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6
Mitigation
Greenhouse warming is a global phenomenon, an important fact
with regard to mitigation because releases of greenhouse gases have
the same potential effect on global climate regardless of their
country of origin. An efficient mitigation strategy for the United
States would allow the United States to take cooperative action in
other countries; some of the most attractive low-cost mitigation
options may be in the poorest developing countries.
This analysis of mitigation costs and the potential for reducing
potential greenhouse warming was developed by the Mitigation Panel
(see Part Three) and is derived almost entirely from experience and
data in the United States. The analytical framework is general,
however, and could be applied in other countries.
The application of this framework to a diverse array of
mitigation options is a pioneering effort. These "first-order"
analyses are meant only to be initial estimates of the
cost-effectiveness of these options. They demonstrate a method that
can be used in determining appropriate mitigation options. The
intent is to illustrate the manner in which options should be
evaluated with the best estimates available.
This analysis is a cross-sectional, as opposed to a
longitudinal, analysis of options over time. It does not attempt,
for example, to project future levels of economic activity and
their implications for greenhouse gas emissions. The analysis does
account, however, for future consequences of current actions. The
direct effect of each option on greenhouse gas emissions is
assessed. The panel does not examine those options under the
different overall emission rates that might occur at future times.
This analysis must therefore be seen as an initial assessment of
mitigation options in terms of their return on investment under
current conditions. A subsequent analysis should consider
appropriate strategies under conditions existing at the time.
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The Role of Cost-Effectiveness
A mitigation strategy should use options that minimize effects
on domestic or world economies. Strategies therefore should be
evaluated on the basis of cost-effectiveness as well as other
considerations. Care must be taken to ensure that estimates of both
costs and effects are comparable. Cost calculations, for example,
need to use consistent assumptions about energy prices, inflation,
or discount rates. Benefits must be evaluated in standard terms,
such as the equivalent amount of CO2
emission reductions.
The cost of mitigation may include a number of components, some
of which are difficult to measure. Three different kinds of costs
need to be distinguished. First are direct expenditures to reduce
emissions or otherwise reduce potential greenhouse warming. These
include, for example, the purchasing of energy-efficient air
conditioners or insulation. Second are long-term investments that
increase the overall efficiency of large-scale systems. Examples
include investment in more efficient electricity generation and
industrial facilities. Third are possible substitutions among final
goods and services that require different amounts of energy. An
example is the substitution of public transit for private
automobiles.
Current expenditures to reduce greenhouse warming are in
principle the easiest to measure because there generally are
current market transactions from which to obtain data. For
longer-term capital expenditures, a discount rate must be used to
calculate the present value of costs so they can be compared with
costs of other options. Where major substitutions of final goods or
services are required, the full costs are difficult to determine.
The potential loss in value to consumers of the changes in
consumption patterns must be estimated.
Technological Costing Versus Energy
Modeling
There are two choices for estimating the costs of various
mitigation options: "technological costing" and "energy modeling."
Technological costing develops estimates on the basis of a variety
of assumptions about the technical aspects, together with
estimates—often no more than guesses—of the costs of
implementing the required technology. This approach can be useful
for evaluating emerging technologies when it is hard to apply
statistical methods to estimate costs from market data.
Technological costing relies implicitly on economic assumptions,
and like energy modeling assumes that direct costs are a good
measure of total cost.
Energy modeling uses a variety of techniques to project energy
uses and supplies by region over time. Often, energy modeling uses
data on prices and quantities consumed to construct statistical
behavioral relationships. Unlike technological costing, energy
models strive to ensure that the projections
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Representative terms from entire chapter:
greenhouse warming
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are internally consistent by keeping track of the overall
relationship between energy supplies and demands.
Neither approach is perfect. Technological costing studies are
often criticized as providing overly optimistic estimates. Their
main weaknesses are that they are not always consistent with
observed market behavior and that they sometimes fail to allow for
impacts on quantities and prices in other markets and therefore
neglect "general equilibrium" effects of major actions undertaken.
Energy modeling analyses are challenged because of weaknesses in
model specification, measurement error, and questionable relevance
of historical data and behavior for future untested policy
actions.
In this study, the cost-effectiveness indicators for mitigation
actions are derived mostly from technological costing rather than
energy modeling analyses In some instances, these analyses show
mitigation actions yielding a net savings, implying that investment
in these actions would yield a positive economic return. Realizing
such net savings, however, would require a set of conditions not
now in existence. In other words, achieving such savings would
require overcoming private or public barriers of various kinds. If
these impediments can be overcome at relatively low cost, society
could achieve substantial benefits from these actions, often even
if greenhouse warming were not a problem.
Technological costing and energy modeling are in rough
agreement, given the large uncertainties in the best available
knowledge. This enhances the credibility of the results.
Planning a Cost-Effective Policy
Investment involves choosing among alternative uses of
resources. Finding the least-cost mix of responses to greenhouse
warming entails comparing all the different possible responses.
Figure 6.1 illustrates that the least-cost plan will probably
involve a mix of responses. For simplicity, only two hypothetical
options are plotted. They are shown as curves giving the cost for
achieving various reductions in greenhouse gas emissions (or the
incident radiation, or changing the earth's reflectivity). For
comparability, all responses are translated into CO2-equivalent emissions.
Both options exhibit increasing cost for increasing reductions
in emission (the curves gradually bend upward). If the only
alternative were to achieve the desired level of reduction by
choosing one option, the clear preference would be option B. Option
B produces each level of reduction at lower cost
(c´´) than option A (c´).
If, however, it were possible to select some of option A and
some of option B, the greatest payoff would come from a mixture of
the two. Option B should be selected up to the point at which the
cost of additional reductions
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with option B exceeds the cost of the first reductions with
option A (shown by the dashed line). Thereafter, the most
cost-effective strategy would be to select some of A and some of B
until the desired level of reduction is achieved.
Figure 6.2 extends the comparison to additional options with
different characteristics. Option C shows "negative cost," or net
positive benefits, associated with achieving the initial reductions
in CO2 emissions. An example is
energy conservation, such as better insulating of hot water heaters
to reduce heat loss. The cost of insulating would be less than the
cost of adding electricity generating capacity if the conservation
measures were not implemented.
Option D illustrates a "backstop technology." A backstop
technology provides an unlimited amount of reduction at a fixed
cost. An example would be an abundant energy source that provides
electricity with no CO2 emissions at
all. Where a backstop technology exists, its cost sets a ceiling on
the investment in reducing emissions. Only options costing less
than D should be considered, no matter how much emission reduction
is desired.
FIGURE 6.1 A comparison of hypothetical
mitigation options. Curves show the
costs of various levels of reduction in CO2-equivalent emissions. Total costs for
the
period of the analysis are divided by the number of years, and all
comparison over time are
assumed to be on the same basis.
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FIGURE 6.2 A comparison of multiple mitigation
options. Curves show the costs of
various levels of reduction in CO2-equivalent emissions for four
hypothetical mitigation options.
Total costs for the period of analysis are divided by the number
of years, and all comparisons
over time are assumed to be on the same basis.
The heavy line in Figure 6.2 shows the cost-effective
combination of options. Option C is selected up to the point at
which option B becomes more cost-effective. Option A is added when
it becomes cost-effective. The heavy line showing the
cost-effective combination becomes horizontal when the cost reaches
that of the backstop technology.
An Assessment of Mitigation Options in
the United States
Several premises are central to the design of a well-conceived
mitigation policy. First, responses to greenhouse warming should be
regarded as investments in the future of the nation and the planet.
The actions required will have to be implemented over a long period
of time. They must, however, be compared to other claims on the
nation's resources.
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Second, cost-effectiveness is an essential guideline. The
changes in energy, industrial practices, land use, agriculture, and
forestry that are likely to be needed to limit emissions of
greenhouse gases require investments over time. These are likely to
be large enough to affect the economy in various ways. The sensible
guideline is cost-effectiveness: obtaining the largest reduction in
greenhouse gas emissions at the lowest cost.
A true cost-effectiveness analysis of reducing greenhouse gas
emissions would measure only the costs of interventions taken
solely because of greenhouse warming. This is difficult in practice
because many of these actions contribute to several social goals,
making it hard to distinguish the costs and benefits attributable
to greenhouse warming alone. There are two ways such complications
might be handled: by adding benefits to reflect contributions to
multiple goals or by reducing costs to reflect their allocation
among different goals. For example, eliminating CFC emissions would
slow both the depletion of the ozone layer and the onset of
greenhouse warming. A proper accounting of reducing CFC emissions
would either assign additional benefits to reflect those gained in
the area of ozone depletion or reduce the cost allocated to
greenhouse warming proportionate to the contribution of those
actions to other goals. In either case, the cost-effectiveness
ratio would be improved if multiple social goals were considered.
Similarly, several actions that would reduce greenhouse gas
emissions are mandated by the Clean Air Act. A full
cost-effectiveness analysis would account for the fact that society
has already decided to bear these costs, so that only additional
costs and benefits would be included in the analysis of greenhouse
warming. Limits on time and resources precluded complete analysis
of these complications in this study, and the results presented
here should be considered a first cut that points the way for
further analyses.
Third, a mixed strategy is essential. A least-cost approach
produces a variety of options. A mixed strategy, however, requires
comparison of options in different sectors of the economy.
In comparing various mitigation options, this panel emphasizes
three factors. The first factor is the cost-effectiveness of the
option. In calculating cost-effectiveness, the panel converted
reductions of all greenhouse gases into CO2-equivalent emission reduction in order
to be able to compare all options on the same basis.
The second factor is the ease or difficulty of implementation of
the option. Although a particular option may be technically
possible for relatively wealthy countries, it may be precluded for
social, economic, or political reasons. These implementation
obstacles are different for each option considered. The panel
estimates emission reductions that could be achieved if explicitly
defined feasible opportunities were executed. For example, one
option calls for reducing energy use in residential lighting by 50
percent through replacement of incandescent lighting (2.5 interior
light bulbs and 1 exterior light bulb
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per residence) with compact fluorescent lights. Another option
calls for improving on-road fuel economy to 25 miles per gallon
(32.5 mpg in Corporate Average Fuel Economy (CAFE) terms) in light
vehicles by implementing existing technologies that would not
require changes in size or attributes of vehicles. Each option is
also evaluated in terms of an optimistic "upper-bound" (100 percent
achievement) or a pessimistic "lower-bound" (25 percent) level of
implementation. A brief description of the mitigation options
considered in this study is found in Table 6.1.
The third factor is the interconnectedness of the option to
other issues in addition to greenhouse warming, for example,
destruction of the ozone layer or biological extinction. These
additional factors, however, were considered only in a qualitative
manner and are part of the reason that recommendations are not
based solely on the cost-effectiveness calculations developed in
this study.
Table 6.2 shows selected mitigation options in order of
cost-effectiveness. Some options, primarily in energy efficiency
and conservation, have substantial potential to mitigate greenhouse
warming with net savings or very low net cost. However, they have
not been fully adopted because of various implementation
obstacles.
Net savings does not mean that no expenditure is required to
implement these options. Rather, it indicates that the total
discounted cost of the option over the period of analysis is less
than its discounted direct benefit, usually reduction in energy
consumption, where the discount rate is 6 percent. At higher
discount rates the relative cost would rise. These are options that
ought to be, and probably will be, implemented, since they are in
the interests of those who implement them. The decisions to start,
however, can be hastened through better information and
incentives.
Table 6.2 also includes some options that are more costly, face
substantial obstacles to their implementation, or have other costs
or benefits that are difficult to characterize. For example,
reduction of CFC consumption is also beneficial in reducing
stratospheric ozone depletion, and the combined benefit derived for
greenhouse warming and ozone depletion would raise CFC control
options in the ranking of preferred actions. Questions about the
appropriateness of current technologies and public opposition to
nuclear power, however, currently make this option difficult to
implement. To the extent that concern about greenhouse warming
replaces concern about nuclear energy and "inherently safe" nuclear
plants are developed, this option increases its priority
ranking.
Table 6.3 presents what the panel calls geoengineering options.
The geoengineering options in this preliminary analysis include
several ways of reducing temperature increases by screening
sunlight (e.g., space mirrors, stratospheric dust, multiple
balloons, stratospheric soot, and stimulating cloud condensation
nuclei) as well as stimulation of ocean uptake of CO2. Several
Page 55
TABLE 6.1 Brief Descriptions of Mitigation Options
Considered in This Study for the United States
RESIDENTIAL AND COMMERCIAL ENERGY
MANAGEMENT
Electricity Efficiency Measures
White Surfaces/Vegetation
Reduce air conditioning use and the urban heat
island effect by 25% through planting vegetation and painting roofs
white at 50% of U.S. residences.
Residential Lighting
Reduce lighting energy consumption by 50% in all
U.S. residences through replacement of incandescent lighting (2.5
inside and 1 outside light bulb per residence) with compact
fluorescents.
Residential Water Heating
Improve efficiency by 40 to 70% through efficient
tanks, increased insulation, low-flow devices, and alternative
water heating systems.
Commercial Water Heating
Improve efficiency by 40 to 60% through
residential measures mentioned above, heat pumps, and heat recovery
systems.
Commercial Lighting
Reduce lighting energy consumption by 30 to 60% by
replacing 100% of commercial light fixtures with compact
fluorescent lighting, reflectors, occupancy sensors, and
daylighting.
Commercial Cooking
Use additional insulation, seals, improved heating
elements, reflective pans, and other measures to increase
efficiency 20 to 30%.
Commercial Cooling
Use improved heat pumps, chillers, window
treatments, and other measures to reduce commercial cooling energy
use by 30 to 70%.
Commercial Refrigeration
Improve efficiency 20 to 40% through improved
compressors, air barriers and food case enclosures, and other
measures.
Residential Appliances
Improve efficiency of refrigeration and
dishwashers by 10 to 30% through implementation of new appliance
standards for refrigeration, and use of no-heat drying cycles in
dishwashers.
Residential Space Heating
Reduce energy consumption by 40 to 60% through
improved and increased insulation, window glazing, and weather
stripping along with increased use of heat pumps and solar
heating.
Commercial and Industrial Space Heating
Reduce energy consumption by 20 to 30% using
measures similar to that for the residential sector.
Commercial Ventilation
Improve efficiency 30 to 50% through improved
distribution systems, energy-efficient motors, and various other
measures.
(Table 6.1 continues on page
56)
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(Table 6.1 continued from page
55)
Oil and Gas Efficiency
Reduce residential and commercial building fossil
fuel energy use by 50% through improved efficiency measures similar
to the ones listed under electricity efficiency.
Fuel Switching
Improve overall efficiency by 60 to 70% through
switching 10% of building electricity use from electric resistance
heat to natural gas heating.
INDUSTRIAL ENERGY MANAGEMENT
Co-generation
Replace existing industrial energy systems with an
additional 25,000 MW of co-generation plants to produce heat and
power simultaneously.
Electricity Efficiency
Improve electricity efficiency up to 30% through
use of more efficient motors, electrical drive systems, lighting,
and industrial process modifications.
Fuel Efficiency
Reduce fuel consumption up to 30% by improving
energy management, waste heat recovery, boiler modifications, and
other industrial process enhancements.
Fuel Switching
Switch 0.6 quadsa
of current coal consumption in industrial plants to natural gas or
oil.
New Process Technology
Increase recycling and reduce energy consumption
primarily in the primary metals, pulp and paper, chemicals, and
petroleum refining industries through new, less energy intensive
process innovations.
TRANSPORTATION ENERGY MANAGEMENT
Vehicle Efficiency
Light Vehicles
Use technology to improve on-road fuel economy to
25 mpg (32.5 mpg in CAFEb terms)
with no changes in the existing fleet.
Improve on-road fuel economy to 36 mpg (46.8 mpg
CAFE) with measures that require changes in the existing fleet such
as downsizing.
Heavy Trucks
Use measures similar to that for light vehicles to
improve heavy truck efficiency up to 14 mpg (18.2 mpg CAFE).
Aircraft
Implement improved fanjet and other technologies
to improve fuel efficiency by 20% to 130 to 140 seat-miles per
gallon.
(Table 6.1 continued on page
57)
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(Table 6.1 continued from page
56)
Alternative Fuels
Methanol from Biomass
Replace all existing gasoline vehicles with those
that use methanol produced from biomass.
Hydrogen from Nonfossil Fuels
Replace gasoline with hydrogen created from
electricity generated from nonfossil fuel sources.
Electricity from Nonfossil Fuels
Use electricity from nonfossil fuel sources such
as nuclear and solar energy directly in transportation
vehicles.
Transportation Demand Management
Reduce solo commuting by eliminating 25 per cent
of the employer-provided parking spaces and placing a tax on the
remaining spaces to reduce solo commuting by an additional 15
percent.
ELECTRICITY AND FUEL SUPPLY
Heat Rate Improvements
Improve heat rates (efficiency) of existing plants
by up to 4% through improved plant operation and maintenance.
Advanced Coal
Improve overall thermal efficiency of coal plants
by 10% through use of integrated gasification combined cycle,
pressurized fluidizedbed, and advanced pulverized coal combustion
systems.
Natural Gas
Replace all existing fossil-fuel-fired plants with
gas turbine combined cycle systems to both improve thermal
efficiency of current natural gas combustion systems and replace
fossil fuels such as coal and oil that generate more CO2 than natural gas.
Nuclear
Replace all existing fossil-fuel-fired plants with
nuclear power plants such as advanced light-water reactors.
Hydroelectric
Replace fossil-fuel-fired plants with remaining
hydroelectric generation capability of 2 quads.
Geothermal
Replace fossil-fuel-fired plants with remaining
geothermal generation potential of 3.5 quads.
Biomass
Replace fossil-fuel-fired plants with biomass
generation potential of 2.4 quads.
Solar Photovoltaics
Replace fossil-fuel-fired plants with solar
photovoltaics generation potential of 2.5 quads.
Solar Thermal
Replace fossil-fuel-fired plants with solar
thermal generation potential of 2.6 quads.
(Table 6.1 continued on page
58)
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(Table 6.1 continued on page
57)
Wind
Replace fossil-fuel-fired plants with wind
generation potential of 5.3 quads.
CO2 Disposal
Collect and dispose of all CO2 generated by fossil-fuel-fired plants
into the deep ocean or depleted gas and oil fields.
NONENERGY EMISSION REDUCTION
Halocarbons
Not-in-kind
Modify or replace existing equipment to use
non-CFC materials as cleaning and blowing agents, aerosols, and
refrigerants.
Conservation
Upgrade equipment and retrain personnel to improve
conservation and recycling of CFC materials.
HCFC/HFC-Aerosols, etc.
Substitute cleaning and blowing agents and
aerosols with fluorocarbon substitutes.
HFC-Chillers
Retrofit or replace existing chillers to use
fluorocarbon substitutes.
HFC-Auto Air Conditioning
Replace existing automobile air conditioners with
equipment that utilizes fluorocarbon substitutes.
HFC-Appliance
Replace all domestic refrigerators with those
using fluorocarbon substitutes.
HCFC-Other Refrigeration
Replace commercial refrigeration equipment such as
that used in supermarkets and transportation with that using
fluorocarbon substitutes.
HCFC/HFC-Appliance Insulation
Replace domestic refrigerator insulation with
fluorocarbon substitutes.
Agriculture (domestic)
Paddy Rice
Eliminate all paddy rice production.
Ruminant Animals
Reduce ruminant animal production by 25%.
Nitrogenous Fertilizers
Reduce nitrogenous fertilizer use by 5%.
Landfill Gas Collection
Reduce landfill gas generation by 60 to 65% by
collecting and burning in a flare or energy recovery system.
GEOENGINEERING
Reforestation
Reforest 28.7 Mha of economically or
environmentally marginal crop and pasture lands and nonfederal
forest lands to sequester 10% of U.S. CO2 emissions.
(Table 6.1 continued on page
59)
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(Table 6.1 continued on page
58)
Sunlight Screening
Space Mirrors
Place 50,000 100-km2 mirrors in the earth's orbit to
reflect incoming sunlight.
Stratospheric Dustc
Use guns or balloons to maintain a dust cloud in
the stratosphere to increase the sunlight reflection.
Stratospheric Bubbles
Place billions of aluminized, hydrogen-filled
balloons in the stratosphere to provide a reflective screen.
Low Stratospheric Dustc
Use aircraft to maintain a cloud of dust in the
low stratosphere to reflect sunlight.
Low Stratospheric Sootc
Decrease efficiency of burning in engines of
aircraft flying in the low stratosphere to maintain a thin cloud of
soot to intercept sunlight.
Cloud Stimulationc
Burn sulfur in ships or power plants to form
sulfate aerosol in order to stimulate additional low marine clouds
to reflect sunlight.
Ocean Biomass Stimulation
Place iron in the oceans to stimulate generation
of CO2-absorbing phytoplankton.
Atmospheric CFC Removal
Use lasers to break up CFCs in the atmosphere.
a1 quad =
1 quadrillion Btu = 1015 Btu.
bCorporate
average fuel economy.
cThese
options cause or alter chemical reactions in the atmosphere and
should not be implemented without careful assessment of their
direct and indirect consequences.
options, including space mirrors and removal of CFCs from the
atmosphere, are not included among those recommended for further
investigation in Chapter 9.
Geoengineering options appear technically feasible in terms of
cooling effects and costs on the basis of currently available
preliminary information. But considerably more study and research
will be necessary to evaluate their potential side effects,
including the chemical reactions that particles introduced into the
atmosphere might cause or alter. The data presented in Table 6.3
were developed during the course of the study and represent iniial
estimates. These or other options may, with additional
investigation, research, and development, provide the ability to
change atmospheric concentrations of greenhouse gases or the
radiative forcing of the planet.
Geoengineering options have the potential to affect greenhouse
warming on a substantial scale. However, precisely because they
might do so, and because the climate system and its chemistry are
poorly understood, these options must
Page 60
be considered extremely carefully. We need to know more about
them because measures of this kind may be crucial if greenhouse
warming occurs, especially if climate sensitivity turns out to be
at the high end of the range considered in this study. Efforts by
societies to restrain their greenhouse gas emissions might be
politically infeasible on a global scale, or might fail. In this
eventuality, other options may be incapable of countering the
effects, and geoengineering strategies might be needed. Some of
these options are relatively inexpensive to implement, but all have
large unknowns concerning possible environmental side-effects. They
should not be implemented without careful assessment of their
direct and indirect consequences.
TABLE 6.2 Comparison of Selected Mitigation Options in
the United States
Mitigation Option
Net Implementation Costa
Potential Emissionb Reduction
(t CO2 equivalent per year)
Building energy efficiency
Net benefit
900 millionc
Vehicle efficiency (not fleet change)
Net benefit
300 million
Industrial energy management
Net benefit to low cost
500 million
Transportation system management
Net benefit to low cost
50 million
Power plant heat rate improvements
Net benefit to low cost
50 million
Landfill gas collection
Low cost
200 million
Halocarbon-CFC usage reduction
Low cost
1400 million
Agriculture
Low cost
200 million
Reforestation
Low to moderate costd
200 million
Electricity supply
Low to moderate costd
1000 millione
NOTE: Here and throughout this report, tons are
metric.
aNet
benefit = cost less than or equal to zero
Low cost = cost between $1 and $9 per ton of
CO2 equivalent
Moderate cost = cost between $10 and $99 per ton
of CO2 equivalent
High cost = cost of $100 or more per ton of
CO2 equivalent
bThis
''maximum feasible" potential emission reduction assumes 100
percent implementation of each option in reasonable applications
and is an optimistic "upper bound" on emission reductions.
cThis
depends on the actual implementation level and is controversial.
This represents a middle value of possible rates.
dSome
portions do fall in low cost, but it is not possible to determine
the amount of reductions obtainable at that cost.
eThe
potential emission reduction for electricity supply options is
actually 1700 Mt CO2 equivalent per
year, but 1000 Mt is shown here to remove the double-counting
effect (see p. 62 for an explanation of double-counting).
Page 61
TABLE 6.3 Cost-Effectiveness Ordering of Geoengineering
Mitigation Options
Mitigation Option
Net Implementation Cost
Potential Emission Mitigation (t CO2 equivalent per year)
Low stratospheric soot
Low
8 billion to 25 billion
Low stratospheric dust, aircraft delivery
Low
8 billion to 80 billion
Stratospheric dust (guns or balloon lift)
Low
4 trillion or amount desired
Cloud stimulated by provision of cloud
condensation nuclei
Low
4 trillion or amount desired
Stimulation of ocean biomass with iron
Low to moderate
7 billion or amount desired
Stratospheric bubbles (multiple balloons)
Low to moderate
4 trillion or amount desired
Space mirrors
Low to moderate
4 trillion or amount desired
Atmospheric CFC removal
Unknown
Unknown
NOTE: The feasibility and possible side-effects of
these geoengineering options are poorly understood. Their possible
effects on the climate system and its chemistry need considerably
more study and research. They should not be implemented without
careful assessment of their direct and indirect consequences.
Cost-effectiveness estimates are categorized as
either savings (for less than 0), low (0 to $9/t CO2 equivalent), moderate ($10 to $99/t
CO2 equivalent), or high (>$100/t
CO2 equivalent). Potential emission
savings (which in some cases include not only the annual emissions,
but also changes in atmospheric concentrations already in the
atmosphere—stock) for the geoengineering options are also
shown. These options do not reduce the flow of emissions into the
atmosphere but rather alter the amount of warming resulting from
those emissions. Mitigation options are placed in order of
cost-effectiveness.
The CO2-equivalent
reductions are determined by calculating the equivalent reduction
in radiative forcing.
Here and throughout this report, tons are
metric.
Comparing Options
Table 6.2 shows estimates of net cost and emission reductions
for several options. It must be emphasized that the table presents
the Mitigation Panel's estimates of the technical potential for
each option. For example, the calculation of cost-effectiveness of
high-efficiency light bulbs (one of the building efficiency
options) does not consider whether the supply of light bulbs could
meet the demand with current production capacities. It does not
consider the trade-off between expenditures on light bulbs and on
health
Page 62
care, education, or basic shelter for low-income families. Nor
does it consider aesthetic issues about different sources of
illumination.
Care must be taken in developing such a table because there is
some "double-counting" among potential mitigation options. For
example, implementation of both the nuclear and the natural gas
energy options assumes replacement of the same coal-fired power
plants. Thus, simply summing up the emission reductions of all
options to give total reduction in emissions would overstate the
actual potential. The options presented in Table 6.2 have been
selected to eliminate double-counting.
Finally, although there is evidence that efficiency programs can
pay, there is no field evidence showing success with programs on
the massive scale suggested here. There may be very good reasons
why options exhibiting net benefit on the table are not fully
implemented today.
Figure 6.3 illustrates the results of different rates of
implementation of those options. The many uncertainties in the
calculations of both costs and emission reductions have been
collapsed into two lines. The line labeled "25% Implementation/High
Cost" assumes incomplete implementation of each option (25 percent
implementation of feasible opportunities) and the high end of the
range of cost estimates for that option (high cost). This line
shows a lower bound of what is reasonable to achieve. The line
labeled
FIGURE 6.3 Comparison of mitigation options.
Total potential reduction of CO2-equivalent
emissions is compared to the cost in dollars per ton of CO2 reduction. Options are ranked from
left to right in CO2 emissions
according to cost. Some options show the possibility of
reductions
of CO2 emissions at a net savings.
See text for explanation.
Page 63
FIGURE 6.4 Comparison of mitigation options
using technological costing and energy modeling calculations.
"100% Implementation/Low Cost" assumes complete implementation
of each option (100 percent implementation) combined with the low
range of cost estimates for that option (low cost). This line
indicates the upper bound that could be achieved with all options
shown. A complete analysis would calculate appropriate
implementation rates for each option. That is beyond the scope of
this study. It should be realistic to achieve emission reduction
and cost results somewhere between the two lines in Figure 6.3.
As pointed out earlier in this chapter, technological costing
and energy modeling sometimes yield different results. For this
reason, both are presented in Figure 6.4. The "100%
Implementation/Low Cost" and "25% Implementation/High Cost" curves
are repeated from Figure 6.3, and the range typical of energy
modeling is shown. As can be seen from Figure 6.4, the United
States should be able to achieve substantial reduction in
greenhouse gas emissions at low cost, or perhaps even a small net
savings.
Implementing Mitigation Options
An array of policy instruments of two different types are
available: regulation and incentives. Regulatory instruments
mandate action and include controls on consumption (bans, quotas,
required product attributes), production (quotas on products or
substances), and factors in design or production (efficiency,
durability, processes). Incentive instruments are designed to
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influence decisions by individuals and organizations and include
taxes and subsidies on production factors (carbon tax, fuel tax)
and on products and other outputs (emission taxes, product taxes),
financial inducements (tax credits, subsidies), and transferable
emission rights (tradable emission reductions, tradable
credits).
Interventions at all levels could effectively reduce greenhouse
warming. For example, individuals could reduce energy consumption,
recycle goods, and reduce consumption of deleterious materials.
Local governments could control emissions from buildings, transport
fleets, waste processing plants, and landfill dumps. State
governments could restructure electric utility pricing structures
and stimulate a variety of efficiency incentives. National
governments could pursue action in most of the policy areas of
relevance. International organizations could coordinate programs in
various parts of the world, manage transfers of resources and
technologies, and facilitate exchange of monitoring and other
relevant data.
The choice of policy instrument depends on the objective to be
served. Although this analysis of mitigation options does not
include all possibilities, the panel is hopeful that it does
identify the most promising options. This analysis provides the
beginnings of a structure and, a process for identifying those
strategies that could appropriately mitigate the prospect of
greenhouse warming.
Conclusions
There is a potential to inexpensively reduce or offset
greenhouse gas emissions in the United States. In particular, the
maximum feasible potential reduction for the options labeled "net
benefit" and "low cost" in Table 6.2 totals about 3.6 billion tons
(3.6 Gt) of CO2-equivalent emissions
per year. (Here, as elsewhere in the report, tons are metric.) This
is a little more than one-third of the total 1990 greenhouse gas
emissions in the United States and represents an optimistic upper
bound on what could be achieved using these options.
A lower bound can be estimated from Figure 6.4. Arbitrarily
using a cutoff of between $10 and $20 per ton of CO2-equivalent emission reduction would
produce a level of about 1 Gt of CO2-equivalent emissions per year, or a
little more than 10 percent of current greenhouse gas emissions in
the United States.
This analysis suggests that the United States could reduce its
greenhouse gas emissions by between 10 and 40 percent of the 1990
level at very low cost. Some reductions may even be at a net
savings if the proper policies are implemented.
