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

of 1,481 km. This corresponded to between 126 min and For future years, an annual average improvement
199 min of travel. The total distance for non-cruise flight in aircraft fuel efficiency of 2% was assumed, 41-43 which
phases was extracted from the predefined operational equated to a 20% reduction in CO -e emissions by 2030
2
profile. The difference between this value and (variable) and a 47% reduction by 2050. In the simulation, these
total flight distance made up the total (variable) distance reductions were defined as improvement factors for 2030
under cruise conditions. (U: 0.75 – 0.85) and 2050 (U: 0.50 – 0.60).
Total aircraft mass was calculated as the sum of The uncertainty (plausible range) in the fleet-average
operational empty weight (OEW), total onboard fuel, TTW emission factors for aircraft was assumed to be similar
passenger load, and cargo load. The total on-board fuel to that for shipping, at about ±15%. The uncertainty in the
included the fuel required for the flight itself, as well as TTW emission factor (kg CO -e/pkm or tkm) estimated by
2
extra fuel that was a legal requirement for contingency. ATEM was, therefore, modeled as a normal distribution,
A discussion with a pilot that flies the Brisbane – Melbourne that is, (N: 100% and 5%), truncated at 85% and 115%.
route suggested that fuel is typically added for 60 min of
cruise. In the simulation, the amount of extra fuel was, 2.6. Simulation of indirect emissions
therefore, computed as a function of the estimated average Indirect emissions were calculated by including upstream
fuel burn during cruise (kg/h) multiplied by a plausible factor (WTT) emissions associated with the extraction, transport,
to reflect 55 – 65 min of extra cruising (U: 0.92 and 1.08 h). refining, and distribution of fossil fuels.

Total on-board fuel was, thus, estimated as the sum 2.6.1. Sea transport
of simulated FC over the entire trip and extra fuel for
contingencies, etc. An internal check was conducted For ships, WTT emissions due to the extraction, transport,
for each simulation to confirm that the estimated total production, and distribution of fuels (e.g., heavy fuel oil,
marine distillate oils, and marine gas oils) were modeled as
on-board fuel did not exceed the maximum fuel loading
capacity of the aircraft. It varied between 35% and 60% in an energy or emissions penalty. Reviews have found that
the simulation. The simulation did not explicitly consider lifecycle assessments (LCAs) for GHG emissions from ships
44,45
the emission impacts of “tinkering” (transporting fuel for are rare. Most studies have focused on the “fuel lifecycle”
only (WTW), but together they cover a wide range of ship
other flights), but the operational Mode 1 simulation was sizes (e.g., tugs, oil tankers and very large crude carriers). They
assumed to cover this situation.
have assessed the impacts of a wide range of alternative fuels
Total passenger load was computed by multiplying the – such as liquefied natural gas (LNG), hydrogen, ammonia,
(variable) number of seats with the (variable) passenger load and methanol – and a variety of production pathways.
and (variable) passenger mass used in each simulation. The This has led to substantial variability in the overall
number of seats was simulated as a uniform distribution, WTW emissions performance and a wide range in
varying between the aircraft-specific minimum and upstream emissions. Since many of these alternatives are
maximum number of passengers (U: 140 – 180 for A320; still in the early stages of development, often with specific
U: 130 – 149 for B737). The average passenger load factor and sometimes unresolved issues (e.g., methane emissions
40
for civil Australian aircraft varies between 75% and 95%, from LNG production and LNG ships, excess nitrous oxide
and was, therefore, defined as (T: 0.75, 0.95, and 0.81). In emissions from ammonia-fuelled ships), the studies have
the simulation, the number of on-board passengers varied often been theoretical and based on several assumptions,
between 98 and 170. Passenger mass (kg, including baggage) with unclear applicability to the current (mainly fossil-
was defined as a uniform distribution (U: 90 and 100). fuelled) shipping fleet. This analysis has, therefore, focused
Cargo payload was computed differently depending on the WTW results for conventional ships using fossil
on the plane mode. In Mode 1, where the plane was fully fuels. The literature suggests that fossil fuel combustion
loaded, the payload was computed as MTOW minus OEW typically dominates WTW emissions for ships, translating
and the simulated mass of on-board fuel (i.e., mission into a TTW multiplier that varies between 1.11 and
fuel and extra fuel). In Mode 2, the total cargo mass was 1.19. 44,46-48 The multiplier was, therefore, defined as a
assumed to equal the computed total passenger load. uniform distribution (U: 1.10 and 1.20) and was applied
In the simulation, cargo payload varied between 9 t and to the ship TTW emissions to estimate WTW emissions.
26 t. For all simulations, an internal check was conducted
to confirm that the estimated total aircraft mass did not 2.6.2. Air transport
exceed the MTOW of the aircraft. It varied between 78% WTT emissions due to the extraction, transport,
and 100%. production, and distribution of jet fuel (kerosene) were

Volume 1 Issue 1 (2024) 7 doi: 10.36922/eer.3471