Page 143 - Materials Chemistry, Second Edition

Life Cycle Assessment: Principles, Practice and Prospects
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While forests and tree planting are almost universally lauded for their positive impacts on
species diversity, carbon capture and climate regulation, a life cycle perspective is still required
to look at the systemic issues involved in increasing forests and tree planting. Young forestry
trees in particular consume large quantities of water. This potentially reduces water flows to
both surface and groundwater systems, depending on local conditions. As many areas in the
world are expected to become water-stressed due to climate change, increased forestry for
sequestration could reduce water available for other uses, including environmental flows. The
National Water Initiative (Council of Australian Governments 2005) indentified large-scale
forestry as having the potential to intercept large volumes of surface and groundwater flows.
This will affect both economic and environmental uses of downstream water flows from such
projects. This issue is being incorporated only recently into some planning for tree planting for
carbon capture.
Similarly, land planted for carbon sequestration means it is not available for other uses.
This may reduce greenhouse gas emissions (e.g. when the carbon content of soil is increased
due to a change from agriculture to forestry). However, it may also mean that a monoculture
of a single tree species is created in place of a previously rich ecosystem of multiple species,
thus reducing biodiversity.
Notwithstanding the uncertainties and difficulties associated with assessment of the
relative value of different forests as carbon sinks, both LCA and greenhouse standards are
being applied successfully. For example, Greenfleet, a relatively long-established not-for-
profit provider of offsets specifically aimed at fossil-based transport users and providers, is
certified under the Greenhouse Friendly™ scheme in Australia (see above) to provide high-
quality abatement offsets.

10.3 Low carbon energy: LCA and biomass technologies
Biomass energy technologies being developed are invariably intended to substitute for existing
fossil fuel-based energy systems (Fig. 10.2). Biomass technologies may be simpler and more
reliable options than other offsets in particular because the timeframe involved in achieving
the abatement is essentially the time up to harvest and utilisation. Indeed, the burning of
biomass as a substitute for the burning of fossil fuels is widely advocated as a method to reduce
greenhouse gas emissions. However, there are a range of concerns about biofuels and other
biomass energy products. For example, they invariably involve fossil fuel consumption in their
production and processing and also often require land that could otherwise be used for food
production or maintained as biodiversity reserves.
Clearly, it is a mistake to assume that burning biomass is always greenhouse-neutral or
desirable just because carbon dioxide emissions from burning biomass are biogenic and part of
the short-term carbon cycle. Although it is true that carbon dioxide emitted in burning is
originally sequestered from the atmosphere when the biomass grows, and therefore overall no
net carbon dioxide emissions occur, there are other greenhouse gases emitted from biomass
energy technologies.
The IPCC considers that biogenic emissions do not add to global greenhouse gas emissions,
and they are therefore not taken into account in most regulatory and accounting schemes.
There is, however, uncertainty in determining the savings achievable by substituting biomass
for fossil fuels. This is an important consideration in the context of an emissions trading
scheme, where a reduction in carbon dioxide emissions results in monetary benefits. The fol-
lowing case study illustrates some issues associated with calculating reduction in carbon
dioxide emissions associated with biomass substitution in energy generation. Similar discus-
sion points are relevant for any biomass substitution scenario.

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