Environmental Engineering Reference
In-Depth Information
11
Harvesting the Biosphere
In an attempt to quantify what clearly appeared to be a disproportionate share of
the Earth's photosynthetic production that is claimed (directly and indirectly) by its
most sapient species, Vitousek et al. (1986) chose net primary productivity (NPP)
as the baseline and expressed the overall effect of harvests and modii cations as
the fraction of NPP appropriated by humans. A very wide range of possible appro-
priations offered by that paper—from as little as 3% for their low calculation to as
much as 40% for their high estimate—made its use for any heuristic purposes, and
even more so for any policymaking purposes, rather questionable.
But this did not prevent the authors from concluding “that organic material
equivalent to about 40% of the present net primary production in terrestrial eco-
system is being co-opted by human beings each year” (Vitousek et al. 1986, 372).
In 1990 a new assessment concluded that humans divert for their own uses biomass
energy l ows amounting to 23.5% of the biosphere's potential NPP (Wright 1990).
No new i ndings were published during the 1990s, and the next decade brought
three new assessments of the human appropriation of the global net primary pro-
duction (HANPP became yet another awkward acronym), the i rst by an American
trio (Rojstaczer, Sterling, and Moore 2001), the second by a larger American team
(Imhoff et al. 2004a), and the third by a group of Austrian researchers (Haberl
et al. 2007).
I will i rst review the key i ndings of all these HANPP studies and show how
different assumptions and different choices among many uncertain totals available
for key stores and l uxes can result in very different outcomes. In order to judge the
degree of human impacts on the global environment, it is highly desirable to quantify
our biomass harvests and compare them with the best estimate of the biosphere's
productivity. At the same time, we must be aware that this is very much a work in
progress: while it would be an exaggeration to say that such studies can produce
