Environmental Engineering Reference
In-Depth Information
In December 1990, the
Galileo
spacecraft came as close as 960 km to the Earth's
surface in order to get a gravitational assist from the planet on its way to Jupiter. This
l yby was used by Sagan et al. (1993) as an experiment in the remote detection of life
on Earth: just imagine that the spacecraft, equipped with assorted detection devices,
belonged to another civilization, and registers what its beings could sense. The three
phenomena indicating that this planet was very different from all others in its star
system were a widespread distribution of a pigment, with a sharp absorption edge in
the red part of the visible spectrum; an abundance of molecular oxygen in the Earth's
atmosphere; and the broadcast of narrow-band, pulsed, amplitude-modulated signals.
The light-harvesting pigment absorbing in red light is chlorophyll, a key enabling
agent of photosynthesis, the planet's dei ning energy conversion mechanism, which
releases oxygen and produces an astonishing variety of biomass, directly as plants and
indirectly as the energizer of all nonphotosynthesizing organisms, from the simplest
heterotrophic bacteria to humans, the species that began, at the turn of the twentieth
century, sending modulated signals into space as yet another demonstration of its
mental prowess. These realities circumscribe and dei ne the subject of this topic: there
would be no story of human evolution and advancing civilization without a parallel
story of harvesting the biomass, and the increasing intensity and extent of biomass
harvests are in turn changing the very foundations of civilization's well-being.
Human harvesting of the biosphere has transformed landscapes on vast scales,
altered the radiative properties of the planet, impoverished as well as improved soils,
reduced biodiversity as it exterminated many species and drove others to a marginal
existence, affected water supply and nutrient cycling, released trace gases and par-
ticulates into the atmosphere, and played an important role in climate change. These
harvests started with our hominin ancestors hundreds of thousands of years ago,
intensii ed during the era of Pleistocene hunters, assumed entirely new forms with
the adoption of sedentary lifeways, and during the past two centuries transformed
into global endeavors of unprecedented scale and intensity.
The story of biomass harvests spans all of human evolution and all of our history,
and its continuation will be a key determinant of our future success or failure as a
civilization. And yet, comprehensive inquiries into this complex harvesting process
are of surprisingly recent origin (only a few decades old), and interest still remains
heavily tilted toward particulars rather than toward a global examination of this
now planetwide transformation. But an important chore must be taken care of
before I proceed. The careless or vague use of undei ned (or poorly dei ned) terms
is all too common in modern scientii c discourse. While putting in place a fairly
comprehensive foundation of accurate dei nitions of many relevant variables is not
a captivating way to start a topic, for the sake of clarity I will briel y do just that.
