The global energy system poses severe threats to the world's well-being that derive from both large-scale fossil fuel use and nuclear energy, albeit in different ways. Human dependence on fossil fuels and other resources that produce greenhouse gases could lead to catastrophic climate change. Currently, the capacity of the biosphere to absorb carbon dioxide is considerably lower than present emission levels.¹ This is leading to an increase of CO₂ concentration in the atmosphere. Since CO₂ is the main greenhouse gas (see article on global warming), fossil fuel use at anywhere near existing levels and with current technology poses grave risks of global climate change.

Proponents of nuclear energy suggest that the problem of greenhouse gases can be solved by nuclear power because nuclear reactors do not emit carbon dioxide into the atmosphere. However, the high costs and many risks that accompany nuclear power make it no less problematic than large-scale fossil fuel use (see article on nuclear power).

Because governments and corporations have focused almost all of their resources and development on fossil fuels and nuclear energy, transforming the world's economy to a healthy, secure, and sustainable energy system will not be easy. This article will look at the technical aspects of some of the options for reducing greenhouse gas emissions in terms of energy supply -- notably fuel for electricity generation -- and lay out some basic criteria for creating a sustainable energy system.

Criteria for a Sustainable Energy System

To be viable and sustainable, a global energy system must be able to meet simultaneously the following basic criteria:

1. It must be reliable.
2. Its cost should be reasonable.
3. It should not produce routine severe pollution.
4. It should be possible to almost wholly confine the environmental and security costs of the energy system to the generations benefiting from it. In other words the system should be amenable to cost internalization.
5. It should be capable of sustaining reasonable levels of energy services² to eight to ten billion people (the projected population of the world in the next century).
6. Its core functions should be resilient to supply, transportation, transmission, and economic shocks.

Nuclear energy use cannot meet these criteria mainly because of (i) the risk of long-term and widespread damage from Chernobyl-scale accidents and (ii) the risks inherent in the production of vast amounts of nuclear-weapons-usable materials. Fossil fuel use in the present manner and scale cannot meet these criteria mainly because of the risk of catastrophic global climate change. Other problems exist also.

A sound strategy would work toward vastly increasing efficiency over the next several decades and securing a mix of renewable energy sources supplemented by a modest amount of fossil fuels. Fossil fuels do not need to be completely phased out in order to mitigate global warming, since nature has some capacity to absorb anthropogenic carbon dioxide (in addition to natural CO₂ circulation between the atmosphere, water, soil, and biota). The long-term goal should be to keep emissions well below this natural absorption level of roughly three billion metric tons of anthropogenic carbon emissions. However, it should be noted that absorption of these emissions into the oceans, biota, and soil occur in ways that are still not well understood.

It may be possible to use fossil fuels at carbon emission levels greater than the natural absorption capacity of the atmosphere, if ways to prevent CO₂ emissions to the atmosphere can be found. Strategies to trap CO₂, which go by the generic term "sequestration," are varied, and include storing CO₂ in underground reservoirs or pumping it undersea. There are considerable environmental uncertainties associated with such proposals and their costs are high. Given that CO₂ emission must be reduced greatly in the next few decades in a manner compatible with increasing energy services, investments in energy efficiency which accomplish both goals at once, and can do so more economically, are more desirable than sequestration strategies. The policies we discuss here, therefore, are not dependent on the use of sequestration as a measure to reduce CO₂ emissions.

Some Sustainable Options for Reducing Greenhouse Gases

A variety of technologies exist that can help achieve substantial reductions in global greenhouse gas emissions and at the same time promote economic well-being. Wind power, cogeneration, fuel cells, natural gas-assisted solar thermal power plants, and replacing inefficient coal plants with renewable and/or natural gas plants are some of the technical options for maintaining the expanding electric power capability while reducing greenhouse gas emissions. Investments in combinations of these technologies would considerably reduce CO₂ emissions, rather than merely preventing CO₂ emissions, as would be the case with building new nuclear power plants. In fact, the expense of nuclear power would actually preempt investments in technologies more appropriate for achieving goals of reducing carbon dioxide emissions.

The table below shows that natural gas combined-cycle plants are more economical than nuclear power plants in all cases. Combined-cycle plants use a fuel such as natural gas in a two-step electricity generation system (see diagram).

First, the natural gas drives a gas turbine and a generator. Then the hot exhaust gases from the turbine are used to raise steam, which drives a steam turbine. The efficiency of such a system available commercially today is about 50 percent.

Note that China, the main prospective customer for new nuclear power plants, is unlikely to have the highest costs of combined cycle plants because it would use piped gas (from its own onshore and offshore fields as well as Central Asia) and not liquid natural gas (on which all three costs are based). This comparison excludes pessimistic scenarios for nuclear power plant costs, which would be substantially higher than the highest nuclear costs given in the table below.³

Each cent per kWhe difference in costs works out to about $66 million per year in additional electricity costs for nuclear power plants (1,000 MW size). This works out to a present value over a 30 year period (at an annual discount rate of 4 percent) of $1.15 billion for every cent per kWhe difference in electricity costs. (Future costs are discounted, since a dollar saved at a future time is worth less than a dollar in hand today.) Using these figures, one can compare a strategy of using nuclear power plants to displace existing coal-fired power plants with one of using combined-cycle power plants. In the table, we have compared the various cases for combined-cycle versus nuclear: low cost versus low cost, medium versus medium, and high versus high. For a typical case, building combined-cycle plants would result in a reduction of about 40 percent more CO₂ than could be achieved with nuclear (comparison of Case 2 combined cycle with the corresponding nuclear power plant). This gain can be expected to increase since efficiencies of combined cycle plants are increasing.

One could also use the capital cost savings achieved by building combined-cycle plants instead of nuclear to develop and promote solar and wind technologies and to increase energy efficiency. The avoided CO₂ emissions in such cases would vary depending on the sites for the power plants or the specific technologies chosen to increase efficiency. If combined-cycle plants were used to retire half the coal-fired power stations in the world, an overall annual global carbon dioxide emissions reduction of about 15 percent could be achieved.

During the 1970s, there was concern that natural gas was a very scarce resource, but it was not well founded. Gas is a widely available resource, and does not carry the proliferation risks of nuclear power. Our approach is not premised on use of natural gas into the indefinite future, but only on its use in high efficiency applications over the next several decades. This use of natural gas as a transition fuel is a sound economic and environmental strategy. During that time we expect, with appropriate action on the part of governments, corporations, and consumers, that renewable energy sources will take over most of the energy supply in an vastly more efficient economy.

World reserves of natural gas have been steadily rising, and now stand at about 75 years of consumption at 1995 levels (corresponding to reserves of about 5.2* 10²¹ joules in reserves, and an annual utilization of about 7*10¹⁹ joules). Global gas reserves have been steadily increasing, despite increasing consumption. ⁴

Coal fired power stations are located in many parts of the world, including western Europe, the United States, the former Soviet Union, China, India, and eastern Europe. While it is unlikely to be economically feasible to immediately replace coal-fired plants with combined-cycle plants, it is possible to phase out coal-fired plants and replace them over time. In some areas, wind capacity would also provide an effective and economical offset for CO₂ emissions.

One drawback to increased use of natural gas is that natural gas pipelines add to methane emissions due to small leaks in the pipelines. One estimate of such leaks is 0.8 percent of natural gas use. Since methane is a far more powerful greenhouse gas than CO₂, it is necessary to offset these emissions in order to maximize the greenhouse gas reductions that can be obtained from natural gas use. Such offsets can be obtained by relatively simple measures, such as building biogas plants at feedlots, and recovery of methane gas emitted from landfills (now a significant pollutant in many areas) for use as a fuel. Landfill gas is used on a limited basis in many places to produce electricity or fuel for heating. For instance, landfill gas from the Fresh Kills landfill, where the municipal waste from New York City is dumped, provide heating fuel for 14,000 homes.⁵

Energy Efficiency and Renewable Energy Sources

How do we make the transition to an energy system that meets energy needs and is also sustainable and environmentally sound? It is not difficult to postulate some distant future when renewable sources of energy might be economical to meet basic energy needs. But how will we get to that future, especially when solar and wind energy have not yet made substantial contributions to global energy supply after many decades of effort, and when energy efficiency improvement has been halting and far below its potential?

The first thing to note is that neither energy efficiency nor renewable energy sources have had anywhere near the level of research and development effort and investment as fossil fuels or nuclear energy. The failed plutonium breeder reactor technology alone, which is just one part of nuclear fission energy, has had far more resources poured into it than wind and solar energy combined.

Secondly, crucial problems in energy efficiency are not even recognized by policy-makers, much less are they objects of substantial research and development. For instance, developing heat exchangers that are highly efficient, compact, and economical for low temperature heat sources would open up vast new possibilities in energy efficiency. But government funds for the needed basic research are meager and private sector research is generally focused on short-term pay-off technologies.

Third, energy statistics are seriously deficient. For example, large sources of energy, notably biomass for draft animals that provide power for agriculture in much of the world, are not included in compilations of energy data. Also not counted in energy data are the large amounts of natural gas that are considered a waste by-product of oil extraction and are flared or vented. For instance, Shell oil company flares most of the natural gas associated with its oil production in Nigeria.⁶

Transforming the world's energy system will be a huge and difficult task. A large part of the problem arises from the fact that large corporations that have profit as their primary purpose and have made huge investments in fossil fuels and nuclear energy control most energy production, conversion, and distribution. As with the Montreal Protocol that resulted in action to protect the ozone layer, governments will now have to use the Kyoto Protocol to create the regulatory structure and the financial incentives and penalties so as to elicit the desired reductions in greenhouse gas emissions from the marketplace. Firm action at the local, national, regional, and global levels is essential and urgent so as to achieve a change from the present energy system fraught with dangers to an environmentally sustainable one.