Environmental Engineering Reference
In-Depth Information
biomass in 1900: the global anthropomass thus more than quadrupled during the
course of the twentieth century. What is much more surprising is the extent to which
the anthropomass and, even more so, the domesticated zoomass increased when
compared not only to the zoomass of wild vertebrates but even to the much more
abundant zoomass of soil invertebrates, whose activities maintain productive agri-
cultural soils.
Even the largest wild terrestrial vertebrates now have an aggregate zoomass that
is only a small fraction of the global anthropomass. The pitiful remnants of once
enormous herds of bison, America's largest surviving megaherbivore, now add
up only to about 40,000 t C (fewer than 400,000 animals, with an average body
mass of 500 kg and a water content of 55%), an equivalent of the anthropomass
of a city of four million people. The latest count of African elephants estimated
470,000 individuals in 2006 (see box 7.3): with an average body mass of 2.6 t
per individual, this equals only about 1.2 Mt of live weight and (at 55% water
and 45% C in dry matter) only about 250,000 t C, equivalent to about 0.5% of
the global anthropomass. Given this huge disparity, it also seems very likely that
today's anthropomass exceeds the global biomass of any other extinct large ver-
tebrate with which our species shared the biosphere (it is unlikely that the peak
mammoth zoomass would have been more than 200 times larger than today's
global elephant biomass).
And even a liberal estimate of the total zoomass of wild terrestrial mammals at
the beginning and end of the twentieth century—assuming averages of 1 kg/ha
in croplands, 2 kg/ha in low-productivity ecosystems (in both cases dominated by
rodents), and 5 kg/ha (dominated by large herbivores) in the richest grasslands and
forests, and using the relevant historical land cover data (HYDE 2011)—yields no
more than about 40 Mt of live weight (about 8 Mt C) in 1900 and 25 Mt of live
weight (about 5 Mt C) in the year 2000, a decline of 35%-40%. In contrast, during
the same time period the global anthropomass rose from roughly 13 Mt C to 55
Mt C. This means that the global anthropomass surpassed the mammalian terrestrial
zoomass sometime during the i rst half of the nineteenth century, by 1900 it was at
least 50% higher—and by the year 2000 the zoomass of all land mammals was only
about a tenth of the global anthropomass (see table 12.2)!
In contrast, Barnosky (2008) concluded that the human biomass had already
surpassed the global megafaunal zoomass about 3,000 year ago, and that in recent
years anthropomass was about 80 times greater than the mass of nonhuman mega-
fuana (all of his comparisons were in terms of live weight). His conclusions are
based on two indefensible assumptions. First, Barnosky assumes that the megafaunal
