The human ecology of climate change - Climate Change: Biological and Human Aspects - page 439

contribute net greenhouse emissions from climate change.) While biomass could the-
oretically make a major contribution to offsetting fossil fuel consumption it is more
likely to be used to meet chemical feedstock demand as oil becomes more expensive,
especially as there are competing land pressures for food production. It has been calcu-
lated that if, for example, the USA were to displace 10% of its car petrol consumption
with biofuel then 12% of US cropland would be required, but a further 38% would
be needed (bringing the total to nearly 50% of currently available cropland) once
the energy requirements for processing, harvesting and transportation are taken into
account (Kheshgi et al., 2000). Here the equation - the balance between land for
food and/or biofuel and/or chemical feedstock - is a complex one. The world has
already seen how in 2007-8 biofuels were a contributing factor to a world food price
increase (see section 7.4.1) and in an evermore populous world (see section 7.1.2) the
food 'opportunity cost' of biofuels will be high. Indeed, such are the energy factors
of growing, harvesting and refining biofuels that their use as fuels (to simply burn)
may be limited compared to use as chemical feedstocks. However, where high energy
content liquid fuel use has few alternatives there may be a role for biofuels. The
obvious example is aviation fuel. The complexity of the policy issues was underlined
in 2008 by a Royal Society report, Sustainable Biofuels: Prospects and Challenges ,
which warned of the need to avoid the untold consequences of solving one problem
at the expense of another.
If demand for food increases (as it almost inevitably will) and there is also pres-
sure for biofuels, then natural systems may be converted to farmland for biofuel
production. Converting forest and grassland to new cropland to replace the grain (or
cropland) diverted to biofuels could end up generating more greenhouse gas than
the reductions that are created by replacing fossil carbon with biofuel. In 2008 US
researchers Timothy Searchinger and Ralph Heimlich used a worldwide agricultural
model to estimate emissions from land-use change. They found that corn-based eth-
anol, instead of producing a 20% saving, nearly doubles greenhouse emissions over
30 years and increases greenhouse gases for 167 years.
Consequently, it is only likely that commercial biofuels could possibly make a
small but significant contribution to meeting future energy needs within an early
to mid 21st-century window of opportunity (see Table 8.2). This would be before
the preference tends to food production, unless in a minority of instances there is a
compelling case for biofuel use.
7.6 Summaryandconclusions
Human ecology is different from the ecology of any other species in that sentience
has enabled a shaping of H. sapiens ' relationships with other species. This shaping
has often been with disregard to possible ecological and environmental side effects
(anthropogenic global warming itself being just one instance). This sentient dimen-
sion to the shaping of human ecology has been enhanced since the Renaissance and the
subsequent Industrial Revolution and this in turn is reflected in the growth in human
numbers and the quantity of energy harnessed by our species, both globally and on