Photo from Monash Universiry
I recently came across a statement to the effect that once we transition away from fossil fuels to renewable energy like solar, wind, and hydro, we would essentially be home free for the long run—tapping into inexhaustible flows. It is a very pleasant notion, to be sure, and one that I believe is relatively common among enthusiasts for renewable energy.
Naturally, I am concerned by the question of: what magnificent things would we do with everlasting copious energy? As an excellent guide, we can ask what amazing things have we done with the recent bolus of energy from fossil fuels? Well, in the course of pursuing material affluence, we have eliminated 85% of primeval forest, made new deserts, created numerous oceanic dead zones, drained swamps, lost whole ecosystems, almost squashed the remaining wild land mammals, and initiated a sixth mass extinction with extinction rates perhaps thousands of times higher than their background levels—all without the help of CO2 and climate change (which indeed adds to the list of ills). These trends are still accelerating. Yay for humans, who can now (temporarily) live in greater comfort and numbers than at any time in history!
But the direction I want to take in this post is on the narrower (and ultimately less important) technical side. All the renewable energy technologies rely on non-renewable materials. Therefore, inexhaustible flows are beside the point. It’s like saying that fossil fuel energy is not practically limited by available oxygen for combustion, so we can enjoy fossil fuels indefinitely. Or that D–T fusion has billions of years of deuterium available, when there’s no naturally-occurring tritium (thus reliant on limited lithium supply). In a multi-part system, the limiting factor is, well, the limiting factor. Sure, into the far future the sun will shine, the wind will blow, and rain will fall. But capturing those flows to make electricity will require physical stuff: all the more material for such diffuse flows. If that stuff is not itself of renewable origin, then oops. The best guarantee of renewability is being part of natural regeneration (i.e., of biological origin). If solar panels, wires, inverters, and batteries were made of wood and the like: alright, then.
Recognizing that biological organisms—plants and the animals that directly or indirectly draw energy from them—have already figured out how to tap into (essentially) inexhaustible flows—solar, primarily—I became interested in comparing the performance of the human animal to that of a solar panel or wind turbine, in terms of mineral requirements. After all, the biosphere gets by without mining the depths. So let’s dig into the material requirements of life.
A Pinch of Dirt
Human construction requires very few mineral elements that do not come to us from water and air. I think that’s really cool. Our caloric intake consists of carbohydrates, fat, and protein—the whole set requiring only four elements that are obtained from air and water.
This Wikipedia page provides a compositional breakdown of the human body—presented both by mass and by atoms. Note, however, that the two forms listed on the Wikipedia page are not wholly self-consistent, so I arbitrarily adopt the by-atom numbers (more significant digits, meaningful or not) and produce by-mass fractions from them—though the result is not qualitatively different if starting from the by-mass numbers instead. Below are two tables that capture approximate numbers, broken up according to elements that derive from air and water, and those that we get from the ground. The first table also notes the elemental origins within our environment.
| Element | % Mass | % Atoms | Source |
|---|---|---|---|
| Oxygen | 61.2 | 24.0 | direct from air and water |
| Carbon | 23.0 | 12.0 | air via plants/photosynthesis |
| Hydrogen | 10.0 | 62.0 | water: direct and via plants/sugars |
| Nitrogen | 2.5 | 1.1 | air via plants and microbes |
| Totals | 96.7 | 99.1 |
So, about 99% of the atoms in our bodies come from air and water, often processed by other lifeforms before entering our mouths. That’s a very neat trick! By mass, it’s 97%. The difference is due to the most abundant elements in our bodies being on the lighter side (especially hydrogen), while the rarer minerals tend to be heavier atoms. Now for the dirt elements.
| Element | % Mass | % Atoms |
|---|---|---|
| Calcium | 1.4 | 0.22 |
| Phosphorus | 1.1 | 0.22 |
| Potassium | 0.19 | 0.03 |
| Sulfur | 0.19 | 0.038 |
| Sodium | 0.14 | 0.037 |
| Chlorine | 0.14 | 0.024 |
| Magnesium | 0.06 | 0.015 |
| Totals | 3.22 | 0.574 |
Other minerals appear in trace amounts, totaling a small fraction of one percent. The elements in the table above are typically found in soils and rocks, accessed by fungi and roots. The comparatively small amount of ash left over from burning a log completely tends to be composed of elements on this list. The sources of these elements in our diets can be found on this website (and similar variants on the URL for other elements).
Power Performance
Now let’s look at the material efficiency of the human body and compare to that of a solar panel. According to the United Nations’ Food and Agriculture Organization, the global average caloric intake is 2,800 kcal per day, translating to an average continuous power of about 135 W. The mineral requirements to accomplish this constitute just over 3% of body mass, or 2 kg for the global average body mass of 62 kg. Thus, a human achieves roughly 70 W per kilogram of minerals. Note that even though the human body is only 20–25% efficient at converting metabolic energy into external mechanical work, the rest is not waste to us: it provides crucial thermal energy to keep body temperature up, and thus counts as a critical contribution.
Let’s look at solar panels. Typical 60-cell panels produce 300 W in full sun, and have a mass around 20 kg. Straight away we compute 15 W/kg—a factor of five lower than human performance. But to be fair, we must account for the fact that the sun is not always directly in front of the panel, producing a typical capacity factor of 20%, or an average power delivery of 60 W. Now the deployed panel delivers 3 W/kg: less than 5% as “efficient” as a human, in mineral terms.
Massive wind turbines at 20% capacity factor (typical global average) score even worse, at 0.4–0.6 W/kg. Without the mass-dominant concrete pad, a wind turbine would pump out 1.6–2.4 W/kg, for the short time it remained standing.
Just as a wind turbine needs a mounting base, a realistic utility-scale solar deployment has a material mass far in excess of the bare panels: support structures, interconnect wiring, inverters, storage (if truly replacing fossil fuels). I would not be surprised if a whole-system figure dropped to 1 or 2 W/kg, while humans stay smugly perched at 70. The score for wind would erode as well once other necessary components are considered—especially storage. Moreover, the minerals needed by humans are in wide circulation within the community of life at the surface: no mining (and associated tailings, energy, processing, pollution) necessary.
Thus, biology has far exceeded technology in capturing the inexhaustible flow from the sun using a minimum of minerals—and those being extracted from and re-deposited to the soil in a continuous, self-sustaining cycle, importantly. Biology and evolution really figured things out! Modernity looks like a bumbling idiot by comparison—like R2D2 in a stair-climbing competition against an athlete.
Replacement Considerations
What about the fact that the human body does not store its minerals indefinitely, but requires dietary replenishment? By contrast, solar and wind infrastructure lasts a few decades (it is not indefinite, either). To get a lower limit for replenishment times, I look at the recommended daily allowance (RDA) of minerals, provided at this site, represented as the RDA column in the table below.
| Element | RDA (g) | In Body (g) | Duration (days) |
|---|---|---|---|
| Calcium | 1.0 | 870 | 870 |
| Phosphorus | 0.7 | 670 | 960 |
| Potassium | 3.0 | 120 | 40 |
| Sodium | 1.5 | 85 | 60 |
| Chlorine | 2.0 | 85 | 40 |
| Magnesium | 0.35 | 40 | 110 |
| Total | 8.55 | 1870 | 220 |
Dividing the amount of elemental mass in the body (obtained via mass percentage in the second table) by the RDA produces a timescale for complete replacement, as indicated in the last column of the table above. It makes some sense to me that calcium and phosphorus—locked up in bones—would persist for a long time, while mediators of biochemistry might flush more routinely. Still, I would imagine the RDA numbers to be conservative (a bit overkill; while staying short of harmful), translating into a more mineral-hungry portrait than is actually necessary. For instance, it seems unlikely that the average dwell time of calcium in your bones is just a few years. I’d be willing to bet that an RDA-consuming person passes unabsorbed calcium (and other minerals) in their poop. But I’m not likely to wade in there, experimentally.
In any case, in a 24-hour day, our 135 W standard human cranks out 3.2 kWh of energy, requiring daily intake of 8.55 grams of minerals according to the RDA standard. In order to compare to renewable energy figures, I’ll translate into tons per TWh to get about 2,600 tons of mineral input needed to produce one TWh of human metabolic energy (probably a lot less under actual body requirements).
According to Table 10.4 of the Department of Energy Quadrennial Technology Review, the production of electricity entails the following material requirements (in the form of aluminum, concrete/cement, copper, glass, steel, etc.):
| Technology | ton/TWh | Factor |
|---|---|---|
| Coal | 1185 | 0.45 |
| Gas | 572 | 0.22 |
| Solar PV | 16447 | 6.2 |
| Wind | 10260 | 3.9 |
| Hydro | 14068 | 5.3 |
We see that on this measure as well renewable energy technologies are more mineral-hungry than biological systems (at 2,600 ton/TWh) by substantial factors—and more if RDA is conservatively overstated. Moreover, the required elements are different from those needed for life—more “exotic” so-as to require mining, vs. readily at hand on the surface in biological circulation.
To help appreciate this difference, imagine placing an end-of-life solar panel and all its accompanying stuff out in the forest. What components are eagerly eaten by the resident biology? At the same time, put a dead plant or animal next to the solar junk and come back in ten years. One will be much the same, while the microbes and fungi have consumed the other, leaving no discernible trace.
Note that the fossil fuel entries in the table above are “cheating” by not including the mass of the fuel itself. The intent is to capture the infrastructural “machinery” needed to convert the flow to electricity. At energy densities of 6 and 13 kcal/g for coal and gas, respectively, the corresponding ton/TWh numbers translate to 143,000 and 66,000—numbers typical of chemical energy. I could make the case that the numbers in the table are still fair in the materials sense, counting the elements that are not provided by derivatives of air and water via photosynthetic processes—much as we ignored the bulk of the human mass (and food intake) for the same reasons. Missing in the other direction is ore purity and thus mine tailings, which can exceed the end-product material mass by factors of hundreds, so that the total extracted mass is far larger than indicated in the table above. Still, this post is not intended as an argument for or against fossil fuels.
One point to note is that for every ton of fossil fuel removed from the land, another six tons are removed in the form of sand, metal, rock, and wood. Inferring from the table and figures above (and common sense), these materials are not primarily devoted to the machinery needed to burn fossil fuels (i.e., engines and power plants). They are going to the human enterprise called modernity: buildings, roads, consumer goods, etc. Replacing modernity’s engine with another source, like renewable energy, aims to keep the bulk of material extraction in full swing—in fact enhancing it to supply the extra materials necessary for diffuse renewable energy to function.
The Inexhaustible Point
For all intents and purposes, biology has figured out a way to tap into the continuous and (seasonally) reliable flow of solar energy using a bare minimum of mineral requirements from the land’s surface. It took billions of years to solve this very hard problem. One could consider the result to be a “circular economy,” in that minerals are recycled into the environment and taken in by microbes, fungi, plants, and on up the food chain. By working within the strictures of multi-level selection (evolution) subject to long-term ecological viability in relation to other life, the result has the word “sustainable” effectively built in: sustain-a-built. No? Okay, yeah, that’s pretty lame.
Our technologies are clumsy and materially insatiable, by comparison—no surprise, given the short development time and our complete disregard for the unforgiving constraint of sustainable practices. Make no mistake: “renewable” energy is not the same as sustainable technology. The only demonstrated sustainable technologies to date are those found outside modernity, in the biodiverse ecological realm (including things made from wood and plant materials, for instance). Until a technology achieves closed-loop sustainability in concert with the rest of the community of life—which may not be possible—it’s not truly “renewable.” Systems that require mining, produce mine tailings/pollution, destroy habitats, and result in collateral damage in the form of permanent species extinctions can’t be considered to be long-term viable, in my view—just part of the jaw-dropping fireworks show that will soon shock itself by self-terminating. Nobody could have seen it coming!
A typical unsubstantiated knee-jerk reaction is that aggressive/complete recycling could address the concerns. But recycling yield is always going to disappoint, so that a moratorium on new mining (or simple exhaustion of economically recoverable material as the low-hanging fruit is depleted) would result in a slow dwindling of available materials until the weakest link falters below some minimum threshold required to keep the industry alive—likely on a timescale that is lightning-fast compared to that of ecological evolution. Recycling also consumes copious energy: more and more as higher and higher yields are sought. It becomes self-defeating: from what source does such energy come, and at what additional material cost? Plus, I always return to the question of what we use the energy to do. Thus far, it’s been 99.9% unsustainable activity (my crude guess: vanishingly little goes into restoration of ecological damage). Sixth mass extinction, anyone?
So: technology is on the verge of inexhaustibly tapping into inexhaustible flows? I don’t think so.
It should not be surprising that we have not yet been—and may never be—able to engineer long-term-sustainable modernity (i.e., high-tech). I strongly suspect that’s not even a thing. Why on Earth would we just assume that it’s possible? Where does that hubris come from? It’s not from a thorough analysis in full ecological context, and certainly not from any demonstration. It’s just a lazy and wishful assumption based on the brief and highly anomalous window on the world to which we’ve been exposed. Comparing modernity-relevant timescales to those relevant to evolution, and looking at the profligate rate of one-time inheritance spending (i.e., of non-renewable resources) that has been required to produce modernity tells us a lot. Unlike biology, this ain’t built to last. I know which team is a better long-term investment—the ultimate victors unless everyone loses first.
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This post was listed in a "compu-nerd" channel, generating the following comment on that platform:
"Fascinating this person doesn't realize the entire civilization is breaking away from "natural cycles" towards more control of environment, instead of retreating into anarcho-primitivist fantasies and purity spiraling into energy veganism."
It is indeed fascinating to me that one person's reality is another's fantasy—in both directions. Both will not turn out to be right. Such a statement does little to shake me of my sense of reality, which I believe to be based on billions of years of context and analysis about limits to growth, energy, materials, and most importantly the critical underpinning of a healthy ecology. The other view would seem to be an extrapolation based on a microscopic moment in time based on wildly unsustainable practices, turning a blind eye to the mounting ills. Each likely as unconvincable as the other, incredibly.
"It is indeed fascinating to me that one person's reality is another's fantasy—in both directions."
As Feynman opined in the Shuttle disaster inquiry and I paraphrase, "we can fool ourselves and each other but nature cannot be fooled."
Bluster and self deception are no protection from the laws of nature.
The Australian economist Steve Keen has done a thorough job of explaining how our culture became convinced that we can separate ourselves from the ecosystem. This view is, I think, completely wrong. Everything we have in modern life is from the Earth and the Sun. Just because we transform it in amazing ways, doesn't change where it came from. If you replace "natural cycles" with "reality" in the above response, I think it better conveys techno-optimism and neo liberal economics.
The person who wrote that comment probably believes themselves well-educated and scientifically informed.
Best practice in science is to suppresses personal attachment to an idea so that nature becomes the arbiter of truth and not our wishes. So what gives?
I'd suggest colleges and universities are not good at demonstrating and teaching how and why we suppress personal attachment in our studies. It starts by identifying, seeing-through, sidelining, and taming our Ego–something few know how to do or recognize what life is like without Ego–and then proceeding from there.
Your work, in my view, demonstrates non-egoic analysis, which is rare. Good work.
"the entire civilization is breaking away from "natural cycles" towards more control of environment" Lol, commedy gold.
It's just a shame that deluded soul won't live long enough to see how wrong they are.
Far too much control "of environment" is precisely the problem, and has been for a very long time.
To me, it seems unhinged: divorcing from "nature." To them, I must seem equally deluded. I agree: the quest for total control is the problem, but apparently intoxicating for many—even though it's an impossible goal.
Yes, 'unhinged' is right. That mindset is completely alien to me. Where does it come from? Maybe Star Trek and other such nonsense.
That compu-nerd comment is not just stupid – it's like a celebration of stupidity.
To assist in the understanding of where such a mindset may come from, I suggest reading Ernest Becker, 'The Denial of Death,' a work that greatly assisted me in understanding (so far as I am able) where all mindsets come from.
Becker suggests that we form our 'mindset' (he calls it our 'immortality project') in reaction to our realization, somewhere in our early youth, that neither we, nor those we love (like our parents, on whose continued existence we are wholly dependent, at the time) are immortal…that, at some point, they (and we) will entirely cease to exist. This realization that engenders, not surprisingly, considerable anxiety. To subdue that anxiety we make up, or take up (there are many such stories available), a story that assures us that we are not, after all, as mortal as all that…for instance, the story that technology will save us, and that if technology seems to be destroying us, it is only because we don't yet have enough of it.
To quote Frank Herbert, "Fear is the mind killer."
As a younger person, I'm very interested to see just what new stories we will tell ourselves when the renewable energy fantasy is exposed and fossil fuels becomes increasingly expensive and scarce. It will be the most traumatic event in history.
Hmm. The problem with that is, plenty of athiests will be on board with the idea of some techno utopia, just as plenty of 'bible bashers' will be dead against the march of technology (eg Amish).
You're conflating two subjects, in order to make a point unrelated to the article.
(PS I am not religious.)
To Will Olliffe,
I am 20 and "predicament-aware" so I suspect to see a lot of "interesting" stories in my lifetime. Rest of the century will be hell of a ride. Wish you all the best.
I think Becker is wrong in a sense, I don't think people realise we really die and we go on with our lives from a very early age without truly comprehending death, the lack of free will and determinism. People simply don't understand the universe or themselves.
One of the most annoying adjectives applied to renewable energies, along with "sustainable" is "clean." There is no such thing as clean energy other than what organisms eat (though there is also associated waste but that gets eaten by something else). Even climate scientists use the term, "clean energy."
Another aspect of renewables that I've toyed with is that they divert some energy that would be otherwise used by natural systems. All of the wind and sun (plus wave and tide) is harnessed by Earth, in some way, and some of that work will not be done as we divert part of the energy, to be eventually dissipated as waste heat.
Some people are betting everything on degrowth and steady state. Although never really detailing what such a society looks like, they blithely expect that degrowth would eventually lead to a sustainable level of activity which can then be flattened to a steady state economy. What a sustainable level is is never articulated. It certainly can't be modernity.
While I agree, on the whole, I must raise one quibble…a quibble that comes to mind regularly in my perusal of discussions of…well, everything.
My quibble is this: You state "Even climate scientists use the term…" I believe the appropriate phrasing would be: "Even SOME climate scientists…" As you have phrased it you impute, as I understand it, to ALL climate scientists.
In the regular course of 'public debate' it is all too common, in my opinion, to forget that 'scientists' are, first and foremost, human beings, and, as such, are subject to the foibles of human beings…hubris, for instance. My personal favorite is the description of the fossils found in the Burgess Shale, which were, at first blush, ascribed to genera that were generally known at the time, and turned out to be members of phyla entirely unknown at the time. This did not stop 'fossil scientists' (some of them, anyway) from insisting that their mis-assignments should be taken as gospel.
One aspect of Tom Murphy's general approach to…well, everything…is his tendency to humility, couching his analyses in language that reflects the essential uncertainty of…well, everything…at least of everything that we 'know' about…everything.
I suggest that we might do well to take a similar humble approach when ascribing particular qualities (both the 'good,' and the 'bad') to any particular group. (Of course, those who do not practice such humility may be forgiven, considering that they are, first and foremost, human beings.)
You're right. My apologies to those climate scientists who don't use the term "clean" in reference to so-called renewable energy infrastructure. They are human and so some can be taken in by the hype.
My father, a manual construction worker with brains, summarized it as follows:
"Better wealth once, than always poverty!"
For those interested in the inevitable depletion of natural resources, there are some excellent books:
* Road to Survival (1948) by William Vogt
* Silent Spring (1962) by Rachel Carson
* The Population Bomb (1968) by Paul Ehrlich
* The Limits to Growth (1972) by the Club of Rome
* Overshoot (1980) by William R. Catton
Dear Mr. Murphy,
Thank you for your writing. You are one of the people who made me see the predicament. I am writing a paper for an Ethics course, its current title is "Ethics independent of the Carbon Pulse" (Nate Hagens uses this term for what you call "one-time bonanza of hydrocarbon energy). I plan to synthesize views of authors such as you, Nate Hagens, Michael Dowd, William E. Rees and many more in order to propose an ethical system likely called "Humility Ethics" (due to respecting the physical limits and the Web of Life) that would allow humanity to exist for thousands or millions of years (if we are not extinct next century and a few other remarks). I will publish it in due time.
Sounds excellent! Good luck with the effort…
I think the immediate (and complete) limiting factor for that would be human psychology, that is one area of my interest with neuroscience. I mean it sounds very nice but also naive and divorced from anything we have learned from history and psychology of humans and all mammals. Probably the best person to learn from is Robert Sapolsky, I highly recommend him for you.
Dear Andrea,
I am aware of many limiting factors such as thermodynamics. I recommend work of prof. Tim Garrett from University of Utah which describes civilization as a "heat engine" (https://esd.copernicus.org/articles/3/1/2012/ and https://esd.copernicus.org/articles/13/1021/2022/ for scientific articles, https://nephologue.blogspot.com/ for his blog and https://www.dr-ricknolthenius.com/Apowers/A7-K43-Garrett.pdf for brilliant presentation by Rick Nolthenius Ph. D (I also recommend checking out all of Rick's presentations under https://www.dr-ricknolthenius.com/astro7/A7PowerIndex.html)). I would try to not write this work to prove a given point, rather to explore what would be necessary for humans to even have a slight chance of existing along the Web of Life for thousands of years and not destroying it at the same time. For example, it seems that in order for humans to be sustainable (using prof. Murphy's meaning of the term) they would have to abstain from mining or/and not expand into areas where they cannot life without using exosomatic energy for heating themselves (and e.g. leading to climate change by logging). Additionally, I assume most people would call my views "deeply pessimistic" (I prefer "reality-adjusted"), so maybe too much hopium would not slide into such a work (although all the assumptions should be questioned whenever possible). Thank you for your response, all the best.
The Atlantic has an article about "The Rise of Techno-authoritarianism" which talks about this ideology that the entire civilization is breaking away from "natural cycles"
The quote Marc Andreessen which is a classic and frightening (from the Atlantic):
Or take what might be considered the Apostles’ Creed of his (Andreessen’s) emerging political movement:
We believe we should place intelligence and energy in a positive feedback loop, and drive them both to infinity …
We believe in adventure. Undertaking the Hero’s Journey, rebelling against the status quo, mapping uncharted territory, conquering dragons, and bringing home the spoils for our community …
We believe in nature, but we also believe in overcoming nature. We are not primitives, cowering in fear of the lightning bolt. We are the apex predator; the lightning works for us.
Yes, this primal battle cry was pretty gross: I could not keep reading. It inspired my "Ugly Magnificence" post:
https://dothemath.ucsd.edu/2023/10/our-ugly-magnificence/
Thank you very much for these valuable thoughts. In my view, one way forward would be to combine an economy that perfects the cradle-to-cradle concept with an economy based on money that is adapted to nature, as developed by Silvio Gesell, for example, who was praised by John Maynard Keynes.
The idea that long-term-sustainable modernity is possible–and even desirable–is indicative of how Ego has hijacked our reasoning. Unfortunately, we've allowed Ego to contaminate our arbiters of truth: science and religion.
By nature, Ego sees only itself and wants to dominate anything not itself. It's our Ego that's the part of us that believes we're the smartest, most rational person in the room, not realizing how Ego clouds our judgement. Most scientists attempt to remain detached in their work, yet most fail to see how Ego causes them to miss the forest through the trees. For example, Carl Sagan begins his TV show Cosmos by standing on a bluff high over the ocean, proclaiming like a prophet:
The Cosmos is all that is, ever was, or ever will be.
This is not a scientific statement of evidence and fact, but a religious statement of unknowable faith. How does Sagan know this? It’s his belief, a supposition, an assumption expressed as an all-encompassing Absolute Truth. Ego loves this statement because it allows Ego to remain convinced we can know everything. Surprisingly, the scientific establishment did not rip him to pieces over his unscientific proclamation, perhaps because it shared the Egoic dream of being on the road to know all things.
We can find similar examples in our religions where practitioners gather to focus their devotions with the hope of gratifying Ego.
Ego is a potentially temporary aspect of us that allowed us as children to mature into unique, individual adults, but if we're to mature Ego needs to be discarded like baby fat.
Iain McGilChrist approaches what life is like without Ego when he discusses the two ways we view the world around us: Either with a part of the brain breaking experience into pieces or the part experiencing the world as oneness; both modes exist as one: a puzzle forming the world we experience. But he doesn't discuss what happens after Ego is permanently gone and our brains learn to use the razor of our discernments to protect and honor the oneness around us.
Ego makes us believe sustainable modern living is desirable. Without Ego, our world becomes vastly more puzzling, beautiful, and wonderful.
I think this post hints also on some possible 'solution' to high-tech, namely high biotech? (coupled with much lower demands)
Yeah, for now ppl tend to forgot their food is completely biological, on massive scale. And I think I saw somewhere figures that even replacing food's embodied energy by some non-biological process will take surprizing amount of … energy. But still, I do not want to see collective (and often involuntary!) work of like 100 billions of humans ever lived to go away completely. It should be something very different from last 250 years of orgy, but I also do not think effectively pushing everyone remaining into wood/stone/bone based world will be most supported by population idea …
I do not think most humans really can care about 1000 years long timescales (sadly!) we apparently can't arrange our pol. life during single generation (70 years)!. But may be one can imagine some hypothetical brain changes that actually enable us to care? Yes, dangerous territory. But alternatives IMO are much worse …
Also, may be revisiting space non-exit using even best ideas put on paper (like Atomic Rockets website section on space mining) might be interesting. Even space can't fix capitalism's way of growth (see Expanse tv series/books. For me it very effectively shows that even with many technomiracles end state become again biggest part of humanity living in very bad conditions but now consuming astronomical amounts of energy! But I bet few read it this way …). But digging into details might be interesting, even as thought excursion.