| About This Report | The Greenhouse Effect and Global Climate Change | Global Climate Change Policy Developments | U.S. Emissions in an International Perspective |
The Energy Information Administration (EIA) is required by the Energy Policy Act of 1992 to prepare a report on aggregate U.S. national emissions of greenhouse gases for the period 1987-1990, with annual updates thereafter. This report is the fourth annual update, covering national emissions over the period 1988-1994, with preliminary estimates of emissions for 1995.
Chapter 1 of this report briefly recapitulates some background information about global climate change and the greenhouse effect and discusses important recent developments in global climate change activities. Chapters 2 through 6 cover emissions of carbon dioxide, methane, nitrous oxide, halocarbons, and criteria pollutants, respectively. Chapter 7 describes potential sequestration and emissions of greenhouse gases as a result of land use changes.
Five appendixes are included with this report. Appendix A provides a detailed discussion of emissions sources, estimation methods, and data requirements and sources. Appendix B describes the derivation of the carbon emissions coefficients used for the inventory. Appendix C describes uncertainties in the emissions estimates. Appendix D describes known emissions sources omitted from the main report due to definitions of “anthropogenic” or due to excessive uncertainty. Appendix E provides some convenient conversion factors.
The Earth is warmed by light from the Sun. Over time, the amount of energy transmitted to the Earth’s surface is equal to the amount of energy re-radiated back into space in the form of infrared radiation, and the temperature of the Earth’s surface stays roughly constant. However, the temperature of the Earth is strongly influenced by the existence, density, and composition of the Earth’s atmosphere. Many gases in the Earth’s atmosphere absorb infrared radiation re-radiating from the Earth’s surface, trapping heat in the lower atmosphere. Without the natural greenhouse effect, it is likely that the average temperature of the Earth’s surface would be on the order of -19o Celsius, rather than the +15o Celsius actually observed [4]. The gases that help trap the Sun’s heat close to the Earth’s surface are referred to as “greenhouse gases.” All greenhouse gases absorb infrared radiation (heat) at particular sets of wavelengths.
The main greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and a host of engineered chemicals such as chlorofluorocarbons (CFCs). Most greenhouse gases occur naturally. Water vapor is by far the most common, with an atmospheric concentration of nearly 1 percent, compared with less than 0.04 percent for carbon dioxide. Concentrations of other greenhouse gases are a fraction of that for carbon dioxide (Table 1).
| Table 1. Global Atmospheric Concentrations of Greenhouse Gases | |||||
| Item | Carbon Dioxide | Methane | Nitrous Oxide | CFC-11 | CFC-12 |
| (parts per million) | (parts per trillion) | ||||
| Preindustrial Atmospheric Concentration | 278 | 0.700 | 0.275 | 0 | 0 |
| 1992 Atmospheric Concentration | 356 | 1.714 | 0.311 | 268 | 503 |
| Average Annual Change | 1.6 | 0.008 | 0.0008 | 0 | 7 |
| Average Change (Percent per Year) | 0.4 | 0.6 | 0.25 | 0 | 1.4 |
| Atmospheric Lifetime (Years) | 50–200 | 12 | 120 | 50 | 102 |
| Source: Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), p. 92. | |||||
It was recognized in the early 1960s that concentrations of carbon dioxide in the Earth’s atmosphere were increasing every year. Subsequently, it was discovered that atmospheric concentrations of methane, nitrous oxide, and many engineered chemicals were also rising. Current concentrations of greenhouse gases keep the Earth at its present temperature. Would increasing concentrations of greenhouse gases make the Earth get even warmer?
In computer-based simulation models, rising concentrations of greenhouse gases nearly always produce an increase in the average temperature of the Earth. Rising temperatures may, in turn, produce changes in weather and in the level of the oceans that might prove disruptive to current patterns of land use and human settlement, as well as to existing ecosystems. To date, it has proven difficult to detect hard evidence of actual temperature changes, in part, because normal temporal and spatial variations in temperature are far larger than the predicted change in the global average temperature. Even when temperature changes are identified, it is not possible to be certain whether they are random fluctuations that will reverse themselves or are the beginning of a trend. The possible effects of rising temperatures on weather patterns are even more uncertain.
The most recent report of the Intergovernmental Panel on Climate Change (IPCC), an international assemblage of scientists commissioned by the United Nations to study this matter, concluded that:
Our ability to quantify the human influence on global climate is currently limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors. These include the magnitudes and patterns of long-term variability and the time-evolving pattern of forcing by, and response to, changes in concentrations of greenhouse gases and aerosols, and land surface changes. Nevertheless, the balance of evidence suggests that there is a discernable human influence on climate [5].
While both the existence and consequences of human-induced climate change remain uncertain, the threat of climate change has put in train an array of efforts by governments both in the United States and abroad to find some mechanism for limiting the risk of climate change and ameliorating possible consequences. To date, efforts have focused on identifying levels and sources of emissions of greenhouse gases and on possible mechanisms for reducing emissions or increasing absorption of greenhouse gases.
Most greenhouse gases have substantial natural sources in addition to human-made sources, and there are powerful natural mechanisms for removing them from the atmosphere. However, the continuing growth in atmospheric concentrations establishes that, for each of the major greenhouse gases, more gas is being emitted than is being absorbed each year: that is, the natural absorption mechanisms are lagging behind. Table 2 illustrates the relationship between anthropogenic and natural emissions and absorption of the principal greenhouse gases.
| Table 2. Global Natural and Anthropogenic Sources and Absorption of Greenhouse Gases | ||||
| Gas | Sources | Absorption | Annual Increase in Gas in the Atmosphere | |
| Natural | Human-Made | |||
| Carbon Dioxide (Million Metric Tons of Carbon) | 150,000 | 7,100 | 154,000 | 3,100–3,500 |
| Methane (Million Metric Tons of Gas) | 110–210 | 300–450 | 460–660 | 35–40 |
| Nitrous Oxide (Million Metric Tons of Gas) | 6–12 | 4–8 | 13–20 | 3–5 |
| Source: Summarized from ranges appearing in Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), pp. 17-19. | ||||
Water Vapor. Water vapor, as noted above, is the most common greenhouse gas present in the atmosphere. It is emitted into the atmosphere in enormous volumes, through natural evaporation from oceans, lakes, and soils, and returned to Earth in the form of rain and snow. Water vapor is so plentiful in the atmosphere already that additional emissions are unlikely to absorb any significant amount of infrared radiation. It is also likely that the amount of water vapor held in the atmosphere is generally in equilibrium, and that increasing emissions of water vapor would not increase atmospheric concentrations [6]. According to currently available information, anthropogenic water vapor emissions at the Earth’s surface are unlikely to be an important element in either causing or ameliorating climate change.
Carbon Dioxide. Carbon is a common element on the planet, and immense quantities can be found in the atmosphere, in soils, in carbonate rocks, and dissolved in ocean water. All life on Earth participates in the “carbon cycle,” by which carbon dioxide (CO2) is extracted from the air by plants and decomposed into carbon and oxygen, with the carbon being incorporated into plant biomass and the oxygen released to the atmosphere. Plant biomass, in turn, ultimately decays (oxidizes), releasing carbon dioxide back into the atmosphere, or storing organic carbon in soil or rock. There are vast exchanges of carbon dioxide between the ocean and the atmosphere, with the ocean absorbing carbon from the atmosphere and plant life in the ocean absorbing carbon from water, dying, and spreading organic carbon on the sea bottom, where it is eventually incorporated into carbonate rocks such as limestone.
Records from Antarctic ice cores indicate that the carbon cycle has been in a state of imbalance for the past 200 years, with emissions of carbon dioxide to the atmosphere exceeding absorption. Consequently, carbon dioxide concentrations in the atmosphere have been steadily rising.
The most important natural sources of carbon dioxide are releases from the oceans (90 billion metric tons per year), aerobic decay of vegetation (30 billion metric tons), and plant and animal respiration (30 billion metric tons) [7]. Known anthropogenic sources account for 7 billion metric tons of carbon per year. The principal anthropogenic source is the combustion of fossil fuels, which accounts for about three-quarters of total anthropogenic emissions of carbon worldwide. Natural processes—primarily, uptake by the ocean and photosynthesis—absorb substantially all of the naturally produced carbon dioxide and some of the anthropogenic carbon dioxide, leading to an annual net increase in carbon dioxide in the atmosphere of 3.1 to 3.5 billion metric tons [8].
Methane. Methane (CH4) is also a common compound. The methane cycle is understood less well than is the carbon cycle. Methane is released primarily by anaerobic decay of vegetation, by the digestive tracts of termites in the tropics, and by several other lesser sources. The principal anthropogenic sources are leakages from the production of fossil fuels, human-promoted anaerobic decay in landfills, and the digestive tracts of domestic animals. The main sources of absorption are thought to be decomposition (into carbon dioxide) in the atmosphere and decomposition by bacteria in soil. Known and unknown sources of methane are estimated to total about 600 million metric tons annually; known sinks (i.e., absorption by natural processes) total about 560 million metric tons. The annual increase in methane concentrations in the atmosphere accounts for the difference of 35 to 40 million metric tons.
Nitrous Oxide. The sources and absorption of nitrous oxide (N2O) are much more speculative than those for other greenhouse gases. The principal sources are thought to be bacterial breakdown of nitrogen compounds in soils, particularly forest soils, and fluxes from ocean upwellings. The primary human-made sources are enhancement of natural processes through application of nitrogen fertilizers, combustion of fuels, and certain industrial processes. The most important sink is thought to be decomposition in the stratosphere. Worldwide estimated known sources of nitrous oxide total 13 to 20 million metric tons annually, and known sinks total 10 to 17 million metric tons. The annual increase in concentrations in the atmosphere is thought to total about 4 million metric tons.
Halocarbons and Other Chemicals. In the twentieth century, human ingenuity has produced an array of “engineered” chemicals not normally found in nature, whose special characteristics render them particularly useful. Some engineered chemicals are also greenhouse gases. The best known class of greenhouse chemicals are the chlorofluorocarbons (CFCs), particularly CFC-12, often known by its trade name, “freon-12.” CFCs have many desirable features: they are relatively simple to manufacture, inert, nontoxic, and nonflammable. Because CFCs are chemically stable, once emitted, they remain in the atmosphere for hundreds or thousands of years. Because they are not found in nature, these molecules absorb reflected infrared radiation at wavelengths that would otherwise be largely unabsorbed, and they are potent greenhouse gases, with a direct radiative forcing effect hundreds or thousands of times greater, gram-per-gram, than that of carbon dioxide.
Because of their long atmospheric lives, a portion of the CFCs emitted into the atmosphere eventually find their way into the stratosphere, where they can be destroyed by sunlight. This reaction, however, releases free chlorine atoms into the stratosphere, and the free chlorine atoms tend to destroy stratospheric ozone, which protects the surface of the Earth from certain wavelengths of potentially damaging solar ultraviolet radiation (ultraviolet radiation, for example, is one cause of human and animal skin cancers). The destruction of stratospheric ozone, notwithstanding its potential damage to living organisms, exerts a net cooling effect on the surface of the planet, making the net effects of CFCs on radiative forcing ambiguous.
The threat posed by CFCs to the ozone layer has caused the United States and many other countries to commit themselves to phasing out the production of CFCs and their chemical cousins, hydrochlorofluorocarbons (HCFCs) pursuant to an international treaty, the 1987 Montreal Protocol. As use of CFCs has declined, many related chemicals have emerged as alternatives, including HCFCs and hydrofluorocarbons (HFCs). HCFCs are similar to CFCs, but they are more reactive and consequently have shorter atmospheric lives, with less effect on the ozone layer and smaller direct global warming effects. HCFCs are also being phased out, but over a much longer time scale.
HFCs have no chlorine, and consequently have no effect on the ozone layer, but they have potentially powerful direct effects on climate. HFCs were rare before 1990, but in 1994 HFC-134a was adopted as the standard motor vehicle air conditioning refrigerant in virtually all new cars made in America. Consequently, HFC emissions are now rising rapidly, though from a negligible base.
Beyond the halocarbons (CFCs, HFCs, HCFCs, and PFCs) there are a range of engineered chemicals, produced in relatively small quantities, which also have direct radiative forcing effects. These include the perfluorocarbons (CF4, C2F6, and C3F8) emitted as byproducts of aluminum smelting; some industrial solvents such as carbon tetrachloride, methyl chloroform, methylene chloride; and other more obscure chemicals such as sulfur hexafluoride (SF6) and, possibly, other chemicals not yet identified. Some of these compounds are regulated in the United States as ozone depleters, or for toxicity, or both.
Criteria Pollutants. There are three gases, emitted primarily as byproducts of combustion (both of fossil fuels and of biomass), which have an indirect effect on global warming: carbon monoxide, nitrogen oxides, and nonmethane volatile organic compounds (NMVOCs). These compounds, regulated in the United Sates pursuant to the Clean Air Act, are often referred to (along with particulates, lead, and sulfur dioxide) as “criteria pollutants.” The criteria pollutants are reactive compounds, and they tend to remain in the atmosphere for only hours or days. The sequence of reactions that removes them from the atmosphere, however, tends to promote the formation of ozone (O3), a reactive and unstable molecular form of oxygen. While ozone in the stratosphere protects life on Earth from ultraviolet radiation, ozone at ground level at high concentrations causes respiratory distress in people and animals and also is, itself, a potent (though short-lived) greenhouse gas [9].
It has not proven possible to make a general determination of the contribution of criteria pollutants to global warming. The reactions that produce ozone are strongly affected by the relative concentrations of various pollutants, the ambient temperature, and local weather. Emissions of criteria pollutants can create very high, though localized, ozone concentrations under favorable conditions (for example, a warm, sunny day combined with still air and low humidity) and negligible concentrations under unfavorable conditions. The criteria pollutants are included in this report for completeness.
Aerosols. Finally, there is a class of gases which probably exert a net cooling effect on the climate. These compounds create a cooling effect by creating tiny solid particles (aerosols) in the atmosphere, which, in turn, act as nuclei for collections of water droplets and stimulate cloud formation. The clouds, in turn, reflect sunlight back into space, cooling the planet. The most important such gas is sulfur dioxide (SO2), which is largely emitted as a byproduct from the combustion of sulfur-containing fossil fuels, particularly coal. Sulfur dioxide reacts in the air to form sulfate compounds that are effective in promoting cloud formation. Sulfur dioxide emissions are regulated in the United States under the Clean Air Act and have declined considerably in recent years. Particulate emissions are also likely to exert a net cooling effect.
Some greenhouse gases are more potent in affecting global temperatures than are others. As a
result,
comparable increases in the concentrations of different greenhouse gases can have vastly
different
heat-trapping effects. Among those identified, carbon dioxide is among the least effective as a
greenhouse gas.
Other compounds, on a gram-per-gram basis, appear to have much greater effects [10].
It would be useful to determine the precise relative effectiveness of various greenhouse gases in
affecting
the Earth’s climate. This information would help policymakers know whether it would be
more effective
to concentrate effort on reducing the very small emissions of powerful greenhouse gases, such as
HFC-134a, or whether they should bend their efforts to controlling the very large emissions of
relatively
ineffective gases, such as carbon dioxide.
There has been extensive study of the relative effectiveness of various greenhouse gases in
trapping the
Earth’s heat. This research has led to the development of the concept of a “global
warming
potential,” or GWP. The GWP is intended to illustrate the relative impacts on global
warming of
various gases, compared with carbon dioxide. Over the past few years, the IPCC has conducted
an
extensive research program aimed at summarizing the effects of various greenhouse gases
through a set
of GWPs. The results of that work were released last year in an IPCC report, Climate Change
1994
[11] and updated this year in Climate Change
1995 [12].
The IPCC’s work has established that the effects of various gases on global warming are
too complex to
permit them to be easily summarized as a single number. The complexity takes several forms:
Despite such complexity, the scientific community is working to develop GWP approximations.
Table 3
summarizes the consensus results of the most recent studies by scientists working on behalf of
the IPCC,
showing estimates of atmospheric lifetimes and global warming potentials across various time
scales.
Relative Forcing Effects of Various Gases
| Table 3. Numerical Estimates of Global Warming
Potentials Compared With Carbon Dioxide (Kilogram of Gas per Kilogram of Carbon Dioxide) | ||||
| Gas | Lifetime (Years) | Direct Effect for Time Horizons of | ||
| 20 Years | 100 Years | 500 Years | ||
| Carbon Dioxide | Variable | 1 | 1 | 1 |
| Methane | 12 ± 3 | 56 | 21 | 7 |
| Nitrous Oxide | 120 | 280 | 310 | 170 |
| HFCs, PFCs, and Other Gases | ||||
| HFC-23 | 264 | 9,200 | 12,100 | 9,900 |
| HFC-125 | 33 | 4,800 | 3,200 | 11 |
| HFC-134a | 15 | 3,300 | 1,300 | 420 |
| HFC-152a | 2 | 460 | 140 | 42 |
| HFC-227ea | 37 | 4,300 | 2,900 | 950 |
| Perfluoromethane | 50,000 | 4,400 | 6,500 | 10,000 |
| Perfluoroethane | 10,000 | 6,200 | 9,200 | 14,000 |
| Sulfur Hexafluoride | 3,200 | 16,300 | 23,900 | 34,900 |
| Note: The typical uncertainty for global warming
potentials is estimated by the Intergovernmental Panel on Climate Change at ±35
percent. Source: Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), p. 121. | ||||
The Intergovernmental Panel on Climate Change has also devoted effort to studies of indirect
and
interaction effects of various gases—particularly the indirect effects of chlorofluorocarbons
(CFCs) and
hydrochlorofluorocarbons (HCFCs) on the ozone layer—compared with their direct
radiative forcing
effects. The IPCC presented GWP estimates for the first time this year that quantified the direct
and
indirect effects of certain CFCs and HCFCs (Table 4). Certain chemicals (halon-1301 and carbon
tetrachloride, for example) are now believed to exert a net cooling influence—i.e., to have a
negative global
warming potential. All of the net global warming potentials for CFCs and HCFCs are
considerably lower
than their direct GWPs. The authors of the IPCC report believe that the relative magnitudes of
the net
GWPs are fairly reliable, but that the absolute levels have an uncertainty of ±50 percent [13].
| Table 4. Numerical Estimates of Global Warming
Potentials, Including Indirect Effects, for Selected Chlorofluorocarbons and
Hydrochlorofluorocarbons Compared With Carbon Dioxide (Kilograms of Gas per Kilogram of Carbon Dioxide) | ||||
| Gas | Magnitude of Effects | |||
| 20-Year Integration | 100-Year Integration | |||
| Direct Effects | Direct Effects and Indirect Effects | Direct Effects | Direct Effects and Indirect Effects | |
| Chlorofluorocarbons | ||||
| CFC-11 | 4,900 | 1,200 to 2,900 | 3,800 | 540 to 2,100 |
| CFC-12 | 7,800 | 6,000 to 6,800 | 8,100 | 6,000 to 7,100 |
| CFC-113 | 4,900 | 2,800 to 3,800 | 4,800 | 2,600 to 3,600 |
| HFCs, PFCs, and Other Gases | ||||
| HCFC-22 | 4,000 | 3,500 to 3,700 | 1,500 | 1,300 to 1,400 |
| HCFC-123 | 300 | 60 to 170 | 90 | 20 to 50 |
| HCFC-124 | 1,500 | 1,300 to 1,400 | 470 | 390 to 430 |
| HCFC-141b | 1,800 | 660 to 1,200 | 600 | 170 to 370 |
| HCFC-142b | 4,100 | 3,600 to 3,800 | 1,800 | 1,600 to 1,700 |
| Halon-1301 | 6,100 | -14,100 to -97,600 | 5,400 | -14,100 to -84,000 |
| Carbon Tetrachloride | 1,900 | -500 to -2,600 | 1,400 | -650 to -2,400 |
| Methyl Chloroform | 300 | -400 to -1,000 | 100 | -130 to -320 |
| Note: The typical uncertainty for net global warming
potentials (including direct and indirect effects) is estimated by the Intergovernmental Panel on
Climate Change at ±50 percent. Source: Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), p. 119. | ||||
Rising concentrations of carbon dioxide in the atmosphere were first detected in the late 1950s. Observations of atmospheric concentrations of methane, nitrous oxide, and other gases began in the late 1970s. However, concern about the effects of rising atmospheric concentrations of greenhouse gases remained largely the province of atmospheric scientists and climatologists until the mid-1980s, when a series of international scientific workshops and conferences began to move the topic onto the agenda of United Nations specialized agencies, particularly, the World Meteorological Office.
The IPCC was established under the auspices of the United Nations in late 1988, to accumulate available scientific research on climate change and to provide scientific advice to policymakers. A series of international conferences provided impetus for an international treaty aimed at limiting the human impact on climate. In December 1990, the United Nations established the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change (generally called the INC). Beginning in 1991, the INC hosted a series of negotiating sessions that culminated in the signing, by more than 160 countries, including the United States, of the Framework Convention on Climate Change in Rio de Janeiro on May 4, 1992 [14]. The objective of the Framework Convention (“the Rio Treaty”) was to:
. . . achieve . . . stabilization of the greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system [15].
The Framework Convention, as it emerged from the negotiations, was based on the concept of voluntary commitments by signatories to take steps to implement the objectives of the Convention. These steps, as described in the treaty, include national commitments to prepare and submit for review national action plans and periodic national emissions inventories. Developed country signatories (including the United States), referred to in the language of the convention as “Annexe I Countries,” made additional commitments:
Each of these Parties shall communicate . . . detailed information on its policies and measures . . . [to limit emissions of greenhouse gases] . . . with the aim of returning individually or jointly to their 1990 levels these anthropogenic emissions of carbon dioxide and other greenhouse gases not controlled by the Montreal Protocol. This information will be reviewed by the Conference of the Parties, at its first session and periodically thereafter . . . [16].
The greenhouses gases “controlled by the Montreal Protocol” are CFCs and HCFCs, which are explicitly defined as being outside the scope of the Framework Convention.
Pursuant to the requirement to “communicate . . . detailed information” on policies and measures, the outgoing Bush Administration prepared a draft national action plan in December 1992 [17]. On April 21, 1993 (Earth Day), President Clinton committed the United States to stabilizing its emissions of greenhouse gases at 1990 levels by the year 2000. The methods proposed by the Government to achieve this objective were described in the President’s Climate Change Action Plan, published in October 1993 [18]. That document spells out a range of largely voluntary programs intended to achieve the stabilization objective. More detail-oriented readers may wish to consult the Technical Supplement to the Plan, published in early 1994, which spells out the assumptions underlying the Plan in greater detail [19].
The Conference of the Parties is required to meet annually to discuss the implementation of the Framework Convention, and to review countries’ voluntary commitments to limit their emissions. The first such meeting was held in Berlin in April 1995. By 1995, the signatories’ focus had shifted from meeting emissions targets for the year 2000 to the question of what steps would be taken beyond 2000. At Berlin, the Conference of the Parties agreed on “the Berlin Mandate,” which was an agreement “to begin a process to enable it [the Conference of the Parties] to take appropriate action for the period beyond 2000 . . . through the adoption of a protocol or another legal instrument” [20]—in other words, to negotiate a successor agreement to the Framework Convention for the next decade. However, the Berlin Mandate accelerated the “two track” approach to emissions limitation already in evidence in the Framework Convention. There were to be no new commitments for developing countries: rather they were to be encouraged to implement their commitments under the Framework Convention. Meanwhile, the Annexe I countries would move ahead with negotiating additional measures.
The past year has been spent in considering the possible forms the successor agreement might take. The most recent report of the IPCC has been cited by member governments, including the U.S. Government, as evidence that motivates further measures to limit emissions of greenhouse gases. The second Conference of the Parties was held in Geneva in July 1996. At that meeting, the Conference issued a “Ministerial Declaration” to the effect that the Governments present would:
Instruct their representatives to accelerate negotiations on the text of a legally-binding protocol or other legal instrument to be completed in due time for adoption at the Third Session of the Conference of the Parties [i.e., by July 1997]. The outcome should fully encompass the remit of the Berlin Mandate, in particular,
Thus, the governments of the United States and Western Europe have agreed to negotiate, within the next year, a treaty with quantified emissions targets over the next two decades. The target levels, and the measures to be proposed to meet the targets, remain to be seen.
The United States is the world’s largest single emitter of carbon dioxide, accounting for about 23 percent of energy-related carbon emissions worldwide. The U.S. share of methane and nitrous oxide emissions, although uncertain, is likely to be much lower than its share of carbon dioxide emissions, as the principal sources of methane and nitrous oxide emissions are more common outside than within the United States. In the case of halocarbons and other gases, the U.S. share is likely to be considerably larger than 23 percent, because the use of cooling and refrigeration equipment is probably much more pervasive in the United States than elsewhere in the world.
In recent decades, the carbon dioxide emissions of North America and Western Europe have been growing relatively slowly (Figure 1). The worldwide growth in energy-related carbon dioxide emissions has come from rapid growth in the developing world and in the former centrally planned economies. The most striking development in the 1990s has been the rapid reduction in energy consumption (and hence carbon emissions) in the countries of the former Soviet Union and Eastern Europe, where emissions dropped by more than 20 percent between 1989 and 1992 and have continued to decline through 1994. Emissions reductions in former communist countries have been sufficient to stabilize world energy-related carbon dioxide emissions at 1990 levels through 1994, despite continuing rapid growth in the developing world, stable emissions in Western Europe, and slow growth in the United States.
This year, the EIA released a projection of worldwide carbon emissions estimates in its International Energy Outlook 1996 [22]. That projection suggests that the post-communist decline in energy consumption is a one-time phenomenon, and that energy consumption in these countries will “bottom out” in the next few years and begin to rise again. Since the EIA also expects rapid growth in energy consumption in the developing world to continue, the prospect is for continued growth in worldwide carbon emissions.
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