Order Code RL33970
Greenhouse Gas Emission Drivers:
Population, Economic Development and Growth,
and Energy Use
Updated February 13, 2008
John Blodgett
Deputy Assistant Director
Resources, Science, and Industry Division
Larry Parker
Specialist in Energy Policy
Resources, Science, and Industry Division

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Greenhouse Gas Emission Drivers: Population,
Economic Development and Growth, and Energy Use
Summary
In the context of climate change and possible responses to the risk associated
with it, three variables strongly influence the levels and growth of greenhouse gas
emissions: population, income (measured as per capita gross domestic product
[GDP]), and intensity of emissions (measured as tons of greenhouse gas emissions
per million dollars of GDP).
(Population) x (per capita GDP) x (Intensity
) = Emissions
ghg
ghg
This is the relationship for a given point in time; over time, any effort to change
emissions alters the exponential rates of change of these variables. This means that
the rates of change of the three left-hand variables, measured in percentage of annual
change, sum to the rate of change of the right-hand variable, emissions.
For most countries, and for the world as a whole, population and per capita GDP
are rising faster than intensity is declining, so emissions are rising.
World GHG Intensity, 1990-2000 (annual % change)
Population
Per Capita GDP
GHG Intensity
GHG Emissions
(1.4)
+
(1.7)
+
(-2.5)
=
(0.7)
Note: Numbers do not add precisely because of rounding.
Within this generalization, countries vary widely. During the 1990s, in some
countries, including India, Japan, Brazil, Mexico, South Korea, Indonesia, and South
Africa, population growth alone exceeded the decline in intensity. For China, India,
Brazil, Mexico, Indonesia, and South Korea, population growth exceeding 1% per
year combined with per capita GDP growth that exceeded the intensity improvement
each achieved. For the United States, Canada, and Australia, income growth alone
exceeded the decline in intensity. Yet several developed countries improved their per
capita GDP while decreasing their emissions: Germany, the United Kingdom, France,
and Poland; each did so by combining slow population growth (0.4% or less per year)
with substantial improvements in intensity (-2.5% or better per year).
Stabilizing greenhouse gas emissions would mean the rate of change equals
zero. Globally, with a population growth rate of 1.4% per year and an income growth
rate of 1.7% per year, intensity would have to decline at a rate of -3.1% per year to
hold emissions at the level of the year that rate of decline went into effect. Within
the United States, at the 1990s population growth rate of 1.2% per year and income
growth rate of 2.0% per year, intensity would have had to decline at a rate of -3.2%
per year to hold emissions level; however, U.S. intensity declined at a rate of -1.8%,
leaving emissions to grow at 1.4% per year. President Bush’s Climate Change
Initiative seeks to increase the rate of intensity decline through 2012 by about -0.4%
per year — well short of stabilizing or reducing greenhouse gas emissions.

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Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Greenhouse Gas Emission Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Sectorial Breakdown of GHG Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Energy Use as a CO Intensity Driver . . . . . . . . . . . . . . . . . . . . . . . . . 12
2
Carbon Intensity of Electricity Generation . . . . . . . . . . . . . . . . . . . . . 17
Carbon Intensity of Travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Effects of Land Use on Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Cumulative Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Interactions of the Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Changes in Intensity To Meet Climate Stabilization Goals . . . . . . . . . . . . . 26
U.S. Greenhouse Gas Intensity: Trends and Targets . . . . . . . . . . . . . . 26
Global Greenhouse Gas Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
List of Figures
Figure 1. Actual and Projected GHG Emission for New Passenger Vehicles
by Country, 2002-2018 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
List of Tables
Table 1. Drivers of Greenhouse Gas Emissions: Selected Countries, 2000 . . . . . 5
Table 2. Rate of Change in Factors Affecting Greenhouse Gas Emissions:
Selected Countries, 1990-2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table 3. GHG Emissions by Sector: Top 20 Emitters, 1990-2000 . . . . . . . . . . . 10
Table 4. Energy Sector GHG Emissions: Top 20 Emitters, 1990-2000 . . . . . . . 11
Table 5. Rate of Change of GHG Emissions by Sector: Top 20 Emitters,
1990-2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 6. CO Emissions Intensity of the Energy Sector: Top 20 Emitters,
2
2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Table 7. Rate of Change in Factors Affecting CO Emissions from Energy Use:
2
Top 20 Emitters, 1990-2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Table 8. Carbon Intensity of Electricity Generation: Top 20 Emitters, 2004 . . . 19
Table 9. Energy Intensity of Passenger Modes: United States, 1970-2005 . . . . . 20
Table 10. Land Use Changes: Impact on Intensity of Greenhouse Gas
Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Table 11. Cumulative CO Emissions from Energy: Top 20 Emitters,
2
1850-2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

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Greenhouse Gas Emission Drivers:
Population, Economic Growth and
Development, and Energy Use
Introduction
The interactions of three variables underlie debates on the issue of climate
change1 and what responses might be justified: the magnitude and rates of change of
(1) population growth, (2) incomes, and (3) intensity of greenhouse gas emissions
relative to economic activities. This report examines the interrelationships of the
variables to explore their implications for policies that address climate change.
Both internationally and domestically, initiatives are underway both to better
understand climate change and to take steps to slow, stop, and reverse the overall
growth in greenhouse gas emissions,2 the most important of which is carbon dioxide
(CO ), emitted by the combustion of fossil fuels.
2
These initiatives include the following bulleted items.
! The United Nations Framework Convention on Climate Change
(UNFCCC), to which the United States and almost all other nations
are Parties. Its stated objective is to stabilize greenhouse gas
concentrations in the atmosphere at levels that “would prevent
dangerous interference with the climate system.”3 It established the
principle that all nations should take action, and that developed
nations should take the lead in reducing emissions. It required
Parties to prepare national action plans to achieve reductions, with
developed countries aiming to reduce year 2000 emissions to 1990
levels. It required preparation of inventories of emissions and
annual reports. And it set up a process for the Parties to continue
meeting.
1 This paper does not explore the underlying science of climate change, nor the question of
whether action is justified. See CRS Report RL33849, Climate Change: Science and Policy
Implications, by Jane Leggett, for more information.
2 For a review of international activities, see CRS Report RL33826, Climate Change: The
Kyoto Protocol, Bali “Action Plan,” and International Actions, by Susan Fletcher and Larry
Parker. For a review of U.S. activities, see CRS Report RL31931, Climate Change: Federal
Laws and Policies Related to Greenhouse Gas Reductions, by Brent Yacobucci and Larry
Parker, and CRS Report RL33846, Greenhouse Gas Reduction: Cap-and-Trade Bills in
the 110th Congress, by Larry Parker and Brent Yacobucci.
3 UNFCCC, Article 2, “Objectives.”

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CRS-2
! The Kyoto Protocol, to which 169 nations — but not the United
States — are Parties. Even as the Framework Convention was going
into force, it was recognized that most nations would not meet their
2000 aims of holding emissions at 1990 levels. Negotiations
through the Conference of Parties ensued, in which the United States
participated. These led to the Kyoto Protocol, which called for
mandatory reductions in greenhouse gases for the period 2008-2012
by developed nations — but not by developing ones. Whether the
reduction goal of the Kyoto Protocol is met, Parties are already
discussing post-Kyoto options.
! The Asia-Pacific Partnership on Clean Development and Climate
(APP), composed of the United States, China, India, Japan,
Australia, and South Korea. The purposes of the Partnership are to
create a voluntary, non-legally binding framework for international
cooperation to facilitate the development, diffusion, deployment, and
transfer of existing, emerging, and longer-term cost-effective,
cleaner, more efficient technologies and practices among the
Partners through concrete and substantial cooperation, so as to
achieve practical results. It has the goal of meeting “national
pollution reduction, energy security and climate change concerns,
consistent with the principles of the U.N. Framework Convention on
Climate Change (UNFCCC).”4
However, these efforts have had to struggle with substantive economic,
technical, and political differences among regional, national, and local circumstances.
Foremost among these differences is the divide between developed and less-
developed nations.5 Conflict arises because any pressure to reduce emissions comes
up against increases in emissions likely to result from energy use fueling economic
development and raising standards of living in developing economies, which contain
a large share of the world’s population. Even in many developed nations, efforts to
constrain emissions by, for example, conservation, increased energy efficiency, and
use of energy sources that emit less or no CO , have been outstripped by increases in
2
total energy use associated with population and economic growth. For example,
during the 1990s in the United States, the greenhouse gas intensity of the economy
declined at a rate of -1.8% per year, but total emissions increased at the rate of 1.4%
4 Charter for the Asia-Pacific Partnership on Clean Development and Climate (January 12,
2006), “Purposes,” 2.1.1. For additional information, see [http://www.asiapacific
partnership.org/].
5 See, for example, CRS Report RL32721, Greenhouse Gas Emissions: Perspectives on the
Top 20 Emitters and Developed Versus Developing Nations, by Larry Parker and John
Blodgett; CRS Report RL32762, Greenhouse Gases and Economic Development: An
Empirical Approach to Defining Goals, by John Blodgett and Larry Parker; and Kevin
Baumert and Jonathon Pershing, Climate Data: Insights and Observations (World
Resources Institute; prepared for the Pew Center on Global Climate Change, December
2004).

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CRS-3
per year.6 Although some countries have experienced declines in emissions — either
through economic contraction7 or deliberate policies — the overall trend, both
globally and for most individual nations, reflects increasing emissions.
This upward trend in greenhouse gas emissions runs counter to the long-term
objectives of these climate change initiatives. This report identifies drivers of the
increase in emissions and explores their implications for efforts to reduce emissions.
During this exploration, it is useful to bear in mind that although short-term efforts
may not achieve emissions reductions that immediately meet goals to prevent
dangerous interference with the climate system, such endeavors may nevertheless
establish a basis for longer-term efforts that do meet such goals.
Greenhouse Gas Emission Variables
The analysis below, which uses data from the World Resources Institute’s
Climate Analysis Indicators Tool (CAIT),8 is based on the following relationships:
Equation 1. (Population) x (per capita GDP) x (Intensity
) = Emissions
ghg
ghg
The CAIT database includes 186 nations with a 2000 population of 6.060 billion,
compared with 191 members of the United Nations and with a 2000 world population
count of 6.080 billion by the U.S. Census Bureau.9 Average income is measured as
per capita Gross Domestic Product (GDP), in international dollars of purchasing
power parity ($PPP).10 (Note that population times per capita GDP equals GDP.)
Greenhouse gas intensity is measured as tons of emissions in carbon equivalents11 per
million dollars of GDP.
6 World Resources Institute, Climate Analysis Indicators Tool (CAIT), as described below.
7 In particular, following the breakup of the former Soviet Union, the economies of various
Eastern European and former Soviet republics contracted in the 1990s, such that their
emissions declined substantially between 1990 and 2000.
8 This database uses a variety of data sources to provide information on greenhouse gas
emissions and other relevant indicators. Full documentation, along with caveats, is provided
on the WRI website at [http://cait.wri.org/].
9 See [http://www.census.gov/ipc/www/worldpop.html].
10 GDP-PPP is gross domestic product converted into international dollars using purchasing
power parity (PPP) rates. An international dollar has the same purchasing power in the
domestic currency as a U.S. dollar has in the United States. The World Bank is the source
of CAIT’s PPP data. (World Resources Institute, CAIT: Indicator Framework Paper,
November 2005, p. 22.)
11 Emissions comprise six greenhouse gases: carbon dioxide, nitrous oxide, methane,
perfluorocarbons, hydrofluorocarbons, and sulfur hexafluoride. To aggregate emissions
data, figures are typically given in millions of metric tons of carbon equivalents (MMTCE).
Thus, global aggregate greenhouse gas emissions for 2000 were 9,125.9 MMTCE, or 9.1
billion tons. In the text, unless otherwise explicitly stated, “tons” of emissions means
“metric tons of carbon equivalents.” To convert carbon equivalents to CO equivalents,
2
multiply by 44/12.

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CRS-4
Characteristics of Intensity
Intensity can be expressed in many different ways; for example, as CO emitted per
2
million $PPP, as all six greenhouse gases emitted per million $PPP, and as CO2
or greenhouse gases emitted per unit of some activity, such as electricity generated
or vehicle miles traveled. Also, measures of intensity can include or exclude
emissions or sequestration associated with land use changes.

In this analysis, intensity is identified as greenhouse gas (GHG) intensity (all
six greenhouse gases of the UNFCCC) or as CO intensity (referring only to CO
2
2
emissions from energy use and cement manufacture). In both cases, tonnage of
emissions is expressed in carbon equivalents. CAIT has data on all six greenhouse
gases only for 1990, 1995, and 2000; analyses referring to other years necessarily
include only CO .
2

Unless otherwise specified, land use changes are not included in emissions
or intensity data cited in this report.

Using international, purchasing power parity dollars can yield figures
different from analyses using other economic measures, such as market exchange
rate dollars. Intensity figures in this report, derived using $PPP, may differ from
comparable intensity figures in other studies using other GDP measures.

For the United States, international $PPP (or market exchange rate dollars)
for GDP yield a decline in intensity for U.S. emissions of all greenhouse gases of
-1.8% per year. The Energy Information Administration, using its emissions data
and “chained dollars,” calculates a decline in intensity for the same gases over the
same period of -1.9% per year.

To ensure consistency, CAIT emissions data and international $PPP are used
throughout this report, unless stated otherwise.
Table 1 provides a snapshot of the equation 1 variables for the top 20
greenhouse gas emitters in the year 2000,12 plus for the European Union 25 (those
members as of 2004) and for the world. The data reflect the wide range of
circumstances faced by any initiative to address GHGs. However, it is the way those
variables are changing that illuminates both the seemingly inexorable rise in GHG
emissions and the challenge of reducing them. A variable changing at an annual rate
of 6.9% doubles in 10 years; at an annual rate of 3%, it doubles in 23 years.
12 The year 2000 is the most recent year for which CAIT has data for all six greenhouse
gases; data for CO are available through 2004. Note that analyses based on 1990-2000 data
2
are affected by the collapse of the former USSR and do not take into account the recent
rapid increases in energy use and emissions for India and China.

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CRS-5
Table 1. Drivers of Greenhouse Gas Emissions:
Selected Countries, 2000
(Excludes land use changes)
Per Capita
Intensity
GDP (2000
(Tons Cequiv/
Total GHG
Population
Int’l $PPP/
million 2000
Emissions
Country
(in 1,000s)
person)
Int’l $PPP)
(MMTCE)
United States
282,224
34,599
192.0
1,874.4
China
1,262,645
3,939
268.0
1,332.6
EU-25
451,659
23,009
124.7
1,295.5
Russian Fed
146,303
7,006
508.3
521.0
India
1,015,923
2,364
182.5
438.4
Japan
126,870
26,089
112.6
372.8
Germany
82,210
25,343
133.1
277.2
Brazil
173,858
7,193
207.3
259.2
Canada
30,770
27,508
219.3
185.6
U.K.
59,743
26,558
112.6
178.7
Mexico
97,966
9,197
173.7
156.5
Italy
56,949
25,302
101.3
146.0
S. Korea
47,008
16,149
188.7
143.2
France
58,896
25,944
93.1
142.3
Indonesia
206,265
2,904
229.0
137.2
Australia
19,153
25,619
275.4
135.1
Ukraine
49,176
4,035
667.1
132.4
S. Africa
44,000
8,764
312.1
120.5
Iran
63,664
5,804
311.8
115.2
Spain
40,263
22,313
114.0
102.4
Poland
38,454
10,548
251.0
101.8
WORLD
6,059,548
7,450
217.7
9,788.5
Source: Climate Analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).

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CRS-6
Incorporating growth, equation 1 becomes
k t
k t
Equation 2. ( Population)e p
( percapitaGDP)e g
(Intensity)e k ti
( Emissions)e k te
×
×
=
in which k = population growth rate, k = per capita GDP growth rate, k = intensity
p
g
i
growth rate, and k = emissions growth rate; t = time; and e = a constant 2.71828
e
(the base of natural logarithms).
The exponents of multiplicands are added, so

Equation 3. (k + k + k ) = k
p
g
i
e
If the sum of the three growth rate variables on the left is positive, emissions are
rising; if the sum is negative, emissions are declining; and if the sum is zero,
emissions are constant.
Equation 3 makes explicit why there is upward pressure on GHG emissions.
For nearly all nations, population is increasing, with developing nations typically
having the highest rate. Thus k is positive globally and for most nations; it is zero
p
or negative for only a few nations.13 The economic development of less-developed
nations is a global objective acknowledged by the UNFCCC; developed nations also
promote economic growth to raise living standards. Thus k is increasing globally
g
and for most nations. With k and k positive, emissions will be rising unless the
g
p
decline in intensity, k , exceeds the growth in population and economic activity,
i
which has seldom been the case. If the goal is to reduce GHG emissions, the larger
the negative k the better.
i
Table 2 shows the changes in these variables for the 1990s. (The figures in the
right-most column are taken from the CAIT database.14) As the table shows, global
growth rates for population and per capita income outpaced the rate of decline in
intensity — so GHG emissions rose; this is also true of the majority of nations,
including the United States. Circumstances in several individual countries highlight
some important points about GHG emissions and their potential control.
! First, for many nations, population growth is an important
contributor to the increase in GHG emissions. For India, Japan,
13 The rate of population growth has declined in many countries in recent decades, partly as
a result of deliberate policies (e.g., birth control programs and, in a few countries, such as
China, limits on family size); and partly as a result of education, higher standards of living,
and cultural changes. Global population growth is expected to continue at least to mid-
century, with projections suggesting a global population of around 9 billion in 2050.
14 In principle, these figures could be calculated by adding the three left-hand data columns;
in fact, a number of rows do not add due to rounding. The one large discrepancy (China,
adding to 3.4 rather than the reported 2.6), probably arises from shortcomings in the
underlying reported data (China’s GDP numbers are particularly suspect), but either figure
would be consistent with the generalizations about trends.

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CRS-7
Brazil, Mexico, South Korea, Indonesia, and South Africa,15
improvements in intensity were cancelled by increases in population
alone.16
! Second, developing countries, focused on developing their
economies, have increasing GHG emissions even when they manage
to improve intensity (e.g., China,17 India,18 Brazil, Mexico,
Indonesia, and South Korea). For these countries, population growth
exceeding 1% per year combined with per capita GDP growth
overwhelmed whatever intensity improvements they achieved.19
! Third, lower emissions can be associated with decreasing economic
activity. For the Russian Federation and Ukraine, economic
contraction following the dissolution of the Soviet Union is the
primary cause of decreases in their emissions. (Some fear that the
cause and effect of this relationship runs both ways — that policies
to reduce emissions will inevitably result in depressed economic
activity.)
! Fourth, perhaps alleviating that fear, several developed countries
managed to improve per capita GDP (at rates near or better than the
United States) while decreasing their GHG emissions; for example,
Germany, the United Kingdom, France, and Poland (see also the
European Union 25). Each did so by combining slow population
growth (0.4% or less) with substantial improvements in intensity
(-2.5% per year or better).
! Fifth, in some developed countries, income growth alone exceeded
the decline in intensity (e.g., the United States, Canada, and
Australia).
Stabilizing emissions would require an accelerated decline in intensity.20 For
global emissions to have remained at 1990 levels during the 1990-2000 period,
intensity would have had to decline at the rate of -3.1% per year, rather than at the
15 For South Africa, both per capita GDP and intensity declined, so the increase in emissions
can be attributed to population growth alone.
16 For Iran and Spain, population and intensity both increased.
17 The discrepancy between the calculated and CAIT reported emissions for China suggests
data shortcomings within the measures of GDP, intensity, and emissions.
18 For India, the intensity improvement offset only its population increase, so GHG
emissions rose at the rate of economic development.
19 For Iran, GHG emissions rose because population and GDP growth had no offset at all
from intensity, which worsened.
20 Emissions could also be stabilized by declines in population or GDP. However, because
U.S. policymakers are unlikely to promote population reduction or GDP contraction,
analysis of these options seems unwarranted. In some countries (e.g., China), deliberate
efforts to constrain population do occur.

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CRS-8
actual -2.5%.21 For the United States, the situation was similar: for emissions in 2000
to have remained at 1990 levels, intensity would have had to decline at the rate of
-3.2% per year, rather than the actual -1.8%.22 Looking to the future, this relationship
holds — absent a declining population or a contracting economy, GHG emissions can
be expected to decline only if intensity declines at a rate faster than it did over the last
decade of the 20th Century.
Table 2. Rate of Change in Factors Affecting Greenhouse Gas
Emissions: Selected Countries, 1990-2000
(Excludes land use changes)
Per Capita
Total GHG
Population
GDP
Intensity
Emissions
(average
(average
(average
(average
Country
annual %)
annual %)
annual %)
annual %)
United States
1.2
2.0
-1.8
1.4
China
1.1
9.3
-7.0
2.6
EU-25
0.3
1.9
-2.7
-0.6
Russian Fed
-0.1
-3.8
-0.2
-4.1
India
1.8
3.6
-1.7
3.7
Japan
0.3
1.0
0.0
1.3
Germany
0.3
1.8
-3.8
-1.8
Brazil
1.5
1.1
0.4
3.1
Canada
1.0
1.9
-1.2
1.7
U.K. 0.4
2.1
-3.4
-1.0
Mexico
1.6
1.8
-1.3
2.1
Italy
0.0
1.5
-0.6
0.9
S. Korea
0.9
5.1
-0.8
5.2
France
0.4
1.6
-2.5
-0.6
Indonesia
1.5
2.7
-0.2
4.0
Australia
1.2
2.4
-1.5
2.0
Ukraine
-0.5
-7.5
2.4
-5.8
S. Africa
2.3
-0.4
-0.1
1.8
Iran
1.6
2.1
1.5
5.2
Spain
0.4
2.4
0.0
2.8
Poland
0.1
3.7
-5.4
-1.8
WORLD
1.4
1.7
-2.5
0.7
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
21 That is, annual population growth (1.4%) + per capita GDP growth (1.7%) + intensity
change (-3.1% [rather than the actual -2.5%]) = 0 emissions growth.
22 That is, annual population growth (1.2%) + per capita GDP growth (2.0%) + intensity
change (-3.2% [rather than the actual -1.8%]) = 0 emissions growth.

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CRS-9
How fast and how far might intensity be driven down? There are two ways to
approach this question: one is to examine the sources of emissions and consider how
much and how fast they could be curtailed; a second is to assess what level of
greenhouse gases can be emitted to the atmosphere without causing “dangerous
interference with the climate system” (in the words of the UNFCCC) and to calculate
from those emissions what the intensity would have to be over time, taking into
account population and income growth.
Sectorial Breakdown of GHG Emissions
Table 3 presents emissions data by economic sector for the top 20 emitting
nations (plus the EU-25 and the world). As the table shows, the energy sector is by
far the largest contributor of greenhouse gases, accounting for about 75% of total
world emissions in 2000; the agricultural sector is second, accounting for about 16%.
These two sectors dominate for almost all countries (industrial process emissions
rank second for Japan and South Korea).
Table 4 presents a breakdown of the energy sector emissions. Electricity and
heat contributes the largest share, accounting for about 43% in 2000, followed by
transportation at about 19%, manufacturing at about 18%, other fuel combustion at
about 13%, and fugitive emissions at about 6%. Emissions by energy subsector vary
considerably among nations; for example, transportation emissions tend to be much
higher absolutely and as a percentage of energy sector emissions for developed
nations, as compared with developing nations.

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CRS-10
Table 3. GHG Emissions by Sector:
Top 20 Emitters, 1990-2000
(Excludes land use changes)
Industrial
Waste (e.g.
Energya
Processes
Agricultureb
landfills)c
Totald
Country
1990
2000
1990
2000
1990 2000 1990 2000 1990 2000
United States
1,409
1,640
44
57
116
121
59
51 1,631 1,874
China
668
866
e36
e103
247
284
42
46 1,027 1,333
EU-25
1,080
1,056
74
62
154
135
48
39 1,376 1,296
Russian Fed
f519
468
18
9
61
30
14
13
791
521
India
178
286
8
16
90
102
26
31
305
438
Japan
292
326
18
24
11
9
2
2
329
373
Germany
277
234
13
9
30
25
10
5
332
277
Brazil
56
88
6
8
116
150
10
11
191
259
Canada
129
161
e7
e5
16
18
6
7
156
186
U.K. 162
151
11
6
15
13
7
4
198
179
Mexico
93
119
4
6
18
20
10
12
127
156
Italy
113
121
9
10
12
11
4
4
133
146
S. Korea
64
119
7
12
5
5
8
4
86
143
France
101
108
12
8
30
28
4
4
150
142
Indonesia
52
91
2
4
29
34
8
31
92
137
Australia
78
102
2
2
26
30
3
3
110
135
Ukraine
f147
108
5
2
22
10
4
4
240
132
S. Africa
72
85
2
3
12
11
5
6
101
120
Iran
55
100
2
4
6
8
4
4
69
115
Spain
58
80
6
8
11
12
2
3
78
102
Poland
102
85
3
3
11
7
5
5
122
102
WORLD
6,072
7,364
285
374 1,426 1,564
356
371 9,087 9,788
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
Notes: Emissions are given in millions of metric tons of carbon equivalents (MMTCE).
a. CO , N O and CH
2
2
4
b. N O and CH
2
4
c. N O and CH
2
4
d. As totaled in CAIT
e. CH data not available.
4
f. Data only for CO in 1992
2

---

CRS-11
Table 4. Energy Sector GHG Emissions:
Top 20 Emitters, 1990-2000
(Excludes land use changes)
Manufacture
Electricity and
and
Other Fuel
Fugitive
Heat
Construction
Transportation Combustion
Emissionsa
Country
1990
2000
1990
2000
1990
2000
1990
2000
1990
2000
United States
576
733
191
180
389
468
166
175
69
63
China
187
400
262
246
32
60
134
106
35
33
EU-25
416
403
203
177
201
240
209
192
32
22
Russian Fed
b302
250
b69
59
b71
48
b72
55
b5
53
India
71
152
46
62
22
25
21
27
8
10
Japan
109
127
80
74
57
70
44
52
1
1
Germany
113
97
49
34
44
47
58
47
b0
6
Brazil
8
14
16
26
22
34
8
10
1
2
Canada
38
51
23
26
34
41
22
27
8
12
U.K. 67
61
23
18
33
34
30
30
8
5
Mexico
29
42
20
18
24
28
8
9
12
20
Italy
39
42
23
22
26
31
21
21
2
2

S. Korea
18
50
13
23
12
24
19
20
2
1
France
17
18
22
21
31
37
26
27
2
1
Indonesia
15
26
9
19
9
17
6
12
11
14
Australia
38
54
12
14
17
20
3
4
6
7
Ukraine
b66
35
b50
21
b11
7
b19
14
b 0
32
S Africa
39
52
19
17
8
10
4
3
2
2
Iran
11
22
12
15
11
20
14
26
6
15
Spain
21
30
12
15
18
25
6
8
1
1
Poland
63
46
13
14
6
8
14
12
6
4
WORLD
2,207
3,161
1,311
1,296
1,062
1,389
916
952
461
436
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
Note: Emissions are given in millions of metric tons of carbon equivalents (MMTCE).
a. In addition to CO , includes N O and CH4 data.
2
2
b. 1992 data for CO .
2

---

CRS-12
The most revealing aspect of sectorial emissions emerges from Table 5, which
shows their rates of change,23 including the energy subsectors (shown in italics). The
fastest growing sectors are Energy (1.9%/year) and Industrial Processes (2.7%/year).
Because Industrial Process emissions24 are a much smaller share of total emissions
than energy, the increase is relatively small in absolute terms; however, the rate of
increase is substantial for nations that are industrializing, especially China, India,
Indonesia, and South Korea. The largest absolute increase in emissions is driven by
the rate of increase for the energy sector. Within that sector, the most rapidly growing
subsector is electricity and heat energy, at 3.7% per year, led by developing nations,
especially China, India, Brazil, South Korea, Iran, and Indonesia. In contrast, for the
EU-25, the rate and absolute emissions for the subsector declined slightly; but for the
Russian Federation, Ukraine, and Poland, the rate and absolute emissions declined
substantially as their economies contracted. The next fastest growing subsector is
transportation, at 2.7% a year, with every nation showing a positive rate of growth
except the Russian Federation and Ukraine, with their contracting economies during
the 1990s.
Energy Use as a CO Intensity Driver. The previous section looked at
2
emissions and the rate of change, 1990-2000, for all six greenhouse gases and all
sectors of the economy. Of the six greenhouse gases, CO dominates, accounting for
2
over 70% of the carbon equivalents of global GHG emissions in 2000 and nearly 85%
of U.S. GHG emissions. Overwhelmingly — not counting land use changes, which
are discussed later — the source of that CO is energy use: for world CO emissions,
2
2
energy use accounts for 95.2%; for the United States, energy use accounts for 98.9%.
Two factors largely determine the intensity of CO emissions of a nation’s
2
economy: energy intensity (energy per unit of GDP) and the fuel mix (emissions per
unit of energy):25
Energy Use
Emissions
Emissions
co2
co2
Equation 4.
x
=
GDP
Energy Use
GDP
23 For fugitive emissions and waste emissions, rates of change were not calculated if both
the 1990 and 2000 emission levels were below 10 million tons. At low levels, even small
changes can yield large rates of change — for example, if emissions went from 2 to 4
million tons between 1990 and 2000, the rate of change would be 6.9% per year, but the
actual emissions are too small to meaningfully affect overall totals.
24 Including CO from cement manufacture, N O from Adipic and Nitric Acid production,
2
2
N O and CH from other industrial processes, plus HFCs, PFCs, and SF .
2
4
6
25 See Timothy Herzog et al., Target: Intensity, An Analysis of Greenhouse Gas Intensity
Targets (Washington, DC: World Resources Institute, November 2006), pp. 3-9.

---

CRS-13
Table 5. Rate of Change of GHG Emissions by Sector:
Top 20 Emitters, 1990-2000
(Excludes land use changes)
Elec & Man &
Other
Ind
Country
Energy
Heat
Const
Transp
Fuel
Fugitivea
Proc
Ag
Wasteb
Total
United
States 1.5
2.4
-0.6
1.9
0.6
-1.0
2.5
0.4
-1.4
1.4
China
2.6
7.9
-0.6
6.4
-1.8
-0.5
11.1
1.4
1.0
2.6
EU-25
-0.2
-0.3
-1.3
1.8
-0.7
-4.1
-1.8
-1.3
-2.1
-0.6
Russian
Fed
c-2.8
-2.3
-1.8
-4.7
-3.3
NAd
-7.2
-6.8
-0.7
-4.1
India
4.9
7.9
2.9
1.2
2.2
6.8
1.3
1.9
3.7
Japan
1.1
1.6
0.8
2.2
1.9
2.9
-1.3
1.3
Germany
-1.7
-1.6
-3.4
0.8
-2.1
-3.5
-1.8
-6.8
-1.8
Brazil
4.5
6.1
5.0
4.5
2.2
3.1
2.6
1.5
3.1
Canada
2.2
3.2
1.0
1.9
2.0
3.1
-3.3
1.5
1.7
U.K. -0.7
-0.9
-2.3
0.4
0.2
-7.0
-0.8
-1.0
Mexico
2.5
3.9
-0.9
1.8
1.5
5.4
4.6
0.7
1.7
2.1
Italy
0.6
0.8
-0.4
1.6
0.5
0.7
-0.2
0.9
S. Korea
6.5
10.9
5.7
7.3
0.7
6.0
-0.5
5.2
France
0.6
0.5
0.5
1.7
0.4
-4.7
-0.5
-0.6
Indonesia
5.7
5.9
7.8
7.1
5.3
2.4
7.0
1.7
4.0
Australia
2.6
3.5
1.4
1.9
2.8
0.7
1.4
2.0
Ukraine
c-7.5
-7.6
-10.0
-4.4
-3.9
NAd
-11.1
-7.1
-5.8
S. Africa
1.6
2.9
-1.1
2.0
-1.2
5.0
-0.8
1.8
Iran
6.1
6.9
2.6
6.4
6.3
8.9
5.6
2.6
5.2
Spain
3.2
3.6
1.9
3.6
3.8
1.7
1.1
2.8
Poland
-1.8
-3.0
0.7
2.8
-1.3
0.7
-3.7
-1.8
WORLD
1.9
3.7
-0.1
2.7
0.5
-0.6
2.7
0.9
0.4
0.7
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
Note: Average annual percentage per year.
a. Not calculated if tonnage for both years <10; N O data not available.
2
b. Not calculated if tonnage for both years <10.
c. 1992-2000, CO data only for energy sector and subsectors.
2
d. Not available.

---

CRS-14
Table 6 presents data on energy sector CO emissions for 2004. The first data
2
column represents energy intensity of the economy, measured in 1,000 tons of oil
equivalent (toe) per million $PPP. The smaller the number, the more efficiently
energy is used to support economic activity in that country. Italy, the United
Kingdom, Spain, Brazil, and Japan are the most efficient; the Ukraine and the Russian
Federation are the least efficient. In general, the higher the number in column one, the
more least-cost options that nation should be able to find for reducing energy use
without adversely affecting the overall economy. Improvements could come, for
example, from upgrading boilers, substituting gas-combined cycle electricity
generation, improving the efficiency of the electricity grid, or upping the efficiency
of the vehicle fleet.
The second data column in the table reflects the fuel mix of energy use, measured
as tons of carbon (C) per 1,000 tons of oil equivalent. The lower the number, the less
CO being emitted by the energy used. Higher numbers would generally reflect a
2
higher proportion of coal combusted in the electricity-generating, manufacturing, and
heating sectors and a low transportation fleet fuel economy; lower numbers would
generally reflect a higher proportion of hydropower, renewables, or nuclear power in
the electricity, manufacturing, and heating sector, and a high transportation fleet fuel
economy. Again, in many cases, the higher the number, the more least-cost options
for lowering CO emissions without adversely affecting the overall economy, for
2
example by substituting natural gas for coal or renewables for oil.
The third data column contains each nation’s intensity of carbon emissions for
the energy sector; it is the product of the first and second data columns. (Note that
this intensity number is for CO emissions only, and is thus different from greenhouse
2
gas intensity, which includes CO plus five other gases.) The higher the number, the
2
less efficiently the economy is using carbon-emitting energy. The last column in the
table provides data on total CO emissions from energy use.26
2
Another question is the relationship between new economic growth and
emissions, which are often influenced by the degree of industrialization and the prices
and availability of different fuels. Table 7 compares this by providing information
on the rates of change of factors affecting CO emissions from energy use. The first
2
three data columns parallel the first three in Table 6, giving the rates of change during
1990-2004. In terms of CO emissions, negative numbers mean that over time a
2
nation is getting more economic activity for less energy (first data column) and more
energy for less CO (second data column). As Table 7 shows, there are wide variations
2
among nations. For example, China’s economy made rapid progress in using energy
more efficiently (energy intensity of -5.6% per year), even though the energy it used
actually produced more CO per unit of energy (+0.9% per year). A number of
2
countries, including the EU-25, improved efficiency and reduced emissions per unit
of energy used. The third data column, which should be the sum of the first two, is
negative if, overall, the country is producing more economic activity for the CO2
26 As given, the emissions data are taken from CAIT tables, but in principle could be
calculated by multiplying the intensity (column 4) times GDP; because of inconsistent data,
the calculations in some cases diverge from the reported emissions, though the general
magnitudes and the relative positions of nations are right.

---

CRS-15
emitted. The fourth and fifth columns in Table 7 give the rates of change of the
nations’ GDPs and total CO emissions from energy use. A nation’s rate of change
2
of CO intensity can be negative, but if GDP is growing faster than CO intensity is
2
2
declining, emissions will rise (the last column).27
Table 6. CO Emissions Intensity of the Energy Sector:
2
Top 20 Emitters, 2004
(Excludes land use changes)
Energy
CO Intensity
CO Intensity
2
2
Intensity
of Energy
of Economy
Total CO2
(1,000 toe /
Sector
(Tons C /
Emissions from
million 2000
(Tons C /
million 2000
Energy Use
Country
$PPP)
1,000 toe)
$PPP)
(MMTCE)
United States
0.22
690
150
1,589
China
0.23
880
200
1,292
EU-25
0.16
620
98
1,064
Russian Fed
0.49
670
331
417
India
0.19
570
106
302
Japan
0.15
670
103
332
Germany
0.16
670
109
232
Brazil
0.15
460
69
89
Canada
0.29
560
161
151
U.K. 0.13
640
86
147
Mexico
0.17
680
118
103
Italy
0.12
710
88
126
S. Korea
0.23
650
152
126
France
0.17
390
67
106
Indonesia
0.24
580
141
94
Australia
0.21
830
171
97
Ukraine
0.50
640
322
83
S. Africa
0.30
890
264
94
Iran
0.31
760
240
107
Spain
0.14
680
96
90
Poland
0.20
900
182
81
WORLD
0.21
740
156
7,704
Source: Climate analysis Indicators Tool (CAIT), version 4.0 (Washington, DC: World Resources
Institute, 2008). CRS calculations.
27 In principle, the sum of the first two data columns should equal the third data column, and
the fifth column should be the sum of the third and fourth columns; however, because of
data inconsistencies, the calculated numbers may not exactly correspond to the CAIT
reported numbers. Nevertheless, the general relationships hold.

---

CRS-16
Table 7. Rate of Change in Factors Affecting CO Emissions from
2
Energy Use: Top 20 Emitters, 1990-2004
(Excludes land use changes)
CO2
Carbon
Intensity of
Total CO
2
Energy
Intensity of
Energy
Emissions of
Country
Intensity
Energy Used
Sector
GDP
Energy Use
United States
-1.6
0.0
-1.7
3.0
1.3
China
-5.6
0.9
-4.3
10.1
5.4
EU-25
-1.1
-0.7
-1.9
2.1
0.2
Russ Feda
1.6
-0.3
-2.3
0.0
-1.8
India
-2.5
1.3
-1.0
5.8
4.5
Japan
0.1
-0.2
-0.1
1.2
1.0
Germany
-1.9
-0.9
-2.7
1.7
-0.9
Brazil
0.6
0.3
0.8
2.5
3.7
Canada
-1.0
-0.1
-0.1
2.8
1.8
U.K. -1.8
-1.0
-2.7
2.5
-0.2
Mexico
-0.8
0.0
-0.8
2.9
1.8
Italy
0.2
-0.3
-0.1
1.4
1.1
S. Korea
0.4
-1.0
-0.6
5.7
5.2
France
-0.5
-1.0
-1.5
1.9
0.6
Indonesia
-0.1
1.7
1.6
4.3
6.1
Australia
-1.5
0.0
-1.4
3.5
2.2
Ukrainea
5.8
-1.2
-2.1
-2.5
-4.6
S. Africa
0.3
0.1
0.4
2.3
2.2
Iran
1.2
0.0
1.2
4.3
5.8
Spain
0.3
0.0
0.4
2.9
3.4
Poland
-4.1
-0.6
-4.5
3.5
-1.2
WORLD
-1.6
-0.3
-1.9
3.4
2.4
Source: Climate Analysis Indicators Tool (CAIT), version 4.0 (Washington, DC: World Resources
Institute, 2008). CRS calculations.
Note: Average Annual Percentage.
a. 1992-2004 trend.

---

CRS-17
The carbon intensity of energy use — that is, the consequences of fuel mix — is
especially notable in looking at the energy mix of electricity generation, as discussed
in the next section.
Carbon Intensity of Electricity Generation. Variations among countries
of the carbon intensity of energy use (see Table 6) are strongly affected by the carbon
intensity of electricity generation, which accounts for about one-third of world CO2
emissions (not counting land use changes and forestry practices). Differences among
countries are marked, as depicted in Table 8.
Choices among generating technologies are the primary driver of disparities
among countries in the carbon intensity of their electricity generation. In general,
countries with high numbers generate a substantial proportion of their electricity by
burning coal, and countries with low numbers generate large quantities of electricity
by nuclear facilities, hydropower, or other renewables. For example, France, with the
lowest carbon intensity of electricity production at 20, generates about 77% of its
electricity by nuclear power, about 13% by hydropower, and 6% by coal. The United
States, with a carbon intensity of electricity production of 153, generates about 20%
of its electricity by nuclear power, about 7% by hydropower, and about 52% by
combusting coal.
Although a nation’s electricity-generating technologies are obviously affected by
its resource endowments in terms of hydropower and fossil fuels, choices can be
made, as exemplified by France. In 1980, France’s electricity was generated 27% by
hydropower, 24% by nuclear, 27% by coal, and 19% by oil. By 1990, with electricity
production up over 60%, nuclear had risen to a 75% share, whereas coal and oil had
fallen to 8% and 2% shares, respectively.28 Not only did nuclear power account for
all the growth in electricity generation during the period, but it displaced half the coal-
fired and more than three-quarters of the oil-fired electricity generation. In 1990, the
electricity produced by nuclear power exceeded France’s total amount of electricity
generated 10 years earlier.
France’s transition to nuclear power meant that its CO intensity (i.e., CO
2
2
emissions/GDP) declined between 1980 and 1990 at a rate of -5.0% per year, and CO2
emissions declined at a rate of -2.4% per year. Thus, between 1980 and 1990,
France’s total CO emissions declined by 22% — at the same time its GDP was
2
growing by 30.9% (+2.7% per year).29 Thus equation 3 yields a negative growth in
emissions (numbers do not add precisely, due to rounding):
28 International Energy Agency, Electricity Information 2002 (OECD, 2002), p. II.285.
29 Climate analysis Indicators Tool (CAIT), version 4.0 (Washington, DC: World Resources
Institute, 2007).

---

CRS-18
France: CO Intensity, 1980-1990
2
Population
Per Capita GDP
CO Intensity
CO Emissions
2
2
(0.5)
+
(2.1)
+
(-4.9)
=
(-2.4)
During the 1990s, the United Kingdom made a major shift from coal to natural
gas in the generation of its electricity. In 1990, the United Kingdom’s electricity was
generated 21% by nuclear, 1% by natural gas, and 65% by coal. In 2000, with
electricity generation up 17%, nuclear’s share was 23%, whereas coal’s share had
dropped to 33% and natural gas’s share had risen to 39%.30 Because natural gas
produces less total CO per kilowatt hour than coal (at a ratio of about 0.6 to 1 on a
2
Btu basis31), CO intensity in the United Kingdom declined between 1990 and 2000
2
at a rate of -2.8% per year, and CO emissions declined at a rate of -0.4% per year.
2
Thus, between 1990 and 2000, total CO emissions in the United Kingdom declined
2
by 3.7% — at the same time its GDP was growing by 27% (+2.5% per year).32 Thus
equation 3 yields a negative growth in emissions (numbers do not add precisely, due
to rounding):
United Kingdom: CO Intensity, 1990-2000
2
Population
Per Capita GDP
CO Intensity
CO Emissions
2
2
(0.4)
+
(2.1)
+
(-2.8)
=
(-0.4)
The examples of France and the United Kingdom show that for a period of time,
at least, greenhouse gas intensity improvements can be sufficient to absorb growth in
population and economic activity, so that actual emissions decline. The examples also
show that the introduction of new technology can cause sudden shifts in emission
rates.
The United States has also had periods when its CO emissions declined. From
2
1977-1986, U.S. CO intensity declined at a rate of -3.7% per year, and emissions
2
declined at a rate of -0.7% per year. But between 1987 and 2004, the intensity rate has
been about -1.8% per year, not enough to compensate for population and per capita
GDP growth, so emissions have risen at 1.2% per year. Over the longer term,
therefore, emissions have risen: in terms of equation 3, U.S. CO emissions for 1975-
2
2004 are as follows:
United States: CO Intensity, 1975-2004
2
Population
Per Capita GDP
CO Intensity
CO Emissions
2
2
(1.1)
+
(2.1)
+
(-2.2)
=
(1.0)
30 International Energy Agency, Electricity Information 2002 (OECD, 2002), p. II.683.
31 If gas combined-cycle technology is considered, the ratio could be 0.4 or 0.5 to 1.
32 Climate Analysis Indicators Tool (CAIT), version 5.0. (Washington, DC: World
Resources Institute, 2008). In terms of all six greenhouse gases, between 1990 and 2000,
the United Kingdom’s greenhouse gas intensity declined at an annual rate of -1.0%.

---

CRS-19
Table 8. Carbon Intensity of Electricity Generation:
Top 20 Emitters, 2004
Intensity
Country
(gC/kWh)
United States
152.6
China
248.2
EU-25
96.6
Russ Fed
91.9
India
257.0
Japan
115.9
Germany
139.7
Brazil
23.3
Canada
56.6
U.K. 127.2
Mexico
142.6
Italy
120.7
S. Korea
121.8
France
19.9
Indonesia
205.4
Australia
222.3
Ukraine
96.1
S. Africa
236.5
Iran
147.5
Spain
99.7
Poland
133.8
WORLD
152.1
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
Carbon Intensity of Travel. The carbon intensity variation of electricity
generation among nations recurs in the transportation sector, one of the fast-growing
sources of emissions (see Table 5). Data are limited, however, making inter-country
comparisons of the carbon intensity of passenger miles or of ton-miles difficult. For
the United States, data are available for comparisons among some modes of
transportation.
Studies indicate that nations vary considerably in the energy efficiency and
greenhouse gas emissions intensity of their transport sectors. For example, one effort

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CRS-20
examining vehicle miles, published by the Pew Center on Global Climate Change,
shows substantial variations among several nations, with the United States being the
highest emitter per vehicle33 (Figure 1). To some extent, these variations reflect
differing geographic, cultural, and infrastructure circumstances among the nations;
however, as with the carbon intensity of electricity generation, a substantial cause of
the variations is deliberate policies, such as fuel efficiency standards, emission
standards, fuel taxes, and choices of investments in transportation infrastructure.
For the United States, the Bureau of Transportation Statistics provides data on
the energy intensity of passenger modes (Table 9).
Table 9. Energy Intensity of Passenger Modes:
United States, 1970-2005
(Btus per passenger-mile)
Passenger Modes
1970
1980
1990
2000
2004
2005
Air, certified carrier
Domestic
10,185
5,742
4,932
3,883
3,297
3,182
International
10,986
4,339
4,546
3,833
3,428
3,523
Highway
Passenger car
4,841
4,348
3,811
3,589
3,509
3,458
Pickup, SUV, minivan
6,810
5,709
4,539
4,509
4,452
4,452
Motorcycle
2,500
2,125
2,227
2,273
1,969
1,969
Transit motor bus
—
2,742
3,723
4,147
3,572
3,393
Amtrak
—
2,148
2,066
2,134
—
—
Source: Bureau of Transportation Statistics: [http://www.bts.gov/publications/national_transportation
_statistics/html/table_04_20.html].
Two important points emerge from Table 9. First, transportation efficiency for
several modes has improved over time. Air traffic gained efficiency in the transition
to jets and larger aircraft. Vehicular passenger miles have gained efficiency, but at a
slowing pace. On the other hand, transit motor bus efficiency per passenger mile has
worsened over time. Second, the choice of transportation mode, which can be
affected by infrastructure investments and other public policies,34 substantively affects
passenger-mile efficiency. Amtrak and, by extension, commuter rail, is considerably
more efficient than any of the other choices, except motorcycles. Moreover, within the
33 Feng An and Amanda Sauer, “Comparison of Passenger Vehicle Fuel Economy and
Greenhouse Gas Emission Standards Around the World,” Pew Center on Global Climate
Change (December 2004).
34 For example, the London “congestion tax” is intended to shift commuters out of passenger
cars and onto public transit.

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CRS-21
highway mode, efficiency varies significantly: in 2000, passenger cars were 25% more
efficient on average than pickups, SUVs, and minivans.
All in all, it appears that policy choices can affect the energy intensity of travel,
and thus opportunities for improvement exist. Because there is clearly a limit on
greenhouse gas emission reductions to be achieved by heightened efficiencies in the
transportation sector, interest turns to alternative fuels that do not generate greenhouse
gases, including renewables and hydrogen. Brazil has made considerable progress in
substituting ethanol for gasoline (40% by volume); however, the U.S. promotion of
ethanol is still a minute proportion of gasoline consumption (3.6% by volume in
2006), and there are questions about the net impact of ethanol use on CO emissions.35
2
Hydrogen remains a distant possibility.
Figure 1. Actual and Projected GHG Emission for New Passenger
Vehicles by Country, 2002-2018
Source: Feng An, et al., Passenger Vehicle Greenhouse Gas and Fuel Economy Standards: A Global Update,
International Council on Clean Transportation (July 2007), p. 8.
35 See CRS Report RL34265, Selected Issues Relate to an Expansion of the Reneewable Fuel
Standard (RFS), by Brent D. Yacobucci and Randy Schnepf.

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CRS-22
Effects of Land Use on Intensity. Although land use changes can affect
emissions and intensity, they have been excluded from most analyses in this report
because the data are limited and less robust than most of the emissions data, and
because for most nations, taking it into account changes little. However, as Table 10
shows, substantial effects result from logging and clearing forests in a few nations:
Indonesia, Brazil, and (to a lesser extent) Mexico and Canada. The greenhouse gas
intensity for each of these countries is much higher when land use changes are
included. Yet these countries’ emissions attributable to land use changes (almost all
CO ) are much smaller in 2000 than they were in 1990, and the rates of intensity in all
2
four countries decreased over the decade.
Even though land use changes may have a small effect on emissions for most
countries, including it in analyses can identify those situations where it is important
and for which interventions might pay large dividends in terms of curtailing
greenhouse gas emissions or sequestering CO .
2
Table 10. Land Use Changes:
Impact on Intensity of Greenhouse Gas Emissions
Annual %
Annual %
Intensity 2000
Intensity 2000
change, Intensity change, Intensity
(excluding
(including
1990-2000
1990-2000
land use)
land use)
(excluding
(including
Country
tCeq/million $PPP tCeq/million $PPP
land use)
land use)
United States
192.0
180.7
-1.8
-1.8
China
268.0
265.4
-7.0
-7.7
EU-25
124.7
124.1
-2.7
-2.5
Russ Fed
508.3
522.8
-0.2
-0.1
India
182.5
177.9
-1.7
-1.6
Japan
112.6
113.0
0.0
-0.9
Germany
133.1
133.1
-3.8
-3.8
Brazil
207.3
506.7
0.4
-3.9
Canada
219.3
240.1
-1.2
-1.6
U.K. 112.6
112.4
-3.4
-3.4
Mexico
173.7
203.0
-1.3
-2.3
Italy
101.3
100.8
-0.6
-0.6
S. Korea
188.7
189.1
-0.8
-0.9
France
93.1
92.0
-2.5
-2.5
Indonesia
229.0
1,396.8
-0.2
-2.0
Australia
275.4
277.7
-1.5
-1.6
Ukraine
667.1
NA
NA
NA
S. Africa
312.5
313.7
-0.1
0.0
Iran
311.8
317.8
1.5
1.3
Spain
114.0
111.4
0.0
0.0
Poland
251.0
249.8
-5.4
-5.4
WORLD
217.7
263.9
-2.5
-2.7
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).

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CRS-23
Cumulative Emissions. Greenhouse gas emissions are long-lived in the
atmosphere, so their effect cumulates over time. A justification for developed nations
taking the lead on reducing emissions, while giving developing ones the opportunity
to increase emissions from activities that are necessary for economic development, is
not just that developed nations are wealthier but also that they account for the bulk of
cumulative emissions affecting climate. Data to assess cumulative emissions are
limited. In general, data are available only for CO and are calculated from fuel use
2
estimates; land use changes over long time spans are important, but data are scanty or
unavailable. CAIT provides figures for CO emissions only from 1850, not including
2
land use changes (Table 11).
Because climate-forcing depends on the cumulative emissions, not current
emissions, it is easy to see from Table 11 why developing nations feel that developed
ones should take the lead. Given CAIT data, the United States and the European
Union-25 account for well over half the cumulative CO emissions from energy use
2
since 1850.
The data on cumulative emissions and on including or excluding land use
changes (see Table 10) highlight why individual nations are so differently affected by
proposals to reduce greenhouse gas emissions. Setting a baseline year for determining
a nation’s emissions means that countries that developed early could do so with no
restrictions on the use of fuels and other resources regardless of their potential impact
on climate, while those nations just now undergoing development might face
restrictions. The emissions of already developed nations are embedded in their
baselines. Similarly, whether certain activities such as land use changes are included
or not affects what is in the baseline. The greenhouse gas emissions of Brazil and
Indonesia, for example, increase markedly when emissions from land use changes of
the last few decades are counted; but comparable land use changes in many other
countries (e.g., the United States) happened in earlier centuries, and the resulting
emissions count only toward cumulation, not against any current baseline.

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CRS-24
Table 11. Cumulative CO Emissions from Energy:
2
Top 20 Emitters, 1850-2004
(Excludes Land Use Changes)
Cumulative
Emissions
Percentage
Rank
Country
(MMTCE)
of World
in World
United States
88,593
29.4
1
China
24,357
8.1
4
EU-25
79,382
26.4
2
Russ Fed
24,600
8.2
3
India
6,869
2.3
9
Japan
11,653
3.9
7
Germany
21,684
7.2
5
Brazil
2,494
0.8
21
Canada
6,531
2.2
10
U.K. 18,534
6.2
6
Mexico
3,129
1.0
16
Italy
4,882
1.6
13
S. Korea
2,458
0.8
22
France
8,672
2.9
8
Indonesia
1,685
0.6
27
Australia
3,279
1.1
15
Ukraine
6,265
2.1
11
S. Africa
3,662
1.2
14
Iran
2,071
0.7
24
Spain
2,772
0.9
18
Poland
6,134
2.0
12
WORLD
301,222
100.0
—
Source: Climate analysis Indicators Tool (CAIT), version 5.0 (Washington, DC: World Resources
Institute, 2008).
Interactions of the Variables
Numerous subtle and indirect interactions occur among population, income,
intensity, energy use, and emissions. These interactions affect policy choices
concerning climate change because of their implications for other important social
policy initiatives and objectives — most importantly, policies to promote income
growth. These interactions also make difficult the projection of trends over time.

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CRS-25
Economic development and growing incomes interact with population growth
in two ways. First, birth rates tend to decline as incomes rise,36 reducing one of the
upward pressures on emissions. Most high-income nations have annual birth rates of
0.5% or lower, compared with developing nations with birth rates that in some cases
exceed 2% per year. Second, the economic opportunity that many developed nations
offer means they may have relatively high immigration rates, so their population
growth is higher than their birth rate.37 Overall, most demographers expect the rate
of population growth to slow, although world population is projected to exceed 9
billion in 2050, with most of the increase in the developing world.38
Economic development and energy use are closely intertwined. The substitution
of fossil fuel energy for human and animal power has been an important driver of the
industrial revolution and consequent higher incomes. Indeed, for many,
industrialization is synonymous with economic development. Yet at some point in
development, the growth in incomes becomes at least partially detached from energy
use, as energy costs lead to attention to energy efficiencies and as economies shift
toward post-industrial services. Public policies can affect the relationship between
economic development and growth and energy use in many ways, including taxation,
infrastructure development, and research and development. The UNFCCC assumes
that developing nations will inevitably have to exploit more energy as they give
priority to reducing proverty. One of the elements of the climate change debate is how
to decouple that economic development-energy use link — or indeed, whether it can
be done. Another element being debated is whether and at what point depressing
energy use would necessarily depress economic activity.
Income and emissions are related in another way, as well. In general, low-
income people in developing nations focus their efforts on survival, whereas nations
and individuals with higher incomes are likely to have more time and money to attend
to environmental needs and amenities. Thus, while richer nations consume more
goods and services, including energy, per capita, they also have generally been the
most aggressive in addressing pollution and other environmental insults. This
empirical relationship is known as the Environmental Kuznets Curve. However, its
applicability to CO emissions has been questioned,39 and to the degree that it does
2
exist for such pollutants as sulfur dioxide, it reflects policy choices to constrain
emissions.
36 This is not a simple cause and effect, but reflects evolutionary changes in areas such as
education, cultural expectations, women’s rights, access to birth control, and health care —
all of which may be affected by social policy.
37 For the United States, in 2005, the annual rate of population increase from the birth rate
was 0.6%, whereas, counting migration, the population growth rate was 0.9%. See
[http://www.census.gov/cgi-bin/ipc/idbsum.pl?cty=US].
38 See [http://www.un.org/News/Press/docs//2007/pop952.doc.htm].
39 The entire March issue of the Journal of Environment & Development, vol. 14 (2005) is
devoted to this topic; see especially Joseph E. Aldy, “An Environmental Kuznets Curve
Analysis of U.S. State-Level Carbon Dioxide Emissions,” pp. 48-72. Also, William R.
Moomaw and Gregory C. Unruh, “Are Environmental Kuznets Curves Misleading Us? The
Case of CO2 Emissions,” in Environment & Development Economics (Cambridge
University Press, 1997), pp. 451-463.

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CRS-26
These interactions have both short-run and long-run implications. For most
nations most of the time, the combination of population growth and per capita GDP
growth has more than offset forces tending to depress emissions, so emissions have
increased. Overall, the most critical interaction is the one between per capita GDP
growth and resource uses, especially energy, but also including cement manufacture,
agricultural practices, waste disposal, and the consumption and release of certain
chemicals.
Changes in Intensity To Meet Climate Stabilization Goals
What might be required to “prevent dangerous interference with the climate
system” remains debatable. The answer actually depends on the concentration of
greenhouse gases in the atmosphere, not the level of emissions at a given point in
time. Ultimate goals, then, are typically expressed in terms of what concentration
would be required to keep global warming below a certain amount with a certain
probability.40 Models are then used to assess what emission reductions would be
required to keep concentrations below the target level.
Developed nations that have agreed to the Kyoto Protocol have interim, 2008-
2012 greenhouse gas reduction targets, based on reducing emissions from 1990 (or
adjusted) baselines. The United States, while it does not have an emissions reduction
target, does have an initiative introduced by the Bush Administration focused on an
intensity reduction target. Various bills introduced into the 110th Congress specify
emission reduction targets.
U.S. Greenhouse Gas Intensity: Trends and Targets. Analyzing and
projecting the values and the rates of change for the variables population, income,
intensity, and emissions depend on the baseline, the time period in question, and
assumptions about changes over time. For the purpose of analyzing U.S. targets for
greenhouse gas emissions, one could assume the following “business as usual”
projection: from the baseline year of 2000, population grows at the annual rate of
+0.9% for 2000-2010 and +0.8% for 2011-2025,41 per capita income grows at an
annual rate of +2.1% (the 1975-2004 rate), and intensity declines at the annual rate of
-1.6% (the 1990-2000 rate for GHG).
President George W. Bush’s Climate Change Initiative, announced February 14,
2002, focused on increasing the rate of intensity decline.42 Observing that the Energy
Information Agency was projecting that total U.S. greenhouse gas intensity would
decline between 2002 and 2012 by -14%, President Bush said that his initiative would
seek to increase that to -18%. The baseline rate of decline for this period is
approximately -1.5% per year, while the objective would be to achieve a rate of
40 See, for example, M.G.J. den Elzen and M. Meishausen, “Meeting the EU 2°C climate
target: global and regional emission implications,” Report 728001031/2005, Netherlands
Environmental Assessment Agency.
41 U.S. Census Bureau, “IDB Summary Demographic Data for United States,”
[http://www.census.gov/cgi-bin/ipc/idbsum.pl?cty=US]
42 See [http://www.whitehouse.gov/news/releases/2002/02/climatechange.html].

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CRS-27
approximately -1.9%. With the assumptions of population and income growth
presented above, this would leave total greenhouse gas emissions increasing at about
1.0% per year (0.8 + 2.1 - 1.9 = 1.0).
An interim target to reducing greenhouse gas emissions would be to stabilize
them. Because the sum of the assumed rates of population growth and per capita GDP
growth equals 2.9% per year after 2010, a decline in the intensity rate of -2.9% would
be necessary to stabilize total greenhouse emissions at the emissions level of the year
that rate of decline went into effect, compared with the recent annual rate of intensity
decline of about -1.6% for the United States.
Now consider the goal, contained in a number of pending bills in Congress, of
returning U.S. greenhouse gas emissions to their 1990 level of 1,631 MMTCE.43
Because it would take time to implement policies and programs to reduce intensity,
one could assume that current trends continue through 2009 and that greenhouse
intensity is then brought down; what rate of intensity decline would be necessary to
achieve the 1990 goal by 2020? This is the typical first-stage emissions limit
established by a number of bills that include economy-wide caps (e.g., S. 280, S. 309,
S. 485, H.R. 620 and H.R. 1590). The answer is, it would take a rate of intensity
decline of about -5.4% per year44 (compared with the recent -1.6% per year),
beginning in 2010, to reach the level of 1,644 in 2020, slightly over the target. At that
point, intensity would be at 95.6 MMTCE/million$PPP, compared with a level of 93.5
for France in 2000.
Over the longer term, S. 485, for example, requires that beginning in 2021,
emissions economy-wide be reduced 2.5% annually from the previous year’s level,
and that beginning in 2031, emissions economy-wide be reduced 3.5% annually from
the previous year’s level. Assuming the “business as usual” rates of growth for
population and income, the 2021-2030 annual reduction target means that intensity
would be declining at a rate of -5.4% per year, equivalent to the decline required to
achieve the bill’s first-stage goal of reducing U.S. greenhouse gas emissions in 2020
to 1990 levels. The 2031-2050 annual reduction target means that intensity would be
declining at a rate of -6.4% per year.
S. 309 sets a 2050 cap on economy-wide greenhouse gas emissions of 326
MMTCE (20% of 1990 emissions). Again assuming population and per capita GDP
grow from 2010 to 2050 at the average annual rates of 0.8% and 2.1%, respectively,
then given the emission rate at the cap, U.S. greenhouse gas intensity in 2050 would
be 8.0 MMTCE/million$PPP. Or, in terms of rate of change, assuming current trends
43 In contrast, S. 2191, ordered reported by the Senate Environment and Public Works
Committee on December 5, 2007, is estimated by its sponsors to result in 2020 GHG
emission 19% below 2005 levels. For reference, 2005 emissions were 16.3% above 1990
levels. See U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2005 (April 15, 2007).
44 Achieving this could include, besides direct reductions in emissions, offsets from
reductions made and paid for in other countries, as well as reductions from land use changes
and sequestration.

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CRS-28
until 2010, intensity would have to decline over the next 40 years, at an average rate
of about -7.6% per year.45
To give perspective to rates of intensity decline, consider an illustrative scenario
in which, for each of the 10 years 2016-2025, two 1,000-megawatt nuclear electrical
generating facilities go into service (or equivalent generating capacity based on
renewables), replacing existing coal-fired facilities. Each plant would displace
approximately 6 million tons of carbon per year; when all 20 coal-supplanting plants
were in service in 2025, they would be displacing 120 million tons of carbon per year.
All else equal, displacing this much carbon would accelerate the rate of decline in
intensity for 2016-2025 by about -0.4% per year, so that in 2025, intensity would be
approximately 125.5, compared with the business-as-usual intensity of 130.7.
This example, which lowers emissions and intensity only incrementally, shows
that large declines in intensity would require multiple initiatives. To meet the goal of
reducing economy-wide emissions to 20% of 1990 levels by 2050 implies some mix
of making tremendous gains in energy efficiency, shifting to energy sources that emit
virtually no CO , and developing the capacity to capture and sequester enormous
2
amounts of CO .
2
Global Greenhouse Gas Intensity. As has been noted, world greenhouse
gas intensity has been declining, but not at a rate sufficient to prevent rising GHG
emissions (numbers do not add precisely, due to rounding):
World GHG Intensity, 1990-2000
Per Capita
Population
GDP46
GHG Intensity
GHG Emissions
(1.4)
+
(1.7)
+
(-2.5)
=
(0.7)
An in-depth analysis of policies and programs for reducing global greenhouse gas
emissions is far beyond the scope of this report. But if greenhouse gases are to be
reduced, the imperative to reduce intensity is clear. Simply put, more people at higher
standards of living means more goods and services, especially energy — to cook, heat
and cool homes, to manufacture goods, to transport people and goods, etc.
To decouple those increases in the numbers of consumers and their consumption
from increases in greenhouse gas emitting energy uses implies policies fostering
greater efficiency in using energy and/or use of non-greenhouse gas-emitting forms
of energy, such as renewables or nuclear. But greater efficiency ultimately reaches
limits from the laws of physics; alternative fuels run into the facts that, in most places,
coal is the least expensive fuel for generating electricity and heat, and oil is the least
expensive fuel for powering transport.
45 Achieving this could include, besides direct reductions in emissions, offsets from
reductions made and paid for in other countries, as well as reductions from land use changes
and sequestration.
46 Economic contractions of several newly independent nations following the breakup of the
former Soviet Union depressed global GDP, so this rate will likely rise in subsequent
decades.

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CRS-29
Beyond the energy sector, moreover, there are many other areas where policies
may affect GHG emissions. Land use and agricultural and forestry policies can have
direct implications for emissions, and could reduce intensity. The non-CO gases,
2
many of which pose particularly long-term climate implications, offer cost-effective
opportunities for reductions from certain industrial processes, landfills, and fuel
production.
Perhaps most importantly, at the global scale, the possibility exists for identifying
and exploiting the least-expensive opportunities for reducing greenhouse gases,
thereby increasing the efficiency with which economies use greenhouse gas-emitting
technologies. This depends, however, on global instruments for accounting for and
verifying such reductions. Reaching practical agreements on international
mechanisms (e.g., for a carbon tax or a cap-and-trade system to obtain economic
efficiencies among nations in reducing emissions) requires divergent national goals
to be focused on what is, ultimately, a global issue. The global nature of climate
change challenges national sovereignty. The UNFCCC, the Kyoto Protocol, and the
Asia-Pacific Partnerships are efforts in multilateral approaches to reducing emissions,
but their individual and complementary successes remain to be seen.
Conclusion
In the end, the interactions of the variables, population, income, and intensity of
emissions (equation 1), together with the inexorable force of compounding growth
rates over time (equation 2), are inescapable conditions determining both the risks of
climate change and the costs, benefits, and tradeoffs of options for responding. If
climate change poses a genuine risk to the well-being of mankind, the nations of the
world, individually and collectively, face two fundamental challenges: adopting and
implementing policies and encouraging the development and use of technologies that
emit lower levels of greenhouse gases, and maintaining a sufficiently high rate of
intensity decline over the long term to ensure declining emissions.
In 1992, Congress enacted the Energy Policy Act of 1992 (EPACT, P.L. 102-
486), which contained provisions to implement the United Nations Framework
Convention on Climate Change (UNFCCC), which had been signed earlier in the
year.47 The UNFCCC’s objective to stabilize “greenhouse gas concentrations in the
atmosphere at a level that would prevent dangerous anthropogenic interference with
the climate system” was echoed in EPACT, which called for a National Energy Policy
Plan to “include a least-cost energy strategy ... designed to achieve [among other
goals] ... the stabilization and eventual reduction in the generation of greenhouse
gases....”48
In ratifying the UNFCCC, the United States agreed to several principles for
achieving this objective, including the following:
47 The United States signed the UNFCCC on June 12, 1992, and ratified it on October 15,
1992 The UNFCCC entered into force on March 21, 1994.
48 Section 1602(a)

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CRS-30
! “[D]eveloped country Parties should take the lead in combating
climate change and the adverse effects thereof.”49
! “Parties should take precautionary measures to anticipate, prevent or
minimized the causes of climate change and mitigate its adverse
effects.”50
! “Parties have a right to, and should, promote sustainable
development....” Climate change policies should take “into account
that economic development is essential for adopting measures to
address climate change.”51
The UNFCCC’s linking of sustainable development and climate change
mitigation reflects the perceived need to decouple economic development and growth
from non-sustainable, greenhouse gas-emitting energy technologies.
As this report suggests —
! An expanding population in many parts of the developing world is an
important driver for economic growth. As affirmed in the UNFCCC,
climate change policies are to take “into full account the legitimate
priority needs of developing countries for the achievement of
sustained economic growth and the eradication of poverty.”52
! Economic development may reduce population pressure in the long-
term but creates increasing demand for resources that, employing
current technologies, contribute to greenhouse gas emissions.
Although economies become more efficient over time, those
efficiencies have yet to overcome the combination of expanding
population and growing economies without the intervention of
governments.
! Satisfying the energy needs of dynamic economies is increasing the
demand for coal and other fossil fuels for economic and other
reasons. Coal is abundant, available locally, and is relatively
inexpensive. To meet the massive reductions in greenhouse gas
emissions in the long term required by various stabilization scenarios
would require either the development of a commercially available
technology to reduce substantively, or to capture and sequester, the
emissions of CO from coal and other fossil fuels or a substantial
2
restructuring of many countries’ economies. The UNFCCC
recognizes the “special difficulties of those countries, especially
developing countries, whose economies are particularly dependent on
49 UNFCCC, article 3.
50 Ibid.
51 Ibid.
52 UNFCCC, Preamble.

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CRS-31
fossil fuel production, use and exportation, as a consequence of
action taken on limiting greenhouse gas emissions.”53
Breaking the current dynamic of increasing populations and economic growth
pushing up greenhouse emissions would depend on developing “sustainable”
alternatives — both in improving the efficiency of energy use and in moving the fuel
mix toward less greenhouse gas-emitting alternatives. In the UNFCCC, developed
nations committed to taking the initiative by “adopt[ing] national policies and tak[ing]
corresponding measures on the mitigation of climate change ... [that] will demonstrate
that developed countries are taking the lead in modifying longer-term trends in
anthropogenic emissions consistent with the objective of the Convention ....”54 Such
development paths are critical not only for any domestic program, but also
participation by developing countries in any global greenhouse gas stabilization
program may be at least partially dependent on the availability and cost of such
technologies.
As stated by the UNFCCC,
The extent to which developing country Parties will effectively implement their
commitments under the Convention will depend on the effective implementation
by developed country Parties of their commitments under the Convention related
to financial resources and transfer of technology and will take fully into account
that economic and social development and poverty eradication are the first and
overriding priorities of the developing country Parties.55
The focus of the Asia-Pacific Partnership on Clean Development and Climate on
technology development and its transfer among nations represents an important
component of the United States’ response to this principle. It remains to be seen how
it will relate to the UNFCCC, the Kyoto Protocol, or other cooperative agreements.
Fostering technological change depends on two driving factors: exploiting new
technological opportunities (technology-push) and market demand (market-pull).56
Currently, U.S. policy is oriented primarily to the technology-push part of the
equation, with a focus on research and development (R&D). In contrast, the European
Union (EU) is complementing its research and development efforts by constructing
a multi-phased, increasingly more stringent market-pull for greenhouse gas-reducing
technologies and approaches, including taxes and regulatory requirements overlain by
the EU’s Emissions Trading System.57
53 UNFCCC, Preamble.
54 UNFCCC, article 4(2)(a).
55 UNFCCC, article 4(7).
56 L. Clarke, J. Weyant, and A. Birky, “On the Sources of Technological Change: Assessing
the Evidence,” Energy Economics, vol. 28 (2006), pp. 579-595.
57 See CRS Report RL34150, Climate Change: The EU Emissions Trading System (ETS)
Enters Kyoto Compliance Phase, by Larry Parker.

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CRS-32
The market-pull side focuses on market interventions to create demand, which
poses questions of —
! Whether, how, and to what extent to use price signals to change
behaviors and to stimulate innovation of technologies that increase
energy efficiency or that emit less greenhouse gases. Direct taxes on
energy or on greenhouse gases could be one approach, whereas the
concept of shifting taxes from incomes to consumption would be a
broader one.
! Whether, how, and to what extent to use regulatory actions to change
behaviors and to require technologies that increase energy efficiency
or emit less greenhouse gases. A direct regulatory effort would be a
renewable power standard for electricity-generating facilities, which
requires some specified portion of electric power to be generated by
renewables, such as water power, solar, or wind (whether nuclear
power might count is an open question). Heretofore, especially in the
United States, regulatory efforts curtailing greenhouse gas emissions
commonly originated in response to other objectives, such as
reducing health-damaging air pollutants or enhancing energy security
by fostering substitutes for imported oil. In these cases, reductions in
greenhouse gases were coincidental (“no regrets”); further co-
reduction opportunities remain (e.g., methane from landfills).
However, the objective of reducing greenhouse gases as the primary
object of regulations is increasingly coming to the fore, especially in
some states.58
The technology-push side focuses on research and development. It raises
questions as to what R&D programs should be supported at what levels:
! Over the short- to mid-term, how can existing technologies be made
more sustainable? How can energy (and other resources) be used
more efficiently? What alternatives can be pursued?
! What are the relative federal and private roles in selecting and
financing R&D of specific technologies?
! Perhaps most important for the longer run, what breakthrough
research should be pursued? Over the past 100 years, a number of
technological changes have occurred (e.g., in nuclear power,
computing, and communications) that demonstrate the low success
rate of predicting technological and societal changes far into the
future. At present, at least two technological breakthrough
possibilities can be discerned: fusion power, which conceivably
58 See CRS Report RL33812, Climate Change: Action by States To Address Greenhouse Gas
Emissions, by Jonathan L. Ramseur.

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could wean economies from fossil fuels, and sequestration,59 which
could capture and store carbon dioxide — and perhaps even remove
excess from the atmosphere. Other breakthroughs are surely possible
— including serendipitous discoveries that cannot be conceived of
now.
If the ultimate, 2050 target for reducing greenhouse gas emissions is as
aggressive as 80% below 1990 levels, as in some proposals, then fundamentally at
issue is whether the risks of climate change can be addressed only by incremental
“muddling through” or whether some extraordinary, aggressive effort is needed.
Certainly, there are many opportunities for incremental and iterative policies to reduce
greenhouse gases, to conserve energy, to find alternative energy sources, to make
vehicles more energy efficient, to enhance carbon sequestration through afforestation
and refined cropping practices, to deter deforestation and land use changes that
increase CO emissions, and so on. The incremental nature of such a response
2
provides flexibility, while a time frame of decades offers hope of unpredictable
breakthroughs or the discovery that climate change is not so threatening as some fear.
Conversely, given the drivers increasing emissions, such as population growth
and economic development and growth, it is hard to see how incremental changes
affecting intensity will achieve the rate of intensity decline sufficient to reduce
emissions to the proposed levels, even over decades.60 From this perspective, an
intense, aggressive pursuit of breakthroughs — a sort of climate change Manhattan
project, or Apollo man-on-the-moon effort — even with high costs and high risks of
failure, has to be weighed against the costs and risks of failing to prevent potentially
dangerous interference with the climate system.
59 See CRS Report RL33801, Carbon Capture and Sequestration (CCS), by Peter Folger.
60 However, some pollution control efforts have had dramatic successes: lead has been
essentially eliminated as an air pollutant; regulated auto emissions have been reduced by
over 90% from unregulated levels; between 1990 and 2005, sulfur dioxide emissions from
acid rain program sources dropped by about 35%; and electricity generated rose about 30%.

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