There are a number of other resilient food solutions that we think are less promising, either because of higher costs or because the solution would feed fewer people. However, future research could change this.
Other high-tech solutions
Petroleum wax turned into fat
Petroleum wax, a common oil processing byproduct, could be converted into a synthetic butter substitute to produce significant amounts of food. (see: Synthetic fat from petroleum as a resilient food for global catastrophes: Preliminary techno-economic assessment and technology roadmap).
Propylene to glycerol (glycerin)
The potential of petroleum for food production is even greater. Propene (a.k.a. propylene), is a common chemical intermediate obtained from petroleum processing, which can be chemically converted to glycerol. It is sweet, contains as many calories as table sugar, and is commonly used as a food ingredient to make vegan cakes.
CO₂ + electricity to glycerol
Glycerol can be obtained via multiple different chemical routes. We’ve identified another production route which is also completely independent of traditional agriculture, requiring only CO₂ and electricity as raw materials (see: Chemical synthesis of food from CO₂ for space missions and food resilience).
Electric microbes producing vinegar
Electrotrophs are a special group of microorganisms capable of “digesting” electricity directly. They can be used to convert CO₂ and electricity into acetic acid (see: Potential of microbial electrosynthesis for contributing to food production using CO₂ during global agriculture-inhibiting disasters), also known as the major ingredient in vinegar. It is a calorie dense compound which is traditionally consumed all around the world, most commonly as a salad dressing.
Fats from microorganisms
Fermentation can be leveraged as a means to obtain dietary fats. Specific microorganisms are capable of synthesizing considerable amounts of fatty acids, even omega and essential fatty acids. One concept is similar to the sugars from plant fiber: the fiber would be turned into a pulp, and then the cellulose would be digested by the microorganisms to produce the fats, or the cellulose could be converted to sugars for the microorganisms to digest. Another concept is similar to the hydrogen single cell protein, in which the microorganisms convert hydrogen and CO₂ into fatty acids.
Other low-tech solutions
Feeding food waste to animals
In a catastrophe, food waste would likely decrease, but there still may be opportunity to feed food discarded by humans to animals. It may be possible to co-opt the municipal trash/recycling system to collect the food.
There are several photosynthetic water-based options that are not seaweed, such as spirulina and duckweed. Though currently relatively high cost, it may be feasible to grow some of these in wastewater economically.
Sprouting seeds can increase vitamins (at the expense of some calories), but greenhouses can provide a variety of vitamins at lower cost.
Artificial light (vertical farming) can produce any food, but it is very expensive and inefficient. Therefore, it should only be used when greenhouses are inadequate, such as for extending the lighting duration for certain crops in greenhouses in the tropics. Another use is for nontropical tree crops if it is too difficult to relocate the trees to the tropics.
Rabbits can eat nonhuman edible food. Food from domesticated rabbits could comprise about 0.1% of human food requirements after one year (ref: https://allfed.info/wp-content/uploads/2019/08/Feeding-everyone-if-the-sun-is-obscured-and-industry-is-disabled.pdf), but utilizing wild rabbits could increase this significantly.
Rats also have some ability to digest fiber, and could produce about 7% of human food after a year.
Since mushrooms can produce a billion spores (their equivalent of seeds) each, they could be scaled up very quickly. They can convert fiber into food, but not as efficiently or as low cost as industrial techniques.
There is significant interest now in insects as human food because of their greater conversion of feed. However, in a catastrophe, feeding insects human edible food is not very valuable. On the other hand, some insects can digest fiber or consume animal waste, so these would be the resilient forms of insect food.
Deep sea fish
There are roughly 10 billion tons of mesopelagic fish (200 m to 600 m or 700 feet to 2000 feet down in the ocean), enough to feed everyone for years. They are generally not economical to harvest now, but they may be in a catastrophe.
The inner bark of some trees is edible, and has been used historically as a famine food.
Shipworms are a clam that can eat wood, and it could scale up very quickly. However, the logistics of moving many logs to the ocean and retaining them would need to be worked out. Other clams might be synergistic with seaweed.
There are also many behavioral techniques that could reduce demand for food. The best options would be those that have other benefits, such as sleeping more, targeting the lower end of healthy body weight, and reducing drug consumption such as nicotine, alcohol, and caffeine. Other options include feeding food scraps to pets, reducing exercise, and raising indoor temperatures/wearing heavier clothing.