Environmental Engineering Reference
In-Depth Information
12
Long-Term Trends and Possible Worlds
Our species has evolved to become the planet's dominant heterotroph in what has
been (when measured on the biospheric time scale of more than three billion
years) a very brief period of time. Less than 2.5 million years have elapsed since the
emergence of our genus (with
Homo habilis
), our species became identii able about
200,000 years ago, and shortly after the end of the last glaciation (less than 10,000
years ago) various societies began to move from subsistence foraging to settled
existence energized by harvesting cultivated plants and domesticating animals. After-
ward our capacities for expansion, extraction, production, and destruction began
to grow rapidly with the emergence of the i rst complex civilizations.
After millennia of slow gains during the Pleistocene and the early part of the
Holocene, global population began to multiply as humans commanded increasing
l ows of energy and potentiated their impacts, thanks to many technical and social
innovations that improved the quality of life, whether it is measured in physical
terms (a much greater average life expectancy) or in economic accomplishments (per
capita economic product or average disposable income). Reconstructions of all of
these fundamental long-term trends are uncertain but are good enough to capture
the magnitude of specii c advances and their relentless growth (table 12.1).
Five thousand years ago, when the i rst complex civilizations began to leave
written records, there were, most likely, fewer than 20 million people; at the begin-
ning of the Common Era the total was about 200 million; a millennium later it rose
to about 300 million; in 1500, at the onset of the early modern era, it was still less
than 500 million. The billion mark was passed shortly after 1800. In 1900 the total
was about 1.6 billion, in 1950 2.5 billion, in 2000 6.1 billion, and in 2012 it sur-
passed 7 billion. Consequently, there has been a 350-fold increase in 5,000 years,
more than a 20-fold gain during the last millennium, and roughly a quadrupling
between 1900 and 2010.
