Research Features

Forcing Agents Underlying Climate Change: Page 8 of 11

Submitted Testmony: 6. Alternative Scenario: Carbon Dioxide

Figure 8
Fig. 8: Annual emissions of CO2 from fossil fuels in the United States (principal data source: Oak Ridge National Laboratory, Department of Energy)
Figure 9
Fig. 9: Annual emissions of CO2 from fossil fuels in the world (principal data source: Oak Ridge National Laboratory, Department of Energy)

CO2 is the largest single human-made climate forcing agent today, and its proportion of the total human-made climate forcing can be anticipated to increase in the future. It is not practical to stop the growth of atmospheric CO2 in the next several decades. However, it is possible to slow the growth rate of CO2 emissions via actions that make good economic and strategic sense

Scenarios for CO2 are commonly constructed by making assumptions about population growth, standard of living increases, fuel choices, and technology. This procedure yields a huge range of possibilities with little guidance as to what is likely. An alternative approach is to examine historical and current rates of change of CO2 emissions, estimate the changes that are needed to keep the climate change moderate, and consider actions that could produce such rates of change. That is the procedure we explore here

Fossil-fuel CO2 emissions. Figures 8 and 9 show U.S. and global CO2 emissions. Emissions in the U.S. grew faster in the 1800s than in the rest of the world, as the U.S. itself was still growing and had rapid immigration. Growth of U.S. emissions was slower than in the rest of the world during the second half of the 20th century, when other parts of the world were industrializing

The important period for the present discussion is the past 25 years, and the past decade. The U.S. growth rate was 1%/year over the past 25 years, as we largely succeeded in decoupling economic and energy use growth rates. The global growth rate was moderately higher, 1.4%, as there was faster growth in developing nations. However, in the past decade the growth rate of U.S. CO2 emissions has been higher than in the world as a whole (1%/year in the U.S. vs. 0.6%/year in the world)


Figure 10 provides a useful summary. The U.S. portion of global fossil fuel CO2 emissions increased from 10% in 1850 to 50% in 1920. Since then the U.S. portion has declined to 23% as other parts of the world industrialized. The temporary spike beginning in 1940 is associated with World War II, including vigorous exertion of U.S. industry

Figure 10
Fig. 10: Percentage of world fossil-fuel CO2 emissions produced in the United States.
to supply the war effort. In the 1990s the U.S. portion of global emissions increased, despite oratory about possible climate change and expectations that the developing world would be the source of increasing emissions

Growth rate required for "alternative scenario". A small change in the CO2 emissions growth rate yields large changes in emissions several decades in the future. A 1%/year growth yields a 64% growth of emissions in 50 years, compared with constant emissions (0%/year growth rate). A growth rate of>

-0.5%/year yields a -22% change of emissions in 50 years. Thus CO2 emissions in 50 years are more than twice as large in a 1%/year scenario than in a -0.5%/year scenario

Incomplete understanding of the EarthÝs "carbon cycle" creates some uncertainty, but to a good approximation the increase in atmospheric CO2 is commensurate with the CO2 emission rate. Therefore full achievement of the "alternative scenario" probably requires the global CO2 emissions growth rate to be approximately zero or slightly negative over the next 50 years

Even if the United States achieves a zero or slightly negative growth rate for CO2 emissions, there is no guarantee that the rest of the world will follow suit. However, the economic and strategic advantages of a more energy efficient economy are sufficient to make this path attractive to most countries. It is likely that the shape of the U.S. and global CO2 emissions curves will continue to be fundamentally congruent. In any case, any strategy for achieving a climate change "soft landing", whether pursued unilaterally or otherwise, surely requires that the downward change in the U.S. CO2 emission growth rates be at least comparable to the change needed in the global average. There are many reasons for the United States to aggressively pursue the technology needed to achieve reduced CO2 emissions, including potential economic benefit and reduced dependence on foreign energy sources

It is not our task to suggest specific policies. However, we must make the case that there are options for achieving the slower CO2 growth rate. Otherwise the alternative scenario is not viable

In the short-term, a case can be made that pent-up slack in energy efficiency (14), if pursued aggressively, can help achieve a zero or slightly negative CO2 emissions growth rate. Renewable energy sources, even though their output is relatively small, also can contribute to slowing the growth rate of emissions. There has been resistance of some industries to higher efficiency requirements. In that regard, the experience with chlorofluorocarbons is worth noting. Chemical manufacturers initially fought restrictions on CFC production, but once they changed their position and aggressively pursued alternatives they made more profits than ever. Similarly, if substantially improved efficiencies are developed (for air conditioners, appliances, etc.), such that there is a significant gap between operating costs of installed infrastructure and available technologies, that could facilitate increased turnover. Perhaps government or utility actions to encourage turnover also might be considered. Corporations will eventually reap large profits from clean air technologies, energy efficiency, and alternative energies, so it is important for our industry to establish a leadership position

In the long-term, many energy analysts believe it is unlikely that energy efficiency and alternative energy sources can long sustain a global downtrend in CO2 emissions. Lovins (15) argues otherwise, pointing out the cost competitiveness of efficient energy end-use, gas-fired cogeneration and trigeneration at diverse scales, wind power and other renewable sources. Certainly it makes sense to give priority to extracting the full potential from efficiency and renewable energy sources. Holdren (16) concludes that meeting the energy challenge requires that we maximize the capabilities and minimize the liabilities in the full array of energy options

Many (my impression is, most) energy analysts believe that the requirement of a flat-to-downward trend of CO2 emissions probably would require increasing penetration of a major energy source that produces little or no CO2. Our task is only to argue that such possibilities exist. It will be up to the public, through their representatives, to weigh their benefits and liabilities. We mention three possibilities

  1. Nuclear power: if its liabilities, including high cost and public concern about safety, waste disposal and nuclear weapons proliferation, can be overcome, it could provide a major no-CO2 energy source. Advocates argue that a promising new generation of reactors is on the verge of overcoming these obstacles (17). There does not seem to be agreement on its potential cost competitiveness.
  2. Clean coal: improved energy efficiency and better scrubbing of particulate emissions present an argument for replacing old coal-fired power plants with modern designs. However, CO2 emissions are still high, so an increasing long-term role for coal depends on development of the "zero emissions" plant, which involves CO2 capture and sequestration (18).
  3. Others: Oppenheimer and Boyle (19) suggest that solar power, which contributes very little of our power at present, could become a significant contributor if it were used to generate hydrogen. The hydrogen can be used to generate electricity in a fuel cell. Of course the other energy sources can also be used to generate hydrogen.

In Holdren's (16) words: there are no silver bullets (in the array of energy options) nor are there any that we can be confident that we can do without. This suggests the need for balanced, increased public and private investment in research and development, including investments in generic technologies at the interface between energy supply and end use (20). The conclusion relevant to the alternative scenario is that, for the long-term, there are a number of possibilities for energy sources that produce no CO2

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