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.HOW CLOSE TO PRACTICAL LIMITS?
."There is accumulating evidence that humanity my soon have to
.confront the real carrying capacity constraints.  For example, nearly
.40% of terrestrial net primary productivity (photosynthesis) is
.already being used ('appropriated') by humans, one species among
.millions, and this fraction is steadily increasing (Vitousek et al.
.1986).  If we take this percentage as an index of the human carrying
.capacity of the earth and assume that a growing economy could come to
.appropriate 80% of photosynthetic production before destroying the
.functional integrity of the ecosphere, the earth will effectively go
.from half to completely full within the next doubling period --
.currently about 35 years (Daly 1991).
.
."The significance of this unprecedented convergence of economic scale
.with that of the ecosphere is not generally appreciated in the
.current debate on sustainable development.  Because the human impact
.on critical functions of the ecosphere is not uniform 'effective
.fullness' may actually occur may actually occur well before the next
.doubling of human activity.  (Liebig's law reminds us that is takes
.only a single critical limiting factor to constrain the entire
.system.)  Indeed, data presented in this chapter suggests that
.long-term human carrying capacity may already have been at less than
.the present 40% preemption of photosynthesis. If so, even current
.consumption (throughput) cannot be sustained indefinitely, and
.further material growth can be purchased only with accelerated
.depletion of remaining natural capital stocks.
.
."This conundrum can be illustrated another way by extrapolation from
.our ecological footprint data.  If the entire world population of 5.6
.billion were to use productive land at the rate of our
.Vancouver/Lower Fraser Valley example, the total requirement would be
.28.5 billion ha.  In fact, the total land area of Earth is only just
.over 13 billion ha, of which only 8.8 billion ha is productive
.cropland, pasture, or forest.  The immediate implications are
.two-fold:  first, as already stressed, the citizens of wealthy
.industrial countries unconsciously appropriate far more than their
.share of global carrying capacity;  second, we would require an
.additional 'two Earths,' assuming present technology and efficiency
.levels, to provide for the present world population at Canadian's
.ecological standard of living.  In short, there may simply not be
.enough natural capital around to satisfy current development
.assumptions.  The difference between the anticipated ecological
.footprint of the human enterprise and the available land/natural
.capital base is a measure 'sustainability gap' confronting
.humankind." [p. 383]
.
.A CAUTIONARY NOTE
."We admittedly make no allowance for potentially large efficiency
.gains or technological advances.  Even at carrying capacity, further
.economic growth is possible (but not necessarily desirable) if
.resource consumption and waste production continue to decline per
.unit GDP (Jacobs 1991).  We should not, however, rely exclusively on
.this conventional rationale.  New technologies require decades to
.achieve the market penetration needed to significantly influence
.negative ecological trends.  Moreover,there is no assurance that
.savings will not simply be directed into alternative forms of
.consumption.  Efficiency improvements may actually increase rather
.than decrease resource consumption (Saunders 1992).  We are already
.the limit in a world of rising material expectations in which the
.human population is increasing by 94 million people per year.  The
.minimal food-land requirements alone each year for this number of new
.people is 18,800,000 ha (at 5 people/ha, the current average
.productivity of world agriculture) -- the equivalent of all cropland
.in France." [p. 386]
.
.      INVESTING IN NATURAL CAPITAL - 1994 - Island Press
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Aloha,
Jay