The human ecology of climate change - Climate Change: Biological and Human Aspects - page 383

part) comes from the decay of radionuclides deep in the Earth: the Earth would have
cooled to a solid long ago if its internal heat had arisen solely from its formation,
notwithstanding the energy arising from the Moon's tidal drag. These radionuclides
were formed from supernovae and so they too have stellar origin.
Humans as a species are unique in that it appears that we learned quickly to use fire
to supplement the biological energy of our own bodies. However, for many millions
of years for this supplement to our energy we were reliant on basic biofuels such
as wood and animal oils and dung. Even so, the use to which this energy was put
was almost invariably confined to cooking, space heating and illumination, and not
motion, or information processing and transference. As discussed in the previous
section, this meant that the energy surplus which early societies had above the level
of subsistence was small and largely dependent on bio-energy in the form of the
excess food that early agrarians could provide to support others engaged in non-food
tasks. Mechanical energy was harnessed from animals, as well as wind and water,
and this made was a substantial contribution to the energy surplus enjoyed by early
agrarian H. sapiens over hunter-gatherers. The benefits of harnessing energy are
clear. This leads to two ultimate societal consequences, as I shall describe.
First, to realise these benefits there was and still is a drive to increase energy
consumption. If such consumption increases globally in an uninterrupted fashion
over time then sooner or later the magnitude of this energy surplus will affect the
biosphere's thermodynamic balance. This is inescapable. It is exactly what is hap-
pening with anthropogenic global warming from fossil fuel burning and its resultant
climate change, although - almost ironically - it is not the energy surplus itself that
is causing the problems but the thermodynamics of its chemical carriers. Prior to
this, energy-related environmental impacts existed but were not climatically signific-
ant. For instance, the early human use of wood as a fuel and construction material
impacted on ecosystems and species as woodland was cleared and replaced by fields,
but did not impact as it does today on biosphere energy flows.
Second, given clear benefits, it follows that there must be equally clear disadvant-
ages to a society that has enjoyed a certain level of energy surplus if that surplus
is reduced. We tend to think of energy crisis as a modern problem but this is not
so. Early societies were constrained by the limitations they had in harnessing and
deploying energy resources. Consider what the Egyptians would have done had their
society's surplus been 10 or 15% rather than just 5%. More recently, in 17th-century
England there was an acute shortage of fuel wood and charcoal. This led to more
than a century of iron shortage. By the late 19th century the use of wood as a major
fuel had declined to negligible levels and coal dominated. However, coal had its
limitations and, while suitable for steam locomotives, was not nearly as suitable as
liquid fossil fuel, oil, for personal transport. That fuel made a major contribution to
society's global energy budget in the 20th century.
Our species' use of energy has therefore been characterised by fuel-switching at an
ever faster rate. Aside from the various early biofuels and the early use of wind and
water, this fuel-switching is clearly seen from the advent of the Industrial Revolution
to the present day in the country where the revolution began. Figure 7.8a depicts
the proportional contribution of various fuels made to the UK's energy budget since