Environmental Engineering Reference
In-Depth Information
it had doubled again, and at the beginning of the twenty-i rst century, when i elds
and permanent plantations claimed about 12% of the ice-free land, the global
harvest of food, feed, and i ber crops was about 2.7 Gt. Their residues added
about 3.7 Gt and forage crops totaled about 1.2 Gt, for a global total of about 7.6
Gt of herbaceous aboveground phytomass. Roughly half of this phytomass (4 Gt)
was fed to animals and produced (all values as fresh weight) nearly 300 Mt of
meat, almost 700 Mt of milk, and 65 Mt of eggs. And annual harvests of woody
phytomass—including fuelwood, industrial roundwood, and pulpwood, as well as
biomass directly destroyed, disturbed, or abandoned during harvesting—reached
at least 13 Gt of dry matter by the year 2000.
During the i rst decade of the twenty-i rst century the annual harvest (and direct
destruction) of terrestrial phytomass thus added up to roughly 20 Gt of dry matter,
or about 10 Gt C; this translates to nearly 17% of the biosphere's annual terrestrial
NPP when assuming the standard rate of 60 Gt C/year, and to a bit more than 13%
when assuming a higher rate of 75 Gt C/year. And while the stocks of many aquatic
species have been seriously depleted, the relative impact of i sheries and aquaculture
on the ocean's NPP is lower than the impact of cropping and wood harvests on
the terrestrial NPP. Catches (including discards) of wild invertebrates and i sh and
aquaculture of an increasing number of these species now surpass 130 Mt (fresh
weight), or about 15 Mt C, and the production of this zoomass requires annual
intakes of nearly 3 Gt C of aquatic phytomass, or roughly 6% of the total oceanic
primary production.
Neither of these shares appears to be alarmingly high, but, as I have tried to dem-
onstrate, the “appropriation” ratio is not the best way to measure the human impact
on the biosphere because many qualitative implications and multifaceted ecosystem
and social impacts of the phytomass harvests are utterly beyond its scope. In any
case, the enormous latent demand for more phytomass associated with lifting the
more than i ve billion of people living in low-income countries closer to the standard
of living enjoyed by a minority of humans could keep raising the ratio for genera-
tions to come. There is plenty of other evidence of the enormous scope of the human
transformation of the Earth, and future interventions may be further complicated
by the unfolding climate change.
Anthropogenic Earth
Many complexities and uncertainties prevent us from developing accurate quan-
titative appraisals of the claim humans make on the biosphere's stocks and annual
