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The quoted argument is too simplistic and ignores feedback processes that would prevent reaching the catastrophic prediction. We can't predict 400 years so flippantly.

The population will most definitely not continue to grow (in fact it will start to decrease slightly the more countries reach "developed" status), and the energy consumption per-capita will also stagnate. After all, there is a huge difference between going from living in a log house to a modern apartment with utilities and AC, and not much of a difference between one laptop and a slightly better one some years down the line. Also, attitudes towards environmental protection are changing with the generations so we are likely making different decisions 50 years from now.

Reminds me of those late 19th century predictions according to which in 50 years London would be neck-deep in horse poop

US per capita energy consumption peaked in 1980.

This idea seems like the CICO (Calories-In, Calories-Out) argument, and is misleading/wrong for exactly the same reasons - neither the Earth+people (or even just the Earth) nor the human body just stock energy like that linearly.

If you increase the amount of energy flowing into the human body, the metabolism increases as well (although almost never proportionally - there are many variables) to compensate.

Similarly, it's rather unlikely that humans will continue to use exponentially increasing amounts of energy, unless we intentionally do something to effect that. Human population growth, which is partially driving energy consumption, is not exponential (it would be exponential absent of resource constraints or cultural factors, but guess what - both of those are in effect rather strongly in the real world) - and neither is energy consumption per capita. For instance, from 2005 to 2020, the US gained 30M people[1] while keeping energy consumption roughly constant[2].

[1] https://datacommons.org/place/country/USA [2] https://www.statista.com/statistics/201794/us-electricity-co...

You can’t just look at electricity consumption. You have to look at total energy consumption. Including the energy necessary to produce the goods you consume. And that is increasing exponentially.

In a way, the US (and Western countries) are outsourcing their energy consumption.

> Including the energy necessary to produce the goods you consume.

Exactly, the original link I posted is more or less an argument against infinite economic growth.

I'd take that statement with a grain of salt. If there's something that COVID has taught me is that in reality exponential curves almost always turn into sigmoids wherever there are limiting factors. The key here is where the curve starts flattening.

The same goes for infinite growth. In the close future it sure looks infinite, but I'd say it's infinitely hard too to predict what will happen in say a 100 years (a fourth of the time before we hit the heat death wall predicted here).

Sigh. I really shouldn't have included a quote in my comment and instead only linked to the full text.

That text is exactly an argument against infinite economic growth – and it carries out said argument by looking at energy consumption (which necessarily grows with economic activity).

Yeah I read it. Thats why I said that bit about infinite economic growth. I felt that by saying that exponential heat growth is probably sigmoid I was somehow validating the notion of infinite growth, which I think sometime in an unforeseeable future will just plateau.

Ah, sorry, looks like I misunderstood. :)

If there is enough ambient energy to literally boil the seas then we're probably going to find it easy enough to leave the earth and go somewhere cooler.

I don't think it'll be easy.

We would have the same (if not higher) energy consumption per capita on any other planet. And unless that planet is humongously large (which would also increase its surface-level gravity, thus rendering it uninhabitable), the relation between surface temperature and energy consumption will be similar[0]. Now there's only a finite number of planets in our solar system and leaving our solar system, say in the direction of Proxima Centauri (the star nearest to the Sun), amounts to traveling ~4.2 light-years. At a velocity of 0.1c (which is a lot – especially if you're trying to move an entire species[1]) that means a travel time of 42 years (as seen from our current frame of reference). Any velocity lower than that and we're getting into hundreds-of-years territory, so we'll be needing space ships across we can live for generations.

Also, a space ship is not that different from a planet, in that it also has to obey thermodynamics. So the surface temperature issue there is just the same. (In fact it's worse, since our space ship will likely be smaller and we also need to factor in additional waste energy of the space ship's propulsion engine or whatever we're using.)

[0]: https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

[1]: Or, say, half the species (or whatever amount necessary to make the total energy consumption on the planets we already inhabit drop to levels such that the planets' surfaces don't start to boil).

We're talking a world where humanity has enough energy on tap that not only could it have feasibly evaporated the Pacific Ocean, but that it basically has evaporated the Pacific Ocean, as a side effect of doing something else.

We can barely speculate about such a world, but interstellar travel would not be much of a challenge with that sort of energy abundance. We'll find a way.

> but interstellar travel would not be much of a challenge with that sort of energy abundance.

I don't think I agree.

1) The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light. Infinity is weird.

Of course we won't be trying to reach the speed of light but the energy (and fuel) required to move half the species (so that the other half can stay on Earth/Mars/…) will still be significant.

2) My second argument was that the Stefan-Boltzmann law is just the same on board the space ship. And if we live there for generations, chances are our energy consumption per capita will be similar as on the planet we left, and so we will be running into similar issues with Stefan-Boltzmann's law. Sure, we can split up the passengers across multiple space ships and make each ship much bigger (to increase surface size) but not only will this increase the total mass and thus fuel required for the trip but we would probably still not achieve the (rather high) surface area per capita ratio that we have on Earth.

Addendum to 1):

Thinking a bit further, just because we can produce a high amount of energy that doesn't necessarily mean we can automatically convert it into kinetic energy for a space ship very well. Most propulsion systems in space still require expelling a propellant and conservation of momentum means this is unlikely to change. (Sure, one could imagine solar sails but the little momentum exchanged there won't get half of humanity to Proxima Centauri very fast.) So while we might have unlimited energy we might still be constrained by momentum requirements.

The only way I can see to solve this conundrum would be producing enough propellant on board the space ship, e.g. (lots of) photons, using a laser. Definitely not impossible (especially not at these energy levels) but it'll be interesting to see what these propulsion systems will look like exactly. :)

Ideally, we would of course try to use the propellant to also get rid of the waste heat mentioned earlier but I'm not sure whether this would work entropy-wise.

> The extremely high (but still finite) amount of energy required to evaporate the Pacific Ocean is still much less than the infinite energy you need to accelerate even one single space traveler to the speed of light.

True, but how many tons of space junk can you accellerate to 95% of light speed for the same amount of energy?

Quick back-of-the-envelope calculation:

    Approx. mass of Pacific Ocean[0]: m_ocean = 7.1×10²⁰kg
    Specific heat of water: c = 4.2kJ/(kg · K)
    Temperature of Pacific Ocean: T_1 ~ 293K
    Temperature at which water starts boiling: T_2 ~373K

=> Energy needed to make Pacific Ocean boil:

    E_heat = c m_ocean ΔT = c m_ocean (T_2 - T_1) ~ 3×10²⁶ J

On the other hand, the relativistic kinetic energy formula is:

    E_kin = (γ-1) m c²,

where γ = 1/sqrt(1-v²/c²) = 1/sqrt(1-0.95²) and m is the space junk's mass.

Setting E_kin = E_heat therefore yields:

    => m = E_heat / [(γ-1)c²) = 3×10²⁶ J / (2.2×10¹⁶ m²/s²)] = 10¹⁰ kg

For comparison: The mass of all of humanity combined is somewhere between 10¹¹kg and 10¹²kg. Now those numbers do look somewhat comparable but:

- We haven't taken into account the space ships required to transport everyone

- E_heat was waste heat but since practically all energy will become waste heat at the end of the day, E_heat gives us a pretty good estimate of the total energy we will have (had) access to.

All in all 0.95·c doesn't seem feasible for moving humanity to Proxima Centauri, given E_heat. For moving 10¹⁰ kg of space junk, sure, though I'm not sure what you were planning to do with all that space junk in the first place?

[0]: https://en.wikipedia.org/wiki/Pacific_Ocean

Not quite sure I follow. On earth we're mostly limited to radiation to get rid of excess heat, I understand that part. But on a space-ship, can we not just expel the heat via mass? I.e. We super-heat some dense materials and just shoot them out.

Where will you be getting all that mass from, though?

> We super-heat some dense materials

This won't work as you would need to put in additional work (leading to additional waste heat) in order for this process to lower ambient temperature. The only thing you could do is shoot stuff out that's precisely at ambient temperature, compare https://news.ycombinator.com/item?id=28471620 .

I believe the two of you are talking about different things.

The argument in the UCSD blog post linked above will apply to any finite system if you assume exponential growth in power use, and exponential beats cubic for expansion to other worlds (I’m assuming no FTL for a cubic limit to expansion).

Abundant power — be it from fusion or solar or quantum magic — does not actually need to guarantee eternal exponential growth of power use, but the absence of such growth would necessarily lead eventually to the absence of economic growth.

We can still have a SciFi future without that, it will just look different in a way our current society can’t properly envision (which I think is an unsurprising a claim to make even in the absence of the rest of this argument).

> So the surface temperature issue there is just the same.

On an interstellar ship far from a star, I think you're more likely to freeze to death, because temperature in space is near zero Kelvin.

Inside the solar system however, you could reflect away the received radiation (and heat) using mirrors.

> I think you're more likely to freeze to death, because temperature in space is near zero Kelvin.

We're talking about a civilization on board an interstellar ship that had to leave their home planet because they were consuming so much energy that the resulting waste heat ended up making the oceans boil. So the assumption that they'll keep on consuming lots of energy (and producing lots of waste heat) on board such a ship sounds rather reasonable to me.

> Inside the solar system however, you could reflect away the received radiation (and heat) using mirrors.

The discussion is about getting rid of heat produced on board the space ship, not heat that's received from elsewhere.

Huh, that's interesting!

I wonder, in a strictly thermodynamic way (ignoring CO2 etc), how big of an impact it would have to remove all internal combustion engines in land-based transportation and power generation (coal plants).

ICE's have like a 30-40% efficiency? Compared to electric engines 80-90%. But on the other hand, you probably consume quite a bit of energy producing the batteries...

Per battery or overall to the planet?

Per unit of storage, Wikipedia says the lifetime storage capacity of batteries etc. relative to energy needed to construct them is:

Lead acid: 5 times construction energy; Vanadium redox: 10; LiIon: 32; Pumped hydro: 704; Compressed air: 792.

I can’t remember where I’ve seen this, but I think a unit of PV produces all the energy it took to manufacture after a month or two.

If you mean overall? As a rough guide we emit about 35GT CO2/year which is about 9.5e12 kg carbon; burning carbon releases about 32MJ/kg; so about 3e20 J/year, or 9 TW, or 19 mW/m^2.

There’s more energy in the hydrogen in gases and oils, this is just a ballpark estimate of the thermodynamic output of burning that much does to directly heat the planet.

How do we know that global temp rise isn't just due to energy usage? I mean "does that calculation fit at all?", not "carbon dioxide is fake".

Because we know that so far humanity's energy use is so small that the heating effect via increased blackbody radiation equilibrium temperature is utterly dwarfed by what mainstream climate focuses on, like GHG gasses.

It's the difference between a hand-warmer and a coat. The hand-warmer adds extra heat to the system (like the heat from burning fossil fuels). A coat doesn't add any extra heat, it just traps some of the heat that would otherwise be lost (like greenhouse gasses).

Hand-warmers can keep part of the body warm for a few hours. Coats can keep the whole body warm for years.

Not even close.

Global energy use is around 170,000 TWh/year (1). This includes electricity generation, as well as fuel for transport, burning wood for heat, etc.

Heat flow from mantle is 403,000 TWh/year (2)

Solar irradiance is ~1200W/m2, which adds up to massive 5B TWh/year.

Extra radiative forcing from greenhouse gases in IPCC scenarios is ~3W/m2, or around 12.5M TWh/year.

The radiative forcing is two orders of magnitude larger than our energy use.

(1) https://en.wikipedia.org/wiki/World_energy_supply_and_consum...

(2) https://www.nature.com/articles/ngeo.2007.44

Thanks, this is the calculation I was looking for.

I believe total annual solar irradiance is closer to 1.5BTWh/yr.

The 1200-ish W/m/m figure is hitting a flat plate circle, not hitting the whole spherical surface.

Taking 173,000TW of continuous solar energy* times 24h/d times 365.25 d/yr yields a little over 1.5B TWhr/yr

* https://news.mit.edu/2011/energy-scale-part3-1026

Well if we transform solar into electric then into motion or bound carbon, that should actually help reduce the heat balance?

> into motion

Kinetic energy will end up getting converted to waste heat nonetheless.

> or bound carbon

This seems hard to imagine. We're dealing with waste energy here, so a very high-entropy type of energy. Bound carbon is low-entropy, so the conversion is impossible[0] unless we put that entropy elsewhere.

As an analogy, consider a fridge: It brings your food from a high-entropy (high-temperature) to a low-entropy (low-temperature) state but in order to do that it also has to produce waste heat (entropy) on the outside.

[0]: https://en.wikipedia.org/wiki/Second_law_of_thermodynamics

We're not necessarily talking about a closed system, though. If you've got an energy supply that rounds to limitless, constructing planet-scale heatsinks starts to look tenable.

> We're not necessarily talking about a closed system, though.

Short of shooting hot lava into space[0] we pretty much are because, once again, thermalization through radiation is governed by Stefan-Boltzmann's law and there's no way around that.

[0]: https://news.ycombinator.com/item?id=28468182

Stefan-Boltmann talks about emission per surface area. So... increase the surface area. We're not limited to a sphere.

The same problem crops up when you're talking about moon bases and so on - you've got the same problem of venting heat from an ecosystem into a vacuum. For that situation, one of the solutions that got designed out was to basically spray an oil mist across a gap, catch it, and recycle it into the cooling system. As a fine mist, the oil has a colossal surface area compared to its mass, and all that surface area can radiate heat off into the vacuum.

So... scale that up? I realise it's a hell of a leap, to go from human-scale to humanity-scale, and I don't know exactly what it would need to look like, but limitless energy is a hell of a springboard.

Absolutely yes. Energy is captured by solar panels. They make a shade, obviously, and what is in their shade does not get heated by the sun.

If you were to use 100% of solar panel energy to heat up something else the overall balance would be 0.

Contrarily, nuclear fission/fusion that releases energy from its fuel, ultimately heating up the planet.

But then what do you do with that motion?

Eventually it all decays to heat, as per the 2nd law of thermodynamics

The thermodynamics argument would hold only for a closed system. If we send big blobs of lava into space, and import big chunks of solid rock back to Earth, then theoretically we should have no problem.

> If we send big blobs of lava into space

I honestly can't tell if you are joking. The energy expenditure to get anything into orbit would produce more heat than you are offsetting.

Depending on the design of the system, the energy could well be expended in orbit and not contribute to the heating of earth (think about designs like a space elevator).

He's basically describing a giant air conditioner... it's definitely theoretically possible.

> it's definitely theoretically possible.

In theory yes, but in practice: Not so much.

Even if we put aside GP's concerns, shooting big blobs of lava into space would require heating up the lava/rock in the first place. But this process doesn't happen on its own (through thermalization) given the average temperatures on Earth, meaning that the process of moving waste heat (from the environment, i.e. air/ocean) to the lava will once again decrease entropy (of the combined lava + air/ocean system) and you thus need to move the missing entropy elsewhere. (Meaning that you have to do work to accomplish this heat transfer / dethermalization and you will once again incur waste heat.)

Sure, we could also try to tap the heat bath of the Earth's core but then we would build a deep-Earth elevator to transport lava and solid rock (or, say, water) back and forth and GP's concerns apply once more.

There's another option, though: Don't build an air conditioning system/fridge – use thermalization with another (lower-temperature) system. That is, don't take lava (or anything that needs to be heated beyond ambient temperature) – "just" take rock at (Earth's) ambient temperature, move it to a lower-temperature $PLANET and then move cool rock from $PLANET back to Earth. I doubt this would be very efficient/fast, though.

In any case, the difference between the two approaches is that an air conditioner (or a fridge) cools things below ambient temperature and requires additional energy for that (which it will expel as waste heat), while the second approach "simply" moves energy from the heat bath that is Earth to some lower-temperature reservoire (i.e. $PLANET). If $PLANET and Earth were thermodynamically connected not just through the exchange of infrared radiation, this would happen by itself over time through thermalization.

>(infrared)

How to tell an undereducated journo.