well a terron (which I may or may not have invented) is one person's share of Terra.  which varies -- depending on how many other people there are, and on what kind of life  we think is an acceptable life.

if you crowd us into 100-storey arcologies (in tiny multifunctional cells or larger multiperson dormitories) so as to reclaim the maximum amount of arable land;  if we kill off every species that isn't directly useful to us (a dangerous undertaking since we have only a very poor and warped grasp of usefulness and interdependency in biotic systems) so as to redirect all photosynthetic activity on earth to feeding humans;  if we produce our food by the absolute bedrock max-efficiency methods (probably algae and fungus farming on a massive scale);  if we scrupulously recycle all our water and other materials, keep the absolute minimum amount of personal possessions each, live under an intrusive and comprehensive set of rules governing each person's behaviour and consumption of resources, etc etc -- my non-quantitative bet is that we could support more people "in comfort" than are now presently alive.

but the quality of that "comfort" is highly questionable -- how would such an existence differ from life in a prison?  the iron discipline of space-station resource management does not make for an open and free society (back to FH's insightful quote).  and the authority necessary to impose that iron discipline suggests an authoritarianism that human beings have never in history managed to implement without abuse and atrocity (another goram Milgram Experiment);  we are not as well suited as bees to living in hives with draconian resource limits.  (remember that bees kick out their surplus drones at season's end to starve, so that the life of the colony may continue -- though egalitarian and delightful creatures, bees are not sentimentalists and the life of each bee means very little compared to the bee polity which is the real organism.)

to accommodate the maximum possible number of humans on earth w/in constraints of physical reality would mean evolving into a hive organism in which individuals had very little scope for freedom, living on a planet from which we have extirpated every aspect of the natural world that makes us happy, for which we were adapted in the previous 200K years or however long it's been.  is that the future we want for our descendants?  is it consonant with our so-called Enlightenment ideals of individual liberty?

one terron might be very small in such a model. and it might be sustainable.  but is it a goal to aim for?

a slightly larger terron might yield a less oppressive and stifling culture -- one in which your neighbour is not morally obligated, as a matter of survival, to report you to the neighbourhood committee for wasting a half gallon of water, and where your diet might be more interesting, tasty, and nutritious.  a larger terron yet -- several acres per person -- could yield an idyllic lifestyle with the luxury of open space, fresh produce, eggs, and moderate amounts of grass-fed meat for everyone.

or -- and this is the traditional human pattern, replicated from the earliest agricultural era through modern capitalism, and the subject of Colman's recent gloomy prognostication -- we could concentrate resource consumption in a small elite and keep everyone else on the ragged edge of malnutrition, exposure, and related diseases or just let them go on dying in droves.  "one terron" for a planet of hyperconsuming billionaires is so much land and biotic productivity that the "one terron" left over for the lower classes is too small to live on.

so the question of what a one-person share of Terra looks like cannot be disentangled from the question of "how many of us should there be," which in turn cannot be disentangled from what lifestyle we think is "decent" or acceptable or happy, and (critically) how much inequality we are prepared to tolerate.  there are people -- I have read their published opinions and even contended with some in person -- who contemplate with equanimity the liquidation of vast numbers of poor people, rural people, indigenes, peasants, brown people, "backward" people etc, so as to "free up resources" for a far smaller number of (presumably worthier, superior) people for whom "the American Way of Life is not negotiable".  I find it hard to distinguish this from the Lebensraum justification for annexing Poland or the Conquistadores' conviction that God really meant the wealth of S America for them.

abundance -- of land, of energy, of water and food -- enables us to practise inequality in relative moral comfort and safety, because the elite (the tapeworm in my previous mini rant) can gorge itself and still leave enough over for the many to get by.  scarcity, however, brings inequality into focus:  as soon as resources are constrained it becomes very obvious that scarcity is in part created by the gorging and conspicuous waste of the few;  and the few start thinking about getting rid of the many rather than sharing.  (back to Jared Diamond).

industrial capitalism seems to be the historical trifecta.  it concentrates wealth in the hands of a tiny elite with greater speed and efficiency than any previous system of accumulation and kleptocracy;  it does so while simultaneously burning up raw materials and resources at a rate unprecedented in human history;  and its very modus operandi is predicated on the creation of scarcity, Enclosure of the commons, etc -- and perhaps worst of all, scarcity and crisis are profit opportunities for capitalists so they have no interest in preventing same, only a short-term enthusiasm for profiting off them (Halliburton, Iraq war;  NOLA, carpetbaggers and mercs;  US energy policy set by the fossil lobby).  a person's "share" of Terra doesn't mean anything in a hegemonic belief system to which the very notion of "sharing" is anathema...

what Gini coefficient is acceptable?
what minimal lifestyle is acceptable?
for how many centuries do we want our culture to persist w/o crashing?
if we have answers to these questions, then with a great deal of effort and some uncertainty we can answer the question of what a terron is, which in turn will offer an answer to "how many of us should there be?"

one thing I know for certain -- as a technogeek and as a simple primate -- is that infinite growth is a fantasy, and therefore the mainspring of faith that drives our culture is irremediably broken.  climax ecosystems are stable;  runaway proliferation of any one species dooms that species and many others in the web around it.

another thing I know for fairly certain is that complex biotic systems (like a farm, a forest, or humanity) cannot be micromanaged and controlled with precision.  they can only be encouraged and discouraged -- more like steering a boat than like carpentry, as I think someone once said?  we already know many of the factors that encourage lower family size, greater equality, better public health:  we have working models for many encouraging guidance signals.  women's emancipation, universal literacy and freedom of communication; suppression of monopolies and encouragement of micro and regional commerce;  land reform;  sustainable agriculture;  least-toxic manufacturing;  prioritising public transit over private autos;  human-scale urban design;  participatory democratic institutions, devolving authority to the most local level possible;  the powerful notion of "human rights";  wealth redistribution via taxation or periodic "jubilee years"; and so on.  we have an extensive menu of excellent 'steering mechanisms' that tend towards lower family sizes, lower resource consumption, better public health and longevity, less violence, and happier people.

and all of them, without exception, are antithetical to maximum profit-taking.

we do seem to be in the Greenland Colony Predicament;  in order to survive and thrive we have to change the foundational assumptions of our culture.   can it be done?

The difference between theory and practise in practise ...