It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Wednesday, February 13, 2008

Globally Sustainable Population and Food

Looks like I poked a sleeping dragon in a passing swipe about the scalability of organic agriculture in an article yesterday.

I'm not sure I'm the right person to lead this conversation, but I'd frame it as "how many people can the earth support indefinitely?"

To make this tractable I begin by making several classes of assumption about diet. So what happens with an American (meat and processed foods) diet adopted universally? A Japanese (wild-caught fish) diet? An Indian (mostly legumes and rice) diet? An organic green-yuppie diet?

Orthogonally, we should consider two cases: energy limited vs. energy abundant.

Then I'd consider the global geochemistry of agriculture. We would need to trace the mass budgets of various elements, as well as fresh water. There may be other terms e.g. representing soil health and erosion.

My guess is that without energy abundance the world is already severely overpopulated. It's not an especially well-informed guess.

I presume there are whole-systems studies of this sort and would welcome any references. I don 't feel especially competent to take this on, but then again I don't have a horse in the race.

Which side of ten billion that number lies is a pretty crucial determinant of our prospects.

I've misplaced my copy of Joel Cohen's book "How Many People Can The Earth Support" which is an admirable place to start.


gravityloss said...

One related idea is the Human Appropriated Net Primary Production or HANPP. Count nature's carbon flows and look at how much humans consume of that.

Marc Imhoff (from NASA) et al published a paper about that in Nature in 2004, that's when I first read about it.
I can't seem to find the article download link now. Anyway, it was a nice conclusion and freely available at one time so it is in public domain, I can send it if you want.

Basically, South America is the best off, Africa next, North America then and Europe and Southeast Asia are using practically everything that the local part of the biosphere produces, something close to 70% or so was estimated.

David B. Benson said...

On the other hand, the researchers in The Netherlands looking at the bioenergy potential of the globe have concluded that over 1500 exajoules per year can be obtained from biomass production, this after enough land for food, fiber and animal feed.

As humans currently consume about 420 exajoules per year from all energy sources, that is a lot of carbon potential!

They rate Africa's potential as first, followed by South America and then Southeast Asia. Obviously, the estimators do not all agree...

tidal said...

This is certainly not my area of expertise, but I will toss some references/factoids out, and look forward to seeing other more authoritative contributions...

E.O. Wilson, in the "Future of Life" claims as follows: "We already appropriate 40 per cent of the planet's organic matter produced by green plants. If everyone agreed to become vegetarian, leaving little or nothing for livestock, the present 1.4 billion hectares of arable land (3.5 billion acres) would support about 10 billion people. If humans utilized as food all of the energy captured by plant photosynthesis on land and sea - some 40 trillion watts - the planet could support about 17 billion people." So that seems to certainly put some upper bounds on the capacity (although, frustratingly, Wilson does not provide references, and when he refers to "energy" from photosynthesis and then quantifies in "watts" he is is mixing up a "power" measurement and comparing to an "energy" requirement (e.g. calories, joules, etc.) which is needlessly confusing...).

A little more structured and referenced, John Holdren's Presidential Address to the AAAS last year (but published this month) - Science and Technology for Sustainable Well-Being, specifically pages 3-5 of the pdf (Land, Water and Terrestial Biota; Oceans) and various of the references. The paper he references on HANPP (human appropriation of net primary production) by Haberl et al is here, and quite good. I really recommend Dr. Holdren's paper as a concise, well-referenced overview of current environmental and energy issues...

By the way, just regarding your "high energy" versus "low energy" scenarios... this isn't really germane to this discussion, but Leach, in Energy and Food Production (1976?) actually showed that from strictly an "energy in versus energy out" ratio (energy measured in Megajoules/hectare/year), pre-industrial agriculture averaged about a 41.1x payback, whereas industrial agriculture averaged only 1.3x... The real payback for industrial agriculture is freeing up human labour (and, I am presuming, expanding the total viable agricultural land...). I can't vouch for those numbers (they are cited in Common & Stagl, Ecological Economics, 2005) but I was quite astonished by the energy payback numbers... As far as I know, this is not the kind of agriculture that Monbiot and others are talking about when they refer to "organic", but still interesting... Again from an "energy" perspective though, the same Leach numbers indicate that of today's industrial agriculture energy requirements, roughly 18% is for fertilizer, and a whopping 46% is for irrigation... which then links back to the commentary in Holdren's article about limits on our freshwater usage - we are already at ~40% of total potential...

I will also put in another short plug for Vaclav Smil's new book Energy in Nature and Society: General Energetics of Complex Systems... I don't have it with me here, but I suspect it has an interesting discussion and references on the topic at hand...

Or, on the other hand, we could just go with the truly unbridled optimism of late Julian Simon of the Cato Institute, who said in 1995: "Technology exists now to produce in virtually inexhaustable quantities just about all the products made by nature - foodstuffs, oil, even pearls and diamonds... We have in our hands now - actually in our libraries - the technology to feed, clothe and supply energy to an ever-growing population for the next 7 billion years... Even if no new knowledge were ever gained... we would be able to go on increasing our population forever...". Well alrighty then! Let's compound 6.7 billion present population with 1% growth for 7 billion years... er, um, er... Maybe we should stick to the HANPP methodology or something similar instead...

Hope that there are useful pointers there. Like I said, I am more interested in hearing what/where others suggest.

Michael Tobis said...

David, have you got a reference or a link?

Michael Tobis said...

Tidal; that it's as much as 1.3x isn't obvious; EROEI on agriculture can be less than one and probably is in some cases (highly processed corn-fed beef...?). In such cases we are literally dining on fossil fuel.

Thanks for the links!

Dano said...

Polyface Farms is one of those places that show how its done. It just requires learning, knowledge, and paying attention.

Problem is, most Murricans have passed off these burdens to 10 or so corporations who are all too willing to pick up that slack. Michael Pollan is a good read for this issue, and this interview on SciFri helps us understand too.



Michael Tobis said...

Cuba as an example is not a very strong constraint. Primary productivity is very high combined with most of the world.

As an additional complication footprint is very low mostly because people are a lot poorer than in the west. That is a very hard sell; people in the west are not interested in living like Cubans.

Also, arguments that organic farming are good for individual farmers don't interest me very much, not being much of a farmer myself. That is a local view.

My question is how many people the world can support, which is a global question.

As with many other complex questions, it's difficult for someone not closely involved to figure out what the active constraints really are and how to model the whole system.

David B. Benson said...

Here is a good link for a web page regarding estimates of bioenergy potential:

Estimates of bioenergy potential around the world