The human ecology of climate change - Climate Change: Biological and Human Aspects - page 378

the time of the Pharaohs (2780-1625 ) had a population of around three million

people, of whom 95% were engaged directly in food production, so being able to
support the remaining 5%, which consisted largely of slaves, some military and a
small aristocracy. Calculations suggest that at that time the 20-year construction of
the Cheops pyramid absorbed nearly all of this agricultural surplus. In later periods
the emphasis of support from this proportionally small agricultural surplus shifted
from slaves to the military. At other times there was little agricultural surplus and
these are known to have been times of social strife (Cottrell, 1955).
The historic period (the time since written records began) has seen a gradual
accumulation of knowledge and technical ability. This enabled there to be a sim-
ilar development of the aforementioned small agricultural surplus and so gradually
this freed more of the population for other endeavours. Virtually all these early
societies relied on (non-fossil) biological energy and as such their impact on the
biosphere's global commons was negligible: climate variation then was determined
by non-anthropogenic factors such as circulation change, solar and volcanic climate
forcing.
For thousands of years plant and animal breeding contributed hugely to the success
of early agrarian societies. Prior to the Industrial Revolution, understanding the
need to lay fields fallow and the use of animal and vegetable wastes as fertilizer
improved agricultural productivity wherever such practices were conducted. The
Industrial Revolution itself enabled agriculture to slowly become more mechanised,
so reducing the need for such a large rural workforce. It also enabled agricultural goods
to be shipped in bulk over long distances. Finally, the mid-20th-century development
of fertilizers and pesticides in the Green Revolution further increased agricultural
productivity to levels comparable with the present day.
By the end of the 20th century in industrialised countries the proportion of the
population directly employed in agriculture had become a small minority. In the UK,
which then produced nearly three-quarters of its own food, just 2% of the population
was directly employed in agriculture, contributing to about 1% of GDP (Cabinet
Office, 1994), with food processing, packaging and transport contributing an addi-
tional 2% of GDP. Allowing for the overseas contribution to current UK food supply, a
reasonable estimate for the total equivalent proportion of the UK population involved
in food production, processing and transport is 7-8%. Although this excludes retail
and catering commercial activities, it is still a dramatic contrast to the involvement
in food production of people in ancient civilisations. Today 92% or more of the pop-
ulation in many industrialised nations are free to engage in activities other than basic
food supply, which is almost a complete reverse of the situation in ancient Egypt.
What enabled this radical change from ancient to modern societies to take place
was the increased contribution made by energy. Indeed, with regards to nitrogen
fertilizer (which commonly comes in the form of urea), fossil fuel is consumed
in two ways. The first way is in the energy-intensive fixing of nitrogen from the
atmosphere. This has in the past mainly been done using energy derived from fossil
fuels, which are finite or so-called fund resources (the fund being finite). However, in
the future nitrogen fixation might be done by energy from renewable (flow resources)
and/or nuclear alternatives. Second, fossil fuel is used to provide urea's carbon content
(mainly from natural gas, methane). With regards to this last, the prospects of not

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