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emissions were zero, the world would still be at 1990 levels and rising rapidly. Even if you add all of the currently developed economies of the world, that is, the OECD countries, you would still by the year 2025 find that even if their emissions were zero the rest of the world emissions would have come up to 1990 levels and would soon go through that level.
And, while the dates at which these events occur may vary depending upon the scenario, the thrust is quite clear: that neither the United States alone nor even the United States plus other OECD members can long control the emissions of fossil fuel carbon dioxide to the Earth's atmosphere.
The final point is that coal is the largest potential source of fossil fuel emissions currently in use, and you can see these are stocks of carbon. That is, in fossil fuels you see the resource base of fossil fuels. These are in pentagrams of carbon, or gigatons, or billions of metric tons—all those things mean the same thing. You can see the atmosphere contains about 740 pentagrams of carbon; that all of the aboveground biosphere contains about 560 pentagrams of carbon; oil and gas together, roughly 300 pentagrams of carbon; and coal, 8,000.
So, even though current releases of fossil fuel carbon to the atmosphere are dominated by oil, which accounts for more than 40 percent of the world's fossil fuel carbon emissions, which is roughly equivalent to coal's contribution globally today, that ultimately it is the coal resource base, which means that there is no natural bound on anthropogenic release of carbon to the atmosphere.
Thank you, Mr. Chairman. I would be pleased to answer any questions.
Mr. SHARP. Thank you very much.
GLOBAL CLIMATE CHANGE
Thank you, Mr. Chairman and members of the subcommittee, for this opportunity to offer testimony on Global Climate Change with particular reference to present and potential future emissions. I would like to discuss two key issues:
1. Current Emissions--including the full array of greenhouse gases, and the relative contribution
and intensity of United States emissions; and
2. Emissions Forecasts--including the range of forecasts, changing role of the United States
contribution, and key assumptions which drive estimates.
I will begin by offering some general information on greenhouse gases and human activities and then move to the two topics enumerated above.
GREENHOUSE GASES AND HUMAN ACTIVITIES
Greenhouse gases are transparent to incoming solar radiation but absorb and re-radiate energy in the infrared spectrum that would otherwise return to space. This characteristic is responsible for the approximately 58°F average global surface temperature. Greenhouse gases include those which occur naturally: water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3), as well as anthropogenic gases such as the chlorofluorocarbons (CFCs) including CFCl, and CF2Cl2. Other gases can affect the concentrations of greenhouse gases through atmospheric chemistry reactions. Such gases include carbon monoxide (CO) and nitrogen oxides (NO and NO2, referred to as NO). Sulphur-containing gases such as sulphur dioxide (SO2) also affect surface temperature when transformed into sulphur aerosol particles which reflect incoming sunlight back to space, affect the concentration of Oz, and possibly increase cloudiness. To describe the set of all gases important to determining global warming we will use the term radiatively important gases (RIGs), regardless of whether the gas is itself a greenhouse gas or whether it simply affects the concentration of another gas that is a greenhouse gas.
Human activities affect the concentrations of many RIGs, including CO2, CH4, CO, N,O, NOx, SO2, and all CFCs (whose only source is chemical manufacture). The release rates for human activities vary from gas to gas, Table 1.
While greenhouse and greenhouse-related gases all affect the Earth's energy balance, they are different in many regards. Greenhouse gases are emitted at greatly differing rates and have different effects on the Earth's energy balance and thereby the rate of global climate change. There is no single common metric for comparing emissions between gases. Scientists have struggled with the problem of creating a set of weights capable of comparing different RIGs. The basic idea of such numbers is to provide a measure of the damage over a period of time that might be caused by the release of an additional kilogram of each gas. Global warming potential (GWP) coefficients were developed by the International Panel on Climate Change (IPCC) and reported in IPCC (1990). These coefficients measured cumulative change in radiative forcing, over a specific period of time (20, 100, and 500 years), for one kilogram of each gas released, as compared to the effect of a one kilogram release of CO2. IPCC (1990) published values for both direct and indirect effects.
Sources: IPCC (1992) Table A3.11 for emissions; IPCC (1992) Table A1.3 for CHĄ,
Note: See appendix for explanation of units. There is no comparable ratio of
Further study of GWP calculations revealed that (i) errors were made in initial calculations, (ii) background emissions assumptions over the course of the integration period were important, especially for CO2, and (iii) the problem of measuring the indirect effect of different gases was much more difficult than initially thought. As a consequence the IPCC prepared a major revision of GWP coefficients for IPCC (1992). In this volume IPCC reports only direct effects by greenhouse gases and only the sign of indirect effects. No calculation was made for sulphur emissions. Table 2 indicates the relative contribution to total GWP-weighted emissions of three major greenhouse gases and the CFCs plus other ozone-depleting substances (ODSs) as a group.
Because indirect effects, through atmospheric chemistry, for non-CO2 emissions are not included, the relative contribution of CO2 is overestimated. Several important gases are not considered, and the indirect effect of CH, on global warming is non-trivial.? Furthermore, there were several systematic biases in the calculation of the GWP coefficients identified in IPCC (1992) which also lead to overestimation of the impact of CO2 emissions. Nevertheless, it seems safe to conclude that, with regard to effect on atmospheric radiation balance, the single most important anthropogenic emission is CO2
Since the most important anthropogenic emission is CO2 and the single most important source of CO2 emissions is fossil fuel combustion, this section discusses first fossil fuel carbon emissions, then the other major source of CO2 emissions, land-use change. In the remainder of the section, we discuss emissions of other gases in turn.
Fossil Fuel Carbon: Global rates of fossil fuel carbon emissions plus CO2 emissions from cement manufacture have been estimated to be 6.1 PgC/yr for the year 1990 (Marland and Boden, 1992). Table 3 shows that of this total, approximately 1.3 PgC/yr were emitted by the United States, which is the largest single national emitter in the world, accounting for 21% of the global total. This fraction has declined from the post-World War II share of 40%. During the period 1945 through 1979 the rate of CO2 emissions from fossil fuel use grew at 4.5%/yr. Emissions declined from 1979 until 1983, but have risen subsequently. The United States, former Soviet Union, and China account for half of the world's fossil fuel CO2 emissions. Since the dissociation of the Soviet Union, China has become the second largest national emitter, slightly surpassing Russia in 1990.
The dominant source of carbon emissions is fossil fuel use (6.0 PgC/yr), with cement manufacture accounting for only 0.15 PgC/yr of the 1990 global total. Emissions from liquids and solids are of approximately equal increments, 40%. Natural gas accounts for 16% of the 1990 total, while gas flaring and cement make up the remaining 4%.
All of the non-CO, greenhouse gases contribute to global warming through their own presence and by causing other greenhouse gases, such as 03, to become more abundant. For some gases, such as CO, this is the only pathway through which they affect global warming. By ignoring these effects, they are implicitly assigned a value of zero. Thus, the global warming potential of CO2 is made to appear greater than it is in fact.
Carbon content varies by fuel. Of fossil fuels, natural gas is lowest (13.7 TgC/EJ); coal is highest (23.8 TgC/EJ); and oil falls between the two (19.2 TgC/EJ). The mining of oil shales in carbonate rock formations would add an additional stream of CO2 to the atmosphere; the magnitude of this stream depends on the grade of the resource and the technology employed to extract it. The transformation of primary fossil fuel energy, as for example from coal to electricity or from coal to synoil or syngas, releases carbon in the conversion process. Energy technologies such as hydroelectric power, nuclear power, solar energy, and conservation (including energy efficiency improvements) emit no CO2 directly to the atmosphere. Traditional biomass fuels, such as crop residues and dung, release CO2 to the atmosphere, but are in a balanced cycle of absorption and respiration whose time frame is short. The use of other biomass fuels such as firewood may provide either a net annual source cr sink for carbon depending upon whether the underlying biomass stock is growing or being exhausted. Improvements in the efficiency of energy conversion technologies reduce the rate of emission of greenhouse gases per unit energy service provided.
Land-Use Change: There are approximately 560 PgC in the form of terrestrial biomass, principally stored in forests. This is estimated to be about 15-20% (=120 PgC) less than was present in the mid-nineteenth century. On a global basis, this is estimated to vary less than about 10 PgC through the seasons as leaves and grasses grow and die. Northern and Southern Hemispheric cycles are temporally reversed.
Knowledge of the net annual emissions of carbon from land-use changes is far less certain than emissions estimates for fossil fuel use. Emissions of net annual CO2 release from land-use changes have been estimated for the year 1980 by various researchers. Net release is calculated as the difference between annual gross harvests of biomass, plus releases of carbon from soils, less biomass carbon whose oxidation is long delayed (e.g., stored in forest products such as telephone poles, furniture, and housing) and additions to the stock of standing biomass. The IPCC (1990) global estimates 1980 carbon emissions from land-use change to be 0.6 to 2.6 PgC/yr. This range is only slightly narrower than that given by Trabalka (1985), 0.0 to 3 PgC/yr.