Wednesday, June 15, 2011

The Numbers of Sustainability: 1

I think it's time and worthwhile to start having this discussion. We may well be getting to the point where sustainability is no longer an option, and it's worth getting past the dress rehersal stage and face squarely the task in front of us. I'd appreciate discussion, feedback, and having folks check my math. There's going to be some major assumptions made here, and values attached to them. I think if they're kept transparent they work, though we can quibble about the details.

So, the question that prompts all this is this one, and I get it asked all the time: "How much land do I need to live "sustainably?" First off, I'm not sure I understand the question, as in most all cases the question comes from someone seeking the lowest possible value. In the years of teaching sailing I never met anyone, contemplating an ocean voyage, who asked "How little water can I get away with on a 2500 mile ocean passage?" Nobody asks questions like that, as it's a serious matter, and the consequences for failure are deadly--and obvious. Because people take ocean passages seriously a different kind of question is asked, much more resembling "How can I stuff as much water as possible aboard my boat?" Unfortunately, no body really takes sustainability really that seriously yet. I suggest we should, and part of the reason it's become even more pressing is precisely that fact: that no one really takes sustainability very seriously.

But let's try to put some real numbers to the "how much land do I need" question, even if without the numbers we've more or less answered it already-- you need as much land as you can personally physically manage by sustainable means. Still, it's worthwhile to put a bottom threshold to the issue. There's a lot of people making wild-ass claims about what "one can get away with." This sells seminars, and books, and offers false hope and security in the name of profit. Let's do a little better.

This is how I think about the issue.

While one can grow a lot of pounds of greens and whathaveyou in a small space, to focus on pounds of product can be very misleading. If we're interested in real sustainability, it's much more important to focus on how many "calories" of food can be produced in a given space, as that's really what we care about. One finds, once one starts to do the research, that numbers like "calories per square meter" are hard to come by from the gardening or permaculture crowd-- but you certainly can find such numbers from the biofuels industry, as, well, calories per square meter is all they're interested in. So that's where I start, and figure we'll factor in reality as we go along.

Plants aren't magical. They're organic solar panels. The energy in food comes from sunlight, and nowhere else, and the function of how many calories produced per square meter is a function of 1) how much sunlight one gets 2) how efficient the plant is at converting it to usable(edible) form.

Let's assume first, that we're growing sugar cane, which is just about the highest yield caloric plant on earth, at least not assuming algae and stuff like that. Suffice to say that most garden crops won't be anywhere as efficient in creating calories as sugar cane, nor are most gardens planted nearly as intensively as a commercial cane field but it's a great starting point to find the upper theoretical limits of reality. In doing the research, I find for industrial, completely unsustainable, NPK, mechanized cane a square meter of sugar can can produce a kilo of sugar per year. If we assume 4 calories per gram of sugar that produces 4000 calories of food a year per meter. If we take that 4000 calories and divide that by 365 days that produces 11 calories of food per day per square meter. If we assume that a large guy capable of handling cane consumes 2500 calories a day(although you'd die pretty quick living on sugar only, but it's efficient)-- you'd need 228 square meters of cane just to meet your basic calorie needs in this wholly unrealistic situation. Let's switch to square feet/acres to make it a bit easier for most of us now. 228 square meters is 2445 square feet, let's round to 2500. Now let's add some reality. Nobody is going to get close to the kinds of yields offered by cane-- if we figure we'll plant a mix of stuff one can actually eat-- so it's easy and conservative to turn that 2500 square feet into 5000. As well, it's wholly unrealistic to expect that sustainable permaculture yields will remotely approximate intensive, mechanized, NPK production--it's very easy to add yet another factor of 2. Remember, we don't want to cheat the numbers, as we plan to actually eat this stuff and survive. There's 10000 square feet of garden, realistically, and conservatively as I see it, assuming no bugs, slugs, pests, drought, pigs, screwups or neglect. An acre is 43560 square feet, so a quarter acre per person is about the absolute minimum I really see as viable, and that isn't living large, nor especially securely, and you'll not be growing fuel to cook any of this--whoops, fuel? We'll leave that out of the question for now, but it's worth noting you'll eat every stitch of what you produce, be a bit glum about that, and won't generate any income for property taxes, trips to Bali, or dental care. Or clothes for that matter.

Thoughts? All in all a half an acre for a strong couple isn't wholly unmanageable, although it's a pretty big project.

Further discussion here:

No comments: