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Explora: Environment
and Resource WTW emissions of road, rail, sea, and air transport

similarly modeled as an energy/emission penalty. Studies study 1.13 for 2030 and 1.43 for 2050), giving 4,077,605
3 (
have shown that WTT emissions for aircraft are quite passengers/year in 2030 and 5,160,155 passengers/year in
variable, and depend on the carbon intensity of crude oil 2050. For freight transport, the total two-way activity for
59
production, refinery configurations, and the country share the route was estimated from ARTC to 3,889,600 t/year
of imported jet fuel (e.g., transportation distance). 49-51 in 2019 and 2030 and 6,406,400 t/year in 2050.
These studies suggested a TTW multiplier varying from
1.05 to 1.55, and a specific multiplier for Australia of 3. Results and discussion
1.25. The multiplier was, therefore, defined as a normal The emission intensity results for sea and air transport
51
distribution (N: 1.25 and 0.02), truncated at 1.20 and 1.30. are presented in Sections 3.1 and 3.2, respectively. Section
This factor was applied to the aircraft TTW emissions to 3.3 then compares the probabilistic assessment of the
estimate WTW emissions. emissions performance of all transport modes. Section 3.4
The simulation also accounted for uncertain, but considers the potential impacts on annual emissions of a
probably significant, non-CO climate effects, which were shift of activity between modes, and Section 3.5 places the
2
specific to air transport and did not apply to land or sea results in an international context.
transport. These effects include the formation of contrails 3.1. Sea transport
(condensation trails), aircraft-induced clouds (AIC),
and ozone formation (secondary air pollutants), which, The total TTW FC for each freight journey by sea
on balance, appear to increase net radiative forcing (RF) depended on a range of simulated variables (e.g., ship
of aircraft GHG emissions. 52-57 This additional effect is specifications, berth time, travel distance, speed of travel
uncertain and depends on geographic location, altitude, including impacts of currents, and total cargo load), each
and time of year. However, evidence suggests that there with its own uncertainty and variability. Figure 2 shows the
will be an effect, and so excluding these impacts altogether MTEM predictions for the route, normalized for distance.
would have created unrealistic results for air transport The data points show the variability and uncertainty in fuel
(i.e., the error of omission would have been larger than use performance due to variability in operating conditions,
the error of commission). It has therefore been assumed as well as vessel type and vessel size. In the case of 4,500
that additional non-CO effects could be described with TEU container ships, the data formed two distinct groups
2
a (variable) non-CO impact multiplier to total simulated as a result of the sampled vessel specifications.
2
CO emissions from aircraft, which was quantified as a The MTEM FC predictions for the route varied between
2
triangular distribution (T: 1.0, 2.5, and 2.0) with a mean 46 and 219 t (of fuel) for bulk carriers, and between 82 and
value of 1.8. 514 t for container ships. Stationary (at berth) conditions
contributed significantly to total trip emissions: 2 – 9%
2.7. Annualization
for bulk carriers, and 2 – 23% for container ships. Large
In the probabilistic analysis, all distributions were contributions from stationary operation to total trip FC
combined. Common inputs for different transport occur where vessels are slow steaming and sea currents
modes and transport units were passed on during the full reduce overall travel distance (with lower emissions in
6
simulation (n = 10 ) to ensure valid and internally consistent transit), whereas smaller contributions occur at higher
results. Total annual emissions were determined for each speeds and vessels moving against the currents (with
transport unit, taking into account the corresponding higher emissions in transit). In this simulation, currents
travel distance (discussed in the previous sections) and reduced or increased FC by about 2 – 4% for container
activity (this section). ships and 4 – 6% for bulk carriers, with larger (relative)
It should be noted that, for each mode, annualized impacts being associated with lower travel speeds.
emissions were calculated on the basis that the mode The WTW emission intensity distributions for sea
would be responsible for all the transport activity between freight transport between Brisbane and Melbourne (or vice
Brisbane and Melbourne (i.e., there was no distribution of versa) are summarized in Table S5 and shown in Figure S1. As
activity across the modes). For passenger air transport, the noted earlier, these combine operational (TTW) emissions
annual activity was based on statistics for air travel between and the upstream (WTT) emissions from the production of
the two cities. The total two-way activity between the two marine fuel. The average emission intensities for container
58
cities was taken to be 3,608,500 passengers/year in 2019. ships (9 – 16 g CO -e/tkm, depending on the year) were
2
For future years, it was assumed that growth in passenger approximately twice as high as those for bulk carriers (4 – 8 g
air transport aligned with the growth rate estimated CO -e/tkm). For both types of ship, the emission intensity
2
for Australian passenger road vehicles in Part I of the approximately halved between 2019 and 2050.

Volume 1 Issue 1 (2024) 8 doi: 10.36922/eer.3471