo­ple to die pre­ma­turely be­cause of cli­mate change. And that’s re­ally bad. It’s similar on a vague scale of bad­ness to things like the num­ber of peo­ple that die in traf­fic ac­ci­dents. So when you look at cli­mate change [hav­ing this level of im­pact] over many decades, it’s very much a big prob­lem.

And then, from a longter­mist per­spec­tive, my ques­tion is: “Where does it rank rel­a­tive to the other ex­is­ten­tial risks?” If I had to guess, I would guess that it’s maybe lower down on the list of things likely to con­tribute the most to ex­is­ten­tial risks than, say, AI or biorisk. I’d put it more among the cluster of things like nu­clear weapons and geo­eng­ineer­ing. For me, that’s still very much a thing de­serv­ing of at­ten­tion and worth work­ing on, and whether it’s re­ally bad de­pends a lot on your defi­ni­tion of “re­ally bad”.

The ur­gency of tack­ling cli­mate change

Nathan: Not to be an­chored to the main­stream ques­tions, but do you feel that it is time now to be mo­bi­liz­ing and trans­form­ing the econ­omy [to re­duce emis­sions], or do you feel like the jury is still out on that and we don’t re­ally have the mechanism for a plau­si­ble story about re­ally bad out­comes that would de­mand [eco­nomic trans­for­ma­tion] at this stage?

Niel: Oh, for sure. I think we should be cut­ting car­bon emis­sions much, much more dra­mat­i­cally than we are right now. I think we should be go­ing to net zero emis­sions. I think there’s a rel­a­tively solid eco­nomic case. So this is a good idea and [will give us] a pos­i­tive re­turn on our in­vest­ment. My guess is that we should be keep­ing the to­tal amount of car­bon that hu­man­ity ad­mits to less than a trillion tons, which would hope­fully keep us at less than two de­grees of warm­ing.

Nathan: And that’s dou­ble what [we’ve emit­ted] in all of his­tory?

Niel: Yeah, ex­actly. So we can emit [as much car­bon] in the fu­ture as we’ve emit­ted in the past, and that means mak­ing pretty dra­matic and quick re­duc­tions.

Nathan: That would hap­pen in the next 50 years? Busi­ness as usual?

Niel: Yeah. Or less. We need to start cut­ting car­bon emis­sions in the next few years.

The cli­mate im­pact of methane clathrates

Nathan: Is there a story about methane de­posit re­lease that would crack your set of pos­si­ble nar­ra­tives here? I don’t know a ton about it, but it’s sup­posed to be the most pow­er­ful green­house gas. There’s a lot of it sit­ting at the ocean floor and in the Tun­dra.

Niel: Yeah, methane clathrates. This is one of the things that I’ve always been a lit­tle wor­ried about. The thing about methane clathrates is that they are very slow to bub­ble up. So in most of the plau­si­ble sce­nar­ios that we see, un­less you go into the sorts of crazy sce­nar­ios that I was talk­ing about, you end up see­ing methane clathrates not emerg­ing for some­thing like hun­dreds or maybe even a thou­sand years af­ter you see your ini­tial warm­ing.

If we got the cli­mate sci­ence wrong, or if the bot­tom of the ocean heated up way faster than we ex­pected, then you could see [clathrate emer­gence] hap­pen­ing faster. But the ocean doesn’t re­ally turn much in the ver­ti­cal di­rec­tion. Al­most all the move­ment in the ocean is hori­zon­tal. So this just makes it very hard for heat to prop­a­gate down­wards. And that means it’s go­ing to take a lit­tle while for those methane clathrates to heat up.

Promis­ing ar­eas for fur­ther research

Nathan: Okay, cool. That’s very in­ter­est­ing. So you’ve cov­ered this one a lit­tle bit, but: how im­por­tant is it for peo­ple to work on this? I think your sug­ges­tion would be that ex­plor­ing the cor­ner cases or the far-out cases is re­ally where the high­est value work is to be done.

Niel: That’d be my guess. Yeah. I’m ex­cited to see peo­ple ex­plor­ing so­cietal col­lapse like the PhDs at Cam­bridge are do­ing. [More peo­ple should be] look­ing at some of these worst-case sce­nar­ios and [how fea­si­ble they are]. And also, geo­eng­ineer­ing is a gi­ant ques­tion mark in my head. I don’t re­ally un­der­stand how that in­ter­acts with ex­is­ten­tial risk [from so­cietal col­lapse]. But my guess is that peo­ple should be figur­ing that out, too.

Nathan: You may want to pass on this be­cause we don’t have a ton of time, but how does this 20-de­gree warm­ing trans­late to true un­in­hab­it­a­bil­ity?

Niel: This part I didn’t re­ally know, I would again just be spit­bal­ling here, but when you look at agri­cul­tural yields, they start drop­ping off a cliff at some point. And then if we move agri­cul­tural zones up into the poles, you end up with very differ­ent grow­ing sea­sons than the ones that they were built for. We don’t have a great sense of how that would work. But the most likely story you could tell is some­thing in­volv­ing so­cietal col­lapse, and the break­down of so­ciety hav­ing a bunch of other bad knock-on effects.

The rel­a­tive im­por­tance of cli­mate change for effec­tive altruism

Nathan: How have your views changed about all of this over time?

Niel: My guess is that my views on cli­mate change have stayed rel­a­tively sta­ble over time, and my views on the im­por­tance of work­ing on AI have gone up. For me, cli­mate change still seems just as im­por­tant as when I worked on it as my full-time job. And now that there’s a ton of folks flood­ing into AI policy and AI safety and things like that, my guess is that it’s time for EAs to re­visit work­ing on cli­mate change tail risks and nu­clear weapons and geo­eng­ineer­ing and some of the other prob­lems in this space.

Car­bon taxes and other interventions

Nathan: Op­tions that we have to ad­dress car­bon im­me­di­ately would in­clude a car­bon tax, car­bon cap­ture, and maybe some oth­ers you’d want to list. How do you think about a more con­ven­tional car­bon tax, ver­sus a car­bon cap­ture (which might fall un­der geo­eng­ineer­ing, de­pend­ing on the strat­egy). What do you think we should be pur­su­ing first to re­duce car­bon?

Niel: On the im­me­di­ate ques­tion of car­bon tax­a­tion ver­sus car­bon cap­ture: car­bon cap­ture is an un­proven, very ex­pen­sive tech­nol­ogy, and car­bon tax­a­tion is a very proven but some­what poli­ti­cally in­fea­si­ble mechanism. I’d be way more ex­cited about a car­bon tax. A car­bon tax of the right size, if im­ple­mented across the world, could go a re­ally long way to helping solve cli­mate change. I don’t know about the poli­ti­cal fea­si­bil­ity of this, but if it were im­ple­mented, it would do a lot of good. Car­bon cap­ture, I think, is go­ing to be very ex­pen­sive and is a long way off, but it’s hope­fully part of the solu­tion in the fu­ture.