Greenhouse Gas Emission Drivers: Population, Economic Development and Growth, and Energy Use

Prepared for Members and Committees of Congress

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 (GHG) 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) × (per capita GDP) × (Intensityghg) = Emissionsghg
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. Globally, for the variables above over the
period 1990-2005, the rates of change (∆) in annual percent sum as follows:
Population ∆ + per capita GDP ∆ + Intensityghg ∆ = Emissionsghg
+1.4 +1.7 -1.6 = 1.6
As can be seen, global emissions have been rising at a rate of about 1.6% per year (the numbers
do not sum exactly, due to rounding), driven by the growth of population and of economic
Within this generalization, countries vary widely. Between 1990 and 2005, in some countries,
including Brazil, Mexico, Indonesia, and South Africa, population growth alone exceeded the
decline in intensity. For most countries, and for the world as a whole, per capita GDP growth
exceeded the intensity improvement each achieved. Countries for whom intensity improvements
were greater than their per capita GDP increases included Germany, the United Kingdom, France,
and South Africa. And both the Russian Federation and the Ukraine, following their economic
contractions in the 1990s, posted negative numbers for population, per capita income, intensity,
and GHG emissions between 1990 and 2005. Besides the Russian Federation and the Ukraine,
only the United Kingdom and Germany reduced their GHG emissions for the period (Germany
being helped by reductions in the former East Germany).
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 1990-2005 population growth rate
of 1.2% per year and income growth rate of 1.8% per year, intensity would have had to decline at
a rate of -3.0% per year to hold emissions level; however, U.S. intensity declined at a rate of
-1.9%, leaving emissions to grow at just over 1.0% per year.

Introduc tion ..................................................................................................................................... 1
Greenhouse Gas Emission Variables...............................................................................................2
Sectorial Breakdown of GHG Emissions........................................................................................7
Energy Use as a CO2 Intensity Driver.....................................................................................10
Carbon Intensity of Electricity Generation.............................................................................14
Carbon Intensity of Travel......................................................................................................17
Effects of Land Use on Intensity.............................................................................................19
Cumulative Emissions.............................................................................................................20
Interactions of the Variables..........................................................................................................21
Changes in Intensity To Meet Climate Stabilization Goals...........................................................23
U.S. Greenhouse Gas Intensity: Trends and Targets...............................................................23
Global Greenhouse Gas Intensity............................................................................................24
Conclusion ..................................................................................................................................... 25
Figure 1. Actual and Projected GHG Emission for New Passenger Vehicles by Country,
2002-2018................................................................................................................................... 18
Table 1. Drivers of Greenhouse Gas Emissions: Top 20 Emitting Countries, 2005........................4
Table 2. Annual Percentage Rate of Change in Factors Affecting Greenhouse Gas
Emissions: Top 20 Emitting Countries, 1990-2005......................................................................6
Table 3. GHG Emissions by Sector: Top 20 Emitting Countries, 1990-2005.................................7
Table 4. Energy Sector GHG Emissions: Top 20 Emitting Countries, 1990-2005..........................8
Table 5. Annual Percentage Rate of Change of GHG Emissions by Sector: Top 20
Emitting Countries, 1990-2005..................................................................................................10
Table 6. CO2 Emissions Intensity of the Energy Sector: Top 20 Emitting Countries, 2005........12
Table 7. Annual Percentage Rate of Change in Factors Affecting CO2 Emissions from
Energy Use: Top 20 Emitting Countries, 1990-2005.................................................................13
Table 8. Carbon Intensity of Electricity Generation: Top 20 Emitting Countries, 2005..............16
Table 9. Energy Intensity of Passenger Modes: United States, 1970-2006...................................17
Table 10. Land Use Changes: Impact on Intensity of Greenhouse Gas Emissions—Top 20
Emitting Countries.....................................................................................................................19
Table 11. Cumulative CO2 Emissions from Energy: Top 20 Emitting Countries, 1850-
2005 ............................................................................................................................................ 21

Author Contact Information..........................................................................................................29

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 2
emissions, the most important of which is carbon dioxide (CO2), emitted by the combustion of
fossil fuels.
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 3
that “would prevent dangerous interference with the climate system.” 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.
• 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

1 CRS Report RL33849, Climate Change: Science and Policy Implications, by Jane A. 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 R. 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 D. th
Yacobucci and Larry Parker, and CRS Report RL33846, Greenhouse Gas Reduction: Cap-and-Trade Bills in the 110
Congress, by Larry Parker, Brent D. Yacobucci, and Jonathan L. Ramseur.
3 UNFCCC, Article 2, “Objectives.”

goal of meeting “national pollution reduction, energy security and climate change
concerns, consistent with the principles of the U.N. Framework Convention on 4
Climate Change (UNFCCC).”
However, these efforts have had to struggle with substantive economic, technical, and political
differences among regional, national, and local circumstances. Foremost among these differences 5
is the divide between developed and less-developed nations. 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 CO2, have been outstripped by increases in total energy use associated
with population and economic growth. For example, between 1990 and 2005, in the United
States, the greenhouse gas intensity of the economy declined at a rate of -1.9% per year, but total 6
emissions increased at the rate of 1.0% per year. Although some countries have experienced 7
declines in emissions—either through economic contraction 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.

The analysis below, which uses data from the World Resources Institute’s Climate Analysis 8
Indicators Tool (CAIT), is based on the following relationships:
Equation 1. (Population) × (per capita GDP) × (Intensityghg) = Emissionsghg
The CAIT database includes 185 nations (plus a separate entry for the European Union) with a
2005 population of 6.462 billion, compared with 191 members of the United Nations and with a

4 Charter for the Asia-Pacific Partnership on Clean Development and Climate (January 12, 2006),Purposes, 2.1.1.
For additional information, see
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; Climate
Data: Insights and Observations (World Resources Institute; prepared for the Pew Center on Global Climate Change,
December 2004),
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
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

2005 world population count of 6.470 billion by the U.S. Census Bureau.9 Average income is
measured as per capita Gross Domestic Product (GDP), in international dollars of purchasing 10
power parity ($PPP). (Note that population times per capita GDP equals GDP.) Greenhouse gas 11
intensity is measured as tons of emissions in carbon equivalents per million dollars of GDP.
Characteristics of Intensity
Intensity can be expressed in many different ways; for example, as CO2 emitted per 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 CO2 intensity (referring only to CO2 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, 2000,
and 2005; analyses referring to other years necessarily include only CO2.
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, using international $PPP (or market exchange rate dollars) for GDP, CAIT yields a decline in
intensity for U.S. emissions of all greenhouse gases between 1990 and 2005 of -1.9% per year.
To ensure consistency, CAIT emissions data and international $PPP are used throughout this report, unless stated
Table 1 provides a snapshot of the equation 1 variables for the top 20 greenhouse gas emitters in 12
the year 2005, plus for the European Union 27, 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.

9 See
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, December 2008, p. 23.)
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 (excluding land use
changes) for 2005 were 10,569 MMTCE, or 10.6 billion tons. In the text, unless otherwise explicitly stated, “tons of
emissions means “metric tons of carbon equivalents. To convert carbon equivalents to CO2 equivalents, multiply by
12 The year 2005 is the most recent year for which CAIT has data for all six greenhouse gases. Note that analyses based
on 1990-2005 data are affected by the collapse of the former USSR and do not take into account the most recent rapid
increases in energy use and emissions for India and China.

Table 1. Drivers of Greenhouse Gas Emissions: Top 20 Emitting Countries, 2005
(Excludes land use changes)
Per Capita GDP (Tons Cequiv/ Total GHG
Population (2005 Int’l $PPP/ million 2005 Int’l Emissions
Country (in 1,000s) person) $PPP) (MMTCE)
China 1,304,500 4,088 369.4 1,970.3
United States 296,507 41,813 153.3 1,900.6
EU-27 490,032 26,592 105.7 1,377.7
Russian Fed 143,150 11,861 315.1 534.9
India 1,094,583 2,230 207.2 505.7
Japan 127,773 30,290 94.7 366.5
Brazil 186,831 8,474 174.8 276.8
Germany 82,469 30,445 106.2 266.8
Canada 32,312 34,972 176.7 199.7
U.K. 60,226 31,371 92.4 174.6
Mexico 103,089 11,387 146.4 171.9
Indonesia 220,558 3,209 229.2 162.2
Iran 69,087 9,314 240.2 154.6
Italy 58,607 27,750 94.9 154.4
France 60,873 30,591 80.7 150.2
S. Korea 48,294 21,273 145.8 149.8
Australia 20,400 31,656 231.9 149.7
Ukraine 47,105 5,583 503.0 132.3
Spain 43,398 27,180 101.5 119.7
S. Africa 46,892 8,478 290.3 115.4
Turkey 72,065 10,370 143.6 107.3
WORLD 6,461,584 8,708 188.1 10,569.3
Source: Climate Analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute, 2008).
Incorporating growth, equation 1 becomes
Equation 2. ()()()()PopulationepercapitaGDPeIntensityeEmissionsektktktktpgie××=
in which kp = population growth rate, kg = per capita GDP growth rate, ki = intensity growth rate,
and ke = emissions growth rate; t = time; and e = a constant 2.71828 (the base of natural
The exponents of multiplicands are added, so
Equation 3. (kp + kg + ki) = ke

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 13
kp is positive globally and for most nations; it is zero or negative for only a few nations. 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 kg is
increasing globally and for most nations. With kg and kp positive, emissions will be rising unless
the decline in intensity, ki, exceeds the growth in population and economic activity, which has
seldom been the case. If the goal is to reduce GHG emissions, the larger the negative ki the better.
Table 2 shows the changes in these variables for the 1990s. (The figures in the right-most column 14
are taken from the CAIT database.) 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 Brazil, Mexico, Indonesia, Iran, Australia, Spain,
South Africa, and Turkey, any improvements in intensity were annulled by 15
increases in population alone.
• Second, developing countries, focused on developing their economies, have
increasing GHG emissions even when they manage to improve intensity (e.g.,
China, India, Mexico, Indonesia, South Korea, and South Africa). For these
countries, population growth combined with per capita GDP growth 16
overwhelmed whatever intensity improvements they achieved.
• 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 contributed to 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
• Fourth, several developed countries improved per capita GDP while holding their
GHG emissions to a 1% increase or less: the United States, Japan, Germany, the
United Kingdom, Italy, and France. Germany and the United Kingdom (and also
the European Union 27) actually decreased their emissions.

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; this may be due to rounding or, where discrepancies are large, from shortcomings in the underlying
reported data. Nevertheless, the figures are consistent with the generalizations about trends.
15 For Iran and Spain, population and intensity both increased.
16 For Iran, GHG emissions rose because population and GDP growth had no offset at all from intensity, which

• Fifth, in some developed countries, income growth alone exceeded the decline in
intensity (e.g., Japan, Italy, Canada, Australia, and Spain).
Stabilizing emissions would require an accelerated decline in intensity.17 For global emissions to
have met the UNFCCC voluntary goal of being at 1990 levels in 2000, intensity would have had 18
to decline at the rate of -2.9% per year, rather than at the actual -2.0%. For the United States, the
situation was similar: for emissions in 2000 to have remained at 1990 levels, intensity would have 19
had to decline at the rate of -3.2% per year, rather than the actual -1.9%. 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 has been.
Table 2. Annual Percentage Rate of Change in Factors Affecting Greenhouse Gas
Emissions: Top 20 Emitting Countries, 1990-2005
(Excludes land use changes)
Total GHG
Population (average Per Capita GDP Intensity Emissions
Country annual %) (average annual %) (average annual %) (average annual %)
China 0.9 9.1 -4.9 4.8
United States 1.0 1.8 -1.9 1.0
EU-27 0.3 1.8 -2.4 -0.4
Russian Fed -0.2 -0.4 -2.0 -2.7
India 1.7 4.2 -2.3 3.5
Japan 0.2 1.0 -0.4 0.9
Brazil 1.5 1.1 0.0 2.6
Germany 0.3 1.4 -2.4 -1.3
Canada 1.0 1.8 -1.2 1.6
U.K. 0.3 2.1 -3.1 -0.7
Mexico 1.4 1.4 -0.8 2.1
Indonesia 1.4 2.9 -0.4 3.9
Iran 1.6 2.7 1.3 5.7
Italy 0.2 1.1 -0.5 0.8
France 0.5 1.4 -1.7 0.1
S. Korea 0.8 4.7 -1.5 4.0
Australia 1.2 2.0 -1.1 2.1
Ukraine -0.6 -2.4 -1.3 -4.3

17 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.
18 That is, annual population growth (1.5%) + per capita GDP growth (1.4%) + intensity change (-2.9% [rather than the
actual -2.0%]) = 0 emissions growth.
19 That is, annual population growth (1.2%) + per capita GDP growth (2.0%) + intensity change (-3.2% [rather than the
actual -1.9%]) = 0 emissions growth.

Total GHG
Population (average Per Capita GDP Intensity Emissions
Country annual %) (average annual %) (average annual %) (average annual %)
Spain 0.7 2.2 0.0 3.0
S. Africa 1.9 0.6 -0.9 1.6
Turkey 1.7 2.2 -1.1 2.7
WORLD 1.4 1.7 -1.6 1.6
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
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.

Table 3 presents emissions data by economic sector for the top 20 emitting nations (plus the EU-
27 and the world). As the table shows, the energy sector is by far the largest contributor of
greenhouse gases, accounting for 73% of total world emissions in 2005; 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 2005, followed by transportation at about 19%,
manufacturing at about 18%, other fuel combustion at about 13%, and fugitive emissions at about


Table 3. GHG Emissions by Sector: Top 20 Emitting Countries, 1990-2005
(Excludes land use changes)
Energy Industrial Waste
(CO2, N2O, Processes Agriculture (e.g. landfills) )Total
and CH4) (All 6 GHG) (N2O and CH4) (N2O and CH4 (All 6 GHG)
Country 1990 2005 1990 2005 1990 2005 1990 2005 1990 2005
China 656 1,441 36a 178a 247 304 42 48 981 1,970
United States 1,412 1,660 44 68 116 121 59 51 1,631 1,901
EU-27 1,179 1,133 75 71 164 137 53 36 1,472 1,378
Russian Fed 710 478 18 12 61 32 14 13 803 535
India 177 338 8 24 90 110 26 34 301 506
Japan 292 333 18 21 11 10 2 3 322 366
Brazil 56 95 6 9 116 161 10 12 188 277

Energy Industrial Waste
(CO2, N2O, Processes Agriculture (e.g. landfills) )Total
and CH4) (All 6 GHG) (N2O and CH4) (N2O and CH4 (All 6 GHG)
Germany 277 230 8 10 30 23 10 4 326 267
Canada 129 166 7a 6a 16 20 6 7 158 200
U.K. 162 153 11 6 15 13 7 3 195 175
Mexico 93 131 4 7 18 21 10 13 125 172
Indonesia 52 111 2 6 29 36 8 9 91 162
Iran 55 135 2 5 6 10 4 4 67 155
Italy 113 129 9 11 12 11 4 3 137 154
France 101 110 12 9 30 28 4 3 147 150
S. Korea 64 125 7 16 12 5 8 4 84 150
Australia 78 114 2 3 26 30 3 3 110 150
Ukraine 224 113 5 3 22 12 4 4 255 132
Spain 58 95 6 9 11 12 2 3 77 120
S. Africa 72 94 2 4 12 11 5 6 91 115
Turkey 42 75 3a 6a 22 21 4 5 72 107
WORLD 6,136 7,753 285 509 1,426 1,658 356 387 8,380 10,569
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
Note: Emissions are given in millions of metric tons of carbon equivalents (MMTCE).
a. CH4 data not available.
Table 4. Energy Sector GHG Emissions: Top 20 Emitting Countries, 1990-2005
(Excludes land use changes)
Electricity and Manufacture and Other Fuel
Heat Construction Transportation Combustion Fugitive Emissions
(CO2) (CO2) (CO2) (CO2, N2O & CH4) (CO2 & CH4)
Country 1990 2005 1990 2005 1990 2005 1990 2005 1990 2005
China 194 728 247 435 32 91 148 148 35 39
United 578 749 191 174 389 495 185 187 69 57
EU-27 464 441 227 180 209 260 240 226 39 25
Russian 333 255 78 60 74 56 115 52 110 54
India 71 190 46 66 22 27 30 42 8 13
Japan 111 140 78 73 58 68 45 52 1 0
Brazil 8 16 16 27 22 37 10 12 1 3
Germany 113 99 49 32 44 43 62 51 a 4
Canada 38 52 23 25 34 44 26 34 9 12

Electricity and Manufacture and Other Fuel
Heat Construction Transportation Combustion Fugitive Emissions
(CO2) (CO2) (CO2) (CO2, N2O & CH4) (CO2 & CH4)
U.K. 67 64 23 17 33 35 32 32 8 5
Mexico 29 45 20 16 24 36 9 11 12 23
Indonesia 15 37 9 26 9 20 9 13 11 16
Iran 11 30 12 21 11 27 15 35 6 23
Italy 39 44 23 23 26 32 23 28 2 2
France 17 20 22 21 31 37 29 31 2 1
S. Korea 17 54 14 26 12 24 19 20 2 1
Australia 38 64 12 12 17 22 5 8 6 8
Ukraine 93 34 56 25 15 8 24 14 37 32
Spain 21 35 12 18 18 30 6 11 1 1
S. Africa 39 58 19 14 8 12 5 8 2 2
Turkey 11 22 9 16 8 10 8 13 6 14
WORLD 2,322 3,359 1,230 1,415 1,082 1,468 1,041 1,035 461 477
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
Note: Emissions are given in millions of metric tons of carbon equivalents (MMTCE).
a. No data.
The most revealing aspect of sectorial emissions emerges from Table 5, which shows their rates 20
of change, including the energy subsectors (shown in italics). Global emissions are growing
fastest in the Industrial Processes sector (3.9%/year); next is the Energy sector, for which
emissions are growing at the same rate as total emissions (1.6%). Because Industrial Process 21
emissions are a much smaller share of total emissions than energy (see Table 4), the increase is
relatively small in absolute terms; however, the rate of increase is substantial for nations that are
industrializing, especially China, India, 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 2.5% per year, led by developing
nations, especially China, India, Brazil, South Korea, Iran, and Indonesia, and also by Spain and
Turkey. In contrast, for the EU-27, the rate and absolute emissions for the subsector declined
slightly; but for the Russian Federation and Ukraine, the rate and absolute emissions declined
substantially as their economies contracted. The next fastest growing subsector is transportation,
at 2.1% a year, with every nation showing a positive rate of growth except the Russian Federation

20 For fugitive emissions and waste emissions, rates of change were not calculated if both the 1990 and 2005 emission
levels were below 10 million tons. At low levels, even small changes can yield notable rates of changefor example, if
emissions went from 2 to 4 million tons between 1990 and 2005, the rate of change would be 3.8% per year, but the
actual emissions are too small to meaningfully affect overall totals.
21 Including CO2 from cement manufacture, N2O from Adipic and Nitric Acid production, N2O and CH4 from other
industrial processes, plus HFCs, PFCs, and SF6.

and Ukraine, with their contracting economies during the 1990s, and Germany, with a minimal

The previous section looked at emissions and the rate of change, 1990-2005, for all six
greenhouse gases and all sectors of the economy. Of the six greenhouse gases, CO2 dominates,
accounting for 73.6% of the carbon equivalents of global GHG emissions in 2005 and 84.6% of
U.S. GHG emissions. Overwhelmingly—not counting land use changes, which are discussed
later—the source of that CO2 is energy use: for world CO2 emissions, energy use accounts for

92.6%; for the United States, energy use accounts for 99.1%.

Two factors largely determine the intensity of CO2 emissions of a nation’s economy: energy 22
intensity (energy per unit of GDP) and the fuel mix (emissions per unit of energy):
Energy Use Emissionsco2 Emissionsco2
Equation 4. x =
GDP Energy Use GDP
Table 5. Annual Percentage Rate of Change of GHG Emissions by Sector: Top 20
Emitting Countries, 1990-2005
(Excludes land use changes)
Energy Elec Man Fuel Fugitive Ind
(CO2, & & (CO2, (CO2, Proc Ag Waste Total
CH4, Heat Const Transp CH4, CH4, (All 6 (CH4, (CH4, (All 6
Country N2O) (CO2) (CO2) (CO2) N2O) N2O) GHG) N2O) N2O) GHG)
China 5.4 9.2 3.8 7.2 0.0 0.7 11.3 1.4 0.9 4.8
States 1.1 1.7 -0.6 2.1 0.1 -1.3 3.0 0.2 -0.9 1.0
EU-27 -0.3 -0.3 -1.5 1.5 -0.4 -2.9 -0.4 -1.2 -2.5 -0.4
Fed -2.6 -1.8 -1.6 -1.9 -5.2 -4.6 -2.6 -4.1 -0.6 -2.7
India 4.4 6.8 2.5 1.2 2.3 3.3 7.5 1.3 1.8 3.5
Japan 0.9 1.6 -0.4 1.1 1.0 1.1 -0.7 0.9
Brazil 3.6 5.2 3.7 3.6 1.4 2.2 1.4 2.6
Germany -1.2 -0.9 -2.7 -0.1 -1.3 1.4 -1.8 -6.7 -1.3
Canada 1.7 2.2 0.4 1.7 1.9 1.9 1.6 1.6
U.K. -0.4 -0.3 -1.8 0.5 0.0 -4.4 -0.7 -0.7
Mexico 2.3 3.1 -1.5 2.8 1.3 4.5 0.9 1.6 2.1
Indonesia 5.2 6.3 7.2 5.8 2.9 2.1 1.5 3.9

22 See Timothy Herzog et al., Target: Intensity, An Analysis of Greenhouse Gas Intensity Targets (Washington, DC:
World Resources Institute, November 2006), pp. 3-9.

Energy Elec Man Fuel Fugitive Ind
(CO2, & & (CO2, (CO2, Proc Ag Waste Total
CH4, Heat Const Transp CH4, CH4, (All 6 (CH4, (CH4, (All 6
Country N2O) (CO2) (CO2) (CO2) N2O) N2O) GHG) N2O) N2O) GHG)
Iran 6.2 6.7 3.8 6.5 5.7 8.7 3.2 5.7
Italy 0.9 0.8 0.0 1.4 1.2 1.6 -0.2 0.8
France 0.5 0.8 -0.2 1.1 0.4 -1.9 -0.4 0.1
S. Korea 4.6 8.1 4.0 4.7 0.1 5.6 4.0
Australia 2.5 3.5 -0.5 1.7 0.9 2.1
Ukraine -4.4 -6.4 -5.3 -3.8 -3.5 -0.9 -3.8 -4.3
Spain 3.3 3.5 2.4 3.7 3.9 1.1 3.0
S. Africa 1.7 2.6 -1.9 2.6 -0.3 1.6
Turkey 3.9 5.0 3.6 2.0 2.8 5.9 -0.3 2.7
WORLD 1.6 2.5 0.9 2.1 0.0 0.2 3.9 1.0 0.6 1.6
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
Notes: Average annual percentage per year.
Blanks = not calculated if tonnage for both years < 10.
Table 6 presents data on energy sector CO2 emissions for 2005. The first data 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. Sevencountries, Japan, Brazil, Germany, the United Kingdom, Italy, Spain, and Turkey
equal or better the efficiency of the EU-27, at 0.14; China, the Russian Federation, Ukraine, and
S. Africa are the least efficient, at 0.32 or worse. In general, the higher the number in column one,
themore 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 thenumber, the lessCO2being emitted by
the energy used. Higher numbers would generally reflect a higher proportion of coal combusted
in the electricity-generating, manufacturing, and heating sectors anda 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 fueleconomy. Again, in many cases, the higher the number, the more least-cost options for
loweringCO2emissions without adversely affecting the overall economy, for 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 CO2
emissions only, and isthus different from greenhouse gas intensity, whichincludes CO2plus five

other gases.) The higher the number, the less efficiently the economy is using carbon-emitting 23
energy. The last column in the table provides data on totalCO2emissions from energy use.
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 annual rates of change of factors
affectingCO2emissions from energy use. The first three data columns parallel the first three in
Table 6, giving the rates of change during 1990-2005. In terms ofCO2emissions, negative
numbers mean that over time a nation is getting more economic activity for less energy (first data
column) and more energy for less CO2(second data column). As Table 7 shows, there are wide
variations among nations. For example, China’s economy made rapid progress in using energy
more efficiently (energy intensity of -5.1% per year), even though the energy it used actually
produced more CO2per unit of energy (+1.3% per year). A number of countries, including the
EU-27, improved efficiency and reducedemissions 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 theCO2emitted. The fourth and fifth columns in Table 7 give the
rates of change of the nations’ GDPs and totalCO2emissions from energy use. A nation’s rate of
change ofCO2intensity can be negative, but if GDP is growing faster than CO2intensity is 24
declining, emissions will rise (the last column).
Table 6. CO2 Emissions Intensity of the Energy Sector:
Top 20 Emitting Countries, 2005
(Excludes land use changes)
Energy Intensity CO2 Intensity of CO2 Intensity of Total CO2 Emissions
(1,000 toe / million Energy Sector (Tons Economy (Tons C / from Energy Use
Country 2005 $PPP) C / 1,000 toe) million 2005 $PPP) (MMTCE)
China 0.32 890 285 1,381
States 0.19 690 130 1,594
EU-27 0.14 620 86 1,086
Fed 0.38 660 252 421
India 0.22 620 137 314
Japan 0.14 640 88 331
Brazil 0.13 460 61 91
Germany 0.14 660 90 222
Canada 0.24 560 135 151
U.K. 0.12 630 78 145

23 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.
24 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.

Energy Intensity CO2 Intensity of CO2 Intensity of Total CO2 Emissions
(1,000 toe / million Energy Sector (Tons Economy (Tons C / from Energy Use
Country 2005 $PPP) C / 1,000 toe) million 2005 $PPP) (MMTCE)
Mexico 0.15 630 96 107
Indonesia 0.25 560 142 95
Iran 0.25 750 190 118
Italy 0.11 700 80 124
France 0.15 390 58 106
S. Korea 0.21 610 126 122
Australia 0.19 850 161 103
Ukraine 0.54 580 314 81
Spain 0.12 690 85 93
S. Africa 0.32 720 231 90
Turkey 0.11 770 88 60
WORLD 0.20 690 138 7,198
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute, 2008).
CRS calculations.
Table 7. Annual Percentage Rate of Change in Factors Affecting CO2 Emissions from
Energy Use: Top 20 Emitting Countries, 1990-2005
(Excludes land use changes)
Energy CO2 Intensity of Energy Sector Total CO2 Emissions
Country Intensity Energy Used CO2 Intensity GDP of Energy Use
China -5.1 1.3 -4.1 10.1 5.7
States -1.6 -0.1 -1.7 3.0 1.7
EU-27 -1.3 -0.8 -2.2 2.1 -0.2
Fed -1.7 -0.3 -1.7 -0.7 -2.3
India -2.3 1.1 -1.4 6.0 4.5
Japan 0.0 -0.3 -0.3 1.3 0.9
Brazil 0.5 0.5 1.0 2.6 3.6
Germany -1.7 -0.8 -2.8 1.6 -1.1
Canada -1.0 -0.1 -1.1 2.8 1.6
U.K. -1.9 -1.0 -2.7 2.4 -0.3
Mexico -0.4 -0.4 -0.9 2.9 2.0
Indonesia -0.8 2.0 1.3 4.4 5.8
Iran 1.5 0.2 1.6 4.3 6.1
Italy 0.0 -0.6 -0.4 1.3 0.9
France -0.4 -0.7 -1.2 1.9 0.6

Energy CO2 Intensity of Energy Sector Total CO2 Emissions
Country Intensity Energy Used CO2 Intensity GDP of Energy Use
S. Korea 0.3 -1.1 -0.9 5.6 4.6
Australia -1.0 0.3 -0.7 3.3 2.5
Ukraine -0.7 -1.7 -2.4 -3.0 -5.4
Spain 0.0 0.3 0.4 2.9 3.4
S. Africa -0.2 -0.5 -0.7 2.5 1.8
Turkey -1.1 0.4 -0.3 3.9 3.6
WORLD -1.5 0.0 -1.5 3.2 1.7
Source: Climate Analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
2008). CRS calculations.
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.
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 46.7% of
world CO2emissions (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
21.8 grams of carbon per kiloWatt-hour, in 2004 generated about 78% of its electricity by nuclear
power, about 11% by hydropower, and 9% by conventional thermal. The United States, with a
carbon intensity of electricity production of 152, generated about 20% of its electricity by nuclear 25
power, about 7% by hydropower, and about 71% by conventional thermal.
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 26
75% share, whereas coal and oil had fallen to 8% and 2% shares, respectively.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.

25 Energy Information Administration, International Energy Annual, 2005, “World Electricity Data, Table 6.3: World
Net Electricity Generation by Type.
26 International Energy Agency, Electricity Information 2002 (OECD, 2002), p. II.285.

France’s transition to nuclear power meant that its CO2 intensity (i.e., CO2 emissions/GDP)
declined between1980 and 1990 at a rate of -4.9% per year, and CO2emissions declined at a rate
of -2.6% per year. Thus, between 1980 and 1990, France’s total CO2emissions declined by 27
23%—at the same time its GDP was growing by 20.4% (+1.9% per year). Thus equation 3
yields a negative growth in emissions (numbers do not add precisely, due to rounding):
France: CO2 Intensity, 1980-1990
Population Per Capita GDP CO2 Intensity CO2 Emissions
(0.5) + (1.9) + (-4.9) = (-2.6)
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 28
risen to 39%.Because natural gas produces less totalCO2per kilowatt hour than coal (at a ratio 29
of about 0.6 to 1 on a Btu basis), CO2intensity in the United Kingdom declined between 1990
and 2000 at a rate of -3.0% per year, and CO2emissions declined at a rate of -0.6% per year.
Thus, between 1990 and 2000,total CO2emissions in the United Kingdom declined by 5.9% 30
(-0.6% per year)—at the same time its per capita GDP was growing by 23.5% (+2.1% per year).
Thus equation 3 yields a negative growth in emissions:
United Kingdom: CO2 Intensity, 1990-2000
Population Per Capita GDP CO2 Intensity CO2 Emissions
(0.3) + (2.1) + (-3.0) = (-0.6)
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 CO2 emissions declined. From 1980-1986, U.S.
CO2intensity declined at a rate of -3.6% per year, and emissions declined at a rate of -0.5% per
year. But after 1986 the rate of intensity decrease slowed: between 1987 and 2003, the intensity
rate averaged about -1.7% per year. After 2003, through 2005 (the last year of CAIT’s data), the
rate of intensity decrease speeded up to an average annual -2.6%. Nonetheless, throughout the

1987-2005 period, the decrease failed to compensate for population and per capita GDP growth,

soCO2emissions rose at 1.2% per year. Over the longer term, therefore, emissions have risen: in

27 Climate analysis Indicators Tool (CAIT), version 4.0 (Washington, DC: World Resources Institute, 2007).
28 International Energy Agency, Electricity Information 2002 (OECD, 2002), p. II.683.
29 If gas combined-cycle technology is considered, the ratio could be 0.4 or 0.5 to 1.
30 Climate Analysis Indicators Tool (CAIT), version 6.0. (Washington, DC: World Resources Institute, 2008). In terms
of all six greenhouse gases, between 1990 and 2000, the United Kingdoms greenhouse gas intensity declined at an
annual rate of -3.5%.

terms of equation 3, U.S. CO2 emissions for 1980-2005 are as follows (numbers do not add
precisely, due to rounding):
United States: CO2 Intensity, 1980-2005
Population Per Capita GDP CO2 Intensity CO2 Emissions
(1.1) + (2.0) + (-2.1) = (0.9)

Table 8. Carbon Intensity of Electricity Generation:
Top 20 Emitting Countries, 2005
Intensity (
Country gC/kWh)
China 230.9
United States 152.2
EU-27 96.1
Russian Fed 90.9
India 257.4
Japan 116.9
Brazil 23.1
Germany 134.6
Canada 53.6
U.K. 127.0
Mexico 136.5
Indonesia 210.4
Iran 145.7
Italy 108.4
France 21.8
S. Korea 115.2
Australia 235.5
Ukraine 94.8
Spain 103.7
S. Africa 231.5
Turkey 121.3
WORLD 142.6
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,

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
Studies indicate that nations vary considerably in the energy efficiency and greenhouse gas
emissions intensity of their transport sectors. For example, one effort examining vehicle miles
shows substantial variations among several nations, with the United States being the highest 31
emitter per vehicle(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, 1970-2006
(Btus per passenger-mile)
Passenger Modes 1970 1980 1990 2000 2005 2006
Air, certified carrier
Domestic 10,185 5,742 4,932 3,883 3,222 3,098
International 10,986 4,339 4,546 3,833 3,813 3,691
Passenger car 4,841 4,348 3,811 3,589 3,585 3,525
Pickup, SUV, minivan 6,810 5,709 4,539 4,509 4,077 4,016
Motorcycle 2,500 2,125 2,227 2,273 1,784 1,754
Transit motor bus — 2,742 3,723 4,147 3,393 3,262
Amtrak — 2,148 2,066 2,134
Source: Bureau of Transportation Statistics:
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 gone up and down. Second, the choice of
transportation mode, which can be affected by infrastructure investments and other public 32
policies,substantively affects passenger-mile efficiency. Amtrak and, by extension, commuter

31 Feng An, et al., Passenger Vehicle Greenhouse Gas and Fuel Economy Standards: A Global Update, International
Council on Clean Transportation (July 2007), p. 8.
32 For example, the London “congestion tax is intended to shift commuters out of passenger cars and onto public

rail, is considerably more efficient than any of the other choices, except motorcycles. Moreover,
within the highway mode, efficiency varies significantly: in 2000, passenger cars were 20% more
efficient on average than pickups, SUVs, and minivans, but in 2006 improvements in the latter
had reduced the difference to 12%.
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 CO233
emissions. 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.
Note: Solid lines denote actual performance or projected performance due to adopted regulations; dotted lines
denote proposed standards; Values normalized to NEDC last cycle in grams of CO2-equivalent per km.
1. For Canada, the program includes in-use vehicles. The resulting uncertainty on new vehicle fuel economy was
not quantified.

33 See CRS Report RL34265, Selected Issues Related to an Expansion of the Renewable Fuel Standard (RFS), by Brent
D. Yacobucci and Tom Capehart.

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: most notably,
Indonesia and Brazil, and (to a lesser extent) Mexico and Canada. Their GHG emission intensities
are much higher when land use changes are included.
For Indonesia and Brazil in 2000 (the last year CAIT has data for land-use change and forestry),
emissions attributable to land use changes accounted for 86% and 74%, respectively, of their total
GHG emissions.
Even though land use changes may have a small effect on emissions for most countries, and the
data lack robustness, including it in analyses can identify those situations where it is undeniably
important and for which interventions might pay large dividends in terms of curtailing
greenhouse gas emissions or sequestering CO2.
Table 10. Land Use Changes: Impact on Intensity of Greenhouse Gas Emissions—
Top 20 Emitting Countries
Intensity 2000 (excluding Intensity 2000 (including Intensity difference,
land use) tCeq/million land use) tCeq/million with land use minus
Country $PPP(all 6 GHG) $PPP(all 6 GHG) without land use % difference
China 389.5 385.7 -3.8 1.0
United States 169.7 159.7 -10.0 5.9
EU-27 113.3 112.7 -0.6 0.5
Russian Fed 412.6 424.3 11.7 2.8
India 249.2 242.9 -6.3 2.5
Japan 98.7 99.1 0.4 0.4
Brazil 185.9 456.9 271.0 145.8
Germany 112.9 112.9 0.0 0.0
Canada 192.1 209.8 17.7 9.2
U.K. 103.4 103.1 -0.3 0.3
Mexico 145.8 170.4 24.6 16.9
Indonesia 244.4 1,489.4 1,245.0 509.4
Iran 235.6 240.1 4.5 1.9
Italy 92.7 99.1 6.4 6.9
France 86.0 85.1 -0.9 1.0
S. Korea 169.3 169.7 0.4 0.2
Australia 248.4 250.5 2.1 0.8
Ukraine 691.6 a
Spain 101.7 99.3 -2.4 2.4
S. Africa 318.7 320.1 1.4 0.4

Intensity 2000 (excluding Intensity 2000 (including Intensity difference,
land use) tCeq/million land use) tCeq/million with land use minus
Country $PPP(all 6 GHG) $PPP(all 6 GHG) without land use % difference
Turkey 160.9 170.4 9.5 5.9
WORLD 197.7 241.9 44.2 22.4
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,
a. No land use data available.
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 cumulativeemissions are limited.
In general,data are available only for CO2and are calculated from fuel use estimates; land use
changes over long time spans are important, but data are scanty or unavailable. CAIT provides
figures for CO2emissions only from 1850, not including 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-27 account for over half the cumulative
CO2emissions from energy use 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

Table 11. Cumulative CO2 Emissions from Energy: Top 20 Emitting Countries, 1850-
(Excludes Land Use Changes)
Cumulative Emissions Percentage Rank
Country (MMTCE) of World in World
China 25,368 8.1 2
United States 89,592 28.7 1
EU-27 82,407 26.3
Russian Fed 24,653 7.9 3
India 7,098 2.3 8
Japan 11,665 3.7 6
Brazil 2,487 0.8 21
Germany 21,570 6.9 4
Canada 6,704 2.2 9
U.K. 18,498 5.9 5
Mexico 3,090 1.0 15
Indonesia 1,708 0.6 25
Iran 2,084 0.7 23
Italy 5,021.6 12
France 8,742 2.8 7
S. Korea 2,526 0.8 20
Australia 3,344 1.1 14
Ukraine 6,552.1 10
Spain 2,836 0.9 17
S. Africa 3,396 1.1 13
Turkey 1,434 0.5 29
WORLD 312,403 100.0
Source: Climate analysis Indicators Tool (CAIT), version 6.0 (Washington, DC: World Resources Institute,

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.

Economic development and growing incomes interact with population growth in two ways. First, 34
birth rates tend to decline as incomes rise,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 35
their population growth is higher than their birth rate. Overall, most demographers expect the
rate of population growth to slow, although world population is projected to exceed 9 billion in 36

2050, with most of the increase in the developing world.

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
poverty. A key element of the climate change debate is how to decouple that economic
development-energy use link.
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 37
applicability to CO2emissions has been questioned,and to the degree that it does exist for such
pollutants as sulfur dioxide, it reflects policy choices to constrain emissions.
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, deforestation, waste disposal, and the
consumption and release of certain chemicals.

34 This is not a simple cause and effect, but reflects evolutionary changes in areas such as education, cultural
expectations, womens rights, access to birth control, and health care—all of which may be affected by social policy.
35 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
36 See
37 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.

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 38
certain amount with a certain probability.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 has not had an emissions reduction target, though the George W. Bush Administration th
focused on an intensity reduction target. In the 110 Congress, a bill that specified emission
reduction targets, S. 2191, reached the floor of the Senate; but after parliamentary maneuvering, it
was never directly acted on.
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, 39
population grows at the annual rate of +0.9% for 2000-2010 and +0.8% for 2011-2025, per
capita income grows at an annual rate of +2.0% (the 1980-2005 rate), and intensity declines at the
annual rate of -1.9% (the 1990-2005 rate for GHG).
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 2.8% per year
after 2010, a decline in the intensity rate of -2.8% 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 -1.9% for the United States.
Now consider a goal of returning U.S. greenhouse gas emissions to their 1990 level of 1,631 4041
MMTCE. Assuming that baseline 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

38 See, for example, M.G.J. den Elzen and M. Meishausen, “Meeting the EU 2uni030AC climate target: global and regional
emission implications,” Report 728001031/2005, Netherlands Environmental Assessment Agency.
39 U.S. Census Bureau,IDB Summary Demographic Data for United States,”
40 This limit appeared in a number of bills that include economy-wide caps introduced in the 110th Congress, including
S. 280, S. 309, S. 485, H.R. 620 and H.R. 1590, and in Barack Obama’s campaign’s environmental factsheet, “Barack
Obama and Joe Biden: Promoting a Healthy Environment,”
41 It is important to recognize that we are looking at trends over an extended time; these assumed average trends blur
short term variations (e.g., higher rates of intensity decline in 2004-2005, or possible variations from the recession that
started in 2008).

by 2020? The answer is, it would take a rate of intensity decline of about -4.9% per year42
(compared with the recent -1.9% per year), beginning in 2010, to reach the level of 1,636 in 2020,
slightly over the target. This represents a substantial, ongoing improvement in intensity, from a
GHG intensity of 153.3 MMTCE/million$PPP in 2005, to an intensity of 85.8 in 2020—but
perhaps not impossible, when one considers that in 2005 France’s intensity level was 80.7.
Over the longer term, much more aggressive goals have been proposed: a typical goal for 2050 43
has been an 80% reduction in 1990 levels of GHG emissions, which would limit U.S. emissions
to 326 MMTCE. Again assuming population and per capita GDP grow from 2010 to 2050 at the
average annual rates of 0.8% and 2.0%, respectively, then given the emission rate at the cap, U.S.
greenhouse gas intensity in 2050 would be 7.4 MMTCE/million$PPP—implying an extremely
low-carbon economy. Or, in terms of rate of change, assuming current trends until 2010, intensity 44
would have to decline over the next 40 years, at an average rate of about -7.4% per year.
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 -0.5% per year. 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 CO2, and developing the capacity to capture and sequester enormous
amounts of CO2.
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, 1990-2005
Population Per Capita GDP45 GHG Intensity GHG Emissions
(1.4) + (1.7) + (-1.6) = (1.6)
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

42 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.
43 This limit appeared in S. 309 and H.R. 1590 of the 110th Congress, and in Barack Obama’s campaigns
environmental factsheet, “Barack Obama and Joe Biden: Promoting a Healthy Environment,
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.
45 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.

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.
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-CO2 gases, 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.

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 46
Change (UNFCCC), which had been signed earlier in the year. 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

46 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.

achieve [among other goals] ... the stabilization and eventual reduction in the generation of 47
greenhouse gases.... ”
In ratifying the UNFCCC, the United States agreed to several principles for achieving this
objective, including the following:
• “[D]eveloped country Parties should take the lead in combating climate change 48
and the adverse effects thereof.”
• “Parties should take precautionary measures to anticipate, prevent or minimized 49
the causes of climate change and mitigate its adverse effects.”
• “Parties have a right to, and should, promote sustainable development.... ”
Climate change policies should take “into account that economic development is 50
essential for adopting measures to address climate change.”
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 51
of poverty.”
• 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
• 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 seem to require the development and deployment of
commercially available technologies to shift economies substantively away from
fossil fuels, and/or the large-scale capture and sequestration of the emissions of
CO2 from coal and other fossil fuels. The UNFCCC recognizes the “special
difficulties of those countries, especially developing countries, whose economies

47 Section 1602(a)
48 UNFCCC, article 3.
49 Ibid.
50 Ibid.
51 UNFCCC, Preamble.

are particularly dependent on fossil fuel production, use and exportation, as a 52
consequence of action taken on limiting greenhouse gas emissions.”
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 53
trends in anthropogenic emissions consistent with the objective of the Convention.... ” 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 54
developing country Parties.
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 55
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 56
taxes and regulatory requirements overlain by the EU’s Emissions Trading System.
The market-pull side focuses on market interventions to create demand, which poses questions
• 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

52 UNFCCC, Preamble.
53 UNFCCC, article 4(2)(a).
54 UNFCCC, article 4(7).
55 L. Clarke, J. Weyant, and A. Birky,On the Sources of Technological Change: Assessing the Evidence, Energy
Economics, vol. 28 (2006), pp. 579-595.
56 See CRS Report RL34150, Climate Change and the EU Emissions Trading Scheme (ETS): Kyoto and Beyond, by
Larry Parker.

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, 57
especially in some states.
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 could wean 58
economies from fossil fuels, and sequestration, 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 CO2
emissions, and so on. The incremental nature of such a response provides flexibility, while a time

57 See CRS Report RL33812, Climate Change: Action by States To Address Greenhouse Gas Emissions, by Jonathan L.
58 See CRS Report RL33801, Carbon Capture and Sequestration (CCS), by Peter Folger.

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 59
over decades. From this perspective, an intense, aggressive pursuit of breakthroughs—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.
John Blodgett Larry Parker
Specialist in Environmental Policy Specialist in Energy and Environmental Policy, 7-7230, 7-7238

59 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