An Omnivorous Gigatonnage

Well, shit. So after getting a teeny tiny bit of feedback about my last post I decided to try my hand at estimating the global carrying capacity K for humans.

I decided to see if I could plug in numbers to the formula I supplied there. And for the record it’s on the left.

Anyway, here goes…

For F, the amount of energy a person needs to live and make babies, I used the 2000 Calorie/day number I always read and hear. Why not. I then converted that to kilojoules because I like kilojoules, ok? I don’t know why. (And by the way, “Calories” with a capital “C” is not “calories” with a lower case “c”, it is actually “kilocalories”. Jesus fuck, I don’t wanna go into that foolishness right now.)

So F = 8368 kj/day. I multiplied this by 365 days and got

F ≈ 3.1×10⁶ (3.1 million) kj for a person for a year.

For R, the supply of resources, I turned to a recent paper titled The biomass distribution on Earth. The authors of this paper estimate that today there is

• 10 Gt C (gigatons of carbon) of vegetable crops,
• 0.1 Gt C of livestock, and like,
• 0.005 Gt C of chickens, basically.

Meat and veggies. However, considering  some of the meat (livestock) consumes maybe 30% of the veggies, then we get 7 Gt C.

I also include shrimp and flounder to the diet. But in case you are wondering the authors estimate

• 1 Gt C for marine arthropods and
• 0.7 Gt C of fish.

Given we’ll pretty much eat anything and that all those sources are viable, then add ‘em up and convert to my irrational love of kilojoules and we get

R ≈ 3.68×10¹⁶ kj of resources available to everybody this year.

This is where things get tricky.

To get α, the regulating factor coefficient, I just took the number of human biomass and added the wild large mammal biomass. If we consider that arable land is for both us and livestock, than large mammals take away from that food supply. Considering that pests are of course always a problem, we still have ways to mitigate the effect of pests, but other large mammals take the land. The land gives us the crops and livestock range. This number for wild large mammals is 0.003 Gt C.

I include us relative to, well, us because we also contend with each other for resources. That is, we would also be regulating our own consumption of these estimated amounts of biomass and so adding 0.06 Gt C and 0.003 Gt C and dividing by 0.06 Gt C gives an α of 1.05. Or

α = (0.06+0.003)/0.06 = 0.063/0.06 = 1.05.

But it could be generalized as

1+∑B/0.06

where ∑B is just the sum of the various biomass estimates of different parts of the biological part of Earth that have a regulating effect on human population size that one could include. But adding any more increases α and lowers K.

I would include large marine mammals (0.004 Gt C) here but overhunting has greatly reduced their numbers, and besides, they seem to only make marine ecosystems richer in biomass we would benefit from by improving the ecosystems they’re members of.

I don’t know if this is the best approach to the problem, but if one simply considers a range of values but trusts and keeps the energy estimates I have made for R and F intact (ceteris paribus), one might be able to say something about it and then go back to some of the estimates to justify their use or disuse. But me, I just use a cut off.

To support 7.7 billion people on Earth today given the R and F estimates provided here, α = 1.019. Clearly then, the estimate I got for α = 1.05 is too high to support that. Including an α of 1.05 estimates Earth’s carrying capacity at

K = 3.39×10⁹ (3.39 billion) people.

Oops. Sure hope I’m way off. But, again, adding any more regulating factors will only reduce the size of K. So maybe I should cut away from the wild large mammal estimate. But where and how do I do that in a way that seems reasonable? Maybe this estimate is reasonable and we’re fucked. That, unfortunately, seems possible.

According to E.O. Wilson (who’s probably pulling from mathematician Joel Cohen on this one), Earth could support 10 billion people if we all became vegetarian. But the same amount of food for omnivores would only support 2.5 billion. So my admittedly omnivorous estimate is somewhere in between.  Estimates have ranged extremely widely so there’s that too. Additionally, there are recent concerns about what current agricultural practices on Earth today can support.

Still, if we are beholden to no one but ourselves where α = 1, then it’s just R/F and

K = 11.9×10⁹ (11.9 billion) people.

And that ain’t bad. Right? If we come to 10 billion by 2050 and 11.2 billion by 2100, then we have a little time, I suppose…to raise the carrying capacity again…

Anyway, concepts and numbers being what they are, I think using a term like α is probably the most suspect thing here. It clearly has me hand waving a lot about things I’m not really comfortable thinking mean much of anything.

It is what it is.