R. J. Andres
Institute of Northern Engineering
School of Engineering
University of Alaska-Fairbanks
Environmental Sciences Division
Publication No. 4473
Date Published: December 1995
1. Global CO2 emissions from fossil-fuel burning, cement production, and gas flaring for 1950-92
2. Regional CO2 emissions from fossil-fuel burning, cement production, and gas flaring for North America and Europe, 1950-92
3. Regional CO2 emissions from fossil-fuel burning, cement production, and gas flaring for 1950-92
4. Ranking of the 20 highest CO2-emitting countries in 1992 and their rank in 1950, contributions to global emissions, and per capita CO2-emission rates
5. Data processing and selection of the United Nations Energy Statistics Database
National CO2 emissions
National per capita CO2 emissions
National per capita CO2 emissions
1. Alphabetical listing of the countries and areas (and their corresponding country and area codes) represented in the United Nations Energy Statistics Database
2. Listing of the countries and areas represented in the United Nations Energy Statistics Database by country and area code
3. Listing of the primary and secondary fuels from the United Nations Energy Statistics Database used in calculating CO2-emission estimates
4. Factors and units for calculating CO2 emissions from fuel production and trade data CO2i = (Pi) (FOi) (Ci)
5. Global annual CO2 emissions from fossil-fuel burning, gas flaring, and cement production for 1950-92
6. Listing of the countries assigned to each of ten global regions
7. Listing and explanation of all negative total CO2-emission estimates
8. Characteristics of numeric variables for the file (gas92.dat) containing the gas fuel statistics from the United Nations Energy Statistics Database
9. Characteristics of numeric variables for the file (liquid92.dat) containing the liquid fuel statistics from the United Nations Energy Statistics Database
10. Characteristics of numeric variables for the file (solid92.dat) containing the solid fuel statistics from the United Nations Energy Statistics Database
11. Characteristics of numeric variables for the file (factor92.dat) containing the United Nations conversion factors
12. Characteristics of numeric variables for the file (cement92.dat) containing the annual hydraulic cement production estimates from the U.S. Bureau of Mines
13. Characteristics of numeric variables for the file (flare92.dat) containing the gas-flaring estimates
14. Characteristics of numeric variables for the file (nation92.ems) containing the national CO2-emission estimates
15. Characteristics of numeric variables for the file (region92.ems) containing the regional CO2-emission estimates
16. Characteristics of numeric variables for the file (global92.ems) containing the global annual CO2-emission estimates
BODEN, T. A., G. MARLAND, and R. J. ANDRES. 1995. Estimates of Global, Regional, and National Annual CO2 Emissions from Fossil-Fuel Burning, Hydraulic Cement Production, and Gas Flaring: 1950-1992. ORNL/CDIAC-90, NDP-030/R6. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A. 600 pp.
This document describes the compilation, content, and format of the most comprehensive CO2-emissions database currently available. The database includes global, regional, and national annual estimates of CO2 emissions resulting from fossil-fuel burning, cement manufacturing, and gas flaring in oil fields for 1950-92 as well as the energy production, consumption, and trade data used for these estimates. The methods of Marland and Rotty (1983) are used to calculate these emission estimates. For the first time, the methods and data used to calculate CO2 emissions from gas flaring are presented. This CO2-emissions database is useful for carbon-cycle research, provides estimates of the rate at which fossil-fuel combustion has released CO2 to the atmosphere, and offers baseline estimates for those countries compiling 1990 CO2-emissions inventories.
According to these estimates, the annual total of CO2 emissions from fossil-fuel consumption, cement production, and gas flaring has grown almost fourfold since 1950. The 1992 estimate of 6097 million metric tons of carbon ended a string of 8 consecutive years of growth in global CO2 emissions and represents a 1.2% decline from 1991. The 1991 estimate of 6172 million metric tons of carbon is the highest CO2-emission estimate since the data record began in 1950; however, it includes 130 million metric tons of carbon emitted to the atmosphere from the Kuwaiti oil field fires.
Regionally, 1992 shows a continuing decline in CO2 emissions for Eastern Europe, and Western Europe experienced its first decline in emissions since 1987-88. Regions where populations continue to grow--such as Africa, Centrally Planned Asia, Central and South America, the Far East, and Oceania--show corresponding increases in CO2 emissions. In 1950, North America, Eastern Europe, and Western Europe (including Germany) accounted for 89.1% of global CO2 emissions from fossil-fuel burning, cement production, and gas flaring, whereas the other regions--Africa, Centrally Planned Asia, Central and South America, the Far East, the Middle East, and Oceania--accounted for only 10.9%. These six regions now contribute 41.1% of the CO2 emitted globally.
Nationally, the United States continues to be the largest single source of fossil fuel-related CO2 emissions; 1332 million metric tons of carbon were emitted in 1992. In fact, U.S. emissions are 45% higher than those of the world's second largest emitter, China. The top three emitting countries--the United States, China, and Russia--were responsible for 43.2% of the world's emissions from fossil-fuel burning in 1992. The top 20 emitting countries accounted for 80% of all the world's emissions.
These data are available without charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of this document and 28 files that comprise the CO2-emissions database. The database requires 8.5 megabytes of disk storage and is available on a variety of media (i.e., floppy diskettes, 8-mm tape, and 9-track magnetic tape) or via the Internet.
Keywords: Carbon dioxide emissions; fossil fuels; cement; gas flaring; energy production and consumption; carbon cycle; atmospheric CO2 concentrations; climate change
Overview of the Database
Evidence that the atmospheric CO2 concentration has risen during the past several decades (Keeling et al. 1989; Keeling and Whorf 1994; Conway et al. 1994) is irrefutable. Most of the observed increase in atmospheric CO2 is believed to result from CO2 releases from fossil-fuel burning. The United Nations (UN) Framework Convention on Climate Change (FCCC), signed in Rio de Janeiro in June 1992 (United Nations 1992), reflects global concern over the increasing CO2 concentration and its potential impact on climate. One of the convention's stated objectives is the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." Specifically, the FCCC asks all 154 signing countries to conduct an inventory of their current greenhouse gas emissions, and it sets nonbinding targets for some countries to control emissions by stabilizing them at 1990 levels by the year 2000. Given the importance of CO2 as a greenhouse gas, the relationship between CO2 emissions and increases in atmospheric CO2 levels, and the potential impacts of a greenhouse gas-induced climate change it is important that comprehensive, accurate CO2-emission records be compiled, maintained, and fully documented.
We have used internationally available data to estimate CO2 emissions from all countries on a uniform and consistent basis. Inventories compiled by individual countries in response to the FCCC agreements may be based on more extensive national data sets and more nation-specific derivation and application of the parameters needed in the calculations, and should ultimately lead to more accurate estimates for individual countries for individual years. Broad national participation and careful adherence to internationally agreed upon methodologies may eventually lead to improved estimates of regional and global-total emissions as well.
Keeling (1973) was the first to establish a systematic method for estimating the amount of CO2 emitted from fossil fuels. Keeling used energy data from the UN Department of International Economic and Social Affairs. Since 1973, both energy data collection and the procedures for estimating CO2 emissions have been refined and improved (Marland and Rotty 1984; United Nations 1994). The global distributions, trends, and patterns of these fossil fuel CO2 emissions have been studied and described by Marland and Rotty (1984), Marland and Boden (1993), and Marland et al. (1994a, b).
Another industrial source of CO2 is cement manufacturing. Hydraulic cement, particularly Portland cement, is the most abundant and widely used type of cement. Portland cement is a combination of two types of raw materials: one rich in calcium, such as limestone, chalk, marl, or clam or oyster shells; the other rich in silica, such as clay or shale (Griffin 1987). In a cement kiln, calcium carbonate (CaCO3) is broken down (calcined) into CO2 and calcium oxide (CaO) (Helmuth et al. 1979). The CaO is used in manufacturing cement, and the CO2 is released to the atmosphere. Several studies (Keeling 1973; Griffin 1987; Rotty 1987) determined the amount of CO2 emitted during cement manufacturing using data published by the UN or the United States Bureau of Mines. Although the amounts of CO2 produced from cement manufacturing are far less (3% of 1992 global CO2 emissions) than those from fossil-fuel consumption, the quantities are large enough to constitute an important source of CO2 emissions.
Biomass derived fuels are specifically not included in the inventories here. The basic philosophy is that a complete accounting of CO2 emissions requires that emissions from loss of forest and other C storage in the biosphere be added to the numbers here for CO2 emissions from fossil fuels. To the extent that use of biomass fuels represent long-term loss of C from the biosphere, this should be reflected in numbers for emissions from forest clearing and attempts to include biomass fuels here would run great risk of double counting. The Intergovernmental Panel on Climate Change (IPCC) methodology for national greenhouse gas emissions inventories suggests that CO2 emissions from biofuels be estimated for the sake of complete accounting of the energy system, but that the numbers not be included when sums are produced.
Another source of CO2 is the flaring of natural gas, a practice used in oil fields to eliminate waste gases and vapors. This practice is used for convenience in oil field operations that lack the ability to adequately handle and recover natural gas while producing oil and is used as a mechanism to quickly eliminate excess gases during unexpected equipment failures or plant emergencies. Like those from cement production, emissions from gas flaring are far less (1% of 1992 global CO2 emissions) than those from fossil-fuel consumption. For some nations (e.g., Kuwait, Oman), however, CO2 emissions from gas flaring constitute a sizeable portion of their total CO2 emissions; these emissions were particularly high during the 1960s and 1970s, before the Middle Eastern countries had the infrastructure and impetus to recover natural gas at their oil fields.
The purpose of this document is to fully document the most comprehensive CO2-emissions database currently available. The database contains global, regional, and national annual estimates of CO2 emissions resulting from fossil-fuel burning, cement manufacturing, and gas flaring in oil fields for 1950-92. This document focuses largely on the format and content of the database and the data used to calculate these emission estimates. The methods used to calculate the global totals are discussed briefly and are described in detail in Marland and Rotty (1984). A copy of the Marland and Rotty (1984) paper is provided in Appendix B of this documentation. More detail of methods and philosophies behind the national estimates is contained in Marland and Boden (1993). The methods and data used to calculate emissions from gas flaring are described here for the first time.
This database provides estimates of the rate at which fossil-fuel combustion and cement manufacturing have released CO2 to the atmosphere. These CO2-emission estimates are useful for carbon-cycle research, provide one of the fundamental data sets needed to assess the magnitude and potential effects of increased concentrations of atmospheric CO2, and offer baseline estimates for those countries compiling 1990 CO2-emission inventories to meet FCCC requirements.
The data described in this document include global, regional, and national annual CO2-emission estimates and the data used in calculating these estimates. This includes a large portion of the 1992 UN Energy Statistics (UNSTAT) Database (UN 1994), hydraulic cement production estimates compiled by the U.S. Department of Interior's Bureau of Mines (Solomon 1993), and supplemental data on gas flaring obtained from the U.S. Department of Energy's Energy Information Administration (DOE/EIA). Annual CO2-emission estimates are provided for the period 1950-92 for the globe, 10 regions, and 240 countries. Global estimates, derived from UN fuel production data, and national estimates, derived from UN data for international trade, were calculated by using the methods of Marland and Rotty (1984). In addition, annual per capita rates of carbon emission are provided. These emission rates were calculated by using population estimates published by the UN Statistical Division (UN 1994).
The primary database used to estimate the amount of CO2 emitted to the atmosphere from fossil-fuel burning and gas flaring is the UNSTAT Database, a comprehensive collection of international energy data compiled by the United Nations Statistical Office (1). This database provides data for primary and secondary forms of energy, for almost every nation in the world (Tables 1 and 2), and by individual fuel types. The complete UNSTAT Database also contains data on production, consumption, capacity, reserves, losses, and trade of heat and power, renewable, and nuclear energy commodities; none of which are used for the calculation of CO2 emissions. The complete 1992 version of the UNSTAT Database contains 440,623 records with 3,084,361 data values and requires 13 megabytes of disk space. The energy statistics in the UNSTAT Database were compiled primarily from annual questionnaires distributed by the UN Statistical Division and were supplemented by data in official national statistical publications. Where official data were not available or were inconsistent, estimates were made by the UN Statistical Division on the basis of governmental, professional, or commercial materials. These international statistics are published annually by the UN in the Energy Statistics Yearbook (originally published as World Energy Supplies in Selected Years, 1929-1950). A 2-year lag typically occurs between the publication of the yearbook and the last year of data (i.e., the 1994 yearbook provides energy statistics through 1992).
The cement manufacturing data, used to estimate emissions from hydraulic cement production, were compiled by the U.S. Department of Interior's Bureau of Mines. The cement production database is a comprehensive collection of international data from 166 countries. These data, like those in the UNSTAT Database, are reported on an individual country basis. In cement production, CO2 is released to the atmosphere through calcination:
CaCO3 -------> CaO + CO2
Because cement manufacturing uses essentially 100% of the calcium oxide obtained from burning the calcium carbonate, the amount of calcium oxide in the finished cement provides a good measure of the amount of CO2 released during production (Griffin 1987).
Gas-flaring CO2-emission estimates are derived primarily from flaring estimates provided in the UNSTAT Database. The UNSTAT Database has incomplete time series for many countries including China, France, Norway, Oman, and Russia and little data before 1970. Gas-flaring estimates provided by DOE/EIA were used to complete or supplement the flaring time series for these countries, and the resulting database contains estimates of gas flaring in 57 countries.
The methods of Marland and Rotty (1984) were used to estimate the amount of CO2 emitted to the atmosphere from fossil-fuel burning, gas flaring, and cement production. This section briefly summarizes these methods and states some of the assumptions used in these methods [for a complete discussion see the copy of the Marland and Rotty (1984) paper provided in Appendix B].
As indicated earlier, the primary data used to calculate the CO2-emission estimates came from the UNSTAT Database. Fuel production data were used in generating global CO2-emission estimates because these data are more complete than energy consumption data. For regional or national emission estimates, however, one needs to know the amount of fossil fuels consumed in each region or nation, and not the amount produced, to calculate the CO2 emitted.
The calculation of CO2 emissions from fossil fuels is conceptually very simple (Marland and Rotty 1984). For each type of fuel, the annual CO2 emissions are the product of three terms: the amount of fuel consumed, the fraction of the fuel that becomes oxidized, and a factor for the carbon content of the fuel (Marland and Rotty 1984). That is,
CO2i = (Pi) (FOi) (Ci), (1)
where subscript i represents a particular fuel commodity, P represents the amount of fuel i that is consumed each year, FO is the fraction of P that is oxidized, C is the average carbon content for fuel i, and CO2 is the resulting CO2 emissions for fuel i expressed in mass of carbon. For CO2 emissions, fossil fuels can be divided into the usual groups of solid, liquid, and gas fuels. An identical procedure has been adopted by the IPCC in prescribing a methodology for countries to use in estimating and reporting greenhouse gas emissions (IPCC 1995).
Global total CO2-emission estimates are generated by using the above equation, where P represents production data from the UNSTAT Database for all primary solid, liquid, and gas fuels. Because secondary fuels are derived from primary fuels, they need not be included.
Trade data are required to calculate regional and national CO2-emission estimates. For these calculations, both primary and secondary fuel data are used. Table 3 lists the UNSTAT primary and secondary fuels used in these CO2-emission calculations. Consumption [i.e., Pi in Eq. (1)] is the sum of production and imports less exports, "bunkers," and stock changes. This is what the UN calls "apparent
consumption" because it relies on production and trade data rather than end-use consumption data. That is,
consumptioni = productioni + importsi - exportsi - bunkersi - changes in stocksi, (2)
where i is a solid, liquid, or gas fuel. Bunkers refer to fuels consumed by ships and aircraft engaged in international trade. Stock changes refer to changes in stocks at producers, importers, and/or industrial consumers from the beginning to the end of each year.
The emissions coefficients (Ci) are defined in such a way as to express as accurately as possible the fuel carbon content in terms of easily accessible measures of the quantity of fuel consumed. As described in Marland and Rotty (1984), we feel that the mean carbon content of liquid fuels is most accurately estimated in terms of the mass fraction while the carbon content of solid and gas fuels is most accurately estimated in units of mass C per unit of energy content. Using energy content in the denominator compensates for the wide variability in the chemical and physical properties of coals (Marland et al. 1994a) and captures the variability of gaseous fuels as well. In order to conform to units used in the U.N. data series, the emissions coefficient for solid fuels is expressed in terms of the lower (net) heating value of the fuel. Units of measure for the heating value of gas fuels in the UNSTAT Database are ambiguous and probably lack consistency and our emissions coefficient is based on the higher (gross) heating value of the fuel.
Emissions of CO2 from the combustion of bunker fuels are shown with the country in which the final fuel loading occurred but the emissions are not included with the national total. On geochemical grounds, these emissions will occur along international shipping lanes rather than from the country where the final loading took place. On geopolitical grounds, it is not obvious how emissions from bunker fuels should be accounted for.
Adjustment is made for the fraction of crude oil converted into nonenergy products (e.g., lubricants, asphalt, naphthas). National totals for emissions from petroleum products are based on energy uses only and do not include emissions from the oxidation of nonfuel products, whereas the global totals do include an estimate of emissions from oxidation of the nonenergy products.
This section thus outlines 4 reasons why the sum of emissions estimated for all countries is not equal to the estimate of global total emissions: 1.) the global total includes emissions from bunker fuels whereas these are not included in any national totals, 2.) the global total includes estimates for the oxidation of non-fuel hydrocarbon products whereas national totals do not, 3.) national totals include annual changes in fuel stocks whereas the global total does not, and 4.) due to statistical differences in the international statistics, the sum of exports from all exporters is not identical to the sum of imports by all importers.
Once consumption and production values have been calculated, these estimates are multiplied by a factor that reflects the fraction of each broad fuel category that is oxidized [i.e., FO in Eq. (1)] and the average carbon content (C) of each fuel category. Table 4 lists the values and units of P, FO, and C for each fuel category.
3.1 CO2 Emissions from Cement Manufacturing
Because cement manufacturing uses essentially 100% of the calcium oxide obtained from burning the calcium carbonate during calcination, the amount of calcium oxide content in the finished cement is a good measure of the amount of CO2 released during production (Griffin 1987). To determine the amount of CO2 released from cement manufacturing, one needs to know how much cement was manufactured, the average calcium oxide content per unit of cement, and a factor to convert the calcium oxide content into carbon dioxide equivalents. Cement production data published by the U.S. Bureau of Mines are currently reported in thousand short tons, but before 1970 the data were reported in barrels. To ensure consistent units throughout the 1950-92 record, two equations were used to convert cement production estimates to units of metric tons. Cement production before 1970 was calculated by using
cement production (in metric tons) = 0.17055 × quantity of cement produced (in barrels), (3)
where 0.17055 is the metric-ton equivalent for a barrel.
After 1969, net cement production was calculated by using
cement production (in metric tons) = 0.90718474 × quantity of cement produced (in short tons), (4)
where 0.90718474 is the metric-ton equivalent for a short ton. The amount of CO2 produced from cement production was calculated by using
CO2 production (in metric tons of C) = 0.136 metric tons of C per metric ton cement
× quantity of cement produced (metric tons) (5)
This conversion factor was obtained by dividing the molar mass of carbon by the molar mass of calcium oxide and multiplying this quotient by the average fraction of calcium oxide contained in cement:
(12.01 g C/mole CaCO3 ÷ 56.08 g CaO/mole CaCO3) × 0.635 g CaO/g cement = 0.136 g C/g cement (6)
The consensus that 63.5% of the typical cement in the world is composed of calcium oxide is based on the opinions of experts consulted in the field, as well as inspection of composition data by type and country (Griffin 1987).
3.2 Per Capita CO2-Emission Rates
Using the UN population data, the authors estimate per capita CO2 emission rates for individual countries, using the equation:
national per capita CO2 emission · year-1 = total national CO2 emission estimate · year-1
÷ national population (7)
The resulting per capita estimates are expressed in metric tons of carbon person-1 year-1.
According to these estimates, the global total of CO2 emissions from fossil-fuel consumption, cement production, and gas flaring has grown almost fourfold since 1950 (Table 5 and Fig. 1). The 1992 estimate of 6097 million metric tons of carbon ends a string of 8 consecutive years of growth in global CO2 emissions and represents a 1.2% decline from 1991. The 1991 estimate of 6172 million metric tons of carbon is the highest CO2-emission estimate since the data record began in 1950; however, it includes 130 million metric tons of C emitted to the atmosphere from the Kuwaiti oil-field fires (2).
Globally, liquid and solid fuels accounted for 79% of the emissions from fossil-fuel burning in 1992. Combustion of gas fuels (i.e., natural gas) accounted for 17% (1045 million metric tons C) of total emissions from fossil fuels in 1992 and reflects a gradually increasing global utilization of natural gas. Emissions from cement production increased slightly and now account for 3% of total emissions. Emissions from gas flaring declined 11% from 1991 to 1992 to 68 million metric tons C (just 1% of the global total), due largely to the end of the Iraq-Kuwait conflict, and remain well below the levels of the 1970s. This trend for gas flaring is not fully clear because of uncertainty about the gas-flaring data for Russia.
Regionally, Eastern Europe continued to have a marked decline in CO2 emissions, North American emissions increased 1.3% during 1992 after 2 successive years of declining emissions, and Western Europe experienced its first decline since 1987-88 (Fig. 2). However, regions where populations continue to grow--such as Africa, Centrally Planned Asia, Central and South America, the Far East, and Oceania--showed increases in CO2 emissions (Fig. 3). In 1950, North America, Eastern Europe, and Western Europe (including Germany) accounted for 89.1% of global CO2 emissions from fossil-fuel burning, cement production, and gas flaring, whereas the remaining six regions accounted for only 10.9%. Now these six regions--Africa, Central and South America, Centrally Planned Asia, the Far East, the Middle East, and Oceania--contribute 41.1% of the CO2 emitted globally. Table 6 lists the countries assigned to each region. The table includes the regional assignments of countries which no longer exist because of subdivision or re-aggregation. Because of uncertainty in how to deal with the data time series, Germany is defined here as a separate region.
The top 20 emitting countries accounted for 80% of all the 1992 world CO2 emissions from fossil-fuel consumption (Fig. 4). The top three countries--the United States, China, and Russia--were responsible for 43.2% of the world's emissions from fossil fuel burning in 1992. Spain, the 20th-highest CO2-emitting nation, contributed slightly less than 1% to this total. The United States continued as the largest single source of fossil fuel-related CO2 emissions, with 1332 million metric tons of carbon emitted in 1992. In fact, U.S. emissions are 45% higher than those of the world's second largest emitter, China. U.S. emissions in 1992 were nearly twice those in 1950, although the U.S. share of global emissions declined from 44% to 23% over the same interval because of higher growth rates in other countries.
Marland and Rotty (1984) estimated that the uncertainty of the annual global CO2-emission estimates derived from the UN's energy data was 6 to 10%. The reliability of the national CO2 estimates presented here are bounded by the accuracy and completeness of the commodity values reported by each country to the UN Statistical Office. Marland and Boden (1993) provides some insight on the accuracy of the national-level data. The values published by the UN are consistent with numbers published elsewhere and represent the best efforts of a staff dedicated to the sole task of bringing together all the available global energy information. It is not possible to independently verify each number reported by individual countries to the UN. When inconsistencies arise in the official data, the UN Statistical Office makes its own estimates based on governmental, professional, or commercial materials.
The issue of significant figures presents some interesting questions in presenting the data in this volume. While the suggestion that the final estimate is good within +10% hardly justifies reporting in four or more significant figures, we do not want to lose sight of small contributions, and many of the numbers which contribute to the sum are indeed significant in what shows in the 4th or 5th place in the regional and global sums. In other cases, growth over the period of record has been so great that digits which were certainly significant at the beginning of a time series would not be significant in the most recent entries of the same time series. In order to preserve the integrity of some small numbers, we have thus chosen to include more digits than are justified in some of the larger numbers. We leave it to the discretion and purposes of the user to truncate where appropriate. National emissions numbers are reported in thousands of tons of C, regional and global totals are reported in millions of tons of C, and per-capita values are reported to 0.01 tons of C.
CO2-emission estimates for some individual countries and regions are less reliable than the global CO2 emission estimates. Global totals depend on only production data with some representation of fuel chemistry and fractions of fuels that are oxidized. Regional and national data rely further on information for additional transactions (e.g., refinery product mix by country, imports, exports, bunker loadings). For some countries, it is difficult for the UN to obtain sufficient production, consumption, and trade data. Also, even though the authors account for all of these mass transfers, we do not attempt to deal with the different carbon content of various products.
Even the casual observer of Appendix A of this report will be struck with the broad year-to-year variability or singular anomalies in some of the plots of national emissions estimates. Some of this is no doubt real variability due to the vagaries of politics, economics, and weather; but other cases are certainly reflections of incompleteness or inadequacies of the data time series. These problems are difficult to verify and fix in the original data sets and it is only through focused attention by national experts, for example through exercises like the national greenhouse reporting exercises mandated by the FCCC, that we can hope to see these resolved. These kinds of data problems are concentrated in smaller countries where shut-down of a single large mine or power plant or omission of a single import stream can indeed have a major impact on the national statistics. We do not find any indication of systematic data problems and these variations in national statistics have little impact on regional or global sums. Data users should be particularly cautious of using data for the most recent year for a small developing country without looking at how it fits in with the trend of earlier values.
As noted earlier, the sum of the CO2 emissions for all of the individual countries for a given year, as reported here, will not equal the global total. The difference between the sum of the individual countries and the global estimates is generally less than 5%.
Griffin (1987) reviewed the cement data and consulted with those responsible for data compilation and concluded that cement production figures from 1950 to 1985 were likely to be within 15% of true values. The conversion factor for cement (0.136 metric tons of carbon per metric ton of cement manufactured) is based on the consensus that 63.5% of the world average cement is composed of calcium oxide. This estimate is based on the opinions of experts in the field as well as an inspection of composition data by type and country. The uncertainty associated with the conversion factor for cement is small with respect to the uncertainty in the cement production data.
The five countries of extreme southern Africa--Botswana, Lesotho, Namibia, South Africa, and Swaziland-- are joined in the South Africa Customs Union and all international trade occurs through this customs union. Trade among these five nations is not captured in international trade statistics. Lesotho, for example has most of its trade with South Africa (which surrounds it) and this trade does not appear in UN trade statistics (Lesotho receives a fixed share of customs receipts from the customs union). The consequence of this in our energy-related analyses is that we cannot clearly distinguish what is attributable to South Africa. The UNSTAT Database distinguishes internal production of energy resources but imports and exports are identifiable only for the group as a whole. Consequently, our emissions estimates, for example, show energy consumption and CO2 emissions as zero for Namibia and Lesotho and very tiny for Swaziland. Because South Africa dominates the five-nation customs union in population (86%) and clearly has the highest per-capita level of consumption, we have taken the position of assuming that all imports and exports attributed to the "Customs Union of South Africa" (i.e., country code 711) are in fact due to South Africa itself. This has the effect of slightly inflating both total and per capita energy consumption and CO2 emissions for South Africa. Energy consumption and related emissions for the other four countries are most likely underestimated. Emissions from Swaziland and Botswana are those from domestically-produced coals only.
In addition to the uncertainty associated with the CO2-emission estimates and the reliability of the data sets used to calculate these estimates, there are some other caveats in the data files that need explanation. Some of these caveats are created by using different types of data from various sources whereas others stem from the methods used to calculate regional and national CO2 emissions. There are sixty-eight instances where CO2-emission estimates from either gas, liquid, or solid fuel consumption were negative and eleven occurrences of negative total CO2-emission estimates for individual countries (Table 7). There are many reasons for these negative values including accounting errors in the national production and trade data, missing data, and our accounting system. For example, envision a hypothetical nation (X) with coal but no crude oil resources. If the country were to produce 100 tons of coal, convert it to liquid fuels in a liquefaction plant, and then export 50 tons of liquid fuels, our algorithm would lead to the following report of fuel consumption.
The total fuel consumption (and subsequent CO2-production) numbers would be correct even though the component numbers for solids and liquids are misleading. Because there are only small amounts of conversion among fuel forms, this seems to remain a useful accounting procedure in spite of a few misleading numbers. For similar reasons the per-capita CO2 values of some small countries will not accurately reflect energy usage in the local economy. Data for Wake Island, for example, show large imports of liquid fuels and nearly the same values for bunker loadings. Inland consumption is the difference between these two large values. Calculations show that per-capita CO2 consumption on Wake Island has been two-to-four times that in the United States since 1960, but with 95% of energy petroleum products allocated to bunker loadings it doesn't take much of a distortion in either the import or bunker numbers to produce a major change in the per-capita consumption number. Some of the population estimates used to calculate per-capita CO2-emission rates were mid-year population estimates.
The CO2-emissions database is derived from a variety of sources and requires considerable data processing, selection, and integration (Fig. 5). Each of the data sets used for calculating the CO2-emission estimates is checked carefully. CDIAC works with the UN Statistical Division annually to
quality assure each new version of the UNSTAT Database. Although the review process is unable to detect some kinds of data problems, it does confirm that the UNSTAT Database meets high standards of data management and internal consistency. The following highlights the quality-assurance checks performed routinely on the entire UNSTAT Database, not just on those data used in the CO2-emission calculations.
6.1 Compare the New Database to the Previous Version
The 1992 UNSTAT Database, released in May 1994, was checked against the 1991 version to identify additions, deletions, and changes. In general, the oldest data (i.e., 1950-69) had no changes whereas in the newer data (1970-92), there were many (>1000) differences. This reflects the dynamic nature of the UNSTAT Database and the constant addition, deletion, and revision of data as new
information is obtained. The dynamic nature of the UNSTAT Database also requires that users of the CO2-emissions database replace previous versions of the database in their entirety, instead of simply appending the most recent years' emission estimates.
6.2 Check for Duplicate Entries
The 1992 UNSTAT Database was sorted by country, year, commodity, transaction code, quantity, and units in a search for duplicate entries. Duplicate entries were deleted from the database.
6.3 Check for Questionable Data
The UNSTAT data were examined to identify suspect data. The checks were performed to identify:
Inappropriate years (outside of the 1950-92 range)
Invalid country codes (checked against the UN documentation)
Invalid transaction codes (certain transaction codes are valid for only some commodities)
Questionable import/export quantities (in relation to production quantities)
Improper signs (some transactions can be only positive or only negative)
Gaps or large changes in quantities between adjacent years for the same country, commodity, and transaction
These checks have identified many "suspicious values." Some are clearly errors, whereas most suggest review by the UN Statistical Division and are referred back to them for consideration. Rarely, and only in the case of unmistakable errors and with the concurrence of the UN Statistical Division, do the authors purge or change values before calculating the CO2-emission estimates. Having performed this exercise for 7 years, and continually refining the quality-assurance process, we now find few "suspicious values" during the annual quality-assurance exercise.
The CO2-emission estimates and underlying data are available in machine-readable form, upon request, from CDIAC, without charge. CDIAC will also distribute subsets of the database as requested. This database may be acquired from CDIAC's anonymous File Transfer Protocol (FTP) area (see FTP access instructions below), on 9-track magnetic or 8-mm tape, or on IBM- or Macintosh-formatted floppy diskettes. Requests for 9-track magnetic tapes should include preferred tape specifications (i.e., 1600 or 6250 BPI, labelled or nonlabelled, ASCII or EBCDIC characters, variable- or fixed-record lengths). Requests not accompanied by tape specifications will be filled on 9-track, 6250 BPI, nonlabelled tapes with ASCII characters, and having the file attributes shown on pages 40-42.
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Conway, T. J., P. P. Tans, L. S. Waterman, K. W. Thoning, D. R. Kitzis, K. A. Masarie, and N. Zhang. 1994. Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network. Journal of Geophysical Research 99:22831-55.
Griffin, R. C. 1987. CO2 release from cement production 1950-1986. Institute for Energy Analysis, Oak Ridge Associated Universities, Oak Ridge, Tenn., U.S.A. In G. Marland et al. (1989), Estimates of CO2 emissions from fossil fuel burning and cement manufacturing based on the United Nations energy statistics and the U.S. Bureau of Mines cement manufacturing data. ORNL/CDIAC-25, NDP030. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.
Helmuth, R. A., F. M. Miller, T. R. O'Connor, and N. R. Greening. 1979. pp. 163-93. In Encyclopedia of Chemical Technology. Vol. 5. John Wiley and Sons, New York, U.S.A.
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Keeling, C. D. 1973. Industrial production of carbon dioxide from fossil fuels and limestone. Tellus 25:174-98.
Keeling, C. D., and T. P. Whorf. 1994. Atmospheric CO2 records from sites in the SIO air sampling network. pp. 16-26. In T. A. Boden, D. P. Kaiser, R. J. Sepanski, and F. W. Stoss (eds.), Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.
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Marland, G., R. J. Andres, and T. Boden. 1994a. Magnitude and trends of CO2 emissions. pp. 215-26. In C. V. Mathai and G. Stensland (eds.), Global Climate Change Science, Policy, and Mitigation Strategies, Proceedings of the Air & Waste Management Association International Specialty Conference, Phoenix, Arizona, U.S.A., April 5-8, 1994.
Marland, G., R. J. Andres, and T. Boden. 1994b. Global, regional, and national CO2 emissions. pp. 505-84. In T. A. Boden, D. P. Kaiser, R. J. Sepanski, and F. W. Stoss (eds.), Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A.
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