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Chapter 5 | Projection and estimation uncertainties
The separate modal contributions to full fuel cycle estimates (of total sectoral
emissions across all major transport utilisation) are displayed in Figure 5.6 for
domestic civil transport and in Figure 5.7 for total transport to, from and within
Australia (based on the aggregate values given in Table 5.2, where modal time series
are provided in Appendix Tables A30 to A32).
Total greenhouse gas emissions from transport
The estimates in Table 5.2, and Figures 5.6 and 5.7, present a comprehensive accounting
of the majority of greenhouse gas emissions due to energy use by Australian transport.
As discussed previously, the net climatic effects of transport-related aerosols (such
as black carbon from particulate emissions and sulphates from SO x
emissions) are
not included in these values and their inclusion would probably contribute some
additional radiative forcing (see Figure 5.10 for a rough estimation of the possible
scale of the net warming contribution due to vehicle emissions of black carbon and
sulphates).
Yet, even with a full accounting of the radiative contribution due to transport fuel use,
there remains one major source of transport-related greenhouse gas emissions still to
be considered: halocarbon releases from motor vehicle airconditioning systems and
from refrigerated transport. Vehicle airconditioning emissions form one of the main
components of the ‘Industrial processes’ sector within the NGGI—and similarly to
the previous section, which re-allocated stationary energy emissions to appropriate
end uses, this section presents estimates of aggregate transport emissions after reallocating
the halocarbon emissions due to transport activities.
Previous BITRE studies have attempted to include transport-related halocarbon
emissions in aggregate sectoral (CO 2
equivalent) estimates—e.g. see, for example,
BTCE (1995a, Chapter 1)—but the accuracy of these initial calculations was limited by
a lack of data on halocarbon release rates. A suitable quantification of such fugitive
releases from transport vehicle air conditioners is now possible due to another detailed
study commissioned by the AGO: Inventories and Projections of Ozone Depleting
and Synthetic Greenhouse Gases used in Montreal Protocol Industries (Burnbank
Consulting 2002), which estimates time series, by industry, for releases of synthetic
gases, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs),
halons, methyl bromide, hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs).
Halocarbon emissions from motor vehicle airconditioning systems arise from
the initial charging of the units with refrigerant, leakage of the refrigerant during
operation, losses during servicing or system replacement, and venting on vehicle or
system disposal. Until 1994, airconditioning units used in Australian motor vehicles
were primarily charged with the ozone-depleting chloroflurocarbon CFC-12 and
since chlorofluorocarbons also happen to be very potent greenhouse gases, CFC
leakage was one of the largest contributors to aggregate greenhouse gas emissions
from Australian transport throughout the 1980s and 1990s.
Since the gradual phase out of CFC production from 1995 onwards (under the
provisions of the Montreal Protocol on Substances that Deplete the Ozone Layer),
use of the synthetic gas HFC-134a has grown rapidly. Not only were most new vehicle
airconditioners then charged with HFC-134a, but subsequent retrofits of systems on
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