Endresen Et Al-2007-Journal of Geophysical Research- Atmospheres (1984-2012)

A historical reconstruction of ships’ fuel consumption and emissions

Øyvind Endresen,1 Eirik Sørgard,2 Hanna Lee Behrens,1 Per Olaf Brett,1

and Ivar S. A. Isaksen3

Received 7 June 2006; revised 10 February 2007; accepted 29 March 2007; published 16 June 2007.

[1] Shipping activity has increased considerably over the last century and currentlyrepresents a significant contribution to the global emissions of pollutants and greenhousegases. Despite this, information about the historical development of fuel consumptionand emissions is generally limited, with little data published pre-1950 and large deviationsreported for estimates covering the last 3 decades. To better understand the historicaldevelopment in ship emissions and the uncertainties associated with the estimates,we present fuel-based CO2 and SO2 emission inventories from 1925 up to 2002 andactivity-based estimates from 1970 up to 2000. The global CO2 emissions from ships in1925 have been estimated to 229 Tg (CO2), growing to about 634 Tg (CO2) in 2002. Thecorresponding SO2 emissions are about 2.5 Tg (SO2) and 8.5 Tg (SO2), respectively.Our activity-based estimates of fuel consumption from 1970 to 2000, covering alloceangoing civil ships above or equal to 100 gross tonnage (GT), are lower compared toprevious activity-based studies. We have applied a more detailed model approach,which includes variation in the demand for sea transport, as well as operational andtechnological changes of the past. This study concludes that the main reason for the largedeviations found in reported inventories is the applied number of days at sea. Moreover,our modeling indicates that the ship size and the degree of utilization of the fleet,combined with the shift to diesel engines, have been the major factors determining yearlyfuel consumption. Interestingly, the model results from around 1973 suggest that the fleetgrowth is not necessarily followed by increased fuel consumption, as technical andoperational characteristics have changed. Results from this study indicate that reportedsales over the last 3 decades seems not to be significantly underreported as previoussimplified activity-based studies have suggested. The results confirm our previouslyreported modeling estimates for year 2000. Previous activity-based studies have notconsidered ships less than 100 GT (e.g., today some 1.3 million fishing vessels), and wesuggest that this fleet could account for an important part of the total fuel consumption(�10%).

Citation: Endresen, Ø., E. Sørgard, H. L. Behrens, P. O. Brett, and I. S. A. Isaksen (2007), A historical reconstruction of ships’ fuel

consumption and emissions, J. Geophys. Res., 112, D12301, doi:10.1029/2006JD007630.

1. Introduction

[2] Over the last 100 years the total fuel consumption andemissions by the oceangoing civil world fleet has signifi-cantly increased as the fleet expanded by 72,000 motorships to a total of 88,000, with a corresponding increase intonnage from 22.4 to 558 million gross tonnage (GT)(Lloyd’s Register of Shipping, statistical tables, 1964(year 1900), and world fleet statistics and statistical tables,2000). This growth has been driven by increased demandfor passenger and cargo transport, with 300 Mt cargo

transported in 1920 [Stopford, 1997] and 5,400 Mt in2000 [Fearnleys, 2002]. There is a significant delay inbuilding up the concentrations of some of the greenhousegases (e.g., CO2) and in the climate impact. Knowledge onhow ship emissions have developed over time is required toquantify climate effects and trends, and to implementeffective regulations. Only limited information has beenpublished relatively to the historical development of fuelconsumption and emissions by the world fleet, and even forthe last 3 decades the estimates being presented differingsignificantly.[3] Smith et al. [2004] have reported an emission inven-

tory covering the period before 1950. The validity of theseestimates may be questioned as the annual coal consump-tion figures appear to be substantially lower than reported inthe literature (coal used for shipping purposes in 1915 wastaken to be only 80 Kt instead of the 80 Mt that waspublished by Annin [1920]). Eyring et al. [2005] have

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D12301, doi:10.1029/2006JD007630, 2007

1Det Norske Veritas, Høvik, Norway.2Centre of Innovation and Entrepreneurship, Bodø, Norway.3Department of Geosciences, University of Oslo, Oslo, Norway.

Copyright 2007 by the American Geophysical Union.0148-0227/07/2006JD007630

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reported simplified activity-based inventories from 1950 upto 1992. After 1992, different approaches and assumptionshave been applied to estimate global shipping emissions,but significant differences are apparent among thesereported emissions inventories. This study has thereforeestablished an historical time series of marine fuel sales tooceangoing ships from 1925 to 2002, and used a fuel-basedapproach to estimate the emissions of CO2 and SO2.[4] It is an ongoing scientific debate regarding the reli-

ability of marine bunker sale statistics to be used forestimates of fuel-based ship emissions [Corbett and Koehler,2003, 2004; Eyring et al., 2005; Endresen et al., 2003,2004, 2005]. Activity-based estimates reported by Corbettand Koehler [2003] and Eyring et al. [2005] are signifi-cantly higher compared to historical sales data covering thelast decades. Moreover, the variation over time betweenreported sales and estimated consumption does not corre-spond. It has been argued that underreporting of salesexplains the large differences [Corbett and Koehler, 2003;Eyring et al., 2005]. An alternative explanation could bethat changes in structure, technology and activity of theexpanding world fleet have to be better captured in theactivity-based models. It has recently been questioned ifthe assumed activity level for the fleet is representative[Endresen et al., 2004], and especially for medium andsmaller ships (which dominate by number). This studyargues that any activity-based approach must take intoaccount variation in the demand for sea transport andoperational and technical changes over the years, to betterrepresent the real fuel consumption and correspondingemissions. To better examine these factors this work hasestablished an improved activity-based modeling approachto estimate fuel consumption for the oceangoing civil worldfleet larger or equal to 100 GT. This model is applied to theperiod 1970 to 2000, and limited to the main engines of thenonmilitary fleet. The estimated fuel consumption is thencompared with historical marine sales data, to investigate ifmarine sales data reported over the last 30 years arerepresentative and could be used as proper bases foremissions estimates.[5] In this study we first present a description and dis-

cussion of the developed CO2 and SO2 emissions inventoriesfor the period 1925 to 2002 (section 2). We describe theactivity-based model developed, the input data applied andthe modeled fuel consumption for the last 3 decades insection 3. Section 4 compares the modeled fuel consumptionfor the last 3 decades with marine sales data. In section 5,major findings are summarized and discussed.

2. Fuel-Based Emissions Inventory: 1925–2002

[6] This section presents estimates from 1925 up to 2002of global CO2 and SO2 emissions from oceangoing civilships by combining estimates for marine fuel sales of coaland oils with their respective fuel-based emissions factors.

2.1. Methodology

[7] Detailed methodologies for constructing ship emis-sion inventories based on fuel sales have been published bythe Atmospheric Emission Inventory Guidebook [EuropeanMonitoring Evaluation Program/Core Inventory of Air

Emissions (EMEP/CORINAIR), 2002]. The emissions arecalculated by means of

Eg; j ¼ Sj � eg; j; ð1Þ

where Eg,j denotes the emissions of individual exhaustcompound g (g = 1 = CO2, g = 2 = SO2) from burning fueltype j ( j = 1 = diesel, j = 2 = heavy fuel, j = 3 = coal),kg emissions/year; Sj denotes the total sales of fuel type j,kg fuel/year; and eg,j denotes the emission factor for exhaustcompound g in relation to fuel type j, kg emissions/kg fuel.[8] The emission estimates presented in this study are

based on bunker sales data (marine oil and coal) obtainedfrom several sources (section 2.2), and average fuel-basedemission factors assumed representative for the differenttime periods (section 2.3).

2.2. Marine Sales

[9] Data exists for sales of fuel to foreign bound shipsfrom 1925 to 1970, but assumptions have to be made forthe national sales. Data for the total marine sale existsfrom 1971 up to 2002, except for the fishing fleet forwhich separate sale estimates are made. The sources,assumptions and inventories are presented below for twoperiods (1) 1925–1970 and (2) 1971–2002. The salesfigures given in bold in Table 1 are used to estimate theemissions for the period. Note that no data is available forthe World War II period.2.2.1. Period I: 1925–1970[10] The international marine sale figures from 1925 up to

1970 are based on coal and oil statistics reported byDarmstadter et al. [1971] and United Nations (UN)[1957–1979]. These data cover sales to foreign bound shipsand aircrafts, irrespective of flag [Darmstadter et al., 1971;UN, 1957–1979]. It is expected that sales to oceangoingmilitary vessels in international operations are included inthe presented inventory. However, no data is available foroceangoing military vessels in national services. This sale issmall compared to sales to the nonmilitary fleet, accordingto estimates reported by Endresen et al. [2003], and is notincluded in this work. As national fuel sales to the nonmil-itary fleet are not included, the total oil and coal sale for thisperiod is estimated on the basis of ratios between nationalsales versus international, which can be established foryears when data is available. The calculated average ratiobetween IEA sales figures of national bunker (category:‘‘internal navigation’’) and international bunker (category:‘‘international marine bunkers’’) figures for the period 1971to 2002 is calculated to be 0.27 (i.e., national sales is onaverage 27% of the international sales). However, theestimated national sales do not include the fishing fleet asIEA reports this sale under the ‘‘agriculture’’ category forthis period. A separate estimate for the fishing fleet is givenin section 2.2.2 and indicates that the fishing fleet consumessome 10% of the total sales. Assuming that these ratios alsoare representative for the period 1925 to 1970, the total sale(Total) is calculated by means of

Total � Int þ National þ Fishing ¼ Int þ 0:27 � Int þ 0:1 � Total:ð2Þ

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[11] Table 1 shows the estimated total figures for theperiod 1925 up to 1970, as well as the reported internationalsales (Int) used as input to equation (2).2.2.2. Period II: 1971–2002[12] Data for the total marine fuel sales exists for 1971 up

to 2002, but this does not include the fishing fleet. Theapplied sales figures from 1971 up to 2002 are based on oilstatistics reported by International Energy Agency (IEA)[1971–2002]. Our data is based on IEA categories ‘‘inter-national marine bunkers’’ and ‘‘internal navigation.’’ Thesales to oceangoing military vessels are expected to beincluded, as IEA defines the ‘‘international marine bunkers’’to cover those quantities delivered to seagoing ships of allflags, including warships [IEA, 2001]. The fishing fleet sale

is reported in the IEA category ‘‘agriculture’’ [IEA, 2001]. Itis not possible to extract sales to fishing vessels from thisoverall category and these sales figures are therefore esti-mated from the 34,379 MW main engine power that wasreported to be installed in the 1.3 million decked fishingvessels in 1998 [Food and Agriculture Organization of theUnited Nations (FAO), 2006a]. This represents nearlytwice the power reported by Corbett and Koehler [2003](18,474 MW) for the fishing fleet larger than 100 GT, andabout 13% of the total main engine power of the oceangoingcivil world fleet larger than 100 GT. We may assume thatthe main engine power installed is roughly proportionalwith the sales to the fishing fleet. The entire fishing fleetconsumption in 1998 is then calculated to be of the order

Table 1. Reported Worldwide Marine Sales of International Marine Bunkers (Oil and Coal) for the Period 1925–2000 and Estimated

SO2 and CO2 Emissions (Equation (1))a

Year

InternationalBunkers asCoal,b Mt

InternationalBunkers asCoal,b Mt

InternationalBunkers asOil, Mt National

Sales, Mt

TotalEstimated Salesas Oil,d Mt

EstimatedEmissions, Tg

UN EWE UN EWE IEAc SO2 CO2

1925 41.6 17.4 66.0 2.5 2291929 41.0 21.9 71.8 2.8 2471933 27.8 19.1 54.7 2.2 1871937 75 30.7 23.6 63.9 2.6 2171938 28.0 21.4 58.1 2.4 1981949 681950 12.2 48.5 80.6 3.8 2611951 9.16 47.9 76.7 3.7 2481952 7.76 50.7 79.3 3.8 2551953 6.16 8.0 52.9 59.9 80.8 3.9 2591954 5.70 53.9 81.7 4.0 2621955 5.35 7.2 60.3 67.0 90.4 4.4 2891956 4.47 66.7 98.6 4.8 3151957 3.80 4.5 72.0 77.9 105.4 5.2 3361958 2.86 68.9 100.1 5.0 3191959 2.22 69.1 99.7 4.9 3171960 1.60 2.2 76.9 81.2 110.1 5.5 3501961 1.08 1.5 84.4 87.4 120.2 6.0 3811962 0.79 1.2 85.5 90.3 121.4 6.1 3851963 0.70 1.1 89.6 92.8 127.1 6.3 4031964 0.79 1.2 97.5 101.6 138.4 6.9 439

1965 0.70 1.2 101.6 104.2 144.1 7.2 457

1966 0.71 97.3 138.0 6.9 4381967 0.51 105.0 148.7 7.4 4721968 0.31 111.6 157.8 7.9 5001969 0.33 102.4 144.8 7.2 4591970 0.34 107.1 151.5 7.6 4801971 0.23 112.8 110.3 30.6 156.8 7.0 4971972 0.20 114.2 115.5 30.0 161.9 7.2 5131973 0.16 121.3 122.0 31.7 170.9 7.6 542

1974 0.11 115.1 113.4 34.3 164.2 7.3 5211975 0.04 101.5 105.0 33.2 153.6 6.7 4871976 0.03 102.5 108.6 33.5 157.9 6.9 5011977 0.02 95.9 108.5 32.2 156.4 6.8 4961978 0.01 95.7 109.2 32.2 157.1 6.7 4981980 110.4 32.7 159.0 7.0 5041985 93.9 30.7 138.5 5.8 4391990 116.9 31.6 165.0 6.9 5231995 129.9 26.8 174.2 7.5 5522000 150.2 30.8 201.2 8.7 6382002 149.0 30.9 199.9 8.5 634

aThe sales data are reported by Darmstadter et al. [1971], UN [1957–1979], and IEA [1971–2002]. The sales figures given in bold are used to estimatethe emissions for the period.

bCoal equivalents, based on UN [1957–1979] for 1960.cOnly the category international bunkers.dOil equivalents, using 1/1.416 as conversion factor from coal to oil equivalents [UN, 1998].


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10% of the total sales by assuming less days at sea for thefishing fleet compared to the cargo ships [Endresen et al.,2004] and by taking into account that some of the reportedIEA sales include military vessels. This study assumes thatthe estimated 10% consumption by the entire fishing fleet in1998 is representative for the period 1925–2002. Lloyd’sfleet data for the years 1970 and 2000 shows little change inthe relative fraction by numbers of fishing vessels, but therelative tonnage fraction was higher and the average vesselsize was lower in 1970 than in 2000. Global fishing fleetdata up to 1970 is not available, but the fish catchstatistics indirectly support our assumption. Fish catchesin 1938, 1950, 1970 and 2000 within marine waters was19.3 Mt (reported by FAO, figures given by AschehougsKonversasjonsleksikon [1956]), 17.3 Mt, 59 Mt and 88 Mt[FAO, 2006b], respectively and this development corre-sponds well with the total fleet development over this period(Figure 1). On the basis of this assumption, the total sale(Total) is calculated by equation (2). Table 1 shows theestimated total figures for the period 1971 to 2002, as wellas the reported international (Int) and national (National)IEA sales data used as input to equation (2).2.2.3. Discussion of the Data Sources[13] We find a good match between international oil fuel

sales reported by Darmstadter et al. [1971] and IEA [1971–2002] with reference to 1965 and 1971, respectively. Thematch between international oil fuel sales reported by UNand IEA is generally good for the period 1971 to 1978, andby UN and EWE from 1953 to 1965 (Table 1). However,the 1977 and 1978 sales reported by UN are lower than IEAdata. The IEA data does not include fuel sales to aviation,indicating that for this time period the reported fuel sales toaircraft is likely to be insignificant in both the EWE and theUN data. This is supported by the fact that airplanes do notuse coal or heavy fuel oils, and that EWE states that thereporting of aviation fuel sales appear to be incomplete.Thus we assume that the aviation fuel included in UN andEWE data is small or negligible, and that the sources giverepresentative data for sale to international shipping. It isimportant to recognize that IEA and UN define international

bunker differently. UN includes only sales to foreign boundships, while IEA defines the ‘‘international marine bunkers’’to cover those quantities delivered to seagoing ships of allflags, including warships [IEA, 2001]. The good matchbetween international bunker sales reported by UN andIEA indicates that the IEA ‘‘international’’ bunker categorymainly includes sale to ships in international operations.

2.3. Emission Factors for CO2 and SO2

[14] We have used a factor of 3.17 tonnes CO2 per tonneoil consumed [EMEP/CORINAIR, 2002] and 2.58 tonnesCO2 per tonne coal consumed to model emissions to air.The emission factor for coal is calculated by combiningthe molecular weight ratio of CO2 to C (44/12), with0.704 tonnes C/tonne fuel [Society of Naval Architectsand Marine Engineers (SNAME), 1983]. The sulphur con-tent varies over time, as pointed out by Endresen et al.[2005]. We have assumed a global average of 2.5% sulphurfor marine oils up to 1970. From 1971 up to 1995, a globalaverage of 2.7% sulphur is assumed for heavy fuel and0.5% for distillates. Global values reported by Endresen etal. [2005] are applied from 1996 to 2001. For year 2002global weighted sulphur contents (heavy fuel and distillates)are applied [Endresen et al., 2005]. The globally weightedaverage content for heavy fuels is found to be 5% higherthan the average (arithmetic mean) sulphur content com-monly used. The likely reason for this is that larger bunkerstems are mainly of high-viscosity heavy fuel, which tendsto have higher sulphur values compared to lower-viscosityfuels [Endresen et al., 2005]. Smith et al. [2004] reports asulphur content in coal of 1.1%, and we assume this value tobe representative for the entire period. The relation betweenburned sulphur and generated SO2 is 2.0 kg SO2/kg S(derived from the chemical equation [Lloyd’s Register ofShipping, 1995; EMEP/CORINAIR, 2002]).

2.4. Modeling of Ship CO2 and SO2 Emissions

[15] Figure 2 shows the calculated CO2 and SO2 emis-sions (equation (2)) using the sale numbers (section 2.2) incombination with the emission factors per tonne oil and coal

Figure 1. Development of the world fleet of oceangoing civil vessels above or equal 100 GT andtransport work, 1900–2000 (not including the military fleet). (left) Development of size and tonnage(Lloyd’s Register of Shipping, statistical tables, 1964 (year 1900–1964), and world fleet statistics andstatistical tables, 1992 (year 1965–1992), 1995 (year 1993–1995) and 2000 (year 1996 and 2000).(right) Development of average size (including also noncargo ships) and transport work (Btm, billiontonne-miles) [Stopford, 1997; Fearnleys, 2002]. Note that no data are available for World War II.


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consumed (section 2.3). Ship emissions are estimated at229 Tg (CO2) in 1925, growing to about 634 Tg (CO2) in2002. The corresponding SO2 emissions are 2.5 Tg (SO2)and 8.5 Tg (SO2).2.4.1. Factors Determining Development in WorldwideFuel Sales[16] This study expects that the demand for sea transport,

technical and operational improvements as well as changesin the fleet composition and size will explain most of thedevelopment in fuel consumption by the fleet during the last100 years. The coal sale peaked in 1913 (80 Mt coal isreported by Annin [1920]), and dominated up to around1920, as the fleet grew and steamers replaced sail ships(Table 1) [Fletcher, 1997]. After 1920, the oil sale started todominate the emissions, as coal gradually was replaced bymarine oils, following the shift to diesel engines and oil-fired steam boilers (Table 1) [Fletcher, 1997; Corbett,2004]. Increased focus on fuel economy [Kofoed, 1926],and a shift from coal to oil, combined with depressions inboth the world economy and the sea borne trade in the

1930s [Stopford, 1997] (e.g., some 21% of the fleet was outof service in 1932) partly explain the gradual reduction insales from around 1925 (Table 1) toward the Second WorldWar.[17] Table 1 illustrates the significant increase in marine

sales after the Second World War and up to 1973. The mainreasons for this significant growth was the demand for seatransportation, as the sea borne trade grew from around500 Mt in 1949 to 3,233 Mt in 1973 [Stopford, 1997] (i.e.,more than a sixfold increase). The growth in sea bornetransport was not reflected by a corresponding growth inthe fleet by vessel numbers (i.e., a twofold increase) ortonnage (3.5-fold increase), indicating the influence ofmodern, larger and more efficient cargo ships, with im-proved cargo handling in ports. For instance, the volume of

Figure 2. Development of CO2 and SO2 ship emissions,based on estimated sales of marine fuel (Table 1), 1925–2002 (including the fishing and military fleet). Note that nodata are available for World War II.

Figure 3. Reported IEA [1971–2002] sales of marine oilproducts (Mt) worldwide (including the IEA categories‘‘international marine bunkers’’ and ‘‘internal navigation,’’but not sales to the fishing fleet) versus world sea bornetrade (Mt cargo), 1971–2000 [Stopford, 1997; Fearnleys,2002].

Figure 4. (top) Fleet data for cargo ships versus noncargoships, (middle) trade volumes of oil and dry bulk versusaverage haul for oil tanker and dry bulk ships, and (bottom)fleet productivity for cargo ships (tanker and cargo fleet)versus non trading tonnage.


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cargo transported per tonne fuel sold significantly increasedin this period (see Figure 3). Note that the transports ofpassengers, important up to around 1960, have had aninfluence on the volume transported per tonne fuel sold.We expect that passenger ships, the largest ship type in thefleet up to around 1960 [Aschehougs og Gyldendals storeNorske Leksikon, 1999], account for some of the coalconsumption for this period and before. For instance, theannual number of European emigrants transported to the USincreased from 350,000 around 1890 to around 1.4 millionin 1910 [Aschehougs Verdenshistorie, 1982]. The largest of

the old passenger liners such as the Olympic and the Titanicburned on average 620 tonnes of coal per day at 21.7 knots(Encyclopaedia Titanic, Daily fuel consumption for Titanicand Olympic, available at http://www.encyclopedia-titanica.org/discus/messages/5919/6509.html, visited 2005).[18] Themarine sales decreased from around 1973 to 1983,

followed by a nearly steady growth up to 2002 (Table 1 andFigure 3). The main reasons for the decrease were theslowdown in world sea borne trade (Figures 3 and 4), thereduction in sailing distances (Figure 4), improved energyefficiency of the fleet (e.g., phasing out of steam ships) anda reduction in speed (and installed power) within somedominating segments (Figure 5). World economy generatesmost of the demand for sea transport, through either theimport of raw materials for manufacturing industry, or tradein manufactured products [Stopford, 1997]. Figure 3 illus-trates that development in bunker sale follow developmentin seaborne trade with a correlation of r = 0.92 for the period1975 to 2000. The correlation between transport work(measured in tonne miles, Figure 1) and fuel sale for thesame period is even better (r = 0.97) (Figure 6, right),indicating that the average length of haul, not surprisingly,is affecting the sales. However, the correlation betweenthese variables is lower (r = 0.88) for the period 1971 to2000 (Figure 6, left), indicating that other factors also wereimportant, especially between 1971 and 1975. For instance,the transport work by the old passenger fleet is not included,as well as effects of changed operational speed and shift todiesel powered ships. The typical operational speed has alsovaried widely over time, which significantly influences thepower requirements. For example Very Large Crude oilCarriers typically operated at 10 knots when freight rateswere low in 1986, but this increased to 12 knots when therates were higher in 1989 [Stopford, 1997]. A reduction inthe average operating speed by 2–3 knots below designspeed may halve the daily fuel consumption of the cargofleet [Stopford, 1997; Wijnolst and Wergeland, 1997].Lloyd’s fleet data [Lloyd’s Register Fairplay (LRF),2005–2006] also indicates a reduction in installed powerand operational speeds for diesel powered crude oil carriersbuilt after 1980, followed by a significant reduction in fuelconsumption (Figure 5). The annual fuel consumption bythe fleet is also strongly affected by the installed propulsionsystems (engine, gear, shaft, propeller arrangement), asmodern diesel engines have about half the daily fuelconsumption compared to the old inefficient steam engineswith the same power outtake (Table 2). The shift to modernmarine diesel engines has typically occurred in periods withhigh oil prices. For instance in 1961, there were still over10,000 steam engine powered ships and 3,536 steam turbinepowered ships in operation (36% by number) (Lloyd’sRegister of Shipping, statistical tables, 1961). By 1970these numbers had decreased to 4,425 and 3,534 shipsrespectively (15% by number) (Lloyd’s Register of Ship-ping, statistical tables, 1970). By 1984 only 1,213 shipswere steam engine powered and 1,743 turbine poweredships (4% by number) remained in service (Lloyd’s Registerof Shipping, statistical tables, 1984).[19] The decrease in marine sales from around 1973 is

also explained by the decline in both sea borne transport ofoil (represented about 50% of the sea borne trade) and theaverage sailing distances (Figure 4, middle). For instance,

Figure 5. (top) Daily main engine fuel consumption,(middle) installed main engine power, and (bottom)operation speed for crude oil tankers with diesel enginesbuilt in the periods 1956 to 1979 and 1980 to 2005 [LRF,2005–2006].


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crude oil tankers reached a peak in productivity in 1972(measured in tonne miles per deadweight (total carryingcapacity)). By 1985 this had nearly halved, and a few yearslater it increased by 40% [Stopford, 1997]. More efficientand specialized ships have also pushed their way into themarked (e.g., the first deep sea cellular container ship in1965 [Stopford, 1997]). The specialized ships have differentoperational and technological characteristics, which resultsin a particular logistic efficiency and energy and emissionprofiles. For example, passenger ships have on average 2.2main engines per ship, while the large passenger ships have5.7 main engines per ship (greater than 100,000 GT) [LRF,2005]. The civil world fleet have on average 1.3 mainengines per ship (above or equal to 100 GT) [LRF, 2005].Engine capacity is not likely to be fully exploited at alltimes, resulting in a lower fuel consumption in practice thanwhat might be expected on the basis of the power installed.It is reasonable to expect that these effects are likely to havedifferent impacts on the total fleet within the period 1970–2000 and so we have included most of them in the fleetmodeling approach outlined in section 3.

2.4.2. Uncertainty[20] The uncertainties in our estimated sales figures are

significant. Reliable inventories are probably best devel-oped by comparing the different modeling approaches andthe different data sets that are available. This extends ourknowledge base and improves our understanding of thegoverning processes. The inventory presented in this studyaims to cover sales in oil equivalents to all oceangoing shipsworldwide (Table 1). However, the marine sales for theperiod 1925 to 1970 is likely to be slightly underestimated,as sales to the oceangoing military fleet in national servicesare not included. Our best estimate today is that the dataafter 1970 should be within a range of ±15%, while the databefore 1970 should be within a range of ±25%. Under-reporting by some countries has been [Endresen et al.,2003] and may still be a problem. The national salesreported by IEA from 1971 to 2002, also include sales tosmaller ships operating on inland waterways. This fleet isreported to account for 42,000 engine powered shipsand 38,000 push-towed vessels in 1992 [Organisation forEconomic Cooperation and Development, 1997]. The enginepowered ships are small (�300 Dwt) and represent around2% of the cargo capacity of the oceangoing fleet. Thus it isassumed that the sale to this segment is small.[21] The variation in carbon content for marine oil prod-

ucts is small [Energy Information Administration, 1994].The uncertainty in the average CO2 emission factor formarine oils is less than ±5%. This is in line with Skjølsvik etal. [2000]. The assumed carbon content in coal for marinepurposes is reported to be 70.4% [SNAME, 1983]. Weexpect the error in the assumed carbon content for coal tobe within ±10%. Taking into account uncertainties in salesnumbers, it is expect that the uncertainties in the CO2

emissions after 1970 should be within a range of ±20%,while the estimates before 1970 should be within a range of±30%. Limited data exists for average sulphur content ofmarine oil up to 1990. This is supported by the fact that theuse of residual fuel in marine diesel engines dates to the1940s. Prior to the 1940s, residual fuels for navigationalpurposes had been used by steam ships [Cullen, 1997]. We

Figure 6. Correlation between reported IEA [1971–2002] sales of marine oil products worldwide (Mt)(including the IEA categories ‘‘international marine bunkers’’ and ‘‘internal navigation,’’ but not sales thefishing fleet) and transport work (billion tonne miles (Bmt)) [Stopford, 1997; Fearnleys, 2002]. (left)Period 1971–2000. The correlation is 0.88. (right) Period 1975–2000. The correlation is 0.97.

Table 2. Reported Specific Fuel Consumption (SFC) for Different

Engine and Fuel Types

Engine Type

Reported SFC

Ib./S.H.P.ha g/kWh

Diesel ships 0.36b–0.47c 200–240d,e

TurbineOil 0.75b 290–305d,e

Coal 1.125b–2.4c,f

Steam engineOil 0.9b 700d

Coal 1.35b–1.54c

aIb-pound = 0.45359237 kg; S.H.P., shaft horse power; 1H.P= 0.7457 kW;h, hour.

bLe Mesurier and Humphreys [1935].cBaker [1915].dSNAME [1988], average figures.eCooper [2002].fAt low speeds, while for high speeds 1.2 Ib./S.H.P.hr.


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judge the error in sulphur content in oil to be within ±20%up to 1990, and within ±10% after 1990. It is expected thatthe total uncertainties in the SO2 emissions after 1990should be within a range of ±20%, while the estimatesbefore 1990 should be within a range of ±30%. We realizethat the modeling is based on a number of assumptionsregarding average sulphur and carbon content (coal) and theresults should therefore be interpreted carefully.

3. Activity-Based Fleet Modeling, 1970–2000

[22] This section presents an improved activity-basedmodeling approach that uses high-resolution time series asinput data to estimate fuel consumption for the oceangoingcivil world fleet larger or equal to 100 GT. Modeling ismade for the period 1970 to 2000, and only for the mainengines. Historical data available is limited, and do notallow for detailed modeling, such as the baseline approachesreported by Corbett and Koehler [2003], Endresen et al.[2003] and others (e.g., breakdown on ship types and sizes).Simplifications and assumptions are therefore made. How-ever, compared to past activity-based modeling studies[Eyring et al., 2005; Corbett and Koehler, 2003], this studyhas developed and applied a more detailed approach, whichincludes the variation in the demand for sea transport, aswell as operational and technological changes.

3.1. Modeling Approach

[23] The average ship size approach applied in this studyassumes an equal size for the total number of ships in theworld fleet of oceangoing civil ships larger or equal to100 GT, and calculates the average size of the ships bydividing total tonnage with the total number of ships. Thefuel consumption for an average ship is estimated on thebasis of average characteristics of installed main enginepower, main engine load, bunker fuel consumed per powerunit (kW) (depends on propulsion and fuel type) and days atsea (based on demand for sea transport). The fuel consump-tion is calculated separately for the diesel and steam ships,as steam ships have a significantly higher fuel consumption(Table 2). The main engine fuel consumption for the period

1970–2000 for all oceangoing civil ships above or equal to100 GT is then estimated by

Fi; s ¼ bi; s � t � p � m� �

per ship� ni; s � N� �

number of ships; ð3Þ

where Fi,s denotes the total fuel consumption of averageships with main engine type i burning fuel type s, kg fuel/year; bi,s denotes the average specific fuel consumption foran average ship with main engine type i burning fuel type s,kg fuel/kWh; t denotes the average number of operatinghours at sea per year for an average ship (see equation (5),below), h/year; p denotes average installed main enginepower for an average ship, kW; m denotes the average mainengine load for an average ship; ni,s denotes the fraction ofthe average ships in the fleet with main engine type iburning fuel type s (see equation (4), below); and N denotesthe total number of active average ships in the fleet (i.e., notlaid up and used as storage).[24] Input data for the different terms in equation (3) is

described below and given in Table 3. It should be notedthat table figures are only given every tenth year, while thenumbers applied in our modeling are given year by year.3.1.1. Number of Active Average Ships, Dieseland Steam Powered[25] As outlined above, the number of average ships

corresponds to the total number of ships reported in theworld fleet of oceangoing civil ships above or equal to100 GT (Figure 1, left). The total number of ships and GT inthe fleet from 1970 to 2000 is based on fleet statistics(Lloyd’s Register of Shipping, world fleet statistics andstatistical tables, 1992 (year 1970–1992), 1995 (year1993–1995) and 2000 (year 1996 and 2000)). The fractionof the average ships (ni,s) in the fleet with main engine type iburning fuel type s is calculated on the basis of thefollowing equation:

ni; s ¼Di; s

D1;1 þ D2;1 þ D2;2; ð4Þ

where Di,s denotes the total tonnage in the fleet with enginetype i burning fuel type s, GT.[26] The tonnage in the fleet with engine type i burning

fuel type s is based on yearly fleet data from Lloyd’sRegister of Shipping (statistical tables, 1972–1975 and1977–1984). From 1985 to 1992 the yearly fleet data isonly available for the steam powered tank and bulk fleet(Lloyd’s Register of Shipping, statistical tables, 1985–1990, and world fleet statistics and statistical tables, 1991,1992). However, we have assumed that the tanker and bulkfleets are representative for the total steam tonnage, as theywere the dominating ships by tonnage. Fleet data is notavailable for the steam powered segment from 1993 on-ward, and the changes in the steam tonnage are estimated byinterpolation between the 1992 tonnage and the actualtonnage in 2004 [LRF, 2005]. The percentage of the coalfired tonnage is available from Corbett [2004] up to 1960.Detailed fleet data from Lloyd’s is available for the years1961, 1962 and 1963 (Lloyd’s Register of Shipping, statis-tical tables, 1961–1963), but no data is available thereafteraccording to our information. A linear reduction from 3.3%of the coal fired tonnage in 1963 to zero in 1979 is assumed,on the basis of the development of coal sales (Table 1). It

Table 3. Input Data to Equation (3), Modeling Main Engine Fuel

Consumption for the World Fleet of Oceangoing Civil Ships

Larger or Equal to 100 GT, Period 1970–2000 (Presented per

Decade)a

Parameter Variable 1970 1980 1990 2000

Time at sea, days t 215 162 167 181Average main engine size, kW p 2032 2452 2705 3251Average engine load (– ) m 0.7 0.7 0.7 0.7Number of active ships (103) N 52.3 71.7 76.2 86.8% main engine powered byDiesel n1,1 0.64 0.68 0.88 0.94Steam, oil n2,1 0.34 0.32 0.12 0.06Steam, coal n2,2 0.02 0.00 0.00 0.00

Average SFCb

at sea for mainengine, g/kWhDiesel b1,1 240 234 228 221Steam, oil b2,1 363 344 329 329Steam, coal b2,2 807 0 0 0aNote that yearly input data is used in the modeling.bSFC, specific fuel consumption.


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should be recognized that other engine types are representedin the oceangoing civil world fleet (e.g., gas turbine), butthese types are negligible by tonnage and number whencompared with steam and diesel. Thus we have not takenthem into account in this study.[27] The number of average active ships (N � ni,s) is

calculated by subtracting the number of average shipscorresponding to the nontrading tonnage. The number ofships out of service is distributed on engine and fuelcategories according to the relative tonnage of the fleet withmain engine type i burning fuel type s. The development inlaid up tonnage and tonnage used for storage from 1970 to1995 is based on Stopford [1997], and on data fromFearnleys [2002] thereafter. The number of active averagesized steam ships (N � n2,s) will then reflect the total amountof tonnage (in service) for the steam powered fleet (D2,s),while number of active average sized diesel ships (N � n1,1)will reflect the total amount of tonnage (in service) for thediesel powered fleet (D1,1).3.1.2. Time at Sea[28] The operational profile is derived by combining

yearly fleet and trade data. This deviates from recentmodeling studies that estimate days at sea on the basis ofengine manufactures data for large engines and trackingstudies. The development of the yearly total number of daysat sea sailing with cargo for the fleet is estimated on thebasis of number of voyages required for an average cargoship (with an average utilization of cargo capacity) totransport the yearly reported worldwide total cargo vol-umes, combined with average voyage time calculated fromreported average length of haul and assumed averageoperational speed. We have only considered the cargocarrying fleet when estimating days at sea, and assumedthat days at sea for cargo and noncargo ships are equal.Noncargo ships normally have less days at sea as indicatedby Endresen et al. [2004], and this assumption may bias ourfuel consumption estimates toward being too high, com-pared to the real situation. The development of the yearlyaverage number of days at sea (t) (with cargo and in ballastcondition) of the active average cargo ships is calculated bymeans of

t ¼ 1þ aN

� �� l

v

� �voyage time

� q

d � h

� �number of voyage

; ð5Þ

where q denotes the total yearly sea borne trade of ships inthe fleet, tonnes/year; l denotes of average length of haul(with cargo), nautical miles (nm); d denotes average deadweight tonnage (Dwt) of ships in the fleet, Dwt; v denotesthe average operational speed of ships in the fleet, nm/h;h denotes the average utilization of cargo capacity of shipsin the fleet, tonnes/Dwt; and a denotes the ballast factor,defined as the average number of days in ballast relative todays sailing with cargo.[29] Input data for the different terms in equation (5) is

described below and given per decade in Table 4. Averageoperational speed (v) is derived from data collected for37,193 cargo and passenger ships in the Lloyd’s 2006 fleetdatabase [LRF, 2005–2006]. The average operation speedfor a given year is based on data for all ships the actual yearand all older ships in the database. The total yearly reportedsea borne trade volumes (q) for 1970 to 1995 are based onStopford [1997], while data for the period 1996 to 2000 arebased on Fearnleys [2002] (Figure 3). The average sailingdistances (l) are calculated by dividing the total transportwork (tonne miles) by the total sea borne trade volumes.From 1970 to 2000 these data are based on Fearnleys[2002] and Stopford [1997].[30] Relatively little information is available about the

average time spent in ballast. Ideally, a ship should com-plete all voyages with cargo. However, many trades requirereturn voyages without cargo. For example, a crude oiltanker typically transports a single cargo load between twoports, then returns to its point of origin or another portwithout cargo. Wijnolst and Wergeland [1997] indicates thatit is not likely for the tanker fleet that the average ballastfactor will be less than 0.8, and it will hardly ever exceed 1.Tracking data reported for 453 Very Large Crude oilCarriers in 1991 illustrated a ballast factor of 0.81. Othership types such as general cargo and container ships, oftensail with some cargo and some ballast and have limited timein ballast, but are frequently not fully laded. For about 100smaller cargo ships operating on a regional basis (mostships around 3,500 Dwt), the ballast factor is reported to bearound 0.2 [Wilson EuroCarriers, 2005]. In the modeling,these ships are ‘‘forced’’ to transport all cargo nearly fullyladen, and then spend time in ballast. On an annual basis, itis expected that this simplification, may give representativenumber of days at sea, as well as cargo volumes transported.Taking into account the fact that larger ships dominate thetransported volumes at sea [Stopford, 1997], the averageballast factor (a) is assumed to be 0.7 (i.e., days with ballastis 70% of the number of days with cargo) for all ship types.[31] Wijnolst and Wergeland [1997] reports that utiliza-

tion of cargo capacity in practice hardly exceeds 0.95, butmay become as low as 0.65. The utilization of cargocapacity of bulk ships and oil tankers larger than 50,000 Dwtin 2001 is reported by Behrens et al. [2003] to be 0.91 and0.87, respectively. These ships account for almost 55% ofthe sea borne trade in 2000 [Fearnleys, 2002], and will ofcourse then have a large impact on the average factor. Weacknowledge that general cargo and container ships have alower utilization of the cargo capacity, and that the averagedensity of cargo could make volume the limiting factor. Forinstance, data reported by Johnsen [2000] for a dry cargoship with carry capacity of about 5,200 tonnes, indicate that

Table 4. Input Data to Equation (5), Modeling Time at Sea for the

World Fleet of Oceangoing Civil Ships Larger or Equal to 100 GT,

Period 1970–2000 (Presented per Decade)a

Parameter Variable 1970 1980 1990 2000

Average haul,b nm l 4380 4606 4307 4236Average speed,c knots v 13.9 14.2 14.1 14.4Total GT (106) 227.5 420.0 423.6 558.1Average ship size, Dwt d 9920 16226 15889 17150Seaborne transport,d Mt q 2433 3606 3977 5434Utilization of Dwt (– ) h 0.8 0.8 0.8 0.8Ballast factor (– ) a 0.7 0.7 0.7 0.7

aNote that yearly input data is used in the modeling.bThe average haul length (l) from 1970 to 2000 is based on Fearnleys

[2002] and Stopford [1997].cBased on data collected from Lloyd’s fleet database.dBased on Fearnleys [2002] and Stopford [1997].


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the ships on average were loaded at 4,000 tonnes. Of this,the average exploited capacity is reported to be 76%(considering different trading routs). Data for containerships serving U.S. trade [PIERS/Journal of Commerce,2005], indicate a utilization rate of the container capacityof about 70% on average. Important to note is that theutilization rate of the container capacity will typical behigher than the average utilization of the cargo capacity.Clearly the utilization of cargo capacity varies for differentship types, as well as for year considered (depending on themarked). We assume that 0.8 is representative for theaverage utilization of the cargo capacity (h) for all cargoships types.3.1.3. Specific Fuel Consumption and Engine Load[32] The main engine specific fuel consumption (bi,s) is

based on data reported in the literature and engine datareported for individual ships. The main engine specific fuelconsumption for an average diesel ship (b1,1) is estimatedfor different periods (up to 1970; up to 1980;. . .; up to2000), combining installed main engine power and the dailyfuel consumption reported for 16,465 diesel powered ocean-going civil ships in the Lloyd’s 2004 fleet database [LRF,2005]. A similar calculation is made for the 770 steamturbine powered cargo and passenger ships running on oil[LRF, 2005–2006]. The daily fuel consumption is normallygiven at full power (85% MCR: Maximum ContinuousRating). We have therefore assumed in the calculation ofspecific fuel consumption (Table 3) that utilized power is85% of installed power.[33] It is important to recognize that no differentiation is

made between steam engines and turbine engines. We havedefined average steam ships using oil (b2,1) or coal (b2,2).Steam engines have higher fuel consumption compared toturbine engines, as illustrated in Table 2. However, limiteddata is available on specific fuel consumption for oldsteamers, and especially for the steam engines. Both steamengines and steam turbines burning coal were phased out ofthe fleet around 1970. We have therefore established typicalconstant averages specific fuel consumption for these ships.Riksheim [1982] compared the fuel consumption of a dieselpowered ship of 142,000 Dwt delivered in 1981, with a coalfired steam turbine ship with the same hull dimension, shaftpower and services speed. He reported that the coal firedsolution used more than 3 times the fuel by weight,compared to the diesel solution (64 tonnes oil per dayversus 198 tonnes coal per day or 140 tonnes of oilequivalents). The data in Table 2 also illustrates thatturbines running on coal typically use 3–3.5 times morefuel per unit power production, compared to the dieselengines. Thus we assume for all years that turbine enginesfuelled by coal consume 800 g/kWh.[34] Table 2 indicates that steam engines running on oil

consume 700 g/kWh, while steam engines using coal haveslightly higher fuel consumption than turbine engines usingcoal. Thus, for steam engines using oil and coal we haveassumed a fuel consumption of 700 g/kWh and 900 g/kWh,respectively. For average steam ships using oil (b2,1) or coal(b2,2), we have estimated the specific fuel consumptionusing these specific consumptions with a weighting accord-ing to the tonnage. In 1961, the steam engines accounted for41% of the steam tonnage (Lloyd’s Register of Shipping,statistical tables, 1961). This is reduced to 8% in 1970

(Lloyd’s Register of Shipping, statistical tables, 1970), 2%in 1984 (Lloyd’s Register of Shipping, statistical tables,1984) and assumed 0% in 1990. The estimated weightedspecific fuel consumptions (b2,1) and (b2,2) are then appliedin the modeling. Table 3 shows the applied averages (onlygiven per decade).[35] We assume an average main engine load of 70%

MCR, when including slow cruise, port maneuvering andballast sailings. This assumption is based on recommenda-tions by Endresen et al. [2003, 2004] and Corbett andKoehler [2004]. The average engine load (m) is assumed forall ships and all years. However, the average main engineload and speed varies a lot for different ship types. Forinstance, Flodstrom [1997] reports an average load of 80%MCR based on data from 82 ships. Bulk vessels tend tohave slightly lower average values (72% MCR), while tankvessels have higher (84% MCR). The load was rangingfrom about 60% MCR up to 95% MCR for the 82 differentships. This illustrates large variations in required engineoutput and average operational speed.3.1.4. Installed Main Engine Power[36] From 1978 to 2000 the yearly average main engine

power (p) is estimated from Lloyd’s fleet database [LRF,2005]. The average installed power for a given year iscalculated using a similar approach as for operational speed.Up to 1978 the change in average power is assumed tofollow the development for ships larger that 2,000 Dwtreported by Eyring et al. [2005] (based on data from UK’strade magazine ‘‘The Motor Ship’’). We believe that thisbetter represents the development of average power in thefleet up to 1978, compared to application of detailed fleetdata available, where larger merchant ships could be under-represented because of scrapping after some 25–30 years(not included in the fleet database). Our calculated averagepower figures per ship correspond to the data reported for1990, 1995 and 2000 by Eyring et al. [2005]. However, ourestimate for 1980 is about 10% lower, compared to Eyringet al. [2005].

3.2. Modeled Fuel Consumption

[37] Figure 7 shows the modeled fuel consumption bymeans of equation (3) for the world fleet from 1970 to 2000.Our results show that the fuel consumption can be modeledby including the major changes in technology, fleet structureand operational factors. Our modeling differentiates onengine and fuel types, and Figure 7 (as well as Figure 8)illustrates that these effects are important around 1970, andshould be included in historical fleet modeling. The in-creased fuel consumption from 1970 to 1973 (1974) isexplained with increased demand for sea transport (i.e.,number of days at sea, Figure 9), as well as long sailingdistances with cargo (Figure 4, middle). The latter havereduced number of port calls and consequently reduced totaltime in port (more time at sea). For the tanker fleet, trans-porting 50% of the sea borne trade around 1970, the averagedistance was about 6,600 nautical miles (nm) in the mid1970s, before rapidly falling to a level of 4,600 nm in themid 1980s (Figure 4, middle). The reasons was that after theoil crisis in 1973, the USA in particular, but also Europeanimporters, started to import more from other, Non-OPECsources, or increased their own production as was the casefor United Kingdom and Norway [Wijnolst and Wergeland,


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1997]. The variation in trade patterns for oil is therefore animportant factor determining demand for crude oil trans-portation, as well as fuel consumption by this fleet segmentand the entire fleet.[38] The results show that growth in the fleet is not

necessarily followed by increased fuel consumption. Forinstance, the stagnation and decline from around 1973 to1983 in fuel consumption is explained with decrease innumber of days at sea (Figure 9), combined with reductionof average sailing distances (oil tankers), increasing numberof ships laid up (Figure 4) and the rapid shift to diesel

powered ships. The stagnation and decline around 1973 inoil transportation (Figure 4), the largest individual com-modity trade by sea, is explained with the very high oilprizes resulting in shift back to coal as fuel for powerstations [Stopford, 1997]. Around 1985, when the laid uptonnage was reduced and most of the ships in the fleet werediesel powered, the stagnation in fuel consumption canmainly be explained by a slow down in sea borne trade(Figures 3 and 4). After 1990, the fuel consumption hasalmost followed the development in sea born trade and fleetgrowth (Figure 4 versus Figure 7).

Figure 7. Modeled main engine fuel consumption for the oceangoing civil world fleet above or equal to100 GT separated on main engine and fuel types, 1970–2000 (not including the military fleet). Themodeled fuel consumption (black) is mostly lower than the estimated worldwide marine bunker sales(red) (including the entire fishing fleet).

Figure 8. Sensitivity analyses, considering alternative input data. Modeling is made for all oceangoingcivil ships above or equal to 100 GT, 1970–2002.


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3.2.1. Discussion[39] Our results indicate that better activity data on a

yearly basis over time is required when fleet modeling isused to determine the actual fuel consumption for the entireworld fleet. If our method for estimating days at sea isextended to cover the main cargo shipping segments sepa-rately, we expect that the uncertainty will be significantlyreduced. However, the method fails for service ships (non-cargo). Yearly tracking data (e.g., movement data available)for such vessels would then increase the reliability in modelresults. Lack of actual service speed data for the fleetsignificantly influences the uncertainty as the specific con-sume is speed-dependent and because the service speeddefines number of days at sea required to carry out thetransport demand. It is recommended that reported days atsea are applied with care since the model results areparticularly sensitive to this parameter.

[40] We expect that in the future the actual service speedwill be estimated on the basis of AIS (automatic identifica-tion systems) tracking data for individual oceangoing ships.Such data also makes it possible to indirectly estimate theengine power utilization per ship (and for fleet segments) bycombining recorded service speed with installed mainengine power for each individual ship (available fromLloyd’s fleet databases). AIS is primarily an anticollisionsystem, and is designed to be capable of automaticallyproviding position and identification information about theship to other ships and to coastal authorities [U.S. CoastGuard, 2002]. The International Maritime Organisation(IMO) requires AIS to be fitted aboard all internationalships of certain size. Dalsøren et al. [2007] also report thatin the future local and regional ship emission inventories(geographical distribution of emissions) will be based onAIS statistics.[41] The model has been applied to periods before 1970

as well. However, the presented approach fails around 1960,when the world fleet still transported large numbers ofpassengers (see equation (5)). It was not until 1958 thatairplanes transported more transatlantic passengers thanlarge passenger ships [Hansen, 2004]. Another problem isthe fact that about half the US fleet of 28 million GT waslaid up in 1949. This was the US reserve fleet andrepresented some 17% of the total world fleet by tonnage[Aschehougs Konversasjonsleksikon, 1951]. Also, historicalshipping data for this period is limited. This illustrates someof the challenges that have to be considered when modelingfuel consumption before 1970.3.2.2. Comparison With Other Studies[42] Our new estimate for year 2000 is some 30 Mt higher

than previously reported by Endresen et al. [2003] (Table 5).The main reason for the deviation, is that our new modelingestimates also include about 45,000 noncargo ships, notconsidered by Endresen et al. [2003]. It is interesting thatthese two models using different approaches and data sets,

Figure 9. Estimated average number of days at sea for theoceangoing cargo fleet, 1970 to 2000.

Figure 10. Distribution of main engine (ME) power (%) within the predefined size categories for theyear 2004, cargo and noncargo fleet [LRF, 2005].


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give nearly similar results, if the consumption by noncargoships is taken into account. The detailed activity-basedestimates for the world fleet (civil) reported by Corbettand Koehler [2003] and Eyring et al. [2005] are still a factorof 1.25 (�50 Mt) higher (Table 5). However, Corbett andKoehler [2004] also considered alternative input data to theactivity-based modeling, and pointed out that the fuelconsumption could be up to 16% lower. This implies thatthe two studies are within the same range when theuncertainty bounds are taken into account.[43] Eyring et al. [2005] also reported simplified activity-

based fuel consumptions estimates for 1950, 1960, 1970,1980 and 1995, and assumed that interpolation betweenthese periods would reflect the development. They alsointerpolated between the simplified 1995 estimate and thedetailed estimate for year 2001. Our modeled fuel estimatesare significantly lower than reported by Eyring et al. [2005]for the period 1980–2000. The main reasons for the largedeviation are probably that they have assumed the numberof days at sea significantly higher than we estimate andinclude less key influencing factors, compared with ourmodel. Note that their assumed number of days at sea isabout 90 days higher for year 1995 than the estimateprovided by this study (179 days). The sensitivity modelingindicates more than two times higher fuel consumption forsome years (e.g., 1983), if the major effects are not includedand if days at sea are assumed equal to 270 (Figure 8). Thisshows that results from simplified activity-based models aresensitive to key input factors. Our model estimates for 1970,1980, and 1995 are about 10–15 Mt higher than reported byEyring et al. [2005], if the days at sea is increased to 270and held constant, and the laid up tonnage is set to zero(Figure 8). This illustrates that the two simplified modelsgives nearly the same response with similar input data.However, Eyring et al. [2005] have not reported detailedinput data for these reference years (e.g., assumed engineload, specific fuel consumption) and some consumption bymilitary ships and the auxiliary engines could have beenincluded. In addition, their model do not take into accountlaid up tonnage, and do not differentiate on engine and fueltypes. Direct comparison is therefore difficult.

3.2.3. Uncertainty in the Estimates[44] The uncertainty in each parameter of equation (3),

including main assumptions, is addressed below with anestimate for the uncertainty in total fuel consumption. Theweakness of the average ship modeling approach comparedto more detailed modeling approaches (separates on shipsizes and types) is that our simplified approach uses averagecharacteristics, separating on only steam and diesel poweredships. The uncertainties in our estimates arise from bothuncertainties in the applied averages, as well as the simpli-fied method. The methodology does not include second-order effects among parameters in equation (3). Moreover, itshould be noted that our model do not take into account thetechnical development on antifouling systems [Evans,2000] which likely have influenced fuel consumption andemissions over the past 100 years.[45] The detailed activity-based approaches, identify size

and type categories with common characteristics. The fuelconsumption is then calculated for each category by apply-ing characteristic factors for each category in combinationwith total power installed within this category. The total fuelconsumption is based on a sum over all categories. Detailedinput data is required for this approach and such data isgenerally not available to derive a historical inventory. Wethen have to simplify by establishing averages that arerepresentative for one large category covering all ships inthe fleet. The applied averages are not weighted with powerinstalled or energy production, introducing an uncertainty.For example, small cargo ships have compared to largecargo ships relatively less installed power, less days at seawith a higher specific fuel consumption and lower averageengine load (e.g., large number of voyages, requires moreoften part loads in port areas). The actual lower specific fuelconsumption for larger ships implies that our model resultsin a too high overall fuel consumption as the larger shipsdominate trade, tonnage and installed effect (Figure 10).Number of days at sea is based on a demand covered by anumber of ships of average size. Larger ships will be moreenergy efficient and smaller ships less energy efficient. Wetherefore expect that our model results will overestimate thetotal consumption as the larger ships actually have more

Table 5. Comparison of Reported Fuel Consumption for the Oceangoing World Fleet

Year

This Study

Eyring et al. [2005] Corbett and Koehler [2003] Endresen et al. [2003, 2005]Fuel Baseda Modeledb

1970 152 111 124c

1980 159 129 213c

1995 174 164 240c

2000 201 195 166d–200e

2001 280f 289g

aEstimates based on equation (2). The coal sales converted to oil equivalents by using 1/1.416 as conversion factor [UN,1998]. Estimates for sales to the fishing fleet (section 2.2) are included.

bEstimates based on equation (3). Cover fuel consumption by the main engines in the oceangoing civil world fleet above orequal to 100 GT. The coal consumption is converted to oil equivalents by using 1/1.416 as conversion factor [UN, 1998].

cSimplified activity-based modeling, covers oceangoing ships above or equal to 100 GT (unclear if fuel consumption by thelarge military ships and auxiliary engines are included).

dFleet modeling, covers the world civil cargo fleet (oceangoing) above or equal to 100 GT.eEstimated sales of marine fuel, based on IEA and EIA data.fDetailed activity-based modeling, covers oceangoing ships above or equal to 100 GT (the civil fleet 254 Mt (includes

noncargo fleet), the noncargo fleet 46.2 Mt, the military fleet 9.4 Mt (1300 navy ships), and auxiliary engines 16.3 Mt).gDetailed activity-based modeling, covers oceangoing ships above or equal to 100 GT (the civil fleet 248 Mt (includes

noncargo fleet), the noncargo fleet 45 Mt, and the military fleet 41 Mt)).


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days at sea at a higher efficiency than the smaller ships (lessdays at sea with a corresponding lower efficiency). Theaverage engine load is actually higher on larger ships thansmaller ships. Our model will then likely underestimate theoverall fuel consumption as larger ships dominate by tradeand tonnage. The net effect of the nonlinear effects isconsequently not straight forward to estimate.[46] The assumed number of days at sea is important, and

we have therefore performed a sensitivity analysis based onmodeling the energy consumption (kWh) of the year 2004civil world fleet [LRF, 2005]. The production within definedsize categories is calculated by combining the installedpower (Figure 10) with the number of days at sea reportedfor the different size categories. We used the number of daysat sea reported for the 5 categories by Endresen et al. [2004]for cargo ships (199 days for <9999 GT; 196 days for10,000–24,999 GT; 205 days 25,000–49,999 GT; 219 daysfor 50,000–99,999 GT; 240 days for >100,000 GT). Thetotal energy consumption for the entire fleet is then calcu-lated by summing up for all categories. A correspondingmodeling was made by using a calculated average (arith-metic mean) for these categories (= 212 days). The devia-tion was only 3%, and the constant average profile gave thehighest estimate. However, most of the installed power forthe noncargo ships originates from the category less than9,999 GT (Figure 10), and they have typically on averageless days at sea. The contribution from noncargo ships onthe overall average operational profile was taken into accountby assuming 150 days (some data given by Endresen et al.[2004]) at sea on average (instead of 199 days) for thelowest category. A similar modeling was repeated. Thisexercise resulted in a deviation of 7% compared with ourbaseline model, and the constant average profile gave thehighest estimate.[47] It is important to recognize that the cargo fleet

(including passenger ships), that account for 80% of theinstalled power (Figure 10), normally have higher engineutilization (load) and number of days at sea, compared tononcargo ships [Endresen et al., 2004]. The energy produc-tion (kWh) by the cargo fleet will then be higher than 80%,and could be as high as 90%. Corbett and Koehler [2003]reported typical average specific fuel consumption by cargoand noncargo ships to be respectively 206 and 221 g/kWh,with reference to year 2001. By weighting according toinstalled power, a weighted average of about 209 g/kWh isobtained. We have applied a value of 220 g/kWh for year2000, indicating that our model will overestimate the fuelconsumption around year 2000. However, the fleet compo-sition with respect to old ships with old engines varies overtime and they are normally in operation for several decades(e.g., the average age for civil fleet was 22.4 years in 2006[LRF, 2005–2006]), with unknown status and maintenancecondition. Our somewhat higher specific fuel consumptiontakes the effect of old engines into account (see section 3.1.3).[48] It is difficult to estimate the uncertainty because of

limited technical and operational data over the decades. It isimportant to notice that some of the effects (e.g., engineload versus specific fuel consumption) will drive results inopposite directions, thus giving a representative averagealthough the uncertainty in each parameter is significant.Our applied averages seem to reflect the cargo fleet and wetherefore claim that the simplified approach will give

reasonable estimates. Including the noncargo fleet in themodeling adds to the uncertainty as these ships have most ofthe power installed below 5,000 GT (Figure 10) and operatesignificantly different from cargo ships (e.g., engine load).However, the energy production in this fleet segment issignificantly less than for the cargo ships (see above).Taking this into account, we expect ±10% as representativefor the error of using a simplified model versus a moredetailed approach (uncertainty related to the nonlineareffects).[49] The uncertainty in the applied averages arises from

the potential bias in data applied and error in average figuresdue to a limited data material. Our estimates for theuncertainty focus on the variable that account for the highestpotential uncertainty. It is assumed that the uncertaintyfigures are independent and representative estimates forstandard deviations. The uncertainties in the calculatedaverages are based on variation ranges reported in theliterature.[50] The modeled fuel consumption is sensitive to the

applied installed engine power. Our year 2000 modeling oftotal installed engine power for the entire fleet of oceango-ing civil ships above or equal to 100 GT (281,000 MW)corresponds very well with numbers reported by Corbettand Koehler [2003] (280,000 MW). This result indicates alow uncertainty in the calculated average power around year2000. We expect the uncertainty in average engine powerper ship to be up to ±10% around 1970 decreasing to nearlyzero for year 2000.[51] The model results are also sensitive to the assumed

number of days at sea per ship. The uncertainty bound fordays at sea is calculated to be ±15% considering typicalvariations in the main input data. The largest contributionresults from the assumed cargo capacity utilization, followedby the assumed ballast factor. We have evaluated our 2000estimate (181 days at sea) with a calculated average activityprofile covering 3,431 AMVER cargo ships [Endresenet al., 2004]. By weighting the reported days at sea foreach category (see above) by the actual power installed inthe year 2004 world fleet (for the same size categories)(Figure 10), the weighted average number of days at sea iscalculated to 205 days. This is some 20 days higher than theapplied average. The deviation could be explained with thefact that the AMVER fleet typically covers cargo ships,mostly larger than 3,000 GT in international trade [Endresenet al., 2003]. The average number of days would decrease ifsmaller cargo ships also were included. An alternativeexplanation is that the world sea borne trade may be 11%higher in year 2000 than assumed. Our calculated 181 daysat sea is based on a trade estimate of 5434 Mt [Fearnleys,2002], while Review of Maritime Transport [United NationsConference on Trade and Development, 2006] reports asomewhat higher figure (5983 Mt). Our calculated averagenumber of days at sea then corresponds with the weightedAMVER operation profile. This result indicates that weprobably slightly underestimate the average days at sea, ifwe only consider the cargo fleet. However, operational dataindicates less days at sea for the noncargo fleet [Endresen etal., 2004]. The expected bias will decrease up to 2000, asthe noncargo fleet have doubled by numbers from 1970 to2000 (Figure 4). Our best estimate is that the combineduncertainty related to the various input data is within ±25%.


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The total uncertainty in fuel consumption is estimated to beabout ±30%, when the methodological uncertainties areadded.[52] Auxiliary engines will also contribute to the total fuel

consumption and emissions for oceangoing civil shipsabove or equal to 100 GT, but this is not included inequation (3). Estimates presented indicate that the fuelconsumed by auxiliary engines in port and at sea mayamount to less than 10% of the total [Whall et al., 2002;Corbett and Koehler, 2003]. Consequently, if auxiliaryengines were included, the modeled fuel consumptionshould have been in the order of +5% higher. The modelestimates presented in this study are thus likely to beapproximately 15% too low because auxiliary engines andall military ships and vessels less than 100 GT are excluded(see section 4).

4. Marine Sales Versus Modeled Consumption

[53] Several activity-based studies have reported fuelconsumption without including oceangoing ships less than100 GT. The fuel consumption by these ships is notaddressed in the literature, and could be significant. Forinstance in 1998, the global number of engine poweredfishing vessels (decked) was about 1.3 millions vessels[FAO, 2006a], while only some 23,000 of these vesselswere larger than 100 GT in year 2000 (Lloyd’s Register ofShipping, world fleet statistics and statistical tables, 2000).The fishing fleet less than 100 GT represents nearly half ofthe installed power for the entire fishing fleet (see section2.2.2). We may therefore assume that these vessels accountfor half of the fuel demand of the fishing fleet (�10 Mtfuel). Norway has approximately 3,000 cargo and serviceships between 25 and 100 GT in coastal trade [StatisticsNorway, 2000]. We do not have data for the rest of theworld fleet less than 100 GT operating mainly in nationalwaters, but we assume that this part represents a con-sumption of at least the same order of magnitude as thefishing fleet less than 100 GT. We also have to take intoaccount the consumption by the military fleet whichconsumed some 5 Mt in 1996 [Endresen et al., 2003]and the consumption by auxiliary engines (�5% of thetotal, see section 3.2.3). Consequently we expect ouractivity modeling estimates for the period 1995 up to2000 to be some 25–35 Mt less than the actual fuelconsumption for the entire worldwide oceangoing fleet.We find that the estimated consumption is about 10% toohigh for this period compared with total estimated salesdata. This indicates that the reported sales number for thisperiod may be representative, and not significantly under-reported. However, the uncertainty in the activity-basedestimates is significant (section 3.2.3), as well as theassumptions used to derive the added consumption of25–35 Mt fuel.[54] Several studies have questioned the reduction in

sales for given time periods without considering the impor-tant changes in the fleet. This has led to the assumption thatsignificant underreporting of sales can have occurred. How-ever, this study illustrates that improved modeling, with theuse of high-resolution time series as input data, givescorresponding trends in modeled fuel consumption and

sales numbers. Our results are supported by the generalchanges in trade and the fleet activity (Figure 4).

5. Conclusion

[55] From 1910 to 2000, the oceangoing world fleet ofcivil ships above or equal to 100 GT grew by number fromaround 22,000 to 88,000 motor ships, by gross tonnagefrom 37 to 558 millions, and by cargo transported fromabout 300 Mt (year 1920) to 5,400 Mt. Oceangoing shipshad a yearly consumption of about 80 Mt of coal(corresponding to 56.5 Mt heavy fuel oil) before the FirstWorld War. This increased to a sale of about 200 Mt ofmarine fuel oils in 2000 (including the fishing fleet), i.e.,about a fourfold increase in fuel consumption. Of this sale,international shipping accounts for some 70–80%. Thefuel-based ship emissions are estimated to 229 Tg (CO2)in 1925, growing to about 634 Tg (CO2) in 2002. Thecorresponding SO2 emissions are about 2.5 Tg (SO2) and8.5 Tg (SO2). The CO2 emissions per tonne transported bysea have been significantly reduced as a result of larger andmore energy efficient ships.[56] We find that the development of fuel consumption

from 1970 up to 2000 can be modeled by including themajor changes in the fleet size, shift in fuels and propulsion,technical improvements, changes in average operatingspeed, average sailing distance and demand for sea trans-port. It is suggested that these key factors are included whenperforming historical activity-based fleet modeling. Thevariation in trade patterns over the years for oil is animportant factor determining demand for crude oil trans-portation (e.g., average sailing distances), as well as fuelconsumption by this fleet segment and the entire fleet. Thisstudy concludes that the growth in the fleet is not neces-sarily followed by increased fuel consumption, as thecomplex interaction among the key influencing variableswill determine the fuel consumption. We find that theestimated fuel consumption corresponds fairly well withthe reported fuel sales from 1970 to 2000, when especiallythe consumption by auxiliary engine power, ships less than100 GT and all military ships are included. It is not possibleto conclude on the actual uncertainty or bias in the marinesales data on the basis of our findings, but our results andother studies indicate that underreporting may occur. How-ever, our results indicate that the reported sales number forthis period may be representative and not significantlyunderreported, as previous activity-based studies have sug-gested. Fuel consumption by ships less than 100 GT (e.g.,about 1.3 millions fishing vessels today) is important toinclude when comparing fuel sales with activity-basedestimates.[57] Interestingly, our results here agree well with our

previous activity-based estimates for the year 2000 (ifconsumption by 45,000 noncargo ships is taken intoaccount) that used an alternative approach and different datasets. However, our simplified model estimates of fuelconsumption from 1980 to 2000 are significantly lower thanpreviously reported activity-based studies. By consideringalternative input data to our simplified activity-based model,we conclude that the main reason for the large deviationbetween activity-based fuel consumption estimates is the


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number of days assumed at sea. Our results indicate thatimproved activity data on a yearly basis are needed todetermine the actual energy demand for the entire worldfleet if a simplified activity-based model is to beused. Such data will also significantly reduce the uncer-tainty for estimates based on more detailed activity-basedmodeling.

[58] Acknowledgments. The preparation of this paper was cofundedby the EU-project QUANTIFY (contract 003893). We sincerely acknowl-edge Kristin Rypdal at CICERO, Norway, for her support and input duringthe work with this paper. We would also like to acknowledge StephenMcAdam at DNV for significantly improving the paper.

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