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I really think that we can feed way more than our current population using more advanced farming IF WE FIND A WAY TO PRODUCE CHEAP RENEWABLE ENERGY.

The solution would be hydroponic vertical farms. If energy is cheap enough lots of new possibilities emerge.

You could create a 100 floor high skyscraper next to the coast.

-freshwater would be made out of saltwater by evaporation

-artificial lights would simulate sunlight on each floor

-minerals would be extracted from seawater or from the earth's crust

-everything is operated by robots in the farm

-electricity is provided by a solar farm or a fusion reactor

Suddenly arable land and water are not an issue anymore. You have 100x more farmable land. With this technology, feeding 10x the current earth's population seems doable.

Would this work on a larger scale to feed 100 billion humans?

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    $\begingroup$ Why bother wasting space with a building? If access to the sun, rain and dirt is unnecessary, you can do all this in a subterranean construction that taps into a network of pipes moving water from the coasts. Then food can still be local, and you can leave more space for people. $\endgroup$ – Mathily Nov 21 '16 at 19:05
  • $\begingroup$ there has been some research into farming ocean algae for food, it is very nutritious but it needs artificial flavoring and texture or it tastes like lt looks, green slime. there is a lot more ocean than land. $\endgroup$ – John Nov 21 '16 at 19:58
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    $\begingroup$ Desalination by evapotransporation is very slow. Since you have access to cheap renewables, consider Reverse Osmosis desal. en.wikipedia.org/wiki/Reverse_osmosis $\endgroup$ – Mikey Nov 21 '16 at 21:29
  • $\begingroup$ Fusion reactor is not strictly renewable. $\endgroup$ – paparazzo Jan 11 '17 at 18:25
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    $\begingroup$ I sorta feel like you answer your own question. It is your world. If you decide that those conditions you list are reality then yes...as you say it seems doable. I think the better question to ask would be, what are the flaws in this system, or why wouldn't this system be feasible? As it stands there is a question and an answer in your post. $\endgroup$ – James Jan 11 '17 at 20:51
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Given a source of power, it is possible.

Where you’ll start to run into problems is with the heat generated. how much power are you using on the planet? Once that becomes comperable to the sunlight, you will be heating up the planet by a significant amount.


By a power source I mean independent of normal sunlight. Locally generated fusion perhaps? It could in fact be sun-based, with space based solar platforms that beam energy down.

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  • $\begingroup$ Isn't only a tiny percentage of sunlight used for anything (including all photosynthesis)? I thought it was almost all used for heating anyway, with a large fraction being radiated away into space on the night side. might be interesting to look into some numbers for this $\endgroup$ – Innovine Nov 21 '16 at 7:56
  • $\begingroup$ What’s used for photosynthesis is still used for heating. $\endgroup$ – JDługosz Nov 21 '16 at 8:03
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100 billion people? Easy. You wouldn't even need to use the vertical farming (though doing so may become cost effective at some point). The earth already has a massive agricultural surplus (we waste ~40 percent of everything we farm, and obesity has become endemic to much of the rich world). Whenever there is starvation, it just about always has to do with war or oppressive governments preventing the food from reaching the people who need it. Moreover, most of the world's agriculture is horribly inefficient. America's farm output per km2 is about 7 times more than Africa's thanks to more technologically advanced techniques. Finally, a lot of what we eat is terrible inefficient (12lb of grain is needed to make 1lb of beef, and fruit and vegetables are nutritious but take up large areas and lack calories).

Since vitamins can me made synthetically, theoretically, all you need is calories, so let's have 2 scenarios: a dystopian hive world where everyone is given 2000 calories per day and appropriate synthetic vitamin substitutes, and a more balanced future where land is given over to less efficient uses like meat and vegetables. For the sake of simplicity I'm guesstimating that this is 5 times less efficient space-wise than the dystopian potato paste. If someone else has a better idea of this ratio please comment.

1 square km of farmland using current methods can produce enough calories to feed 2350 people. ~11% of the earth's land area is used for crop cultivation (I'm ignoring pastures etc). This means that there are 56 million square km of farmland currently under cultivation. If all of this land was given over to potatoes and used efficient methods you could feed over 100 billion (this kinda jives with my 5:1 balanced diet ratio as that land now inefficiently feeds 7 billion people with a relatively balanced diet).

If you want a better diet, it's time to start looking at other solutions, like your towers. On top of space efficiency, another important aspect is they can control their environments to be vastly more efficient than traditional farms. It's estimated that by combining hydroponics and aereoponics you could feed up to 50,000 people per square km. Since there will be 100 floors, this increases to 5,000,000 people per square km of farming towers (on potatoe paste). Since we're talking balanced diet, lets say only 1,000,000 people. At that rate, you'd need 100,000 square km of farming towers to feed 100 billion people healthy balanced diets. This sounds like a lot, but it's basically 1/4 of California (or 25 Tokyos), and since these are environmentally controlled you can build them anywhere. The upside of this is that former farmlands can be reclaimed as nature preserves, or developed into new cities. A massive logistical effort would be needed to transport this food into cities, so perhaps these farms would take up city blocks to reduce the spoiling of food during transport.

Finally, this doesn't take into account possible efficiency gains that could be made through the use of GMOs and other new advancements we haven't even thought of. If history is any guide, those could give us an even more massive efficiency improvement (perhaps 100 times, perhaps more). If this is in a future where that sort of mass construction is possible, these techniques have probably been developed already so my 100,000 square km of buildings could be a vast Mathusian overestimate (if you don't know who Malthus is, look him up!).

Note: see here for sources: How many people can you feed per square-kilometer of farmland?

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Each farming tower would need to be separate from its closest neighboring framing towers to keep their shadows from reducing each other's sun-facing surface area. As a result, not every acre of current farmland could be converted into a tower. You would therefore never reach 100 times our current crop output.

Also, the logistics of storing and transporting that much food would consume massive quantities of space, energy and manpower (or robotpower). Add to that, the additional space which will be needed to house and entertain another 94 billion humans, the waste disposal services, etc.

You're better off simplifying the entire process. Remove the growing of food from the equation entirely. Instead, apply your unlimited energy and advanced science to figuring out how to re-energize and reconstitute post-digestive byproducts (feces) into edible, appetizing and biologically sustaining foods. Then you can get rid of all the plants and use those pretty towers of yours to store more humans.

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    $\begingroup$ He doesn’t need sunlight because he has power to generate light indoors. $\endgroup$ – JDługosz Nov 21 '16 at 7:48
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With convenient energy source, like a thermonuclear reactor, yes, viable, no problems.

It does not have to be on coasts, in that case, we build 1000's km long oil transfer pipes, water is even easier.

U may also build some kind Acropolis, which is more or less closed loop with water, so it may have no need to replenish the water too much.

With renewable sources, everything isn't so well.

This or another way all energy comes from the Sun.

The cheapest and most renewable source of energy are the plants themselves. Everything you need is a plant seed, and care about it, and it will convert energy to food. After you give good care to it, and after some time passing by, you can eat the product, or feed it to livestock.

The point is, any energy which you will extract from renewable sources your intention is to feed this energy to the plants, and they are the bottleneck.

Photosynthetic efficiency - efficiency is about 1-2%

Some kind of delicious Nutrient paste may help, some kinda another way to generate food may greatly improve the efficiency of energy to food conversion.

With plants it needs about 10kW 24/7/365 - to feed one human.

Interesting maps of solar irradiation here - it varies 2500kWh/year/m2 for hot climate to 1500-700 kWh/year/m2 for mild and cold climate.

In average you need something between 350 to 800 square meters to feed a human (a bit more sophisticated system than usual green house, but theoretically)

For 100 billion people we need about 14-31% of surface of our Planet.
So answer is yes, no problem here.

If we think, the ocean is such sophisticated green house I mention before, it keeps the temperature in a lot of places above freezing, it stores energy, etc.

If we would like to improve the situation further, then the main problem which has to be attacked is the efficiency of plants itself.

New Way of Transforming CO2 Is More Efficient Than What Plants Do

By tinkering with the process that plants use to breathe in carbon dioxide, a team of German scientists has just discovered a far more efficient way to get rid of it. ..... Plants, algae, and other organisms turn CO2 into fuel. Erb and his colleagues reengineered this process, making it about 25 percent more energy efficient and potentially up to two or three times faster.

Based on Photosynthetic efficiency wiki article, maybe another 2-3 times improvement (convert not used light to useful one, make night period of breathing shorter)

Against solar panes etc as main source for all energy we may need(especially for food production), is the fact - animals, insects etc can't be a part of ecosystem of solar panes and wind turbines. But they can and are part of plants ecosystem - so if we have intention to keep Earth biosphere(and that is very important, as it is living history, living data base of genes which we may use for us in the future and which helps to understand evolution processes etc) - then we should have solutions which integrate earth biosphere. But keeping this biological base is expensive process by itself - but my recommendation is to keep it by any means possible - it will help us a lot in future and it is extremely expensive (energy wise) to generate it from scratch - maybe 10000 years using sun with 100% efficiency - at least in the way I can imagine for my self, but it is simplest and not very sophisticated one - just by keeping earth copies space habitats)

100 billion people is not a problem if we go to space, 100 billion and much more, and it is an easier way to solve the problem. Mention that just in case if you would like to consider such way to solve the problem.

As conclusion

Yes, it is possible to feed 100 billion people on the Earth, energy wise there is no problems, some technological challenges but no major problems.

And thanks to Bert Haddad for pointing out errors in calculation.

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  • $\begingroup$ Your numbers are WAY off. 1 square km of farmland feeds about 2300 PEOPLE, and that can go as high as 50,000 people in a controlled enviornment like this one. Source: worldbuilding.stackexchange.com/questions/9582/… $\endgroup$ – Bert Haddad Jan 11 '17 at 21:57
  • $\begingroup$ @BertHaddad shame on me, have no clue how such error could get in to my calculations $\endgroup$ – MolbOrg Jan 12 '17 at 0:11
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    $\begingroup$ @MoldOrg All good, been there tons of times :). $\endgroup$ – Bert Haddad Jan 12 '17 at 2:28
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There are a lot of inefficiencies in food production and distribution that can be removed and the excess food used to support growing population. First, studies have shown that in the developed world around 50% of all food ends up in the trash. Second, in the developed world, people tend to eat much more calories than they actually need. Thirdly, raising cattle could be very inefficient. If you eliminate corn feeding, you can use the corn (or whatever crop you plant instead of it) to feed people. Fourthly, you can export the high yield agricultural techniques (use of pesticides and machinery, GMOs etc) currently used in the developed world to developing and third world countries and get much higher yields per acre.

You could probably double the world's population with just those improvements in efficiency.

Add to that bountiful cheap energy and there are no limits to what you can achieve. You can build desalination plants and convert north & west Africa into a grass land (or marsh if you want to plant rice) thus adding millions of acres of farm land. You can reclaim land from the sea. You can illuminate your fields thus allowing the crops to grow through the night.

Once you have (virtually) unlimited energy, you are in post-scarcity world.

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Fusion reactor is not strictly renewable

That is about 14 times the food production of today.

When you consider the amount of farm land today that is a LOT of 100 story buildings. If you start as the building and walk inland you are very likely to come more than 1 story of farm land. Would need to stack the coast with multiple 100 story buildings.

Bring top soil and water to deserts would probably be more effective. Use the oceans for plant life (e.g. seaweed).

As already covered that is producing a lot of heat.

You also have deal with 14 times the human waste. Will our ground water, rivers, lakes, and oceans deal with it.

Not doable. Heat and human waste. Not sure you could build enough 100 story buildings.

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  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – Azuaron Jan 11 '17 at 19:59
  • $\begingroup$ @Azuaron In case I was not clear not doable. $\endgroup$ – paparazzo Jan 11 '17 at 20:05

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