IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

5.2.2 Transport in the future

There seems little doubt that, short of worldwide economic collapse, transport activity will continue to grow at a rapid pace for the foreseeable future. However, the shape of that demand and the means by which it will be satisfied depend on several factors.

First, it is not clear whether oil can continue to be the dominant feedstock of transport. There is an on-going debate about the date when conventional oil production will peak, with many arguing that this will occur within the next few decades (though others, including some of the major multinational oil companies, strongly oppose this view). Transport can be fuelled by multiple alternative sources, beginning with liquid fuels from unconventional oil (very heavy oil, oil sands and oil shale), natural gas or coal, or biomass. Other alternatives include gaseous fuels such as natural gas or hydrogen and electricity, with both hydrogen and electricity capable of being produced from a variety of feedstocks. However, all of these alternatives are costly, and several – especially liquids from fossil resources – can increase GHG emissions significantly without carbon sequestration.

Second, the growth rate and shape of economic development, the primary driver of transport demand, is uncertain. If China and India as well as other Asian countries continue to rapidly industrialize, and if Latin America and Africa fulfil much of their economic potential, transport demand will grow with extreme rapidity over the next several decades. Even in the most conservative economic scenarios though, considerable growth in travel is likely.

Third, transport technology has been evolving rapidly. The energy efficiency of the different modes, vehicle technologies, and fuels, as well as their cost and desirability, will be strongly affected by technology developments in the future. For example, although hybrid electric drive trains have made a strong early showing in the Japanese and US markets, their ultimate degree of market penetration will depend strongly on further cost reductions. Other near-term options include the migration of light-duty diesel from Europe to other regions. Longer term opportunities requiring more advanced technology include new biomass fuels beyond those made from sugar cane in Brazil and corn in the USA, fuel cells running on hydrogen and battery-powered electric vehicles.

Fourth, as incomes in the developing nations grow, transport infrastructure will grow rapidly. Current trends point towards growing dependence on private cars, but other alternatives exist (as demonstrated by cities such as Curitiba and Bogota with their rapid bus transit systems). Also, as seen in Figure 5.2, the intensity of car ownership varies widely around the world even when differences in income are accounted for, so different countries have made very different choices as they have developed. The future choices made by both governments and travellers will have huge implications for future transport energy demand and CO2 emissions in these countries.

Figure 5.2

Figure 5.2: Vehicle ownership as a function of per capita income

Note: plotted years vary by country depending on data availability.

Data source: World Bank, 2004.

Most projections of transport energy consumption and GHG emissions have developed Reference Cases that try to imagine what the future would look like if governments essentially continued their existing policies without adapting to new conditions. These Reference Cases establish a baseline against which changes caused by new policies and measures can be measured, and illustrate the types of problems and issues that will face governments in the future.

Two widely cited projections of world transport energy use are the Reference Cases in the ongoing world energy forecasts of the United States Energy Information Administration, ‘International Energy Outlook 2005’ (EIA, 2005) and the International Energy Agency, World Energy Outlook 2004 (IEA, 2004a). A recent study by the World Business Council on Sustainable Development, ‘Mobility 2030’, also developed a projection of world transport energy use. Because the WBCSD forecast was undertaken by IEA personnel (WBCSD, 2004b), the WEO 2004 and Mobility 2030 forecasts are quite similar. The WEO 2006 (IEA, 2006b) includes higher oil price assumptions than previously. Its projections therefore tend to be somewhat lower than the two other studies.

The three forecasts all assume that world oil supplies will be sufficient to accommodate the large projected increases in oil demand, and that world economies continue to grow without significant disruptions. With this caveat, all three forecast robust growth in world transport energy use over the next few decades, at a rate of around 2% per year. This means that transport energy use in 2030 will be about 80% higher than in 2002 (see Figure 5.3). Almost all of this new consumption is expected to be in petroleum fuels, which the forecasts project will remain between 93% and slightly over 95% of transport fuel use over the period. As a result, CO2 emissions will essentially grow in lockstep with energy consumption (see Figure 5.4).

Figure 5.3

Figure 5.3: Projection of transport energy consumption by region and mode

Source: WBCSD, 2004a.

Figure 5.4

Figure 5.4: Historical and projected CO2 emission from transport by modes, 1970–2050

Source: IEA, 2005; WBCSD, 2004b.

Another important conclusion is that there will be a significant regional shift in transport energy consumption, with the emerging economies gaining significantly in share (Figure 5.3). EIA’s International Energy Outlook 2005, as well as the IEA, projects a robust 3.6% per year growth rate for these economies, while the IEA’s more recent WEO 2006 projects transport demand growth of 3.2%. In China, the number of cars has been growing at a rate of 20% per year, and personal travel has increased by a factor of five over the past 20 years. At its projected 6% rate of growth, China’s transport energy use would nearly quadruple between 2002 and 2025, from 4.3 EJ in 2002 to 16.4 EJ in 2025. China’s neighbour India’s transport energy is projected to grow at 4.7% per year during this period and countries such as Thailand, Indonesia, Malaysia and Singapore will see growth rates above 3% per year. Similarly, the Middle East, Africa and Central and South America will see transport energy growth rates at or near 3% per year. The net effect is that the emerging economies’ share of world transport energy use would grow in the EIA forecasts from 31% in 2002 to 43% in 2025. In 2004, the transport sector produced 6.2 GtCO2 emissions (23% of world energy-related CO2 emissions). The share of Non-OECD countries is 36% now and will increase rapidly to 46% by 2030 if current trends continue.

In contrast, transport energy use in the mature market economies is projected to grow more slowly. EIA forecasts 1.2% per year and IEA forecasts 1.3% per year for the OECD nations. EIA projects transport energy in the United States to grow at 1.7% per year, with moderate population and travel growth and only modest improvement in efficiency. Western Europe’s transport energy is projected to grow at a much slower 0.4% per year, because of slower population growth, high fuel taxes and significant improvements in efficiency. IEA projects a considerably higher 1.4% per year for OECD Europe. Japan, with an aging population, high taxes and low birth rates, is projected to grow at only 0.2% per year. These rates would lead to 2002–2025 increases of 46%, 10% and 5%, for the USA, Western Europe and Japan, respectively. These economies’ share of world transport energy would decline from 62% in 2002 to 51% in 2025.

The sectors propelling worldwide transport energy growth are primarily light-duty vehicles, freight trucks and air travel. The Mobility 2030 study projects that these three sectors will be responsible for 38, 27 and 23%, respectively, of the total 100 EJ growth in transport energy that it foresees in the 2000–2050 period. The WBCSD/SMP reference case projection indicates that the number of LDVs will grow to about 1.3 billion by 2030 and to just over 2 billion by 2050, which is almost three times higher than the present level (Figure 5.5). Nearly all of this increase will be in the developing world.

Figure 5.5

Figure 5.5: Total stock of light-duty vehicles by region

Source: WBCSD, 2004a.


Civil aviation is one of the world’s fastest growing transport means. ICAO (2006) analysis shows that aviation scheduled traffic (revenue passenger-km, RPK) has grown at an average annual rate of 3.8% between 2001 and 2005 despite the downturn from the terrorist attacks and SARS (Severe Acute Respiratory Syndrome) during this period, and is currently growing at 5.9% per year. These figures disguise regional differences in growth rate: for example, Europe-Asia/Pacific traffic grew at 12.2% and North American domestic traffic grew at 2.6% per year in 2005. ICAO’s outlook for the future forecasts a passenger traffic demand growth of 4.3% per year to 2020. Industry forecasts offer similar prospects for growth: the Airbus Global Market Forecast (Airbus, 2004) and Boeing Current Market Outlook (Boeing, 2006) suggest passenger traffic growth trends of 5.3% and 4.9% respectively, and freight trends at 5.9% and 6.1% respectively over the next 20 or 25 years. In summary, these forecasts and others predict a global average annual passenger traffic growth of around 5% – passenger traffic doubling in 15 years – with freight traffic growing at a faster rate that passenger traffic, although from a smaller base.

The primary energy source for civil aviation is kerosene. Trends in energy use from aviation growth have been modelled using the Aero2K model, using unconstrained demand growth forecasts from Airbus and UK Department of Trade and Industry. The model results suggest that by 2025 traffic will increase by a factor of 2.6 from 2002, resulting in global aviation fuel consumption increasing by a factor of 2.1 (QinetiQ, 2004). Aero2k model results suggest that aviation emissions were approximately 492 MtCO2 and 2.06 MtNOx in 2002 and will increase to 1029 and 3.31 Mt respectively by 2025.

Several organizations have constructed scenarios of aviation emissions to 2050 (Figure 5.6), including:

  • IPCC (1999) under various technology and GDP assumptions (IS92a, e and c). Emissions were most strongly affected by the GDP assumptions, with technology assumptions having only a second order effect;
  • CONSAVE 2050, a European project has produced further 2050 scenarios (Berghof et al., 2005). Three of the four CONSAVE scenarios are claimed to be broadly consistent with IPCC SRES scenarios A1, A2 and B1. The results were not greatly different from those of IPCC (1999);
  • Owen and Lee (2005) projected aviation emissions for years 2005 through to 2020 by using ICAO-FESG forecast statistics of RPK (FESG, 2003) and a scenario methodology applied thereafter according to A1 and B2 GDP assumptions similarly to IPCC (1999).

Figure 5.6

Figure 5.6: Comparison of global CO2 emissions of civil aviation, 1990–2050

The three estimates of civil aviation CO2 emissions in 2050 from IPCC (1999) show an increase by factors of 2.3, 4.0 and 6.4 over 1992; CONSAVE (Berghof et al., 2005) four scenarios indicate increases of factors of 1.5, 1.9, 3.4 and 5.0 over 2002 emissions (QinetiQ, 2004); and FAST A1 and B2 results (Owen and Lee, 2006) indicate increases by factors of 3.3 and 5.0 over 2000 emissions.


Around 90% of global merchandise is transported by sea. For many countries sea transport represents the most important mode of transport for trade. For example, for Brazil, Chile and Peru over 95% of exports in volume terms (nearly 75% in value terms) are seaborne. Economic growth and the increased integration in the world economy of countries from far-east and southeast Asia is contributing to the increase of international marine transport. Developments in China are now considered to be one of the most important stimulus to growth for the tanker, chemical, bulk and container trades (OECD, 2004b).

World seaborne trade in ton-miles recorded another consecutive annual increase in 2005, after growing by 5.1%. Crude oil and oil products dominate the demand for shipping services in terms of ton-miles (40% in 2005) (UN, 2006), indicating that demand growth will continue in the future. During 2005, the world merchant fleet expanded by 7.2%. The fleets of oil tankers and dry bulk carriers, which together make up 72.9% of the total world fleet, increased by 5.4%. There was a 13.3% increase in the container ship fleet, whose share of total fleet is 12%.

Eyring et al. (2005a) provided a set of carbon emission projections out to 2050 (Eyring et al., 2005b) based upon four traffic demand scenarios corresponding to SRES A1, A2, B1, B2 (GDP) and four technology scenarios which are summarized below in Table 5.2.

Table 5.2: Summary of shipping technology scenarios

Technology scenario 1 (TS1) – ‘Clean scenario’ Technology scenario 2 (TS2) – ‘Medium scenario’ Technology scenario 3 (TS3) – ‘IMO compliant scenario’ Technology scenario 4 (TS4) – ‘BAU’ 
Low S content fuel (1%/0.5%), aggressive NOx reductions Relatively low S content fuel (1.8%/1.2%), moderate NOx reduction  High S content fuel (2%/2%), NOx reductions according to IMO stringency only High S content fuel (2%/2%), NOx reductions according to IMO stringency only 
Fleet = 75% diesel, 25% alternative plant Fleet = 75% diesel, 25% alternative plant Fleet = 75% diesel, 25% alternative plant Fleet = 100% diesel 
Note: The fuel S percentages refer to values assumed in (2020/2050). Source: Eyring et al. 2005b. 

The resultant range of potential emissions is shown in Figure 5.7.

Figure 5.7

Figure 5.7: Historical and projected CO2 emissions of seagoing shipping, 1990-2050

Note: See Table 5.2 for the explanation of the scenarios.

Source: adapted from Eyring et al., 2005a,b.