Surfing YouTube, I came across an interview of Ezra Klein by Stephen Colbert. He was promoting a new book called Abundance, basically arguing that scarcity is politically-manufactured by “both sides,” and that if we get our political act together, everybody can have more. Planetary limits need not apply. I’ve often been impressed by Klein’s sharp insights on politics, yet can’t reconcile how someone so smart misses the big-picture perspectives that grab my attention.
He’s not alone: tons of sharp minds don’t seem to be at all concerned about planetary limits or metastatic modernity, which for me has been a source of perennial puzzlement.
The logical answer is that I’m not the sharpest tool in the shed. Indeed, many of these folks could run cognitive/logical circles around me. And maybe that’s the end of the story. Yet it’s not the end of this post, as I try to work out what accounts for the disconnect, and (yet again) examine my own assuredness.
Imagined Basis
What is the basis of pundit-level rejection of my premise? Oh yeah: my premise is that modernity is a fleeting, patently unsustainable mode of life on Earth that will self-terminate on a historically relevant (i.e., brief) timescale—likely to convincingly crest the peak this century. Modernity can’t last.
I will reconstruct how I think an ultra-smart person might react, were I to present in conversation the premise that modernity can’t last—based on past interactions with such folks. Two branches stand out.
One branch would be the unwittingly spot-on admission of “I don’t see why not.” I could not have identified the core problem any better, and would be tempted to say: “Wow—what a courageous first step in recognizing our limited faculties. That humble confession is very big of you.” My not having the wit to prove conclusively to such folks that modernity can’t work (and I would say that no human possesses such mental powers) says very little about the complex reality of our future—operating without giving a flip as to what happens in human brains. But it’s also quite far from demonstrating convincingly how something as unsustainable as modernity—dependent on one-time exploitation of non-renewable resources—might possibly address the host of interacting elements that will contribute to its crumbling.
That branch aside, the common reply I want to spend more time on goes something like: “Just look at the past. No one could have foreseen the amazingness of today, and we ought to recognize that we are likewise ill-equipped to speculate on the future. In other words, anyone expressing your premise in the last 10,000 years would have turned out to be wrong [well, so far]. Chances, are: so are you.”
Damn. Blistering. How can one get up from that knockout? And the thing is, it’s a completely valid bit of logic. I also appreciate the intellectual humility involved. Why, then, am I so stubborn on this point? Is it because I want to be popular or rich? Then I’m even stupider than I thought, because those things are basically guaranteed to be incompatible with such a message. Is it because I crave end-times, having been dealt a bad hand and never “good at the game?” Nope: I thrived as an all-in astrophysicist and had/have a rather privileged and comfortable life that I would personally, selfishly prefer not to have disrupted. Is it out of fear of collapse? Getting warmer: that was a big early motivation—the alarming prospect of losing what I held until recently to be a glorious civilization. But at this point all I can say is that based on multiple lines of evidence I really think it’s the truth, and can’t easily or honestly argue myself out of this difficult spot. Denial, anger, bargaining, and depression don’t help us come to terms with the hard reality..
Returning to the putative response: I’ll name it as lazy. It’s superficial. It’s a shortcut, sidling up to: “Collapse hasn’t happened yet—in fact quite the opposite—and thus most likely will not.” It declines to examine the constituent pieces and arguments, falling back on a powerful and persuasive bit of logic straight out of the left brain. It has all the hallmarks: certain, crisp, abstract, decontextualized, logical, clever.
It carries the additional dual advantage of simultaneously avoiding unpleasant confrontation of a scary prospect and inviting starry-eyed wonder at magic the future might bring. No wonder it’s so magnetically attractive as a go-to response!. We’re both driven to it and attracted by it! The very smartest among us, in fact, often have the most to lose, and may therefore be among the most psychologically attached to modernity. We mustn’t forget that every human has a psychology, and is capable of impressive levels of denial for any number of reasons.
Some Metaphors
Its time for a few metaphors that help to frame my approach. I offer two related ones, because none are perfect. Together, they might work well enough for our purposes.
Take One
Imagine that someone tees up a golf ball in an indoor space full of hard objects: concrete walls and steel shelves—maybe loaded with heavy glass goblets and vases, etc. Poised to deliver a smashing blow to the ball with an over-sized driver, they ask me: “What do you think will happen if I hit this ball?” Imagining a comical movie scene where the ball makes a series of wild-ass bounces shattering priceless collectables as it goes, it might seem impossible to guess what all might or might not happen. So, I “cheat” and say: “The ball will come to rest.”
And guess what: I’m right! No matter how crazy the flight, it is guaranteed that in fairly short order, the ball will no longer be moving. I could even put a timescale on it: stopped within 10 seconds, or maybe even 5—depending on the dimensions of the room. I can say this because each collision will remove a fair bit of energy from the ball, and the smaller the room, the shorter the time between energy-sapping events.
During the middle of the experiment, it is clear that mayhem is happening, and it’s essentially impossible to predict what’s next. That’s where we are in modernity. So, yes: some intellectual humility is called for. We could not have predicted any of the particulars, after all. But one can still stand by the prediction that the ball will come to rest, much as one can say modernity will wind itself down.
Take Two
The golf ball metaphor does 80% of the work, but I don’t fully embrace it because the ball is at maximum destructive capacity at the very beginning, its damage-potential decaying from the first moment. Modernity took some time to accelerate to present speed, now at a fever pitch. For this, I think of a rock tumbling down a slope.
I do a fair bit of hiking, sometimes off trail where—careful as I am—I might occasionally dislodge a rock on a steep slope. What happens next is entirely unpredictable (even if deterministic given initial conditions). Most of the time the rock just slides just a few centimeters; sometimes it will lazily tumble a few meters; or more rarely it will pick up speed and hurtle hundreds of meters down the slope in a kinetic spectacle. Kilometer scales are not entirely out of the question in some locations.
Still, for all these scenarios, I am sure of one thing: the rock will come to rest—possibly in multiple fragments. I can also put a reasonable timescale on it, mid-journey, based on its behavior to that point. I can tell if it’s picking up speed. I can evaluate if the slope is moderating or will soon come to an end. It’s not impossible to make a decent guess for how long it might go, even if unable to predict what hops, collisions, or deflections it might execute along the way.
Maybe the phrase “a rolling stone gathers no moss” can be re-interpreted as: kinetic mayhem is no basis for a healthy, relational ecology. If tumbling boulders were the normal/default state of things, mountains would not last long (or more to the point: never come into being!). Likewise, one species driving millions of others to extinction in mere centuries is not a normal, sustainable state of affairs. That $#!+ has to stop.
Modernity’s Turn
Modernity is far more complex than a tumbling rock. But one side effect of this is a multitude of facets to consider. When many of them line up to tell a similar story…well, that story becomes more compelling. I offer a few, here.
Population
Global human population has been a super-exponential, in that the annual growth rate as a percentage of the total has steadily climbed through the millennia and centuries (0.04% after agriculture began, up to 2% in the 1960s). It is no shock to anyone that we may be straining (or overtaxing) what the planet can support. Indeed, the growth rate has been decreasing for the last 60 years, and the drop appears to be accelerating lately. Almost any model predicts a global peak before this century is over, and possibly as soon as the next 15–20 years. This is, of course, highly relevant to modernity. Economies will shrink and possibly collapse (being predicated on growth) as population falls from a peak. Such a turn could precipitate a whole new phase that “no one could have seen coming.” I’m looking at you, pundits!
The argument of “just look to the past” and imagining some sort of extrapolation begins to seem dubious or even outright silly in the context of a plummeting population. Let’s face it: we don’t know how it plays out. Loss of modern technological capabilities is not at all a mental stretch, even if such “muscles” are rarely exercised.
Resources
Modernity hungry!. Fossil fuels have played a huge role in the dramatic acceleration of the past few centuries. We all know this is a limited-time prospect. Oil discoveries peaked over a half-century ago, so the writing is on the wall for production decline on a timescale of decades. Pretending that solar and wind will sweep in as substitutes involves a fair bit of magical thinking and ignorance of myriad practical details (back to the “I don’t see why not” response). We face an unprecedented transition as fossil fuels wane, so that the acceleration of the past is very likely to run out of steam. Even holding steady involves an unsubstantiated leap of faith—never fleshed out as to how it all could possibly work. “I don’t see why not” is about the best one can expect.
Mined materials are likewise non-renewable and being consumed at an all-time-high rate. Ore grade has fallen dramatically, so that we now must pursue increasingly marginal and deeper deposits and thus impact more land, while discharging an ever-increasing volume of mine tailings. This happened fast: most material extraction has occurred in the last century (or even 50 years). We would be foolish to imagine an extrapolation of the past or even maintaining similar levels of activity for any long duration. More realistically, these practices will be undercut by declining population and energy availability. I’ve spent plenty of time pointing out that recycling can at best stretch out the timeline, but not by orders of magnitude.
Water/Agriculture
Agricultural productivity has also steadily increased, but on the back of “mining” non-renewable resources like ground water and soils—not to mention an extraordinary dependence on finite fossil fuels. Okay: at least water and soils can renew on long timescales, but our rate of depletion far outstrips replenishment. Land turned to desert by overuse stops even trying to maintain soils, while also suppressing water replenishment by squelching rainfall. This is yet another domain where the fact that the past has involved a steady march in one direction is quite far from guaranteeing that direction as a constant of nature. Its very “success” is what hastens its failure. The simple logic of “hasn’t happened yet” blithely bypasses a lot of context sitting in plain sight.
Climate Change
I don’t usually stress climate change, because I view it as one symptom of a more general disease. Moreover, should we magically eliminate climate change in a blink, my assessment is hardly altered since so many other factors are contributing to the overall phenomenon of modernity’s unsustainability. I include climate change here because it seems to be the one element that has percolated to the attention of the pundit-class as a potential existential threat. It isn’t yet clear how modernity trucks on without fossil fuels. Yet, even if we were to curtail their use by 2050, the climate damage may be great enough to reverse modernity’s fortunes (actually, the most catastrophic legacy of CO2 emissions may be ocean acidification rather than climate change). Again, the “logic” of extrapolation becomes rather dubious. The faith-based assumption is that we will “technology” our way out of the crisis, which becomes perfectly straightforward if ignoring all the other factors at play. Increased materials demand to “technofix” our ills (and the associated mining, habitat destruction, pollution) puts a fly in the ointment. But most concerning to me is what we already do with energy. Answer: initiate a sixth mass extinction by running a resource-hungry, human supremacist, global market economy. Most climate change “solutions” assign top priority to maintaining the destructive juggernaut at full speed—without question.
Ecological Collapse
This brings me to the ultimate peril. As large, hungry, high-maintenance mammals on this planet, we are utterly dependent on a healthy, vibrant, biodiverse ecology—in ways we can’t begin to fathom. It’s beyond our meat-brain capacity to appreciate. Long-term survival at the hands of evolution has never once required cognitive comprehension of the myriad subtle relationships necessary for a stable community of life. An amoeba, mayfly, newt, or hedgehog gets on just fine without such knowledge. What is required is fitting into the niches and interrelationships patiently worked out through the process of evolution. Guess what: in a flash, we jumped the tracks into a patently non-ecological lifestyle not vetted by evolution to be viable. It appears to be not even close.
This is not just a theoretical concern. Biologists are pretty clear that a sixth mass extinction is underway as a direct result of modernity. The dots are not particularly hard to connect. We mine and spew/dispose materials alien to the community of life into the environment. Good luck, critters! We eliminate or shatter wild space in favor of “developed” land: exterminating, eradicating, displacing, and impoverishing the life that depends on that land and its resident web of life. The struggle can take decades to resolve as populations ebb—generation after generation—on the road to inevitable failure. Even this decades-long process is effectively instant compared to the millions of years over which the intricate web was crafted.
I have pointed out a number of times that we are now down to 2.5 kg of wild land mammal mass per human on the planet. It was 80 kg per person in 1800 and 50,000 kg per person before the start of the agricultural revolution—when humans held a roughly proportionate share of mammal biomass compared to the other mammal species. In my lifetime (born 1970), the average decline in vertebrate populations has been roughly 70%. Fish, insects, birds decline at 1–2% per year, which compounds quickly. Extinction rates are now hundreds of times higher than the background, almost all of which has transpired in the last century.
Just like the golf ball in the room or the rock tumbling down the mountainside, these figures allow us to place approximate, relevant timescales on the phenomenon of ecological collapse—and that timescale is at the sub-century level. We’re watching its opening act, and the rate is alarming. The consequences, however, are easily brushed aside in ignorance. Try it yourself: mention to someone that humans can’t survive ecological collapse and—Family Feud style—I’d put my money on “I don’t see why not” being among the most frequent responses.
So, Don’t Give Me That…
I think you can see why I’m not swayed by the tidy and fully-decontextualized lazy logic of extrapolation offered by some of the smartest people. This psychologically satisfying logic can have such a powerfully persuasive pull that it short-circuits serious considerations of the counterarguments. This is especially true when the relevant subjects are uncomfortable, inconvenient, unfamiliar, and also happen to be beyond our capacity to cognitively master. Just because we can’t understand something doesn’t render it non-existent. Seeking answers from within our brains gets what it deserves: garbage in—garbage out.
We used the metaphors of a golf ball or rolling stone necessarily coming to rest. Likewise, a thrown rock will return to the ground, or a flying contraption not based on the aerodynamic principles of sustainable flight will fail to stay aloft. Modernity has no ecological context (no rich set of evolved interrelationships and co-dependencies with the rest of the community of life) and is rapidly demonstrating its unsustainable nature on many parallel, interconnected fronts. This would seem to make the default position clear: modernity will come to rest on a century-ish timescale, the initial reversal possibly becoming evident in mere decades. [Correction: I think it will likely be mostly stopped on a century timescale, but it may take millennia to fully melt into whatever mode comes next.]
Retreating to the logic of extrapolation or basic unpredictability amounts to a faith-based approach that deflects any actual analysis: a cowardly dodge. Given the multi-layer, parallel concerns all pointing to a temporary modernity, it would seem to put the burden of proof that “the unsustainable can be sustained” squarely on the collapse-deniers. The default position is that unsustainable systems fail; that non-ecological modes lack longevity; that unprecedented and extreme departures do not become the rule; that no species is capable of going-it alone. Arguing the extraordinary obverse demands extraordinary evidence, which of course is not availing itself.
When logic suggests an attractive bypass, recognize that logic is only a narrow and disconnected component of a more complete, complex reality. Most importantly, the logic of extrapolation only serves to throw up a cautionary flag, without even bothering to address the relevant dynamics. That particular flag is later recognized as a misfire once the appropriate elements are given due consideration: this time is different, because modernity is outrageously different from the larger temporal and ecological context. Pretending otherwise requires turning a spider’s-worth of blind eyes to protect a short-term, ideological, emotionally “safe” agenda. Pretend all you want: it won’t change what’s real.
Thanks Tom; Yet another crucially important cogent, logical, smart but likely never read (by the people who need to read it) piece of writing
I’ve often been impressed by Klein’s sharp insights on politics, yet can’t reconcile how someone so smart misses the big-picture perspectives that grab my attention.
It could be that Klein is aware of the big picture, but he still has to make ends meet in the modern world we all live in. And until collapse becomes too obvious to avoid, insightful books about current political alternatives will sell. A guy's gotta make a living.
This is the Keynesian "In the long run we are all dead" response to the rather obvious limitations of modernity you have succinctly summarized. Very smart people can justifiably point out that while the end of modernity is obviously coming soon, it isn't here yet, so something has to occupy the work day. To this end, a book about "abundance", a post about modernity, and a comment about that post all serve the same semi-useful purpose.
The alternative is to become an irritating scold, insisting that only working on pre- and post-modern hunting, gathering and horticulture skills makes rational sense, which of course happens to be the case (even though nobody wants to hear it).
"Smart" is a value judgment for a particular form of cleverness. In our society it has positive connotations. Personally, I think "smart" should be a pejorative. It connotes an acute angle, that is, an extremely narrow point of view. It also connotes destructive power, the ability to cut down whatever suits you to cut down, whether it's a tree or someone else's well thought out analysis.
So yeah, Ezra Klein is "smart". He is a narrow thinker, adept at cutting down differing points of view.
I wasted several years listening to his podcasts. I find your epistomy far more compelling.
Have a look at Sand Talk by Tyson Yunkaporta for some aboriginal insights into a more holistic way of knowing.
As for "never happened before" quip, that makes no sense. Just look at all the fallen civilizations of the past! Read Joe Tainter, Jared Diamond and Peter Turchin, for crying out loud.
Meanwhile, I don't know what to do about malignant narcissism and other dark triad types. Nor do I know what to do about international prisoner's dilemmas, tragedies of the commons, and other games of trust or lack thereof. Historically, the indigenous societies who managed to sustain a way of life for many thousands of years eventually get wiped out by Alexander the Great or the Teutonic Order of Knights or British, Spanish and Dutch carrying muskets and disease.
When did modernity begin, anyway? The amount of damage people managed to do in the seventeenth century using horse power, wind power and gun powder is astonishing. I think that even without the discovery of fossil fuels, humanity would have reached this point of insanity eventually, it just might have taken a few additional centuries.
So even if you manage to persuade a few people out of either the "I don't see why not" position or the "never happened before" position, we still have to confront both the trust game and the dark triad threat.
"Personally, I think "smart" should be a pejorative. It connotes an acute angle, that is, an extremely narrow point of view. It also connotes destructive power, the ability to cut down whatever suits you to cut down, whether it's a tree or someone else's well thought out analysis."
A sharp tool can be used either for destruction or construction. (The tool-edge metaphor is probably why we call sharp angles "acute" and wide, or dull angles "obtuse" in the first place.) The effectiveness of a tool is value-neutral. It all depends on how we use it. And an analysis can be well-reasoned and yet still be defective if it is based on false premises or contains bad information. An analysis or an argument should properly stand or fall on its own merit. Showing how arguments are defective is a service to–and one of the central purposes of–the public forum of ideas.
"The amount of damage people managed to do in the seventeenth century using horse power, wind power and gun powder is astonishing."
I would add slave power to that. The transition to machines doing the work has been helping to undermine the institution of slavery.
"I think that even without the discovery of fossil fuels, humanity would have reached this point of insanity eventually,"
Before we figured out coal, we burned trees. This devastated the forests of Europe and they didn't begin to recover until we switched to coal. Before petroleum, we used whale oil. Petroleum is what made whaling uneconomic. Coal and oil have their own problems, but now nuclear gives us the chance at another transition to something better.
I am a 20 by 25 supporter. This is not related to this year, or a specific reduction of fossil fuel use. I think the planet can support an economy where per capita consumption is 1/5 what it is now (about like Costa Rica or Cuba), but only if there is 1/4 of the present population. We are sadly naïve and mislead to think we can continue as we are. A blending of ecological reality with human interactive wisdom is the only path, though ecological wisdom is place based and takes many forms. We do not have it in dominant western thought, and it is lost in much of the rest of the world, except for some isolated pockets. I suspect the rock falling down the slope will stop abruptly when it hits a much larger rock, and the entire system will crash. At this point I am unsure if we can avoid the crash. Regenerative ag and permaculture are tentative stabs in the right direction, but even they are too dependent on energy intensive inputs in their present form.
This may need revising very soon, as Climate Breakdown rapidly increases its effects on critical systems (thinking agriculture here). Just years ago, essentially nobody spoke openly of a ~1.5C world in 2025. Even my worst-case guess was by 2030 (I was trying to see if Wadhams was right, so I built an AA model…)
I am really interested in this summer, as well as next year!
the lack of safe drinking water is the most effective issue to raise with doubters, as it is here now and extremely widespread.
only a desperate nation would resort to this:
https://www.resilience.org/stories/2024-10-31/the-southwest-offers-blueprints-for-the-future-of-wastewater-reuse/
exactly how are they removing the pfas and excreted pharmaceuticals? in a semi-closed system the contaminant build up will eventually render the system unusable.
The golf ball receives all its kinetic energy in the first instant and thereafter only loses momentum. An object rolling down a slope has potential energy being converted into kinetic while rolling, but the duration is limited by the length of slope. Both of these are poor analogs for modernity, and they do not make a compelling case that modernity will end soon. Murphy's argument that modernity cannot continue for much longer basically boils down to: he doesn't see how it can. That is not going to be very convincing to anyone who does see how it potentially could continue, especially when it appears Murphy is using selective blindness to avoid seeing how it can. He acknowledges that fossil fuel energy played a huge role in the development of modernity to introduce the notion of impending energy resource scarcity, but makes no mention whatsoever of nuclear energy–except perhaps by oblique reference when he mentions modernity's dependence on non-renewable resources (since nuclear fuel is technically non-renewable–in the same way that fuel in the sun is also non-renewable). And this omission wasn't because Murphy doesn't know about nuclear energy, nor is it because he is unaware that nuclear fuels on earth hold orders of magnitude more total energy than fossil fuels ever did. I expect the "do the math" physics guy did the math on that long ago. So why the glaring omission? Murphy in the past has indicated his suspicion that proponents of advanced nuclear may be engaging in a sort of hopium–without showing why their proposals cannot work. With his selective blindness, my suspicion is that Murphy may be protecting some cherished doomium.
Even if nuclear were a viable option (and I don't agree with you on that point), having an alternative energy source would not solve the other issues Tom raises – pollution, resource depletion, soil degradation, biodiversity, etc.
It is not a certainty that some of the new kinds of nuclear will work, but we are definitely going to try a number of them, and some of them look like they have good operational and economic potential. And just a good possibility of working is enough to undo any argument that they cannot work. And though a broad deployment of advanced nuclear will not solve all of our problems, it does have a large spillover potential to help with many big ones. Nuclear heat could drive a large amount of CO2 removal from the atmosphere (helping with both the climate problem and ocean acidification). Nuclear heat could also power a lot of liquid synfuel production (to help with hard-to-decarbonize sectors and to displace large fuel-crops). Nuclear powered ships could reduce air pollution from shipping (including large scale fresh-water transport). Countries with energy abundance tend to have below-replacement reproductive rates and higher percentages of the population living in cities (shrinking the human residence footprint–which will be important to any natural restoration effort). Nuclear could displace fossil mining and reduce the mined materials needed relative to far-flung renewables and battery-heavy grids. There is a lot of recycling we currently don't do because the energy cost is too high. High-concentration food systems, like aquaponics, become more feasible with cheaper energy. Nuclear can't help with actually rebuilding soil, but we know of ways to do that. There are some kinds of pollution nuclear won't help with, so we'll need to figure out how to tighten restrictions on those. Yeah, it's going to take a lot of work, but I'm thoroughly in the camp of not seeing why it can't be done. I know Murphy sneers at the "I don't see why not" position, but sneering at it doesn't rebut it. The only thing that can do that is at least one example of a fatal problem with modernity which cannot be avoided or solved by any means.
Whilst theoretically nuclear could solve many of the problems, it seems very unlikely that it can solve enough to make modernity feasible. For example, we only have a finite supply of the resources required for modern life. Yes, more can be recycled, and this will prolong modernity, but ultimately quality is reduced through recycling.
I accept that it is possible that new kinds of nuclear could replace fossil fuels, but the timescales are unfeasible.
Let's say India's 500MWe thorium reactor proves successful this year. It will take a few years of observation and approval before mass production of reactors begins. Current fossil fuel electricity generation is 4.5 terrawatts (4500000MW). So just to replace current consumption we would need 9000 reactors of this size (OK, perhaps we build 10000MW reactors, but still we need 450 reactors).
It seems likely that these reactors will take at least 10 years to construct, at least to begin with. Let's take a huge gamble and build all of them at once. In 15 years time we have enough electricity to replace current fossil fuel electricity (although we know from experience that adding capacity increases consumption and not all of the existing capacity will be replaced).
How much more power still required to suck carbon out of the atmosphere, produce hydrogen for 1.5 billion cars, de-acidify the oceans and fix all of the other problems of modernity?
In the meantime, we are currently at 1.5 degrees C above pre-industrial, with 2 degrees reasonably likely baked in. We are on the threshold of numerous planetary boundaries and already we are starting to face unprecedented weather whilst living standards are moving downwards.
Within 15 years of business as usual, we are likely to see 2 degrees of warming and be committed to another 0.5 degree by the carbon already released. The Amazon will likely have collapsed and become a carbon source rather than sink and the same for the oceans as acidification causes mass phytoplankton dieoff. With the glaciers massively depleted, fresh water supplies will be severely depleted and further climate feedbacks created. By this point, we may well be committed to 4 degrees of warming by these and various other feedbacks.
Are any nuclear technologies feasibly going to be able to replace fossil fuels within 15 years? Or even 30 years?
How many years will they last? I read somewhere that USA had enough thorium to replace electricity generation for 1000 years. Even if you ignore the extra demands of fixing the polycrisis, that isn't very long. If modernity lasted 1000 years it would still be a blip.
"Let's say India's 500MWe thorium reactor proves successful this year."
I think only a few Gen 4 designs have good economic potential. I would not include any sodium-cooled fast-breeders in that. (But India won't care. They are on their own unique development path.)
"…years of observation and approval before mass production of reactors begins."
Several Gen4 teams are aiming to begin mass production in the early 2030's.
"Current fossil fuel electricity generation is 4.5 terrawatts (4500000MW). So just to replace current consumption we would need 9000 reactors of this size"
Plus thousands of reactors for heat-only applications, and thousands more for shipping, plus more to handle the future energy demand increase. But the material needs for the new reactors could be quite small. Finished weight on a full-size Kairos reactor is roughly that of two empty 40' shipping containers (of which there are millions).
"It seems likely that these reactors will take at least 10 years to construct,"
Several of the Gen 4 teams are aiming for two-year construction times, with their factories able to support dozens of simultaneous builds in progress. Kairos fabricated their first full-scale reactor vessel in a matter of months–without benefit of automation or mass-production techniques and with no prior experience.
"How much more power still required to suck carbon out of the atmosphere, produce hydrogen for 1.5 billion cars, de-acidify the oceans and fix all of the other problems of modernity?"
For several of the from-air CO2 removal systems, most of the energy they need is in the form of heat. With hotter Gen 4 reactors, the "waste" heat from a 200 MWe plant could power around a million tonnes of CO2 removal per year at current capture efficiencies (2 MWh(th) per tonne CO2). The first wave of Gen 4 reactors will not gain much over current fuel efficiency, but that should improve greatly when we get to molten salt fast reactors. In such reactors, a thousand tonnes of uranium could generate a terawatt-year of electricity while also capturing 5 billion tonnes of CO2. And we have roughly a million tonnes of uranium already in storage in the U.S..
"Within 15 years of business as usual, we are likely to see 2 degrees of warming and be committed to another 0.5 degree by the carbon already released.:
And that warming would continue for centuries, just from the CO2 that is already in the air–even if we reached net-zero immediately. To actually reverse warming and ocean acidification, we'll need to rapidly remove hundreds of billions of tonnes of CO2 from the air. (About a trillion tonnes overall to get us back to pre-industrial levels.)
"Are any nuclear technologies feasibly going to be able to replace fossil fuels within 15 years?"
No energy scenario that we know of has a good chance of accomplishing that.
"Or even 30 years?"
That's more feasible. It will depend mostly on how cheap they can get the price. But I think we'll also need to ramp up CO2 removal long before we fully get off fossil fuels.
"How many years will they last?"
Overall plant life could be indefinite for designs where all the wearing and degrading parts are replaceable. (Thorcon plans to swap out reactors each 8 years. Kairos plans to replace their reactor vessels each 15 years.)
"I read somewhere that USA had enough thorium to replace electricity generation for 1000 years."
Current U.S. primary energy consumption averages a bit less than 100 quads per year–roughly the energy you'd get from fissioning 1300 tonnes of uranium. So just the uranium we have in storage would last us around 750 years at that rate (after we get to fuel-efficient molten salt fast reactors in another decade or two). But we've been improving ways of extracting uranium from seawater, and recent advancements put the cost at around double the current cost of terrestrial mining–which, even with no further advancements, would still be really cheap fuel for molten salt fast reactors. Around 35,000 tonnes of uranium washes into our oceans each year. We could pull 10% of that influx out per year indefinitely without appreciably reducing the 4.5 billion tonnes of uranium presently suspended in seawater, and that would give us 270 quads of primary energy per year. That's not counting energy from renewables, or thorium, or uranium from land sources, or the uranium we have in storage, or potential gains in efficiency, or the development of new kinds of nuclear, or the benefits of a shrinking population.
"If modernity lasted 1000 years it would still be a blip."
Modernity today is almost unrecognizable from what it looked like just 200 years ago, and the pace of change is accelerating. We have no idea what things could look like in 1000 years. But even if a set of crisis solutions buys us only a hundred years, that would still be way more breathing room than we have right now, and it would give us time to develop more options. But at least on the energy front, we will never run out of nuclear fuels on Earth. They are simply too abundant. And lots of nuclear would make it easier to fix the climate and acidification problems. As for our future existential crises, we'll have to figure them out as we get there. But the high probability of future crises does not ensure that modernity will fail soon, nor even that we will never reach a more stable and sustainable version of modernity.
That is the most dismal world I can possibly imagine. I sincerely hope you are wrong on every single point.
Does this mean that you are simply incapable of imagining a world of runaway climate catastrophe, the breakdown of civilization, global warfare and mass starvation, or do you mean that you would find that sort of world more pleasing and more to your liking than one with abundant and cheap, clean energy and massive CO2 drawdown?