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

fuel and energy use for different types of main engine Eastern Australian Current, which has a broad southward
(e.g., slow/medium/high-speed diesel and gas/steam flow between Brisbane and the Bass Strait, and the current
turbine), auxiliary engines, and boilers and subsequently in the north of the Bass Strait, which has a general eastward
uses fuel-based emission factors (g/kg fuel) to estimate air flow. The speeds and directions of these currents vary
pollutant and GHG emissions (CO , CH , and N O). by location. 18,19 The distance-weighted average current
2 4 2
MTEM typically uses detailed information on ship speed for travel between Brisbane and Melbourne was
movements from high-resolution terrestrial or satellite estimated to be 0.32 m/s (0.62 knots) (or −0.32 m/s for
Automatic Identification Systems (AIS). For this analysis, Melbourne to Brisbane). The Bernoulli distribution was
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the operational inputs were simplified. The ship operation used to allocate distance-weighted current speeds to each
profile was defined in terms of two modes of operation: simulation (Table S2). The ratio of the corrected (variable)
(i) Time at berth (the vessel is moored) for cargo loading speed (speed of vessel at sea minus speed of current) to the
or unloading, and (ii) in-transit cruising conditions. Two speed of vessel at sea was, then, used to correct the travel
other modes of operation were excluded: (i) maneuvering, distance.
which typically occurs over short periods, and (ii) at The maximum cargo-carrying capacity was estimated
anchor, which has similar emissions behavior to being to be 80% of DWT for both bulk carriers and containers.
at berth (excluding the impacts of cold ironing). These The average payload was assumed to vary between 50%
exclusions would not have materially affected the results. and 70% of maximum capacity, given that bulk carriers can
The Australian Maritime Safety Authority (AMSA) regularly have empty back-hauls (U: 0.50, 0.70). 8,20,21 For
recently surveyed ship operations in Australian waters. container ships, a higher cargo utilization was assumed,
Analysis of the survey data found that the average time with the average payload varying between 60% and 80% of
spent at berth was 33 h, with a 95% confidence interval maximum capacity (U: 0.60, 0.80).
(CI) of 28 – 39 h. Time spent at berth was therefore The shipping sector relies heavily on fossil fuels, and
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approximated using a normal distribution, truncated at 28 establishing a successful decarbonization pathway for the
and 39 h (normal distribution N: 33, 3). sector has proven difficult. For future years, improvements
For transit conditions, a plausible range of speeds in energy efficiency (or emission intensity in CO -e/tkm)
2
was used to simplify the analysis, rather than a detailed for bulk carriers and container ships were derived from
analysis of AIS data. The service speed was taken as the a study by the International Maritime Organization
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maximum plausible speed. Service speed is defined as (IMO). IMO considered improvements between 2018
the speed a vessel can maintain at sea in normal weather and 2050 under a business-as-usual scenario with modest
conditions and at normal service draught. “Slow steaming” economic growth. The projections took into account
is increasingly applied in less time-sensitive shipping changes in fleet composition, the impacts of existing
operations (particularly for larger vessels) to save on fuel regulations for energy efficiency (fleet renewal, with
costs. In practice, slow-steaming vessels typically have a more efficient ship designs) and fuel, as well as market-
reduction in speed. For container ship, this changes from driven impacts. Based on the IMO report, and the base
around 20 – 30 knots to around 15 – 20 knots. The year of 2018 being close to one in this study, for both bulk
5,17
service speeds for bulk carriers are usually lower (around carriers and container ships the fleet average emission
15 knots). In this analysis, operational speeds were, intensity would decrease by 15% in 2030 (U: 0.80 – 0.90),
therefore, defined as uniform distributions, with a minima and by 25% in 2050 (U: 0.70 – 0.80), relative to 2019.
of 10 knots for bulk carriers and 15 knots for container An update of the IMO GHG strategy in 2023 defined
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ships, and maxima as the vessel-specific service speeds more ambitious targets than previous ones from 2018,
(ν ) (uniform distribution U: 10/15, ν ). including a target of net-zero emissions by 2050, but did
ss ss
The total route distance was required for the estimation not set out a pathway to achieving them.
of annual emissions. The distance was simulated as a The uncertainty (plausible range) in the FC and GHG
uniform distribution, with an assumed initial variability emission factors from MTEM was based on two recent
of between 2,200 km and 2,300 km (U: 2,200, 2,300). studies: an on-board emission testing study and a survey
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The impacts of ocean currents were also included in the commissioned by AMSA. These studies suggested that the
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simulation. In MTEM, the speed of a vessel is defined uncertainty in fleet average emission factors for Australian
relative to the water. Ocean currents effectively increase ships was ±15%. The uncertainty in the TTW emission
or decrease the total distance traveled, depending on the factor (kg/min) estimated by MTEM was, therefore,
direction of the vessel and the local currents. The two main modeled as a normal distribution (N: 100%, 5%), truncated
ocean currents that were relevant to the analysis were the at 85% and 115%.

Volume 1 Issue 1 (2024) 5 doi: 10.36922/eer.3471