> At present, the waste heat term is about four orders of magnitude smaller than the solar term. But at a growth factor of ten per century, they would reach parity in roughly 400 years. Indeed, the surface temperature of Earth would reach the boiling point of water (373 K) in just over 400 years under this relentless prescription. Clearly, extrapolating our recent — seemingly modest — 2.3% annual energy growth very far into the future quickly becomes ridiculous, and cannot happen.
> This is not intended to suggest that waste heat is a bigger problem than, say, climate change from carbon dioxide emissions (...)
So unless we get faster than light travel or we greatly reduce the amount of space into which you can physically cram a living human we are under 13000 years away from a pretty hard upper limit.
Make more realistic assumptions than speed of light expansion of humanity and that limit gets a lot shorter even with growth rates quite a bit lower than 1%.
And if we sustained a 0.03% annual population reduction rate (like South Korea recently experienced) there would be less than 100 people on Earth after just 600 years.
So I agree that exponentials can get away from you a lot faster than you might expect, but I also think that trying to predict cultural norms 13 millennia from now is likely to be counter-productive.
In a way I agree that the feasible limits, even on Earth, may be orders of magnitude larger (say, in terms of population, perhaps) than we currently have. But the current rate of growth in any case is probably unsustainable because of imbalances like co2 emissions. I do think it's feasible to change to renewable energy in the short term, if only political motivation was a bit higher (please, go out and vote focused on climate change, folks!). If I were to lay out a strategy for humankind, I'd say we should focus on climate change for the next few decades, and then we can resume growing (to avoid possible collapse).
Limits to technology are actually non-trivial due to the atomic nature of objects, limited number of chemical elements with limited range of properties, etc.. Intelligence itself isn't free and keeping the Great Self-sustaining Rube Goldberg contraption working is not trivial. It's very hard to predict what limitations we can overcome -- see Moore's law slowing down. Some limits we've almost reached such as luminous efficacy (LEDs in lm/W). Soon we'll be faced with the question of whether we want to make Earth into a Caves of Steel landscape (ending most natural life to create a hyper-efficient human/machine habitat) capable of sustaining more humans or a Solarpunk landscape (preserving natural ecosystems) with a more limited population. I think there's a large degree of arrogance to the first, because I don't feel competent enough to evaluate the true value of animal lives, supposing a large quantity of animals are sentient, and they have intrinsic scientific and cultural value. I think this requires an exercise in imagination from all of us. In any case, it's probably a great idea if we could at least keep the oceans, rainforests, and major national parks healthy.
One crazy dream I have is to colonize not Mars, but Mercury. In Mercury solar energy density is crazy high. There's even some thermal energy from the solar thermal gradient. You can dig to get to nice temperature ranges and be safe from radiation, all this works well since the planet is tidally locked and therefore doesn't rotate, there's no diurnal variation. You can build a crazy Cave-of-Steel there and live your life in a cramped cell playing video games (or [insert activity]), if that's what your vision of heaven is.
In any case: Hack the Planet!*
*: In a good way, of course :)
PS Mercury is too far in-system to be that useful. It takes less energy to get to/from the outer planets than it does Mercury. The cold traps on the poles are interesting though--mercury potentially has all the raw material needed for a self-sufficient industrial colony.
The ironic thing is that some of the earth's most fertile periods were associated with high levels of co2.
Because co2 reduces plant need for water, reduces desertification, and massively increases the food supply.
Given that solar power beaming is technologically feasible and practical, it is likely that the future will not be power limited like we are today.
Higher CO2 levels will result in vastly more arable land, mostly from the reduction of deserts and the warming of permafrost. Higher CO2 levels make agricultural crops grow faster and bigger. Higher CO2 levels (within the range I was talking about) has no effect on human respiration. Ideal for plants is good for us too.
- http://www.omafra.gov.on.ca/english/crops/facts/00-077.htm
"They found that if the outdoor CO2 concentrations do rise to 930 ppm, that would nudge the indoor concentrations to a harmful 1,400 ppm.
…
In fact, at 1,400 ppm, CO2 concentrations may decrease basic decision-making ability by 25%, and complex strategic thinking by around 50%, the authors found."
- https://penntoday.upenn.edu/news/continued-CO2-emissions-wil...
So yes, going down to that would be an improvement ;)
In actual real world systems, the growth curve is sigmoidal: it starts out with exponential growth, becomes linear, then asymptotically flattens as system constraints are approached. This is already happening with human population, and should be expected to start happening with other resource curves in the fairly near term. Any properly grounded analysis would look at the situation from this point of view.
Similar remarks apply to just about anything we currently call "waste"; sooner or later, if we need to, we will find ways to recycle all of that "waste" into something usable. The key limitation is population growth, but as I've already said, population growth is already into the "asymptotically flattening" phase.
It's possible, of course, that population growth will in fact go negative (many projections assume that); but that doesn't mean it will stay that way. The exact sigmoid curve is obviously an idealization; real world systems do oscillate about reasonable equilibrium points instead of just staying stuck at them.