The growing threat of global warming, air and water
pollution, and rising energy costs are a few of the many problems that result
from our current over-reliance on petroleum-based transportation fuels.
Alternative transportation fuels, in conjunction with an array of other
energy-related strategies, have the potential to help mitigate these
problems—if public policy prioritizes those fuels that can deliver the greatest
benefit for the environment and the American people.
America’s dependence on oil for transportation
causes massive environmental impacts.
Emissions
from transportation accounted for 28 percent of global warming emissions
in the United States
in 2005. Gasoline and diesel were responsible for 78 percent of
transportation-sector emissions.
Global
warming is a growing threat to the environment and our way of life. Within
a century, the average world temperature could increase by another 2 to
11.5°F. Sea level could rise by 7 to 23 inches, and snow and ice cover
will continue to contract.
Our
heavy reliance on petroleum-based fuels has also created widespread air
and water pollution.
Alternative
transportation fuels can reduce our dependence on petroleum, but vary greatly
in their impact on the environment.
Corn-based ethanol has greater life-cycle global warming
emissions than gasoline, when produced at the high volumes forecast for coming
years and in ways that increase demand for cropland worldwide. Corn-based
ethanol can also contribute to air pollution problems if used in low-percentage
blends in gasoline and may potentially trigger significant environmental
impacts from increased farming. Cellulosic ethanol made from agricultural
residues or from crops grown on abandoned or marginal cropland may achieve
emission reductions with less environmental impact, but is still in the very
early stages of development.
Biodiesel is generally recognized to produce less air pollution
than conventional diesel, but soybean-based biodiesel produces more global
warming pollution than conventional diesel when it is produced in ways that
increase demand for cropland worldwide. Oil crop production is land-intensive,
spurring cultivation of new land and resulting in high emissions. Biodiesel
made from waste oil is 98 percent cleaner than conventional diesel, but
supplies are extremely limited.
Electricity can be used to power “plug-in hybrid” vehicles and
all-electric vehicles, both of which draw electricity from the power grid.
Because electric motors are far more efficient than internal combustion
engines, vehicles that use electricity almost always produce less global
warming pollution than gasoline vehicles, even when the electricity used to
fuel them is generated from coal. The benefits are even greater when vehicles
are fueled with renewably generated electricity. However, few electric vehicles
are currently available to consumers.
Natural gas reduces air pollution and global warming pollution
compared with gasoline vehicles. But natural gas fueling infrastructure is
expensive and domestic supplies of natural gas are both finite and increasingly
constrained.
Hydrogen has long been touted as the transportation fuel of the
future. But the environmental impacts of hydrogen depend greatly on how it is
produced, and hydrogen-powered vehicles are still a long way from being
available to American consumers.
Coal-to-liquids fuels would vastly increase global warming
pollution from transportation, while exacerbating environmental impacts from
coal production. Even if emissions from coal-to-liquids plants are captured and
sequestered underground, coal-to-liquids fuels are likely to be no better, in
global warming pollution terms, than today’s petroleum-based fuels.
Figure ES-1 provides a comparison of the global warming
impacts of non-biomass alternative fuels. Emissions from ethanol and biodiesel,
included in Figure ES-2, are based on future production at a higher volume that
researchers assume would trigger worldwide shifts in land use patterns.
Figure ES-1. Relative
life-cycle global warming emissions of non-biomass alternative fuels
Figure ES-2. Relative
life-cycle global warming emissions of biomass alternative fuels at high
production volumes
* Data is not available on
the full life-cycle emissions of cellulosic ethanol produced from feedstock
grown on marginal or abandoned cropland, but such fuel has the potential for
lower emissions than gasoline.
America needs a comprehensive strategy to reduce
global warming pollution from transportation. Low-carbon transportation fuels
can play an important part in that strategy.
To reduce global warming pollution from transportation, America must
reduce the amount of miles we drive, use more efficient vehicles, and shift to
lower-carbon fuels. A low-carbon fuels strategy for the United States should:
1) Combine
the most promising approaches to maximize environmental benefits.
America
should work to make vehicles more fuel efficient, reduce liquid fuel
consumption by increasing the use of electricity (in the short-term, through
plug-in hybrids), and replace a
significant share of the liquid fuel that remains with lower-carbon options.
Such a comprehensive approach can slash per-mile global warming pollution from
vehicles by as much as 74 percent compared to conventional gasoline vehicles.
Figure ES-3.
Life-cycle emissions achieved by combining the best vehicle technologies and
fuels
(1) Vehicle
is recharged with electricity that has the same carbon emissions as the U.S. national
average.
(2)
Cellulosic ethanol produced from crop waste. Electricity has same carbon
emissions as U.S.
national average.
2) Develop
fuels with long-term potential.
Natural gas, for example, has the potential to reduce global
warming pollution in the short term, but has little long-term potential as a
transportation fuel due to limited domestic gas supplies. Some sources of
cellulosic ethanol have comparatively lower life-cycle global warming emissions,
but technological breakthroughs and infrastructure developments will be
required before the fuel becomes widespread. Public policy should emphasize the
development of infrastructure to support promising long-term fuel options over
those with only short-term potential.
3) Set stringent
environmental standards and mitigate environmental and social impacts.
America
will be more likely to reduce the environmental impacts of transportation fuels
if we set stringent environmental standards for those fuels. The first step
should be to establish a low-carbon fuel standard that encourages the
development of fuels with lower life-cycle global warming emissions. Standards
should also be developed and implemented to mitigate the impacts of alternative
fuels on the quality of our air, water and natural ecosystems.
Achieving large
reductions in global warming pollution from cars and light trucks in the years
to come will require strong public policies. Necessary steps include:
Adopting
requirements to lower the carbon content of transportation fuels and
rejecting policies to promote fuels that would make the problem worse.
Requiring
that by 2020, all new vehicles are capable of using lower carbon fuels,
whether electricity or biofuels.
Supporting
additional research into cultivation techniques for cellulosic feedstock
and into technologies for converting cellulosic feedstocks, especially
waste, into fuel.
Improving
vehicle fuel economy and pursuing measures to reduce total driving. These
measures would further cut global warming emissions and reduce our
vulnerability to rapid changes in the global petroleum market.
