Technical and Economic Feasibility of Deep Decarbonization in the United States

AuthorJames H. Williams, David Ismay, Ryan A. Jones, Gabe Kwok, and Ben Haley
Page 21
I. Introduction
Scientic assessments of the eart h’s climate conclude that
limiting the anthropogenic increase in global mean sur-
face temperature to less than 2 degrees Celsius (
will require global net greenhouse gas (GHG) emissions
to approach zero by the second half of the 21st century.1
For industrialized countries, t his implies a reduction on
Authors’ Note: e authors wish to acknowledge the other principal
co-authors of the original U.S. Deep Decarbonization Pathways
Project studies on which this chapter is based, including Fredrich
Kahrl, Jack Moore, Haewon McJeon, Andrew D. Jones, and
Margaret Torn, also contributing authors Sam Borgeson, Jamil
Farbes, Elaine Hart, Amber Mahone, Katie Pickrell, Rich Plevin,
Snuller Price, and Alexandra von Meier.
the order of 80% below 1990 levels by 2050 (the “80 x
50” target),2 the long-term target announced by the
United States in Copenhagen in 20093 and rea rmed in
1. I P  C C, C C
2014: S R. C  W G I, II, 
III   F A R   I P
 C C, S  P M, tbl. SPM.1 (2015),
available at
2. e “80 x 50” goal is not specically described by Intergovernmental Panel on
Climate Change (IPCC) reports, but is based on an interpretation of IPCC
results that incorporates a number of scientic and political assumptions.
It has been adopted as a long-term goal by the G8, the European Union,
and a number of industrialized country governments, including the United
States under the Obama Administration prior to the Copenhagen climate
summit in 2009.
3. Press Release, e White House, President to Attend Copenhagen Climate
Talks (Nov. 25, 2009), available at
the-press-oce/president-attend-copenhagen-climate-talks. See also John M.
Broder, Obama to Go to Copenhagen With Emissions Target,” N.Y. T, Nov.
Chapter 1
Technical and Economic Feasibility of Deep
Decarbonization in the United States
by James H. Williams, David Ismay, Ryan A. Jones, Gabe Kwok, and Ben Haley
e Deep Decarbonization Pathways Project (DDPP) is an international research collaboration that explores how
individual countries can reduce their greenhouse gas (GHG) emissions consistent with limiting global warming
to 2° Celsius (C) or less. e term “deep decarbonization” refers to dramatic reductions in carbon dioxide (CO2)
emissions from fossil fuel combustion, which is the primary global challenge in reducing GHG emissions. e
DDPP consists of independent research teams from 16 countries who do not necessarily reect the policy posi-
tions of their national governments. From the outset, the DDPP aimed to steer the focus of climate policy away
from limited incremental emissions reductions toward the complete transformation of the energy system. To this
end, the DDPP teams emphasized an analytical approach that demonstrates why near-term decisions about long-
lived infrastructure investments must be made with the ultimate emissions goals in mind. is chapter starts with
a brief background of the DDPP and its inuence on subsequent decarbonization studies and climate policy dis-
cussions. e remaining sections describe the study conducted for the United States by the U.S. DDPP research
team, including the main objectives and research questions, the modeling approach employed, the scenarios
explored, and the main ndings of the project. ese scenarios include a mixed case in which energy eciency,
renewable energy, nuclear power, and carbon capture and sequestration are used to achieve deep decarbonization.
e ndings include detailed analytical results describing the sector-by-sector transition to deep decarbonization,
along with general principles and quantitative benchmarks for deep decarbonization of energy, and mitigation of
non-energy and non-CO2 GHGs. e nal sections of the chapter identify key policy cha llenges and oer recom-
mendations for eective policymaking.
Page 22 Legal Pathways to Deep Decarbonization in the United States
Paris in 2015.4 e U.S. research team of the Deep Decar-
bonization Pathways Project (DDPP) has produced two
reports Pathways to Deep Decarbonization in the United
States5 and Policy Implications of Deep Decarbonization in
the United States6—that assess in detail what achieving an
80 x 50 target in the United States will require, with par-
ticular emphasis on reducing carbon dioxide (CO2) from
energy use. ese reports (“the U.S. study”) were designed
to address four research questions:
1. Is achieving this target technically feasible, given
realistic constraints?
2. What changes in physical infra structure and tech-
nology are required?
3. What is the expected cost of these cha nges?
4. What are the policy and political economy implica-
tions of these changes?
is chapter summarizes the main nding s and methods
of the U.S. study, which provides the principal basis for the
scenarios whose legal and polic y challenges are explored by
the chapter authors in the present volume. In response to
the research questions above, the study nds that achiev-
ing the 80 x 50 target is technically feasible, at a net cost
for supplying and using energy equivalent to 0.8% of gross
domestic product (GDP), with an uncertainty range of
-0.2% to +1.8%. ese costs do not include non-energy
benets such as avoided damages from climate change or
air pollution. is is demonstrated for four distinct tech-
nology scenarios, in which emissions goa ls are achieved
within U.S. borders and without the use of international
osets, by replacing current infrastructure and equip-
ment at the end of its nancial lifetime with ecient and
low-carbon infrastructure and equipment, using existing
commercial and near-commercial technologies. Each of
these scenarios delivers the sa me level of economic growth,
industrial production, and energy serv ices as a business-as-
usual case ba sed on U.S. government long-term forecasts.
e detailed ndings of the study challenge a number
of common assumptions in energy and climate policy,
including the roles of natural gas as a transition strategy,
25, 2009, at
4. John Kerry, China, America, and our Warming Planet, N.Y. T, Nov. 11,
2014, at
5. J H. W  ., P  D D  
U S, U.S. 2050 R, V 1: T R (Deep
Decarbonization Pathways Project & Energy and Environmental Economics,
Inc., 2015), available at
pdf [hereinafter DDPP T R].
6. V 2: P I  D D  
U S (Deep Decarbonization Pathways Project & Energy and
Environmental Economics, Inc., 2015), available at
downloads/2015-report-on-policy-implications.pdf [hereinafter DDPP
P R].
fuel switching relative to energy e ciency in building s and
transportation, energy storage and hydrogen (H2) produc-
tion in low-carbon electricity system operations, carbon
pricing, a nd planning.
It is useful to understand some thi ngs that the U.S. study
is not. It shows some pathways by which an 80 x 50 target
might plausibly be achieved, but it is not an exclusive list;
other scenarios are possible, both for emissions reductions
target levels and the mea ns of achieving them. It calculates
net costs for the four scenarios considered, but does not
claim these are optima l from a cost perspective. It involves
certain al locations of resources and costs, for exa mple by
sector or end use; dierent allocations are possible. It does
not explore major changes in industrial processes or mate-
rial uses, though suc h changes could have signicant emis-
sions benets. It is not a legal or policy study per se, and
contains no embedded assumptions about carbon prices
or regulations; rather it raises the question of what kinds
of laws and policies would be needed to achieve the sorts
of infrastructure changes, technology deployments, con-
sumer uptake, and coordination across sectors indicated by
these results. e needed laws and policies are the subject
of the rest of this book. e U.S. study does not assume
dramatic change s in behavior and consumption patterns,
though these are val id topics to explore (as is done in Chap-
ter 3). Finally, it is not a study of GDP or jobs impacts of
deep decarbonization, though, as discussed later, it can be
and has been used as t he basis for such a study.
II. Background
e DDPP is an international research collaboration
that explores how individual countries can limit GHG
emissions consistent with
reducing CO2 emissions from fossil fuel combustion,
a transition referred to as “deep decarbonization.” e
DDPP consists of research teams from 16 countries
representing three-fourths of current global CO2 emis-
sions: Australia, Brazi l, Canada, China, France, Ger-
many, India, Indonesia, Italy, Japan, Mexico, Russia,
South Africa, South Korea, t he United Kingdom, and
the United States.7 e research teams a re independent
and do not necessarily reect the policy positions of their
national governments. Starting in t he fall of 2013, the
teams developed road maps of potential routes, or “path-
ways,” to deep decarbonization in their respective coun-
tries.8 e DDPP studies are distinguished from other
7. e DDPP was inaugurated in 2013 by the Sustainable Development Solu-
tions Network, directed by Jerey Sachs, and the Institute for Sustainable
Development and International Relations, directed by Laurence Tubiana,
with the support of United Nations Secretary General Ban Ki-moon.
8. Individual DDPP country pathways studies, along with reports synthesiz-
ing results across countries, are available on the DDPP website at http://
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 23
low-carbon transition studies both in goa ls and execution.
From the outset, the DDPP aimed to change the focus
of climate policy discussions from incremental emissions
adjustments to transformation of the energy system, in
a way that obliges near-term decisions about long-lived
infrastructure investments to be made with the ultimate
emissions goals in mind. is objective is operational-
ized through backca sting, an approach that starts with a
scientically based objective (e.g., an 80 x 50 target) and
works backward to understand the sequence of physical
changes required to achieve it. is enta ils bottom-up
assessments of sectoral infrastructure and tech nology
needs over time, at a level of detail sucient to move
policy beyond the setting of aspirational targets toward
grappling with the concrete challenges of implementa-
tion. is detailed, country-specic analy tical approach
is well-aligned with the similarly bottom-up architecture
of post-Copenhagen climate policy, based on voluntary
emissions reduction commitments—such a s nationally
determined contributions —made by i ndividua l coun-
tries, rather than centra lly allocated. e DDPP country
teams set their own emissions ta rgets, and their ana lyses
variously take into account national conditions, preexist-
ing infra structure, local resource endowments, preferred
policy mechanisms, and aspirations for socioeconomic
development. i s emphasis on local k nowledge a nd
preferences contrasts sharply with the top-down model-
ing and generic assumptions on which past climate polic y
discussions have often been based.
e DDPP has had a considerable impact on the global
climate discussion, evident for example in references to
long-term decarbonization in the U.S.-China joint agree-
ments of 2014 and 2015, in U.S.-Canada joint agreements
in 2016, and in the ubiquitous use of the terms “deep
decarbonization” and “pathways” in many post-Paris con-
texts.9 e DDPP’s philosophy and approach are felt in
Paris Agreement Article 4.19, which acknowledges the
importance of transparent pathways analysis by calling on
all Parties “to formulate and communicate long-term low
greenhouse gas emission development strategies” no later
than 2020.10 Since Paris, several countries—including
the United States, Canada, Mexico, and Germa ny—have
published mid-century strategies (MCS) as a demonstra-
tion of climate leadership. e U.S. and Canadian DDPP
9. e text of the “U.S.-Canada Joint Statement on Climate, Energy, and
Arctic Leadership” can be found at
10. Conference of the Parties, Adoption of the Paris Agreement, art. 4.19, U.N.
Doc. FCCC/CP/2015/L.9/Rev/1 (Dec. 12, 2015). e text of the Paris
Agreement can be found on the United Nations Framework Convention on
Climate Change website at
php. Laurence Tubiana, co-founder of the DDPP and French ambassador
for climate change during the 21st Conference of Parties, played a key role
in the formulation and adoption of Article 4.19.
studies were explicit points of reference in the development
of both countries’ MCS.11
In addition to helping shape the U.S. government’s
MCS, U.S. DDPP research was the principal basis for a
business-oriented report on U.S. low-carbon strategy by the
Risky Business g roup, From Risk to Return: Investing in a
Clean Energy Economy,12 and America’s Clean Energy Fron-
tier: e Pathway to a Safer Climate Future,13 by the Natu-
ral Resources Defense Council. e U.S. DDPP research
team has also conducted deep decarbonization pathways
studies in collaboration with severa l state governments,
including California,14 New York, and Washington,15 as
well as a regional study for the northeastern U.S.16 ese
studies, similar in methods and ndings to the U.S. study,
are playing signicant roles in energy and climate policy
development in t hese state s.
III. Objectives
e U.S. study is based on a detailed year-by-year analy-
sis of the changes in U.S. physical inf rastructure required
to achieve deep decarbonization by mid-century. Using
transparent and conservative economic and engineering
assumptions (see Table 1), the authors built multiple sce-
narios to understand the technical requirements and costs
of dierent technology alternatives— or “pathways”—for
meeting the 80 x 50 goal.
e main objective of this work is to reorient climate
policy toward implementation, especially of transforma-
tional changes in t he energy system. e emphasis on
physical stocks, high sectoral granularity, and long time
horizon in the analysis supports this objective in three
ways. First, it aims to provide policymakers a nd busi-
nesses with a more detailed understa nding of what deep
11. T W H, U S M-C S  D
D (2016), available at https://obamawhitehouse.archives.
gov/sites/default/les/docs/mid_century_strategy_report-nal.pdf. E-
  C C C, C’ M-C L-T
L-G G D S (2016), available at http://les/focus/long-term_strategies/application/pdf/canadas_mid-
12. R B, F R  R: I   C E
E (2016), available at
13. V G  A L, A’ C E F-
: T P   S C F (2017), available at https://
14. Energy and Environmental Economics, Inc., Public Proceedings—Summary
of the California State Agencies’ PATHWAYS Project: Long-Term GHG Reduc-
(last visited Oct. 6, 2017).
15. Washington Governor Jay Inslee, Deep Decarbonization, http://www.governor. (last visited
Oct. 6, 2017).
16. J H. W  ., D D   N
U S  E C W H-Q (2018),
available at
Page 24 Legal Pathways to Deep Decarbonization in the United States
decarbonization will actually require in terms of scale and
timing of investment, rates of technology adoption, dis-
tribution of costs and benets, and risks associated with
dierent options.
Second, it aims to move the focus of policy discussion
beyond aspirational emissions targets to t he required end
state of an energy system that c an meet those targets.
Working backwards from that end state— or “backcast-
ing”—the analysis maps out the physical and economic
requirements of the transitional steps along the way.
is is meant to give insight into the challenges and
opportunities of the transition across sectors, industrie s,
jurisdictions, and levels of government, and to provide
concrete guidance for what policy must accomplish in
all these area s.
ird, it aims to provide a fresh lens on analytical
approaches and policy prescriptions in the energy and cli-
mate domain, with the key question being whether and
under what conditions they are eective in driv ing an
energy system transformation. Some of the policy insights
derived from this work depart from current conventions,
often dramatically, while highlighting new questions that
are not yet on the policy radar.
IV. Methods
e analytica l methods used in the U.S. study are similar
to those developed by the same team for use in Ca lifornia
climate policy, where they have played a key role in both
the setting of emissions targets and in the implementation
of energy-sector policies.17 Because these methods emerged
in a regulatory context in which is sues such as rate impacts
and the prudence of utility investments are paramount,
they embed many best-practice features required to pa ss
regulatory scrutiny, such as use of public data and trans-
parent assumptions, high sectoral granularity, rigorous
demonstration of energy system operability, detailed anal-
ysis of incremental capital and operating costs, and clear
allocation of these costs to di erent parties. In contrast,
many kinds of academic ana lysis of the low-carbon transi-
tion have been developed for other purposes, and are less
useful for providing information of this kind.
e U.S. study analyzed the technical requirements
and costs of dierent pathways for reducing net U.S.
GHG emissions of all types (expressed as CO2 equiva-
lent, or CO2e) to 80% below the 199 0 level by 2050. e
80 x 50 target was chosen because it was then the stated
long-term target of the U.S. government and the subject
of considerable scholarly research, including the Global
17. James H. Williams et al., e Technology Path to Deep Greenhouse Gas Emis-
sions Cuts by 2050: e Pivotal Role of Electricity, 335 S 53-59 (2012),
available at e analysis used
by the state in setting California’s 2030 target is available at Energy and
Environmental Economics, Inc., supra note 14.
Change Assessment Model (GCAM) study used here for
non-energy and non-CO2 mitigation.18 is target is also
used by a number of other countries such as Canada a nd
the United Kingdom, which were studied by the DDPP
and to which the U.S. study can be compared.19 Note
that 80 x 50 is not necessarily the “right” emissions tar-
get for the United States—a complex question subject to
ongoing revision based on scientic evidence and interna-
tional agreement on the relative responsibility of dierent
countries—but is suciently deep to require the tra ns-
formational changes th is study explores. In this regard,
the main focus was on deep decarbonization of the U.S.
energy system, dened as reducing CO2 from fossil f uel
combustion to 1.7 metric tons (MT) per capita in 2050,
an order of magnitude below recent U.S. levels.20 e 80 x
50 target translates to 1,080 million metric tons (MMT)
CO2e in 2050, with a secondary target for energy CO2 of
750 MMT (based on 1.7 tons/person times a mid-century
U.S. population estimate of 440 million), and an upper
limit for non-e nergy and non-CO2 emis sions of 330 MMT
CO2e, including reductions in CO2 due to its absorption
from the atmosphere by vegetation on managed lands (“the
land use, land use change, and forestry sink ”), which was
assumed to be held constant at the 1990 level (Table B-1).21
e energy system ana lysis was performed using PATH-
WAYS, a tool developed by the U.S. team for this purpo se.
Analysis of non-CO2 GHGs and GHG emissions from
non-energy activities was conducted using GC AM, an
integrated assessment model developed by Pacic North-
west National Lab oratory.
PATHWAYS is an energy system model t hat represents
the supply and demand sides of the energy system as it
responds to changes in demand for energy ser vices over
time (Figure A-1 shows a conceptual diagram of how the
model works).22 e model is very granular, representing
more than 80 demand subsectors (for example, light duty
18. e target announced by the U.S. government in 2009 and subsequently
rearmed, 83% reduction in CO2e below 2005 levels by 2050, is essentially
equivalent to 80% below 1990 levels by 2050. e values have converged
or diverged slightly based on post hoc adjustments in historical emissions in
U.S. E P A, I  U.S. G-
 G E  S: 1990-2012 (2014) (EPA 430-R-14-003),
available atles/2015-12/documents/
us-ghg-inventory-2014-main-text.pdf. See Allen A. Fawcett et al., e EMF24
Study on U.S. Technology and Climate Policy Strategies, 35 E J. Special
Issue 1 (2014).
19. U K, C C A 2008, at http://www.legislation. e DDPP studies of Canada, the United
Kingdom, and other countries are available at http://deepdecarbonization.
20. e 1.7 tons/person target was derived from an aspirational goal of the
DDPP, for the countries represented to converge on the same per capita
emissions level by mid-century, calculated based on an Intergovernmental
Panel on Climate Change-derived 2°C emissions budget divided by a U.N.
population forecast.
21. e 1990 level was 831 MMT CO2e; see U.S. E P
A, supra note 18. is implies an upper limit on gross non-energy and
non-CO2 emissions in 2050 of 330 + 831 = 1161 MMT CO2e.
22. DDPP T R, supra note 5, at 6-9.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 25
autos and residential dish-
washing) and 20 supply
subsectors (for example, gas
pipelines and wind power
plants) separately for each of
the nine geographical areas
into which the U.S. Census
Bureau divides the country.23
In these regards, PATH-
WAYS was designed to share
a common architecture with
the National Energy Model-
ing System (NEMS), built
by the U.S. Energy Informa-
tion Administration (EI A) to
produce its long-term Annual
Energy Outlook (AEO).
Annual changes in equip-
ment stocks by subsector are
calculated based on cha nges in energy serv ice demand,
equipment vintages, survival rates, and economic life-
times. e stock-rollover feature imposes a realistic inertia
on eetwide change, avoiding the tendency in less granu-
lar models to change energy s ystem infrastructure over-
night. An example of how this feature works is illustrated
in Figure A-2, which shows annual changes in the motor
vehicle eet in a deep decarbonization scena rio. Electricity
demand is calculated bottom up, and balanced with sup-
ply based on an hourly dispatch of the electricity system in
each of the three syncronous U.S. interconnections. (e
U.S. electricity system is composed of three independent,
geographically based systems referred to as synchonous
interconnections. ese are the Eastern, Western, and
Texas Interconnections. Figure A-3 shows an example of
hourly supply and demand in t he Western Interconnec-
tion for a week in March 2050.)24 In the dispatch model,
intermittent renewable energy generation is represented by
hourly proles by type (e.g. wind, solar) by state.
PATHWAYS is a scenario model, meaning t hat deep
decarbonization cases are constructed by the modeler,
based on changing the types and uptake rates of tech-
nologies adopted on the supply and demand side s of the
energy system. ese technologies are characterized by
features such as fuel t ype, eciency, operating lifetime,
capital cost, operation and maintenance cost, and shape
of adoption curves. e scenario approach was chosen in
lieu of an optimization that adopts technologies based on
23. For a map showing the nine U.S. census divisions, see U.S. C B,
C R  D   U S, available at https://
24. Electricity supply and demand must be in balance at all times for the elec-
tricity system to function. e primary role of electricity system operators
is maintaining this balance by controlling the output of generators, and
increasingly by adjusting demand as well.
price, a common approach in energy system models, in
part to avoid dependence of results on estimates of rela-
tive prices decades into the future. A reference scena rio was
constructed in PATHWAYS based on the AEO reference
case, a well-vetted long-term energy forecast by the U.S.
government.25 PATHWAYS calculates changes in energy
use, CO2 emissions, and costs of deep deca rbonization sce-
narios relative to the reference case.
Energy service demand (e.g., for lighting, heating,
etc.) in each end-use sector is a function of activity driv-
ers such as population, nu mber of household s, household
size, commercial and residential oor space, vehicle mi les
traveled (VMT), freight miles traveled, and industrial
output by subsector (value of shipments). ese activity
drivers were drawn from NEMS and the A EO reference
case. is approach was adopted to reduce the uncertainty
inherent in forecasting change s in the U.S. economy and
lifestyles over such a long time horizon and to focus atten-
tion instead on the dynamics of the energ y system in a
low-carbon transition. It is also intended to be conservative
to illustrate the scope and magnitude of the technology
changes needed to reach 750 MMT CO2 in a world that
resembles the present.
e U.S. analysis was subjected to a number of con-
straints that make the analysis more rigorous and the
assumptions more conservative (Table 1). As described
above, these constraints included infrastructure inertia,
electricity system reliability, and the same levels of energy
services in both t he reference and the deep decarbonization
25. e U.S. study was conducted using data available in 2014, including the
2013 AEO. A more recent update based on the 2015 AEO is not discussed
here, but showed broadly similar results. However, some eects of updated
input data, such as rapid reductions in solar photovoltaic prices in the in-
tervening years, are reected in the results (e.g., higher proportions of solar
in renewable generation mixes).
Table 1
Constraints and Conservative Approaches in U.S. Pathways Analysis
Constraint Analysis Approach
In-country reductions No use of interna tional offsets to reduce U. S. emissions
Energy ser vices Same level of ener gy service demand in all ca ses
Technology availability Only commercial or near-commercial technologies
Infrastructure inertia Stock rollover model with equipment lifetimes
Early retirement Ear ly retirement requires payment o f stranded costs
Electric reliability Hourly dispat ch model ensures adequate cap acity and f‌lexibility
Environmental sustainability Sust ainability limits on biom ass use and hydropower
Carbon sink Assume 1990 carbon sink (less than current) on managed lands
Future cost trajectories Conservative technology cost and performance assumptions
New infrastructure Building new infrastructure (e.g., H2 pipeline) entails cost
Robustness Multiple dif ferent technology pathw ays that meet t arget
Sensitivit y of cost results Distributi ons of fuel prices and technolog y costs
Source: Ad apted from DDPP TECHNICAL R EPORT, supra note 5, tbl. 5.
Page 26 Legal Pathways to Deep Decarbonization in the United States
cases. In addition, all emissions reductions were achieved
within U.S. borders based on well-described physical mea-
sures. Only demonstrated commercial and near-commer-
cial technologies were assumed. Heroic assumptions about
technolog y performance improvement or cost reduct ions
were avoided. Environmental su stainabil ity limits were
applied to biomass and hydroelectric resource use. Early
retirement, if it occurred, would entail nancia l costs (cal-
culated in the model). Multiple distinct pathways were
developed to demonstrate that the technical ability to meet
the 80 x 50 target was robust and not dependent on the
deployment of any single technology. Sensitivity analyses of
results were performed based on distributions in key input
parameters such as fossil f uel prices and technology costs.
e PATHWAYS model was coupled with GCAM, a
global integrated assessment model used in the Intergov-
ernmental Panel on Climate Change’s Fifth Asse ssment
Report.26 GCAM includes energy, land use, and economic
modules that interact in a dynamic-recursive optimiza-
tion.27 GCA M represents all GHGs from both energy
and non-energ y sources, and couples the U.S. economy to
the global economy. ese features allowed it to serve as
a complement to PATHWAYS to provide a complete pic-
ture of reducing net GHG emissions in the United States
consistent with the 80 x 50 target. GCA M was used in
three areas: (1) non-energy and non-CO2 GHG mitiga-
tion measures and costs, (2) biomass-related GHG emis-
sions including those from indirect land use cha nge, and
(3)sensitivity to terrestrial carbon sink assumptions.
V. Decarbonization Strategies
e transition to a low-carbon energy system rests on th ree
principal strategies: (1) highly ecient end use of energy
in buildings, transportation, and industry; (2) decarbon-
ization of electricity and other fuels; and (3) fuel switch-
ing of end uses from high-carbon to low-carbon supplies,
primarily electrication. ese strategies are implemented
in practical terms th rough the staged deployment of a vari-
ety of physical measures in buildings, transport ation, and
industr y (Table 2).
VI. Scenarios
Four deep decarbonization scenarios were developed in t he
U.S. study, to determine whether dierent technological
pathways could reach the 80 x 50 target, and to explore
the interactions among decarbonization measures within
each pathway. ese scenarios are the High Renewables,
26. DDPP T R, supra note 5, at 9.
27. e standard release of GCAM 3.2 was used in this analysis. GCAM model
documentation is available from the Joint Global Change Research Institute
High Carbon Capture and Storage (CCS), High Nuclear,
and Mixed Scenarios, a fter the principal form of electric-
ity generation in each. Despite this naming convention,
other aspects of both energy supply and demand are a lso
varied across the cases, with dierent approaches in light-
duty tra nsport ation, heav y-duty transpor tation, industry,
and so on (Table B-2).
Mixed Scenario. is scenario features an elect ricity
generation mix in 2050 composed primarily of renew-
able energy (51%), nuclear power (27%), and natural gas
with CCS (12%). ere is no deployment of CCS out-
side the elec tricity sector. Non-dispatchable renew ables28
and nuclear power are balanced with electricity storage
(pumped hydro), exible end-use elec tric loads (electric
vehicles (EVs) and thermal loads like water heating), and
electric fuel loads (production of H2 and other fuels using
electr icit y). H2 and synthetic natural gas (SNG) produced
from both electricity and biomass are mi xed with fossil
natural gas to pa rtially decarbonize “pipeline gas”—a term
describing gaseous fuels, including fossil natural ga s, that
use the existing nat ural gas pipeline system for storage and
distribution—which is used as a low-carbon combustion
fuel in freight transport a nd industry.
High Renewables Scenario. is scenario features high
levels of non-hydro renewables (79%) in the 2050 genera-
tion mix. ere is no CCS. High penetrations of wind a nd
solar energy are bala nced by higher levels of electric fuel
production than the Mixed Scenario. SNG production
is used to balance the renewable portfolio on a seasonal
basis, taki ng advantage of the existing gas distribution sys-
tem for storage capacity when there are extended periods
(weeks to months) of overgeneration on the electricity grid.
Most available biomass resources are gasied and used in
the pipeline, which, combined with SNG, leads to a low
life-cycle CO2 pipeline gas mix (only 17% fossil natural
gas). is allows pipeline gas to be used as a n alternative to
electrication in industry and freight transportation.
High Nuclear Scenario. is scenario features high levels
of nuclear power (40%) and non-hydro renewables (45%)
in the 2050 generation mix. ere is no CCS. In this
scenario, liquid fuels are the dominant nonelectric fuel.
Electricity imbalances in this case a re on shorter times-
cales (days to weeks), and do not require SNG production
and pipeline storage as in the High Renewables Scenario.
Electricity balancing is done primarily in the form of H2
production. H2 and liquid biofuels are used to deca rbon-
ize the transportation fuel supply. is results in a higher
share (58%) of fossil natural gas remaini ng in the gas pipe-
28. “Dispatchable” refers to the ability to change the output of an electrical
generator to a certain level when desired. Solar and wind energy vary with
natural conditions and are generally considered non-dispatchable. By con-
ventional practice, nuclear energy in the United States is not dispatchable,
but produces only at a constant level of output (baseload), though this is
not the case in some other countries.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 27
line, which is therefore used in more limited applications,
primarily in industry.
High CCS Scenario. is case is closest to a status quo
energy mix, both on the supply and consumption sides,
based on the assumption that CCS will be available to
capture CO2 from fossil fuel combustion in both electric-
ity generation and industry. Coal and natura l gas retain a
signicant share of the electricity generation mix (55%),
requiring large volumes of storage for captured CO2 and
higher residual CO2 emissions in electricity that must be
oset by reductions elsewhere in the energy system. is
is accomplished by applying CCS in industry. Application
of CCS to biomass rening, to produce renewable diesel as
a freight transport fuel, results in negative net CO2 emis-
sions (the only scenario in which this occurs). End-use fuel
switching is otherwise limited to buildings and passenger
vehicle elec trication.
e strategy of each scenario can be seen in the transi-
tion of energy supply and demand by demand sector and
fuel type over time (Figure 1). e four scenarios are not
Table 2
Key Decarbonization Measures by Sector and Decarbonization Strategy
Strategy a nd Sector Measures
Energy Eff‌iciency Strategies
Residential and commercial
energy eff‌iciency
• Highly eff‌icient b uilding shell required for all new build ings
• New buildings require el ectric heat pump heating, ve ntilation, and air conditionin g (HVAC) and water
• Existing building s retrof‌itted to electri c HVAC and water heatin g
• Near universal light -emitting diode (LE D) lighting in new and existing b uildings
Industrial energy eff‌iciency • Improved process des ign and material eff‌icienc y
• Improved motor eff‌icie ncy
• Improved capture and reuse o f waste heat
• Industry-spec if‌ic measures, such as direct re duction in iron and steel
Transportation energy
• Improved internal combustion engine eff‌iciency
• Electric drive tr ains for both battery and fue l cell vehicles (light-dut y vehicles (LDVs))
• Materials improveme nt and weight reduction in both LDVs and frei ght
Energy Supply Decarbonizatio n Strategies
Electricity supply
• Different low-ca rbon generation mixes with c arbon intensity* 2 per kilowatt hour
(g CO2/kWh) th at include renewable, nuclear, and car bon capture and storage (CCS ) generation
Electricity balancing • Flexible demand ass umed for electric vehicle char ging and thermal building loads
• Flexible intermedi ate energy production for H2 a nd power-to-gas processes to t ake advantage of
renewable ove rgeneration
• Hourly/daily s torage and regulation from pump ed hydro
• Natural gas with CC S
Pipeline gas su pply
• Synthetic natural g as (SNG) from gasif‌i ed biomass and anaerobic digest ion
• H2 and SNG produce d with wind/solar overgen eration provides smaller but p otentially important
additional sour ce of pipeline gas
Liquid fuels decarbonization • Diesel and jet-fuel replacement biofuels
• Centralized H2 production through electrolysis
• Centralized H2 produc tion through natural gas re formation with CCS
Fuel Switching S trategies
Petroleum • LDVs to H2 or electricity
• Heavy-duty vehi cles (HDVs) to liquef‌ied natur al gas (LNG), compr essed natural gas (CNG ), or H2**
• Industrial-se ctor petroleum uses elect rif‌ied where possible, with t he remainder switched to pipe line
Coal • No coal without CCS u sed in power generation or industr y by 2050
• Industrial-sector coal uses switched to pipeline gas and electricity
Natural ga s • Low-carbon energ y sources replace most natura l gas for power generation; no n-CCS gas retained for
balancing in so me cases
• Switch from gas to ele ctricity in mo st residential and commercial e nergy use, including majo rity of
space and water he ating and cooking
* “Carbon inte nsity” is a measure of t he carbon emissions as sociated with an activ ity, such as CO2 per unit of elec tricity generated , energy consumed, o r
GDP produced.
** In all scen arios except the High CCS S cenario, the content s of LNG and CNG includes pa rtly decarbonize d pipeline gas.
Source: DD PP TECHNICAL REPORT, supra note 5, t bl. 6.
Page 28 Legal Pathways to Deep Decarbonization in the United States
optimized for least cost, and many other combinations
are possible. However, in ensemble they cover most of the
possibilities for sectoral transitions that can be envisioned
using com mercial a nd near-commercial tec hnologies
(Ta ble B- 3).
e specic features of a decarbonized energy system
are largely determined by ve elements: electricity supply
mix, electricity balancing strategy, fuel switching strateg y,
biomass availability and application, and CCS availability
and application. e choices made for each of these ele-
ments in real-world situations would be inuenced by
many exogenous factors, such as resource endowment,
preexisting infrastructure, market choice, technology sta-
tus, policy decisions, and social preference. However, these
choices cannot be entirely independent; for example, as
described above, electricity balancing strategies necessari ly
depend on generation mix. For another example, the con-
tinued use of high levels of fossil fuel as a primary energy
source requires CCS to capture the euent. e under-
lying logic of the four deep decarbonization scenarios is
seen in the variations in these ve elements across scena rios
(Figure A-5).
VII. Main Findings
In response to the research questions posed at the begin-
ning of this chapter, the main ndings of the U.S. study
are the fol lowing:
Deep decarbonization is technically feasible. It is techni-
cally feasible to reduce U.S. GHG emissions 80% below
1990 levels by 2050, including reducing energy CO2 emis-
sions below 750 MMT. Multiple pathways exist to achieve
these reductions using existing commercial or near-com-
mercial technologies, as demonstrated by the four deep
decarbonization scenarios (Figure A-6).
Deep decarbonization requires ongoing replacement of
conventional fossil fuel-based energy supply and end-use
infrastructure and equipment with ecient, low emis-
sions technologies. In all four scenarios, the 80 x 50 target
could be achieved through natu ral replacement at the end
of existing infra structure’s economic life, and early retire-
ment was not required.
Deep decarbonization is aordable. In 2050, the net
energy system cost—the net cha nge in capital, fuel, and
operating costs of supplying and using energy—across the
four deep decarbonization scena rios has an average median
value of $300 billion, equivalent to 0.8% of a forecast
2050 GDP of $40 trillion (see Figure A-9, which shows
net energy system cost in each year). Uncertainty analysis
shows a range across scenarios of -0.2% to +1.8% of GDP
(negative $90 billion to $730 billion).29 Figure A-11 shows
29. is represents the interquartile range of a Monte Carlo simulation of key
cost paramaters, primarily technology costs and fossil fuel prices.
net cost for each scenario, including the reference case, as
a share of 2050 GDP.
Based on these ndings, one ca n visualize t he main
characteristics of a deeply deca rbonized energy system in
the United States as follows:
Physical energy system. Deep decarbonization will pro-
foundly transform the physical energ y system of the
United States. On average across the four scenarios, fossil
fuel use decreases by t wo-thirds from today while decar-
bonized energy supplies expand by a factor of ve (Figure
A-7).30 However, this can be achieved while supporting all
anticipated demand for energy services —for example, cur-
rent or higher levels of driving, home heating and cooling,
and use of appliances (Figure A-8).
Energy economy. Deep decarbonization will profoundly
transform the U.S. energy economy, in terms of what
money is spent on and where investment will ow. In con-
trast to today’s system in which more than 80% of energy
costs go to fossil fuel purchases, in a deeply decarbonized
system more than 80% of energy costs will go to xed
investments in low-carbon infrastr ucture such as wind
generation and EVs (Figure A-9). However, the net change
in consumer costs for energy services is likely to be small
(Figure A-11, Figure A-32).
Macroeconomy. Deep decarbonization will have a small
net cost relative to U.S. GDP, as increased spending on
low-carbon infrastructure and equipment is oset by
reduced spending on fossil fuels. In all deep decarbon-
ization scenarios, U.S. energy costs actually decrease as a
share of GDP over time, from about 7% today to about
6% in 2050 (Figure A-10). While the overall impact on
energy costs is modest, the transition to deep decarbon-
ization nonetheless oers signicant benets for the U.S.
macroeconomy, such as insulation from oil price shocks,
even without counting the potential economic benets of
avoiding severe climate change.
While the U.S. study did not undertake an analysis
of the implications of deep decarbonization for jobs and
household income, such an analysis has been done by a
third party using the U.S. study’s physical results as its
basis. e REMI (Regional Economic Models, Inc.) mac-
roeconomic model was used to explore the impacts of
lower fossil fuel production and consumption, and higher
deployment of ecient and low-carbon equipment and
infrastructure, in the Mixed and High Renewables Sce-
narios relative to the reference case. e study found net
gains U.S.-wide in employment (one million by 2030, up
to two million by 2050), in GDP (0.6% by 2030, up to
0.9% by 2050), and disposable household income ($300
by 2030, up to $600 by 2050). e study showed regional
30. Fossil fuel use is reduced by approximately 80% from today in the High
Renewables Scenario, 70% in the Mixed and High Nuclear Scenarios, and
40% in the High CCS Scenario.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 29
Figure 1
Energy Supply and Demand Transitions in High Nuclear, High CCS, High Renewables, and Mixed Scenarios
For each scenario, t he f‌igure shows the transition f rom 2015 to 2050 in energy demand by sect or (top row), energy sup ply by type (middle row), an d carbon intensity of energ y supply (bottom row)
for liquid fuels ( left column), gas fuels (mi ddle column), and electr icity (right column) .
2014 2050
2014 2050
2014 2050
Gas Fuels
Liquid Fuels
Sectoral Demand (EJ)
Energy Supply (EJ)
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
50 41
Fossil (CCS)
Synthetic Natural Gas
Pipeline Gas CCS
Natural Gas
2014 2050
2014 2050
02014 2050
Gas Fuels
Liquid Fuels
Sectoral Demand (EJ)
Energy Supply (EJ)
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
68 54 50 10
Fossil (CCS)
Synthetic Natural Gas
Pipeline Gas CCS
Natural Gas
2014 2050
2014 2050
02014 2050
Gas Fuels
Liquid Fuels
Sectoral Demand (EJ)
Energy Supply (EJ)
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
68 47 50
Fossil (CCS)
Synthetic Natural Gas
Pipeline Gas CCS
Natural Gas
2014 2050
2014 2050
2014 2050
Gas Fuels
Liquid Fuels
Sectoral Demand (EJ)
Energy Supply (EJ)
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 20502032
2014 2050
50 29
Fossil (CCS)
Synthetic Natural Gas
Pipeline Gas CCS
Natural Gas
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i gs. 52-55.
Page 30 Legal Pathways to Deep Decarbonization in the United States
variations, with job losses in two census divisions (West
South Central and Mountain) and job increases in the
other seven, and the same pattern in GDP. Sectorally, min-
ing (including oil and gas) has job losses, oset by gains in
construction and manufacturing.31
VIII. Key Benchmarks
e energy transformation rests on the execution of the
three principal strategies of eciency, fuel decarboniza-
tion, and fuel switching described above, independent of
scenario or the technical details of how they are imple-
mented. Aggregate, economy-wide performance metrics
can be established as performance benchmarks t hat must
be met in each of these areas if the 80 x 50 target is to be
met (Figure 2):
Highly ecient end use of energ y in buildings, transporta-
tion, and indust ry. Energy intensity of GDP (energy con-
sumed per dollar of GDP) must decline by 70% from 2018
to 2050, with nal energy use reduced by 20% despite
forecast increases of 40% in population and 166% in
GDP. Relative to the reference case, 2050 energy intensity
and nal energy use are 33% lower.
Nearly complete decarbonization of electric ity, and reduced
carbon in other kinds of fuels. e carbon intensity of elec-
tricity must be reduced by at least 97%, from more than
31. ICF I, E A  U.S. D
P (2015), available at
A summary can be found at ICF I, E A 
U.S. D P: S  F (2015), available
500 grams of CO2 per kilowatt hour (g CO2/kWh) today
to 15 g CO2/kWh or less in 2050.
Electrication where possible and switching to lower car-
bon fuels otherwise. e share of end-use energy coming
directly from electricity or fuels produced from electricity,
such as H2, must increase from less than 20% in 2010 to
more than 50% in 2050, displacing the majority of direct
fossil fuel combustion.
Another set of benchmarks ca n be determined from
the extent of transformation required in each major sec-
tor (Table 3). As with the three principal strategies, these
metrics hold true independently of how the changes are
implemented. For example, elec tricity g eneration must
approximately double from today’s level. At the same
time, emissions intensity (CO2 emissions per kWh of
electricity) must be reduced by a factor of 30. Light-duty
vehicles (LDVs) must achieve a level of energy eciency
equivalent to more than 100 miles per gallon (mpg).
Energy use in both residential a nd commercial buildings
must be more than 90% electried with near-zero carbon
electricit y. Industria l energy eciency must be doubled,
and electrication of industrial end use must increase to a
minimum of 40%.
IX. Sectoral Transitions
e transition process by which each of the main energy
supply and end-us e sectors achieve the benchmarks indi-
cated in Table 3 is shown over time by scenario in Figure 1.
Sectoral transitions for electricity, dierent types of fuels,
residentia l buildings, commercial bui ldings, LDVs, heavy-
Figure 2
Metrics for the Three Principal Strategies for
Mid-Century Deep Decarbonization of the
Energy System (Mixed Scenario),
Compared to Current
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 11.
End-use E nergy Eff‌icie ncy
Decarbonization of Electricity
Fuel Switching
0.0 1.0 2.0 3.0 4.0 5.0 6.0
Energy Inte nsity of GDP (g igajoules /$2012)
0 100 20 0 30 0 4 00 500 600
Electricity Emissions Intensity (gCO2/kWh)
0.0% 10.0% 20.0% 30.0% 40.0% 50.0% 60.0%
Electrici ty and Electri c Fuels in Final E nergy (%)
Figure 3
Electricity Transition by Generation
Mix and Demand Sectors, Present to 2050
(Mixed Scenario)
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 28,
Exajoule (EJ)
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 31
duty vehicles (HDVs), other forms of transportation, and
industry are described in more deta il below.
Electricity: e Mixed Sc enario illustrates the interaction
between supply decarboniza tion and end-use elect rication
that occurs, to dierent extents, in a ll of the decarboniza-
tion cases (Figure 3). Demand for electricity doubles by
2050, with particularly rapid growt h after 2030 (whereas
in the reference case, electricity increa ses by 33% by 2050).
Some of this growth occurs as a result of the electrication
of end uses, such as EVs and electric space and water heat-
ing. In addition, signicant additional demand resu lts from
the use of electricity to produce fuels derived from elec-
trolysis of water, such as H2. Fossil fuel generation declines
steadily from the present to 2050, and in the 2030s,
remaining coal-red generation is retired and replaced
with gas-red generation equipped with CCS. e only
remaining non-CCS fossil generation remaining in 2050
is a small amount of gas generation for peak ing.32 Across
all the case s, increased demand from electrication, normal
demand growth, and retirement of conventional fossil gen-
eration is met by increases in nuclear, CCS, wind, and solar,
such that generation is nearly completely decarbonized by
2050 (Figure A-21). CCS is only used in the Mixed and
High CCS Scenarios. Nuclear has an expanded share only
in the Mixed and High Nuclear Scenarios. e share of
renewable generation is greatly expanded in all c ases (from
a minimum of 21% to a maximum of 79%), mostly wind
and solar, with small shares of geotherma l and biomass in
situations where these resources have favorable economics.
Conventional hydro ranges from 5% to 7%.
Electricity balancing: L arge penetrations of non-dispatch-
able decarbonized resources (wind, solar, nuclear) present
challenges for balancing electricity supply and demand
(load). Due to the lack of coincidence between these gen-
eration sources and conventional loads, high penetrations
32. In the High CCS Scenario, both coal- and gas-red generation are used
with CCS.
under steadily tightening ca rbon constraints require bal-
ancing solutions beyond conventional dispatchable fos-
sil generation. By 2050, dispatchable generation must be
primarily low carbon—either generation from conven-
tional hydro (the expansion of which is environmentally
highly constrai ned) to electricity storage faci lities (pumped
hydro, batteries, compressed air) or gas power plants with
carbon capture, plus whatever residual fossil generation is
consistent with electricity emission intensity targets. ere
are several other important str ategies for balancing. One of
these—integration of electricity operations and planning
across wider geographic areas—increases the diversity of
both renewable resource proles and loads, which tends
to atten peaks and va lleys in demand and provide more
continuous supply from intermittent sources. is strategy
is a low- or even negative-cost option if institutional bar-
riers (the proliferation of separate balancing authorities in
the United States) can be overcome.33 Curtailment of over-
generation is an important option, but a costly one as the
magnitude of the imbalance increases.
Even with all of the above measures deployed, dispatch-
able loads become an increasingly important balancing
solution. e U.S. study incorporates exibility in newly
electried loads such as water heating, space heating, and
EVs. Signicant additional dema nd side dispatchability
comes in the form of electric fuel production—H2 and
SNG—in which the facilities are purposely oversized
in production capacity in order to allow them to operate
exibly and absorb excess generation (Figure A-3). While
electric fuel production may be inecient from a primary
energy perspective, its ability to operate exibly reduces
33. E  E E, I.  N R
E L, W I F A
(2015), available at
WECC_Flexibility_Assessment_Report_2016-01-11.pdf. E 
E E, I., I  H R
P S  C—E S (2014),
available at
Table 3
Key Transformations by Sector
Sector Current Energy System Deep Decarbonized
Energy System
Key Metrics in 20 50
Electricity Coa l and natural gas dominated Renewable, nucle ar, or CCS Double output while reducing
CO2/kWh 30x
Transportation Oil dominated Ele ctric ity, H2, CN G, LNG,
Fuel economy >100 mpg
Buildings Natural g as and oil dominate
Electrif‌ication, end-use
Building ener gy use >90%
Industry Fossil fuel dominated Electrif‌ication, CCS , eff‌iciency,
low-carbon fuels
Double eff‌ic iency, >40%
Source: DD PP POLICY REPORT, supra note 6, t bl. 2.
Page 32 Legal Pathways to Deep Decarbonization in the United States
curta ilment, inc reasing system-wide ineciency and low-
ering total costs. When the value of H2 and SNG as fuels
that can be used when electrication is dicult is added to
the system benets of a very large-scale exible load, elec-
tric fuel production can provide large system benets. e
economics of this approach look very dierent from those
of conventional analyses of round-trip H2 production (in
which H2 is produced from electr icity and then used to pro-
duce electricity), and thus provide an example of the need
for the costs of decarbonization to be ana lyzed in terms of
the net eect of linked changes in the whole system rather
than in terms of individual measures in isolation.
Fuels: Fossil fuel combustion without CCS decreases
dramatical ly both in absolute terms and in comparison to
the reference case by 2050, as must be the case to meet t he
80 x 50 target (Figure A-7). Across all scenarios, including
High CCS, fossil fuel use is reduced by 90% or more in
LDVs and buildings, where electrication is both techni-
cally feasible and economic. In electricity, non-CCS fossil
generation is reduced to a very small share us ed for balanc-
ing. Coal is retired from the generation mix in all scenar-
ios except High CCS, and remains in limited quantities
even in that case due to high residua l emissions, given the
assumption that CCS capture s 90% of combustion CO2.34
e allocation of the residual carbon budget of 750 MMT
in 2050 to the dierent fossil fuels and end uses diers
widely across the four scenarios, in direct relationship to
the decarbonization strategies (the “ve elements” identi-
ed in Section VI, Figure A-5). For example, only in the
High CCS Scenario is it as sumed that CCS is available for
use in industry, and therefore that fossil natura l gas can be
combusted and captured in the industria l sector (Figure 1,
upper right, middle column).
Low-carbon fuel production quantities, types (gas or
liquid), and allocations to end uses also var y widely across
scenarios as a funct ion of strategy (Figure A-5). Both alter-
native liquid fuels and pipeline gas var y in blend as a func-
tion of three factors: (1) availability and most economic
use of biomass, (2) the presence or absence of CCS as an
option, and (3) the value of electric fuel production for grid
balancing. For example, due to balancing needs, the High
Renewables and Mixed Scenar ios have the highest gase ous
energy production, with electric fuels added to bio-SNG in
a signicantly deca rbonized pipeline gas mix (Figure 1). In
both of these scenarios, internal c ombustion in heavy-duty
transportation transitions away from diesel to pipeline gas
in the form of compressed natural gas (CNG) and lique-
ed natural gas (LNG). In contrast, in the High Nuclear
and High CCS Scenarios, a much smaller share of avail-
able biomass is gasied for use in the pipeline, and is used
34. e diculty and cost of capturing CO2 from an euent increases with the
proportion captured. A 90% capture rate is a conventional assumption.
instead in liquid fuel production, primarily for renewable
diesel (Figure 1). is is enabled in the High CCS Sce-
nario by the use of CCS in industr y to capture the CO2
produced by combustion of mostly fossil pipeline gas. In
the High Nuclear Scenario, industria l CO2 emissions from
natural gas c ombustion consume most of the U.S. residual
carbon budget.
e dierent blends of pipeline gas (Figure A-22) and
liquid fuels (Figure A-23), their resulting emission intensi-
ties (Figure A-24), and their allocations to end uses (largely
as a function of the relative chal lenge of electrication)
lead to very dierent allocations of the residual 2050 CO2
emission budget to sectors (Figure A-25). is result has
distributional implications across industries and regions
(Figure A-26).
Residential: Signicant gain s in end-use energy eciency
oset a 36% increase in population and associated oor
space from now to 2050. Improvements in eciency result
from three primary strategies: (1) electrication of space
and water heating, the two prima ry residential energy end
uses; (2) aggressive eciency improvements in electric end
uses, such as clothes washers, d ishwashers, and lighting;
and (3) improvements in residential building envelopes
(e.g., windows, roofs, insulation) to reduce the demand for
space heating and cooling. e combined eects of elec-
tric heat pumps, light-emitting diode (LED) lighting, and
eciency measures result in dr amatic reductions in energy
intensity (Figure A-16). As a result of the electrication
of space and water heating, electricity accounts for more
than 90% of residential na l energy demand by 2050 in
all scenarios (Figure A-15). Maintaining a higher share of
pipeline gas in residential end uses is possible, but there
are environmental limitations on the use of biomass feed-
stock. us, its allocation to residential use represents a
lower value use of a limited resource than other applica-
tions, such as industry and heavy-duty transportation, in
which electrication currently appea rs more challenging.35
Commercial: e basic commercial decarbonization
strategy is similar to the residential strategy. Most com-
mercial-sector end uses currently involving direct fossil
fuel combustion are electried, and electricity becomes
the dominant energy carrier. rough improvements in
eciency, commercial nal energy use remains relatively
at over 2014-2050, despite a more than 40% increase in
commercial oor area (Figure A-17). e largest gains in
commercial end-use eciency are in space and water heat-
ing due to the use of high-eciency electric heat pumps,
and in lighting due to the prevalence of LEDs.
35. See, however, E3’s PATHWAYS analysis for SoCal Gas, the nation’s larg-
est natural gas utility, proposing a decarbonized pipeline gas option using
both biomass and electric fuels. E, D P G 
H M C’  G G R G (Jan.
2015), available at
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 33
LDVs: L DV stocks transition from the fossil fuel-pow-
ered internal combustion engines (ICEs) prevalent today
to a mix of EVs, plug-in hybrid electric vehicles (PHEVs),
and H2 fuel cell vehicles (HFCVs), with the relative shares
depending on the scenario. Electricity is the dominant
energy carrier for passenger vehicle transport in all sce-
narios except for High Nuclear, where H2 produced from
electrolysis is the primary energy carrier. In the High
Renewables and High CCS Scena rios—which have large
shares of PHEVs in their LDV mix—biomass is allocated
to other end uses. erefore, in those scenarios, gasoline
remains the residual fuel for PHEVs traveling beyond their
electric range, and continues to make up a nontrivial por-
tion of LDV energy use. By 2050, no signicant numbers
of purely ICE LDVs remain in any scenario. To achieve
this, non-ICE vehicles must form the dominant share of
new car sales no later tha n 2035 (Figure A-18).
HDVs: e HDV fuel mi x in 2050 is primarily deter-
mined by whether biomass is used to make a renewable
diesel “drop-in” fuel (that is, a fuel that ca n be used with-
out modication of a conventional diesel engine) or to
make SNG that is blended into the pipeline gas mix. In
cases where renewable diesel dominates (High Nuclear,
High CCS), ICE diesel vehicles remain the main form
of heavy-duty transport. W here biomass is used for pipe-
line gas, it necessitates a technology transition to lique-
ed pipeline gas ICE or H2 fuel cell HDVs. A complete
conversion of the HDV eet to H2 is not assumed tech-
nically feasible in any of the ca ses, a reection of expert
opinion about commercialization time lines and energy
density limitations. e High Nuclear Scenario has the
highest penetration of HDV HFCVs (50%). e addition
of various alternative-fuel HDVs raises average eet fuel
economy across all cases to at least 12 mpg diesel equiva-
lent (Figure A-19).
Other transportation: HDVs and LDVs account for
roughly two-thirds of transportation-sector energy
demand. e remaining one-third includes aviation,
freight rail, passenger rail, medium-duty trucking, buses,
and military use. For these modes, a combination of elec-
trication, hybridization, and fuel cells (freight rail, pas-
senger rail, medium-duty truck ing, buses) were employed
to reduce emissions. Biofuel use is limited, due to the
allocation of scarce biomass to other applications. ese
changes in technology a re accompanied by energy e-
ciency improvements (including inherent electric motor
thermodynamic benets) resulting in around 35% reduc-
tions in nal energy demand (Figure A-20). In accordance
with the AEO reference case service demand, the deep
decarbonization scenarios do not include extensive mode
shifting and a mbitious improvements in public transit,
options that could reduce overall transport ation energy
demand and emissions. “Other transportation” is an area
ripe for additional research.
Industry: Following the A EO reference case, the U.S.
study is based on an industria l structure simila r to that
of today. In order to maintain comparability in energy
services between the reference and deep decarboniza-
tion cases, the study assu mes few changes in materia l
use and industrial processes, with the exception of iron
and steel (discussed below). e decarbonization impacts
of major changes in industrial structure, technology,
and process are subjects for furt her research. In the four
deep decarbonization scenarios, industrial nal energ y
demand does not change signicantly from the reference
case. Energy eciency is improved through electrica-
tion of some heating (heat pumps) and steam (boiler)
loads. ere is fuel switching from diesel to electricity
in agricultural pumping and construction vehicles, as
well as fuel switching related to process changes in iron
and steel. e High CCS Scenario is the most dierent
from the others because it assumes the lea st changes in
technology, with fossil fuel combustion emissions being
captured by CCS. e consequent lack of electrication-
related eciency improvements, plus the fact that CCS
requires additional energy to operate, makes industrial
nal energy demand in t he High CCS Scenario hig her
than in other scenarios.
Steam production is similar across scena rios, but the
mix of energy sources for steam va ries (Figure A-27). In
the deep decarbonization ca ses, the highest-emissions fossil
fuels (coal, coke, and petroleum) are replaced by electricity
(Mixed, High Renewables, High Nuclear) and by pipeline
gas (High CCS). Steam generation from combined heat
and power (CHP) facilities and biomass-fueled boilers are
kept at reference case levels. Boiler electrication is high-
est in the High Renewables Scena rio, while no boilers are
electried in the High CC S Scenario, which instead relies
on CCS. e most signicant fuel switching in the indus-
trial sector is in iron and steel. In this sector, there is an
acceleration of the reference case trend of converting basic
oxygen furnaces uti lizing pig iron as a feedstock to electric
arc furnaces, wh ich use scrap steel or direct reduced iron.
is strategy is used in all scenarios except the High CCS
Scenario, which maintains the reference case process and
utilizes CCS to capture emissions (Figure A-28).
X. Mitigation of Non-Energy and
Non-CO2 GHGs
e analysis of non-energy and non-CO2 emissions was
conducted using dierent methods from the energy sys-
tem analysis. e GCA M model was used to identify
low-cost non-CO2 GHG mitigation measures that would
Page 34 Legal Pathways to Deep Decarbonization in the United States
complement the CO2 emissions reductions modeled in
PATHWAYS, at the level needed to meet the 80 x 50
target. Methane (CH4), nitrous oxide (N2O), and uori-
nated gases (f-gases)36 represented nearly 20% of U.S. total
gross GHG emissions in 1990, and 20% of GCAM refer-
ence emissions (without mitigation) in 2050.37 In terms of
mitigat ion, some non-C O2 emissions are associated with
fossil energy production, such as CH4 leakage from coal
and natural ga s extraction and processing. CO2 mitigation
strategies that reduce fossil fuel production also result in
non-CO2 emissions reductions, or “co-mitigation.” Deeper
reductions beyond co -mitigation require addition al mea-
sures such as CH4 aring, c atalytic reduction of N2O from
industrial processes, a nd switching to low-global warm-
ing potential refrigerants (Figure A-29). Active mitigation
of non-CO2 emissions in GC AM is driven by the same
carbon price that induces CO2 mitigation in GC AM,
based on marginal abatement supply curves (MACs) for
each technology and each non-CO2 gas represented by the
model. e MACs, which are based on U.S. Environmen-
tal Protection Agency (EPA) estimates, specif y percent
reductions feasible at various carbon price levels. Table 4
shows the non-CO2 mitigation in 2050 used in the deep
decarbonization scenarios, derived from GCAM scenarios
for pricing levels that achieve economy-wide CO2e emis-
sions reductions of 80% below 1990.38
e GCAM results achieve non-CO2 emissions (992
MMT CO2e) that are lower than the maximum level
required to meet the overall net GHG target of less tha n
1,080 MMT CO2e, given the assumption of no change in
the 1990 terrestrial carbon sink of 831 MMT CO2. ere
is scientic uncertainty reg arding the future sink, but the
overcomplianc e in non-CO2 emissions in the GCAM case
means that the 80 x 50 target could still be met, given
achievement of the 750 MMT target for energy CO2, even
if the current (2012) sink level of 979 MMT CO2 falls by
25% in 2050.
GCAM was also used to ensure that biomass feed stock
and fuel production are consistent with the PATHWAYS
model assumption of zero net life-cycle carbon. Pur pose-
grown bioenergy production was limited to a level con-
sistent with this assumption, including emissions from
indirect land use change in other countries. Current
Renewable Fuel Standard requirements for corn ethanol
were eliminated, with production falling to zero over time
as other feedstocks and bioenergy products were ra mped
up. GCAM modeled this by retiring the farmland cur-
rently used to grow corn for ethanol, while adding produc-
36. ese include HFC-125, HFC-134a, HFC-245fa, carbon tetrauoride
(CF4), and sulfur hexauoride (SF6).
37. DDPP T R, supra note 5, at 49-53.
38. EPA, G M  N-CO2 G G (2006)
tion of new feedstocks such as misc anthus and switchgrass,
grown on marginal la nds.
XI. Policy Challenges
Policies for deep decarbonization must begin with an
understanding of what policy actually needs to accom-
plish, namely the physical, nancial, and institutional out-
comes required by deep decarbonization. Some of the key
policy challenges indicated by our analysis include:
Sustained transformation. Deep decarbonization
requires the economic intensity of GHG emissions to
decrease 8% per year, and per capita emissions to decrease
5.5% per year.39 ese rates of change ca n be achieved
technically and at an aordable cost, but require a sus-
tained commitment to infrastructure transformation over
decades. Incremental improvements that do not facilitate
complete transformation are likely to result in technology
lock-in and emissions dead ends (Figure A-12). A sustained
transformation requires stable policy and a predictable
investment environment, and it also requires planning.
Deferring responsibility to a carbon market, ad hoc deci-
sions, or inconsistent incentives will not produce a sus-
tained transition.
Timely replacement. Deep decarbonization can be
achieved in the United States without retiring exist ing
equipment before the end of its economic lifetime, dened
39. For comparison, from 2014 to 2015, economic intensity of energy-related
CO2 emissions fell by 5.2% per year and per capita emissions fell by 3.3%
per year. Over the prior decade, the average rate of economic intensity decline
was 2.4% per year, and per capita decline was 1.9% per year. See EIA, U.S.
E- C D E 2015 (2017), available at
Table 4
Principal Non-CO2 Mitigation by Gas and
Subsector in 2050
(MMT CO2e)
Landf‌ills 82 73%
Coal 35 58%
Enteric fermentation 16 9%
Natural ga s 16 19%
Agricultural soils 33 9%
Adipic acid production 27 96%
Nitric acid produ ction 10 89%
Air conditioning 64 63%
Solvents 32 82 %
Source: DDP P TECHNICAL REP ORT, supra note 5, tbl. 8.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 35
as the time required to recoup initial c apital investment
including nancing costs.40 However, because these life-
times are long, there is only one natural replacement cycle
before mid-century for some of the most important infra-
structure, such as elect ric power plants, buildings, and
industrial boilers (Figure A-13). Failure to replace retiring
infrastructure with ecient and low-carbon successors
will lead either to failure to meet emissions goa ls or to early
retirement of the replacement equipment.
Cross-sector coordination. As deep decarbonization pro-
ceeds, interactions between mitig ation measures in dif-
ferent sectors (e.g., electricity and transportation) become
dominant in determining overall emissions (Figure A-4,
Figure A-14, Figure A-32). Purely sectoral policies that do
not recognize the importance of these interactions will
produce suboptimal outcomes, yet there are currently few
institutional mechanisms for coordination across sectors.
Anticipatory development of shared institutional struc-
tures, both market and regulatory, will be required for
ecient coordination of operations, planning, investment,
and research.
Integration of supply and demand side planning and pro-
curement. Related to the cross-sector coordination chal-
lenge is the supply-demand side challenge within the
electricity sector. Maintaining reliability in an electric-
ity system with high levels of wind, solar, and/or basel-
oad nuclear will require corresponding levels of ex ible
demand, such as EV charging and H2 production (Figure
A-3). Currently these would be seen as outside the purview
of electricity planning. To build a low-carbon system that
matches supply and demand resources at the required spa-
tial and timescales, however, will require integrated plan-
ning and procurement well beyond the scope of what is
currently thought of as “integrated resource planning.”
Suitable investment environment. e annual invest ment
requirement for low-carbon and ecient technologies rises
from less than $100 billion today to more than $1 tril-
lion in a span of about 20 years (Figure A-9). is is a
large increase from the standpoint of energy-sector capital
investment, but not from the standpoint of the share of
investment in U.S. GDP as a whole. Financial markets can
supply this level of capital if investment needs are antici-
pated and a policy framework is constructed that limits
risk and ensures adequate returns.
e right kinds of competition. Competition is poten-
tially an importa nt tool for driving innovation and
reducing costs, but poorly informed policies can lead to
unproductive competition. An example of this is cur-
40. While this indicates that it is possible to deeply decarbonize the economy
without creating the problem of stranded investments, the question of what
to do with fully depreciated coal plants and other highly emitting equipment
continuing to operate after their nancial lifetimes are complete is a separate
policy challenge.
rent policies that have biofuels competing with gasoline;
in the long run, this will be a poor use of scarce biomass
resources, because ga soline ICE vehicles have preferred
substitutes such as battery electr ic vehicles (BEVs) and fuel
cell vehicles (FCVs), while the biomass will be needed for
production of low-carbon fuels used in applications that
are dicult to electrif y. Long-term pathways analysis will
help policymakers and investors understa nd what types of
competition have value.
High rates of consumer adoption. Achieving necessary
rates of consumer adoption of equipment ranging from
heat pumps to alternative vehicles (Figure A-2, Figure
A-32) will require a combination of incentives, nanc-
ing, market strategies, a nd supporting infrastr ucture.
is requires a high level of public-private cooperation
among, for example, government agencies, auto manu-
facturers, and utilities in rapidly expanding alternative
vehicle markets in tandem with t he expansion of fueling
or charging infra structure.
Cost reductions in key technologies. Policymakers can
drive cost reductions in key technologies by helping to
create large markets. High production volumes drive
technologic al learning, e cient manuf acturing, and
lower prices (Figure A-30). is eect—called “Moore’s
Law” in the computer industry—is already seen in wind
and solar photovoltaic (PV) energy. Large markets ca n be
built through tech nology standard s, consumer incentive s,
coordinated research and demonstration, trade, a nd long-
term policy certa inty.
Cost increases faced by consumers. Businesses, utilities,
and policymakers have a mutual interest in limiting the
level and rate of consumer cost increases during a low-ca r-
bon transition. Coordinating energy eciency i mprove-
ments with decarbonization of energy supplies limits
increases in total consumer bills even if per unit energy
prices increase (Figure A-11). In addition, long-term path-
ways planning facilitates  nancial strategies t hat spread
the impact of large, lumpy costs.
Distributional eects. To be socially and politically sus-
tainable, a low-carbon transition must minim ize regressive
cost impacts. A powerful tool in a n energy system that
depends on network suppliers is public utility commissions,
which can mandate lower rates for low-income customers
through utility ratema king (Figure A-31). Distributional
eects across regions, sectors, and industries are largely a
function of technology strategies, which can be tailored to
mitigate these eects (Figu re A-25, Figure A-26).
Page 36 Legal Pathways to Deep Decarbonization in the United States
XII. Improving Policymaking
e development of eective policy to achieve the trans-
formational outcomes described in the U.S study is a great
challenge that ca n benet from rethinking how energy
and climate policy are made. Four keys to eective policy
are proposed below.
e rst key is that since eect ive policy requires
ongoing clarity about objectives and conditions, it is crit-
ical to invest in the ongoing analysis needed to provide
that clarity.
Sustained investment in deep decarbonization path-
ways analysis is critica l for updating assumptions,
critiquing existing policies, anticipating future forks
in the road and determining what dat a are needed to
inform them, linking climate policy to other societal
goals, and coordinating policies across sectors, juris-
dictions, and levels of government.
e second key is understanding the ma rket and jurisdic-
tional landscape in wh ich the U.S. energy system operates.
Some important characteristics of this landscape include:
Energy markets are highly imperfect in ways that
often require regulatory remedies, including natural
monopolies, ma rket power, under investment, geo-
graphic fragmentation, environmental externalities,
and information asymmetries.
Energy systems have strong geographic identities
that can aec t low-carbon strategies, including local
resource endowments and associated industries, con-
struction practices inuenced by regional climate,
and transportation choices driven by regional pat-
terns of settlement.
Energy policy is divided across federa l, state, and
local jurisdictions. In general, states have the stron-
gest jurisdictional levers over the key infrastructure
investment decisions underlying the “three pillars”
of decarbonization: energy eciency, decarbonized
electricit y, and elect rication.
e third key is understanding the available policy toolkit
and how best to t the tools to the task.
Common tools include pricing; emissions caps;
consumer rebates; producer subsidies; per formance
standa rds; technology mandates; public-private pa rt-
nerships; a nd research, deve lopment, and demonstra-
tion support.
Sectoral characteristics la rgely determine the suit-
ability of dierent policy instruments. For example,
pricing and other market instruments are less likely
to succeed in sectors that have short payback period
requirements, limited access to information, unso-
phisticated market participants, a lack of substi-
tute products, or an inability to mitigate regressive
impacts (Table 5).
e fourth key to eective policy i s to begin policy discu s-
sions with questions and an open mind, as many commonly
accepted policy prescriptions and analy tical approaches
have important limitations as they relate to deep dec arbon-
ization. Some examples of ndings of the U.S. study that
dier from common assumptions are shown in Table 6.
Table 5
Matching Policy Instruments to Characteristics of Market Segments
Industry/ Market Segment/
Sector Example
ness to See
a Relatively
Long Payback
Period on
Buyers With
Access to
ent Market
Substitut e
Ability to M iti-
gate Regressive
Cost Impact s of
Emissions Price?
Suitable Policy
1. Utility investm ent in elec-
tricity generation
Yes Ye s Yes Yes Emissions tax
2. Consumer p urchase of EVs/
No Yes Yes Diff‌icult Incentives & minimum
3. Consumer purch ase of eff‌i-
cient/electric appliances
No No Yes Ye s Incentives
4. Homeowner pur chase of
energy-eff‌icient building
No No No Yes Minimum stand ards
5. Business deve lopment of
emerging technologies
No N/A No N/A Researc h & development
Source: DD PP POLICY REPORT, supra note 6, t bl. 5.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 37
Table 6
Frequent Assumptions Challenged by Deep Decarbonization Analysis
Frequent Assumption System Transformation Perspective
Energy ef f‌iciency is the main demand si de strategy. Fuel switchi ng is of comparab le or greater importance to e ff‌i-
ciency as a dem and side strategy. Electrif‌i cation is itself a major
source of energ y eff‌iciency due to thermod ynamic advantages of
EVs and heat pumps.
Reducing primar y energy demand is a key polic y objective. Primary en ergy is a key measure in a fossil fuel- based energy sys-
tem, but a second ary consideration when t he main sources are
decarbonize d, and the cost of energy is base d on capital costs
rather than fuel consumption.
Electric gen eration growth in a decarbo nized energy system will
be low due to energ y eff‌iciency.
Electric gen eration will inc rease despite e nergy eff‌iciency, due
to major new loads fro m electrif‌ication of vehicle s, buildings,
and industry.
Biomass feed stocks will be used primari ly for ethanol as a gasoline
substitute in LDVs.
Biomass feed stocks will be used in higher val ue application s
such as biogas i n the natural ga s pipeline or renew able diesel in
heavy-dut y transport. Gasol ine has bette r substitutes i n elec-
tricity and H2.
H2 is an ineff‌icie nt and costly fuel. H2 production is a potent ially critical balancing re source in a High
Renewables ele ctricity system. This c apability, added to the value
of H2 as a fuel in appl ications that are diff‌icult t o electrify, dramati-
cally improves th e economics of H2.
Storage is the p rimary solution to solar and w ind intermittency. S torage plays a limited role in elec tricity system balanc ing. It is one
element in a sys temic solution that includes re gional grid integra-
tion, curt ailment, hydro, natural gas ge neration within carbon li mi-
tations, and f‌l exible loads. As renewable pe netrations increase and
other elements are limited, f‌lexible load becomes dominant.
Coal to natura l gas in power generation is the ma in low-carbon
transition s trategy for the United St ates.
CO2 emissions from n atural gas generation are to o high in later
years for non- CCS natural gas to be the main c omponent of the
generation mix.
Any new natural g as power plants will be strande d, or are incom-
patible with deep decarbonization.
Natural ga s plants will be valuable at low ut ilization for helping
maintain reli ability. Favorable economics for pl ants used in such a
role will require ch anges in wholesale electr icity market rules.
$/ton is t he main cost metric to use in evalua ting climate mitiga-
tion policies.
Net system cos t is the best cost metric for evalu ating cost to soci-
ety and to dif ferent consumers. Policy deci sions based on a strict
$/ton me tric for individual measures wou ld result in the non-
deployment of hi gh-cost mea sures that reduce overall system c ost.
$/ton is an alytically ambiguous over t ime, across geographies, and
across sectors.
The social cost of c arbon (SCC) should be the m ain guide to cli-
mat e polic y.
After a jurisd iction has made a commitment t o deep decarbon-
ization, the co st-effectiveness of a lternatives is a better guid e
to policy. SCC, whic h assesses the damage to socie ty of carbon
emissions, is g enerally used in a cost-bene f‌it comparison to inform
whether, not how, to reduce emis sions. SCC has played a useful
role in regulator y proceedings as a proxy in cost- effectiveness
tests, for ex ample in energy eff‌icien cy regulation.
Carbon price is t he main tool of climate policy. Carbon price is a co mplementary tool that c an be applied to
market segment s with the right characte ristics (Table 5). Carbon
pricing, which i s inherently linked to the var ying price of fossil
fuels, is ver y diff‌icult to in corporate into many kinds of lon g-term
investment dec isions that need a stable poli cy signal. Given the
need for coordinat ion across sectors and over time, t he main tool
of climate polic y is planning, which is needed to p rovide a basis for
policies and mar kets to achieve mitigation goals.
Page 38 Legal Pathways to Deep Decarbonization in the United States
XIII. Conclusion
To successfully achieve deep decarbonization, all levels of
government and private actors should engage in integrated
planning based on the ecient and transparent sharing of
information between stakeholders, ma ny of whom have not
historically coordinated their eorts. State utility commis-
sions and public utilities should create, frequently update,
and administer clear, data-driven roadmaps to cross-sector
deep decarbonization to ensure emissions reduction goals
are met on time and at reasonable cost. To help minimize
carbon lock-in and stranded assets, a ll levels of government
and private actors should assess all nea r-term decisions
against long-term goals and viable pathways to achieve
them, balancing replacing retiring fossil fuel-based infra-
structure with av ailable low-carbon technologies.
For the United States, achieving a GHG emissions
target of 80% below 1990 levels by 2050 is technically
feasible and economically aordable. is requires a trans-
formation of the infrastructure and equipment that sup-
plies and uses energy. is transformation can be achieved
without retiring current infrast ructure before the end of
its economic lifetime, but requires its replacements to use
ecient and low-carbon technologies. is is demon-
strated for four distinct scenarios: High Renewables, High
Nuclear, High CCS, and Mixed. Each of these scenarios
delivers the same level of economic growth, industria l pro-
duction, and energy services as a business-as-usual ca se
based on U.S. government long-term forecasts. Each of the
scenarios maintains electricity system reliability, improves
energy security, and avoids overconsumption of limited
natural resources such a s hydro and low-carbon biomass.
Feasible alternative low-carbon transitions in electricity
generation, f uel supply, buildin gs, tra nsportat ion, and
industry are demonstrated. e ndings highlight key
policy challenges a nd question some common assumptions
in policymaking.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 39
Appendix A. Figures
Figure A-1
PATHWAYS Model Architecture
Activity drivers such as GDP and population produce a demand for energy services (e.g., lighting, heating, cooling , and
people and freight moved) in dierent sectors. ese demands are met by dierent ty pes of energy supply. Results for
emissions, energy, and cost depend on the eciency and fuels used by the technologies employed in reference and low-
carbon scenarios.
Activity Drivers
Electricity Pipeli ne Gas Liquid Fuels
CO2 Emissions Final/ Primary
Energy Syste m
Industrial Sector Residential
Energy Service Demand
Energy Supply
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 4.
Page 40 Legal Pathways to Deep Decarbonization in the United States
Figure A-2
Example of Stock Rollover in PATHWAYS Model for LDVs
e left side shows annual sales by vehicle t ype from present to 2050. e right side shows vehicle stocks, reecting retire-
ments of old vehicles and the new sales shown on the left. Note dierent vertical sc ales in left- and right-hand gures.
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 5.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 41
Figure A-3
Electricity Dispatch Example in PATHWAYS for a High Renewables Scenario
e upper gure shows electricity generation by hour by generation type, for a week in 2050 in the Western Intercon-
nection. e lower gure shows demand, including dierent kinds of exible load used in balancing supply and demand.
Electrici ty Dispatch: March 2- 8, 2050
Hydrogen Electrolysis
Synthetic Methane
Electric Vehicle Charging
Industrial Flexible Demand
Commercial Flexible Demand
Residential Flexible Demand
Inf‌lexible Demand
Solar PV
Onshore Wind
Offshore Wind
Conventional Gas
Gas with CC S
Small Hydro
Coal with CC S
Conventional Coal
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 35.
Page 42 Legal Pathways to Deep Decarbonization in the United States
Figure A-4
Low-Carbon Transition Illustrated for LDVs, 2014 to 2050
Rows from top to bottom: total VMT, new vehicle sales, total vehicle stocks, VM T by fuel type, nal energy by fuel t ype,
and CO2 emissions.
Emissions by
fuel (MMT )
Final Energ y
by fuel (EJ )
VMT by Fuel
Total Stock
New Vehicles
Total VMT
Diesel ICE
Diesel ICE
Gas fuels (CNG/LPG)
Gas fuels (CNG/LPG)
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 56.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 43
Figure A-5
Pathway Determinants by Scenario in 2050
e approaches taken with each of ve key elements (columns showing alternatives for biomass, CCS, ba lancing, fuel
switching, and generation mix) are shown for eac h of the ve scenarios (rows for Mixed, High Renewables, High Nuclear,
High CCS, Mixed, and reference).
Source: DD PP TECHNICAL REP ORT, supra note 5, f‌ig. 7.
Page 44 Legal Pathways to Deep Decarbonization in the United States
Figure A-6
Energy CO2 Emissions in 2014 and 2050 Scenarios
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 8.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 45
Figure A-7
Changes in Energy System Under Deep Decarbonization (Mixed Scenario)
Fossil Primary Energy:
Non-Fossil Primary Energy :
Electric F uels Production :
Electric Emissions Intensity:
tons CO2/ MWh
Building Energy:
Light Duty S tock:
2015 2050 2015 2050 2015 2050
2015 2050 2015 2050 2015 2050
Oil and
Other Fossil
Natural Gas
Natural Gas
Oil and
Other Fossil
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 4.
Page 46 Legal Pathways to Deep Decarbonization in the United States
Figure A-8
Energy Service Demand Examples, 2015 and 2050
Light Duty Vehicle Travel:
vehicle miles t raveled per capita
2015 2050 2015 20 50 2015 2050 2015 2050
cycles per household
Clothes Drying:
pounds per household
kilolumen-hours per square foot
8,380 8,294 14 8 148
1,589 28 29
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 5.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 47
Figure A-9
(Above) Net Energy System Cost
(Below) Changes in Fossil Fuel and Technology Spending, 2015-2050
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 6.
Page 48 Legal Pathways to Deep Decarbonization in the United States
Figure A-10
Net Energy System Cost by Scenario as a Share of 2050 GDP
For each scenario, the range of net costs based on an uncertainty a nalysis of technology costs a nd fuel prices is shown.
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 11.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 49
Figure A-11
Average Household Spending for Energy Goods and Services, 2050 Mixed Scenario
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 7.
Home Fossil
Fuel Costs
Vehicl e
Electric ity
($150) ($ 100) ($50 ) $0 $50 $100
$(80 ) $(60 ) $(40 ) $(20 ) $ - $ 20 $ 40 $6 0 $ 80
Costs $36
Page 50 Legal Pathways to Deep Decarbonization in the United States
Figure A-12
Illustrative Deep Decarbonization Trajectory and “Dead End” Trajectory
U.S. CO2 Emissions from Fossil Fuels
1990 2000 2010 2020 2030 2040 2050
Pathway B
Pathway A
Other non-CO2 ,
non fuel GHGs net of sinks
Electr ic Power
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 25.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 51
Figure A-13
Typical Lifetimes of Key Infrastructure and Equipment
2015 2020 2025 2030 2035 2040 2045 2050
Equipment Infrastructure:
opportun ities between 2015 and 2050
Technology Replacements
Light duty
Power plant
Heavy dut y
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 26.
Page 52 Legal Pathways to Deep Decarbonization in the United States
Figure A-14
Vehicle Emission Intensities for Reference Case ICE, High Eff‌iciency ICE, and EV
2015 2050
Year 1 Vehicle Emissions Intensity:
kG CO2/mile
Reference Gasoline
High Eff‌iciency Gasoline
Battery Electric
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 29.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 53
Figure A-15
Residential Energy Demand by Fuel Type , All Deep Decarbonization Scenarios
2014 2018 2022 2026 2030 2034 2038 2042 2046 2050
Electricity Pipeline Gas Residual Fuel Oil LPG Kerosene Biomass
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 13.
Figure A-16
Residential Energy Intensity: 2014 and 2050 Deep Decarbonization
MJ/ Sq. Ft.
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 14.
Page 54 Legal Pathways to Deep Decarbonization in the United States
Figure A-17
Commercial Energy Demand by Fuel Type, All Deep Decarbonization Scenarios
2014 2018 2022 2026 2030 2034 2038 2042 2046 2050
Electricity Pipeline Gas Diesel Fuels LPG Kerosene
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 15.
Figure A-18
2050 LDV Stock, All Scenarios
Reference Mixed High Renewables High Nuclear High CCS
2050 LDVs Million s
Gasoline ICE Diesel ICE Other PHEV EV Hydrogen FCV
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 18.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 55
Figure A-19
HDV Energy Mix and Fuel Economy Across Scenarios
Reference Mixed High
High Nuclear High CC S
Average Fleet Fuel Economy (Miles/Gallon of
Diesel Equivalent)
2050 EJ
Gasoline Fuels Diesel Fuels
Liquiged Pipeline Gas (LNG) Hydrogen
Average Fuel Economy
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 22.
Figure A-20
Other Transportation Energy Demand by Energy Type
Reference Mixed HighRe newables High Nuclear High CCS
2050 EJ
Electricity Gasoline Fuels
Diesel Fuels Liquiged Pipeline Gas (LNG)
Compressed Pipeline Gas (CNG) Hydrogen
Jet Fuels LPG
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 24.
Page 56 Legal Pathways to Deep Decarbonization in the United States
Figure A-21
Electricity Generation by Resource Type and Scenario, 2050
Reference Mixed High
High Nuclear HighCCS
Fossil Fossil (CCS) Nuclear
Hydro Geothermal Biomass
Wind Solar Emissions Intensity
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 29.
Figure A-22
Pipeline Gas Blend by Resource Type and Scenario, 2050
Reference Mixed High
High Nuclear High CCS
Emissions intensity (gCO2/MJ)
Gas energy use (EJ)
Natural Gas Hydrogen
Power to Gas Biogas
Natural Gas w/ End-Use Capture Emissions Intensity
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 34.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 57
Figure A-23
Liquid Fuel Mix by Resource Type and Scenario, 2050
Reference Mixed High
High Nuclear High CCS
Diesel Gasoline Kerosene Kerosene-Jet Fuel
LPG Biofuels Hydrogen Emissions Intensity
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 36.
Figure A-24
Emissions Intensities by Fuel Type Across Scenarios
Reference Mixed High
High Nuclear High CCS
Emissions intensity (g CO2/MJ)
CO2 emission (MtCO2)
Electricity Gas Liquids
Electricity Emissions Rate Gas Emissions Rate Liquid Emissions Rate
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 38.
Page 58 Legal Pathways to Deep Decarbonization in the United States
Figure A-25
Residual CO2 Emissions by Sector in 2050 Across Decarbonization Scenarios
Mixed High Renewables High Nuclear High CCS
Industrial Transportaon Commercial Residenal
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 37.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 59
Figure A-26
Emissions Intensity by U.S. Census Division, for 2020, 2030, and 2050
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 39.
Figure A-27
2050 Steam Production Final Energy Demand by Fuel Type, by Scenario
Reference Mixed High Renewables High Nuclear High CCS
Coal Coke Other Petroleum Pipeline Gas Heat Biomass Electricity
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 26.
Page 60 Legal Pathways to Deep Decarbonization in the United States
Figure A-28
2050 Iron and Steel Industry Final Energy Demand by Fuel Type , by Scenario
Reference Mixed High Renewables High Nuclear High CCS
Coal Coke Elec tricity Pipeline Gas Regnery and Process Gas Heat
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 27.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 61
Figure A-29
CH4 Emissions, Historical and 2050 Scenarios
1990 2010 2050 no
2050 with CO2
2050 with CO2
nd non-CO2
Col G Oil A nd Lnd Ue Wte Other
Source: DD PP TECHNICAL REPORT, supra note 5, f‌i g. 46.
Page 62 Legal Pathways to Deep Decarbonization in the United States
Figure A-30
Technology Costs With Technological Learning in Go-It-Alone Case and With Global Markets
DDPP Aggregate Clean Technology
Market Potential and Its Effect on Costs
Fuel Production
Yea r
Vertical axis:
cost in $B
Go-It Alone Global Markets
Hydrogen Vehicles
Pipeline Gas Vehicles
Electric Fue ls (H2 and CH4 )
Biogas Produ ction - SNG
Bioref‌i nery - Ethanol
Bioref‌i nery - Diesel
Solar Thermal
Solar PV
Natural gas w CC S
Oil w CCS
Coal w CCS
2010 2020 2030 2040 20502010 2020 2030 2040 2050
2010 2020 2030 2040 20502010 2020 2030 2040 2050
2010 2020 2030 2040 20502010 2020 2030 2040 2050
Decarbonized Electricity GenerationDecarbonized Fuel Production
Alternative vehicles
With Cost Redu ctionsWithout Cost Reductions
$117B $ 127B
Source: De ep Decarbonizatio n Pathways Project, P athways to Deep Decarbo nization 2015 Report, E xecutive Summary, f‌i g. 8 (2015).
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 63
Figure A-31
Average Electricity Rates by Scenario and Component
Average Electric Rate:
2012 c ents /kWh
Distribution Transmission Renewables Variable an d
Convention al
Fixed To ta l
DDPP Reference Case
3.9c 2.0c 2 .7c 4.3c 3 .9c 16. 7c
DDPP Mixed Case
2.8c 2.6c 6.6c 1. 8c 5.2c 19. 1c
3.7c 2 .0c 3.9c 4.6c 7. 6c 21. 8c
Renewables Case
2.8c 4.5c 10.0 c 0.4c 2.0c 19 .5c
DDPP Nuclear Case
2.6c 2.6c 6 .7c 0.8c 4. 7c 17.4 c
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 8.
Page 64 Legal Pathways to Deep Decarbonization in the United States
Figure A-32
Water Heater Transition
A.) Residential Water Heaters:
Annual Sales
B.) Residential Water Heaters:
Total Stock
C.) Resident ial Water Heating Ene rgy:
D.) Residential Water He ating Emissions:
E.) Resident ial Water Heating Cost s:
$2012 net of Refere nce Case
2016 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 20 40 2042 204 4 2046 2048 2050
2016 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 20 46 2048 2050
2015 2020 2030 2040 2050 2015 2020 2030 2040 2050 2015 2020 2030 2050
$150 B
$100 B
($15 0B )
Fuel Combustion
Heat Pumps
Resistance Electric
Fuel Combustion
Heat Pumps
Resistance Electric
Electricity Costs
Water Heater Costs
Fuel Costs
Source: DD PP POLICY REPORT, supra note 6, f‌i g. 24.
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 65
Appendix B. Tables
Table B-1
U.S. GHG Emissions in 1990 and 2012, and 2050 Target Levels
1990 2 012 2050 Target 1990 to 2050 C hange
CO2 from fossil fuel combustion 4 ,745 5, 066 750 -84%
Fossil fuel CO2 per c apita 19.0 16. 1 1.7 -91%
Gross other GHG e missions 1,485 1, 435 1,161 -22%
Land use and fores try sink -8 31 -979 - 831 0%
Net GHG emissi ons 5,399 5, 522 1,08 0 -80%
(2014) (EPA 430 -R-14-003), available at https :// /f‌iles/2015-12/documents/us-ghg-inventory-2014-main-text.pdf.
Page 66 Legal Pathways to Deep Decarbonization in the United States
Table B-2
Scenario Summary for 2014, 2050 Reference Case, and Four 2050 Deep Decarbonization Scenarios
Indicator Units 2014 Reference Mixed H igh
High CCS
Residential MMT 1,053 1,128 28 35 54 119
Commercial MMT 942 1,080 48 57 73 141
Transportation MMT 1,797 1, 928 450 385 247 -73
Industry MMT 1,3 61 1,50 3 220 263 374 555
Total all sectors MMT 5,153 5, 639 746 74 0 747 741
Final Energ y Demand
Residential EJ 11 13 7 7 7 7
Commercial EJ 911 8 8 8 8
Transportation EJ 27 29 15 15 14 15
Industry EJ 22 27 24 24 23 26
Total all sectors EJ 68 80 54 55 53 56
Electricity Share (Final Energy)
Buildings—Residenti al %46.0% 51.9 % 94.2% 94.2 % 94.2% 94.2%
Buildings—Comme rcial %57. 8 % 61.2 % 89.9 % 89.9 % 89.9 % 89.9 %
Transport—Passenger (primarily
LDV) %0 .1% 0.2% 28.2% 45.8 % 20.2% 46 .1%
Transport—Freight (primarily
HDV) %0.0 % 0.0% 3.7% 2. 5% 3.4% 2.6%
Industry %22.7% 18. 9% 27. 1% 24.9 % 28.2% 20 .4%
Total all sectors % 20.8% 24.1 % 42.9 % 42.9% 43.0% 40.5%
Electric Fu el (H2 and SNG) Sha re (Final Energy)
Buildings—Residenti al %0.0% 0.0% 0 .4% 0.8% 0. 2% 0.0%
Buildings—Comme rcial %0.0% 0.0% 0.9% 1.7% 0.5 % 0.0%
Transport—Passenger (primarily
LDV) %0.0 % 0.0 % 29.3 % 1.7% 55.4 % 1.5 %
Transport—Freight (primarily
HDV) %0.0 % 0.0 % 21.5 % 31.4 % 39.3 % 5.7%
Industry %0.0% 0.0% 4.9% 8.3% 2.8% 0.0 %
Total all sectors % 0.0% 0.0 % 8.5% 8.8% 12. 3 % 0.9%
Electric Generation
Total net generation EJ 15 20 30 32 32 24
Delivered electricity (f‌inal
energy) EJ 14 19 23 23 23 23
Share wind % 5.4% 7. 2 % 39.2 % 62.4 % 34.1% 14 .2 %
Share solar %0.4 % 4.0% 10. 8% 15 .5 % 11. 3 % 5.3%
Share biomass %1.1% 0.9% 0.6% 0.6% 0.6% 0.8%
Share geothermal %0.5% 1.0 % 0.7% 0.6% 0.6% 0. 8%
Share hydro %6.2% 7.0 % 5.6% 5.3% 5.4 % 7.0 %
Share nuclear %19.2 % 15. 2% 27. 2 % 9.6 % 40.3% 12. 7%
Share gas (CC S) % 0.0% 0.0% 12 .2 % 0.0% 0.0% 26.3 %
Share coal (CC S) % 0.0% 0.0% 0.0 % 0.0% 0.0% 28.6 %
Technical and Economic Feasibility of Deep Decarbonization in the United States Page 67
Indicator Units 2014 Reference Mixed H igh
High CCS
Share gas (non-CCS) %21.9% 31.4 % 0.5% 2.8 % 4.6% 0.1%
Share coal (no n-CCS) % 41. 5% 28 .1% 0.0% 0.0 % 0.0% 0.0%
Share other (fossil) %0.0% 0.0% 0.0% 0.0% 0.0% 0.0 %
Share CHP % 3.3 % 5.2% 3.3% 3 .1% 3.2% 4.2%
Final energy EJ 16.2 17.1 11. 8 16 .0 8.2 10. 6
Fossil share of f‌in al energy % 100 .0% 10 0.0 % 6.4 % 17.1 % 58.1% 81. 2%
Biomass sha re of f‌inal energy % 0.0% 0.0 % 81.9% 60. 2% 35.3% 6 .1%
H2 share of f‌inal ene rgy % 0.0% 0.0 % 6.7% 6.7% 6.6% 0.0%
SNG share of f‌ina l energy % 0.0 % 0.0% 5.0% 16 .0 % 0.0% 0.0%
Fossil with CCS s hare of f‌inal
energy 0.0% 0.0 % 0.0% 0.0% 0.0 % 12 .7%
Liquids and Solids
Final energy EJ 34 37 15 12 18 19
Share biomass %2.0% 2.3% 0.8% 1.0 % 24.0 % 28.8%
Share liquid H2%0.0% 0.0% 20.7% 10 .3% 32 .6% 2.6%
Share petroleum %80.6% 78.7% 43.4% 41. 8% 13 .9 % 32.5 %
Share coal and coke % 4.6% 4.0% 1.1% 1. 3% 0.8 % 6.7%
Share feedstocks %12. 8% 15 .1% 34 .1% 45.5% 28.7 % 29.3 %
Intensity Metrics
U.S. popul ation Million 323 438 438 438 438 43 8
Per capita ene rgy use rate
(GJ)/p erson 211 183 12 3 125 121 12 8
Per capita emissions
t CO2/
person 16. 0 12.9 1. 7 1.7 1.7 1.7
U.S. GDP B 2012 $ 16, 378 40 ,032 40,032 40, 032 40,032 40, 032
Economic energy intensity MJ/$ 4. 17 2.00 1.35 1. 37 1.32 1.40
Economic emission intensity kG CO2/$ 0.31 0 .14 0.02 0.02 0.02 0.02
Electric emission intensity g CO2/kWh 51 0.9 413 .5 13. 5 16.0 23.4 54.7
Source: DD PP TECHNICAL REPORT, supra note 5, Table 7.
Page 68 Legal Pathways to Deep Decarbonization in the United States
Table B-3
Technologies Included in Each of the Four 2050 Deep Decarbonization Scenarios
Technology Included in 2050 Scenario?
Mixed Renewables CCS Nuclea r
CCS for generati on, 90% capture Y N Y N
CCS for generati on, >90% capture N N N N
Nuclear Gen I II Y Y Y Y
Nuclear Gen I V N N N N
Solar PV Y Y Y Y
Concentrati ng solar power Y Y Y Y
Onshore wind YYYY
Shallow offshore wind YYYY
Conventional geothermal YYYY
Deep offsh ore wind N N N N
Advanced geothermal N N N N
CCS for industr y, 90% ca pture Y N Y N
CCS for industr y, >90 % capture N N N N
H2 from electric ity generation Y Y N Y
H2 from natural g as reforming wit h CCS N N Y N
Continental-scale H2 distribution pipeline N N N N
Power-to-gas—SNG from electricity generation Y Y N N
Liquid fuels from e lectricity generatio n N N N N
Biomass conver sion to SNG by anaerobic digestio n or gasif‌ication Y Y N Y
Fischer-Tropsch liquid biofuel s, 35% eff‌iciency N N Y Y
Advanced cellulosic ethanol N N N N
Advanced biodiesel N N N N
Advanced bio-jet fuel N N N N
Biomass gene ration w CCS N N N N
Fuel cell LDVs Y N N Y
Battery electric LDVs Y Y Y Y
CNG passenge r and light truck N N N N
LNG freight Y Y Y N
Fuel cell freight N N N Y
Heat pump HVAC Y Y Y Y
LED lighting Y Y Y Y
Heat pump elec tric water heat Y Y Y Y
Maximum ef f‌iciency shell for new building s Y Y Y Y
Maximum ef f‌iciency shell for retrof‌it s N N N N
Industrial process redesign NNNN
Manufactured product redesign NNNN
Source: DD PP POLICY REPORT, supra note 6, Table 3.

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