Greenhouse Gas Results

To summarize:

  • “Business as usual”--100% gasoline cars: if we all kept driving regular (non-hybrid) gasoline-powered internal combustion engine vehicles (ICVs), then GHGs would fall slightly due to reduced number of vehicles sold (after the 2008 recession), and GHG emissions remain above 1990 levels, as shown by the upper dashed line labeled “ICVs only” on the chart above[of course, this is not plausible, since HEVs are already a significant and growing fraction of new car sales.]
  • Gasoline-powered hybrid electric vehicle (HEV) Base Case scenario: adding gasoline-powered hybrid electric vehicles (HEVs) helps; GHGs are reduced substantially, falling below the 1990 levels by 2040 (still far short of the goal of reducing GHGs 80% below 1990 levels)
  • Gasoline plug-in hybrid scenario: introducing gasoline-powered plug-in HEVs (orange line) also cuts GHGs slightly by mid-century when the model assumes that the electrical utility grids substantially cut their use of coal power, and/or install carbon capture and storage (CCS) technology at most coal plants.  According to the Argonne National Laboratory 2012_1 GREET model, PHEVs would not significantly reduce GHGs compared to gasoline HEVs, even though the electrical grid is nearly carbon-free by the end of the century.
  • Biofuel plug-in hybrid scenario: biofuels such as cellulosic ethanol can also play a significant role, when combined with plug-in hybrids. As shown in the graph, the scenario with biofuel-powered PHEVs are projected to cut GHGs to 29% below 1990 levels by 2060 and to 44% below 1990 levels by 2100.
  • battery electric vehicle (BEV) scenario: The BEV scenario can  reduce GHGs to 55% below 1990 levels by the end of the century; BEV market penetration is limited in this case to approximately 40% of all light duty vehicles, based on our estimate of the number of small cars, small SUVs, small vans and small pickup trucks and including 50% of all midsize sedans as vehicles that could be affordably powered by batteries.
  • Fuel cell electric vehicle scenario: Our detailed computer simulations demonstrate that, in order to achieve our goal of reducing greenhouse gases to 80% below 1990 levels (dashed red line at bottom of graph), society will have to begin the process of replacing the internal combustion engines on HEVs and PHEVs with all-electric vehicles.  The fuel cell EV scenario would reach an 80% reduction below 1990 levels by approximately 2065 with the parameters in this model, and to 87% below 1990 levels by 2100. To achieve the 80% reduction goal by 2050 would require a more rapid introduction of FCEVs and/or more rapid introduction of lower carbon hydrogen sources such as landfill and waste water treatment plant gases and renewable electricity. [Note: the bottom orange line in the graph above represents a 95% reduction below 1990 levels, which some think may be necessary for motor vehicles, given that other sectors of the economy may have difficulty achieving an 80% reduction target.]
    • For a detailed description of the input assumptions for these models, see an article published in December of 2009.


  • Early GHG reductions.  Advocates of plug-in hybrid electric vehicles claim that we need to begin deploying PHEVs now to achieve reasonable GHG reductions after 2020. Our model does assume that PHEVs enter the marketplace first, as shown in this graph: Sales of PHEVs reach 100,000 by 2018, but FCEVs do not reach the 100,000 mark until 2023.  (Note: the PHEV market penetration is falling far behind earlier predictions, but the model still relies on extrapolations of actual sales through 2011, with 761,900 PHEVs on the road by 2020 when there are 186,000 FCEVs on the road):
  • Despite this 5- to 6-year head-start for PHEVs, the hydrogen-powered FCEVs cut GHGs more than gasoline-powered PHEVs during the period from 2020 to 2060 as shown below. The FCEV scenario provides the largest reductions in GHGs by 2030, since FCEVs cut GHGs by 50% compared to gasoline ICVs even if all the hydrogen is made from natural gas, while PHEVs still use some gasoline, and the operation of BEVs requires some oil to prospect for, mine, process and transport the fuel (Primarily coal) used to generate electricity (However, the major reason that BEVs to not cut GHGs is due to their low market penetration, limited to approximately 40% of new car sales, as described above.)



  • The FCEV Scenario cuts GHGs more since FCEVs immediately reduce GHGs by 50% compared to gasoline-powered cars, even if the hydrogen is made from natural gas, while PHEVs still rely on gasoline for part of their travel, and most electricity used to charge PHEV batteries in the US comes from burning coal, the dirtiest (Highest carbon content) fuel.
  • Greenhouse gases (GHGs) with 100% Coal-generated electricity. Some advocates of BEVs and PHEVs have claimed that BEVs and PHEVs will generate lower GHG emissions even if all the electricity is generated by burning coal. The highly respected Argonne National Laboratory GREET model [1] refutes this supposition. As shown in this figure, a BEV would generate 11% more GHGs (450g/mile) than a conventional (non-hybrid) gasoline car (405 g/mile), and plugging in a gasoline HEV will generate more GHGs (321 to 415 g/m) than running that HEV on gasoline only (290 g/mile):
  • In addition, even with the average US grid mix (which produces lower GHGs than the marginal grid mix that is recommended to be used by the Greenhouse Gas Protocol [1], plugging in HEVs that are using lower carbon fuels such as hydrogen, E-85 (mixture of 85% ethanol and 15% gasoline) and even diesel fuel always increases GHGs (in other words, the GHGs for AER =0 corresponding to an HEV is lower than any PHEV with finite AER...the lines all rise as you go to higher all-electric range (AER)) Thus owners of PHEVs like the Chevy Volt will produce lower GHGs if they run on gasoline all the time and never plug in their PHEVs!:
  • For more details on GHGs from coal-based electricity, see this report.
  • [1] D. Breoekhoff, “The Greenhouse Gas Protocol: Guidelines for quantifying GHG reductions from grid-connected electricity projects,” World Resources Council and the World Business Council for Sustainable Development, August 2007


  • EPA/DOT 2012 Motor Vehicle Fuel Economy Labels include GHG ratingsThe Good news: The US Environmental Protection Agency and the US Department of Transportation added greenhouse gas (GHG) emissions data to the vehicle fuel economy stickers placed on all new vehicles.  This is welcome news, since consumers should be given credible information regarding the climate change impact of new car purchases. The Bad News: Unfortunately, they list only the vehicle tailpipe GHG emissions, excluding all upstream emissions from fuel processing and, in the case of electric vehicles, the GHGs that come from electricity generation plants (most of which are fueled by coal in the U.S.),  the dirtiest (highest carbon content) fuel. The impact of this GHG rating system is illustrated in these two tables.  The first table shows the ratings of a set of alternative vehicles based on the full well-to-wheels (WTW) GHG emissions, the only fair measure of the total impact of motor vehicles on climate change gases.
  • The second table shows these same vehicles sorted according to tailpipe emissions only, metric used by the EPA:
  • Finally, we plotted the alternative vehicle GHG rankings with tailpipe-only emissions against the GHG rankings for WTW GHGs.  The results look like a random scatter diagram, indicating that there is no serious correlation between tailpipe-only GHGs and WTW GHGs, the true measure of climate change impact (If tailpipe GHGs were a good surrogate for WTW GHGs, then the red dots would all end up on the straight line), :
  • For more details on our calculations of GHGs for the 31 alternative vehicles, see this report.
  • DOE GHG alternative vehicle GHG Estimates.
  • The U.S. Department of Energy uses this bar chart to compare the estimated WTW GHGs from various mid-sized alternative vehicles and fuels in the 2030 to 2045 time period (except for the top bar for current gasoline ICVs) The GHGs for FCEVs (green bars) are less than the GHGs for BEVs with 100-mile range with the average US grid mix (turquoise bar), and lower than GHGs from PHEVs (light purple bars)

 [Source:  2011 DOE Hydrogen and Fuel Cell Program plan, Figure 1.8a on page 21, available at this link  

  • [1]“The Greenhouse gases, regulated emissions and energy use in transportation model”, by the Argonne National laboratory, available at http://greet.es.anl.gov/main




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