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

5.4.1 Available worldwide studies

Two recent studies – the International Energy Agency’s World Energy Outlook (IEA, 2004a) and the World Business Council on Sustainable Development’s Mobility 2030 (WBCSD, 2004a) – examined worldwide mitigation potential but were limited in scope. The IEA study focused on a few relatively modest measures and the WBCSD examined the impact of specified technology penetrations on the road vehicle sector (the study sponsors are primarily oil companies and automobile manufacturers) without regard to either cost or the policies needed to achieve such results. In addition, IEA has developed a simple worldwide scenario for light-duty vehicles that also explores radical reductions in GHG emissions.

World Energy Outlook postulates an ‘Alternative scenario’ to their Reference scenario projection described earlier, in which vehicle fuel efficiency is improved, there are increased sales of alternative-fuel vehicles and the fuels themselves and demand side measures reduce transport demand and encourage a switch to alternative and less energy intensive transport modes. Some specific examples of technology changes and policy measures are:

  • In the United States and Canada, vehicle fuel efficiency is nearly 20% better in 2030 than in the Reference scenario and hybrid and fuel-cell powered vehicles make up 15% of the stock of light-duty vehicles in 2030;
  • Average fuel efficiency in the developing countries and transition economies are 10–15% higher than in the Reference scenarios;
  • Measures to slow traffic growth and move to more efficient modes reduce road traffic by 5% in the European Union and 6% in Japan. Similarly, road freight is reduced by 8% in the EU and 10% in Japan.

The net reductions in transport energy consumption and CO2 emissions in 2030 are 315 Mtoe, or 9.6% and 997 MtC, or 11.4%, respectively compared to the Reference scenario. This represents a 2002–2030 reduction in the annual growth rate of energy consumption from 2.1-1.3% per year, a significant accomplishment but one which still allows transport energy to grow by 57% during the period. CO2 emissions grow a bit less because of the shift to fuels with less carbon intensity, primarily natural gas and biofuels.

IEA has also produced a technology brief that examines a simple scenario for reducing world GHG emissions from the transport sector (IEA, 2004b). The scenario includes a range of short-term actions, coupled with the development and deployment of fuel-cell vehicles and a low-carbon hydrogen fuel infrastructure. For the long-term actions, deployment of fuel-cell vehicles would aim for a 10% share of light-duty vehicle sales by 2030 and 100% by 2050, with a 75% per-vehicle reduction in GHG emissions by 2050 compared to gasoline vehicles. The short-term measures for light-duty vehicles are:

  • Improvements in fuel economy of gasoline and diesel vehicles, ranging from 15% (in comparison to the IEA reference case) by 2020 to 35% by 2050;
  • Growing penetration of hybrid vehicles, to 50% of sales by 2040;
  • Widespread introduction of biofuels, with 50% lower well-to-wheels GHG emissions per km than gasoline, with a 25% penetration by 2050;
  • Reduced travel demand, compared to the reference case, of 20% by 2050.

Figure 5.14 shows the light-duty vehicle GHG emissions results of the scenario. The penetration of fuel cell vehicles by itself brings emissions back to their 2000-levels by 2050. Coupled with the nearer-term measures, GHG emissions peak in 2020 and retreat to half of their 2000-level by 2050.

Figure 5.14

Figure 5.14: Two possible scenarios for GHG reductions in Light-duty vehicles

Source: IEA, 2004b.

The Mobility 2030 study examined a scenario postulating very large increases in the penetration of fuel efficient technologies into road vehicles, coupled with improvements in vehicle use, assuming different time frames for industrialized and developing nations.

The technologies and their fuel consumption and carbon emissions savings referenced to current gasoline ICEs were:

Technology Carbon reduced/vehicle (%) 
1. Diesels 18 
2. Hybridization 30 (36 for diesel hybrids) 
3. Biofuels 20-80 
4. Fuel cells with fossil hydrogen 45 
5. Carbon-neutral hydrogen 100 

Figure 5.15 shows the effect of a scenario postulating the market penetration of all of the technologies as well as an assumed change in consumer preferences for larger vehicles and improved traffic flows. The scenario assumes that diesels make up 45% of light-duty vehicles and medium trucks by 2030; that half of all sales in these vehicle classes are hybrids, also by 2030; that one-third of all motor vehicle liquid fuels are biofuels (mostly advanced) by 2050; that half of LDV and medium truck vehicle sales are fuel cells by 2050, with the hydrogen beginning as fossil-based but gradually moving to 80% carbon neutral by 2050; that better traffic flow and other efficiency measures reduce GHG emissions by 10%; and that the underlying efficiency of light-duty vehicles improves by 0.6% per year due to steady improvements (e.g., better aerodynamics and tyres) and to reduced consumer preference for size and power. In this scenario, GHG emissions return to their 2000-level by 2050.

Figure 5.15

Figure 5.15: The effect of a scenario postulating the market penetration of all technologies

Source: WBCSD, 2004a.

Mobility 2030’s authors make it quite clear that for this ‘mixed’ scenario to be even remotely possible will require overcoming many major obstacles. The introduction and widespread use of hydrogen fuel cell vehicles for example requires huge reductions in the costs of fuel cells; breakthroughs in on-board hydrogen storage; major advances in hydrogen production; overcoming the built-in advantages of the current gasoline and diesel fuel infrastructure; demonstration and commercialization of carbon sequestration technologies for fossil fuel hydrogen production (at least if GHG emission goals are to be reached); and a host of other R&D, engineering and policy successes.

Table 5.8 summarizes technical potentials for various mitigation options for the transport sector. As mentioned above, there are few studies dealing with worldwide analysis. In most of these studies, potentials are evaluated based on top-down scenario analysis. For combinations of specific power train technologies and fuels, well-to-wheels analyses are used to examine the various supply pathways. Technical potentials for operating practices, policies and behaviours are more difficult to isolate from economic and market potential and are usually derived from case studies or modelling analyses. Uncertainty is a key factor at all stages of assessment, from technology performance and cost to market acceptance.

Table 5.8: Summary table of CO2 mitigation potentials in transport sector taken from several studies

Study Mitigation measure/policy Region CO2 reduction (%) CO2 reduction (Mt) 
2010 2020 2030 2050 2010 2020 2030 2050 
IEA 2004a Alternative scenario World 2.2 6.8 11.4   133 505 997   
OECD 6.9 11.5  77 308 557  
Developing countries  2.8 6.8 11.4  49 170 381  
Transition economies 2.3 6.2 11.2  27 59  
IEA 2001 Improving Tech for Fuel OECD   30            
Diesel    5-15      
IEA 2002a All scenarios included NA 6.6 14.4     148 358     
All scenarios included Western Europe 6.6 15.6   76 209   
All scenarios included Japan 8.3 16.1   28 61   
IEA 2004d Improving fuel economy World     18           
Biofuels   12      
FCV with hydrogen refuelling        
IEA 2004b Reduction in fuel use per km World   15 25 35         
Blend of biofuels  13     
Reduction in growth of LDV travel  10 20     
using hydrogen in vehicle  75     
ACEEE 2001 A-scenario USA 9.9 26.3     132 418     
B-scenario 11.8 30.6   158 488   
C-scenario 13.2 33.4   176 532   
MIT 2004     USA      (2035)           
Baseline  3.4 16.8           
Medium HEV  5.2 29.9      
Composite  14.9 44.4      
Combined policies 3-6 14-24 32-50           
Greene and Schafer 2003 Efficiency standards USA   (2015)            
Light-duty vehicles  18 
Heavy trucks  
Commercial aircraft             
Replacement & alternative fuels               
Low-carbon replacement fuels       
Hydrogen fuel (all LDV fuel)       
Pricing policies               
Low-carbon fuel subsidy       
Carbon pricing       
Land use & infrastructure       
System efficiency       
Climate change education       
Fuel economy information       
Total   22 48           
WEC 2004 New technologies World   30   46         
WBCSD 2004b Road transport Diesels (LDVs) Hybrids (LDVs and MDTs) Biofuels-80% low GHG sources Fuel Cells-fossil hydrogen Fuel Cells-80% low-GHG hydrogen Mix shifting 10% FE improvement 10% Vehicle travel reduction- all vehicles World    0.9 2.4 5.7 5.9 5.9 6.7 9.4  2.1 6.1 15.6 16.7 17.2 18.8 22.8  1.8 6.1 29.5 32.7 45.3 47.3 51.9    61 161 386 400 400 451 639  160 474 1207 1293 1333 1455 1765  181 623 3030 3364 4650 4864 5335