ingredient of increased economic prosperity around the world. To the extent that U.S. energy R&D can contribute to this end, it will be building potential markets for all of the products that the United States might like to export.

ENVIRONMENTAL CHALLENGES IN OUR ENERGY FUTURE

Energy is perhaps the most intractable part of the planet's environmental problems, both because the impacts of energy systems are the dominant drivers of many of the most troublesome environmental problems at every geographic scale from the local to the global and because the energy-system characteristics that cause these problems are often costly and time-consuming to change. Environmental concerns, similarly, may well prove to be the heart of the energy problem, in the sense that environmental constraints and the costs of coping with them, much more than resource scarcity or the monetary costs of energy technology other than those arising from environmental considerations, may turn out to be the most important considerations in society's choices about how much energy should be supplied from what

sources.

At the local level, the most pervasive and difficult environmental problems include acute air pollution, both in the outdoor environment of the world's cities (to which problem the hydrocarbons and particulates emitted in burning fossil and biomass fuels are invariably major contributors, albeit not the only ones) and in the indoor environment of poorly ventilated dwellings in both the urban and rural sectors of developing countries (where coal, fuelwood, charcoal, crop wastes, and dung are burned for heating and cooking). The latter problem is, in light of the combination of extremely high pollutant concentrations and large numbers of women and children exposed to them during a high proportion of the hours of the day, quite clearly an even more consequential problem for global public health than is the outdoor air-pollution problem. Among the world's many local water-pollution problems, those produced by coal-mine drainage, oil-refinery emissions, oil spills from pipelines and tankers, and leakage into groundwater from underground fuel-storage tanks (this last problem one of the most pervasive contributors to putting toxicwaste sites on the Superfund list) are prominent contributions from the energy sector.

Energy-related environmental problems at the regional level include air-basin-wide smogs from the interaction of hydrocarbons and nitrogen oxides and acidic hazes and fogs fed by varying combinations of nitrogen and sulfur oxides. The associated hazards include damage to crops and forests as well as to public health; the culprits are mainly fossil fuels burned in vehicles and power plants. Emissions of oxides of nitrogen and sulfur are also the primary sources of acid precipitation, arguably the dominant form of regional water and soil pollution in areas where soils and surface waters are poorly buffered (a description that applies to tens of millions of square kilometers of the world's land area), with potential impacts on forest health, fish and amphibian populations, nutrient cycling, and mobilization and uptake of toxic trace metals.

At the global level, the emission of heat-trapping carbon dioxide gas from fossil fuel combustion is the largest contributor to the possibility that amplification of the atmosphere's "greenhouse effect" by human activities will significantly change the global climate. (Other important contributors to the buildup of GHGs include carbon dioxide added to the atmosphere by deforestation; methane emanating from agriculture, waste disposal, and fossil fuel production and use; nitrous oxide from agriculture and industrial processes; halocarbons from a variety of industrial processes and products; and tropospheric ozone resulting mainly from emissions of carbon monoxide, nitrogen oxides, and various hydrocarbon compounds.)

*Smith (1987,1993).

The evidence is compelling that the global composition of the atmosphere with respect to these heat-trapping gases has already been significantly influenced by human activities, but there has been uncertainty and controversy about whether the imprint of GHG-induced climate change is already discernible in the complex patterns of global temperature, precipitation, cloudiness, oceanic circulation, and so on, all of which are subject to substantial natural variability (which is visible in both the recent and the geologic record). Considerable uncertainty and controversy have also surrounded estimates of the pace at which climatic change will become more pronounced as GHG concentrations continue to grow and about the magnitude and geographic distribution of the physical, ecological, and human consequences.

In the face of growing concerns and continuing controversies about the potential magnitude of this problem and what to do about it, the World Meteorological Organization and the United Nations Environment Programme jointly established, in 1988, the Intergovernmental Panel on Climate Change (IPCC), with a mandate to “(i) assess available scientific information on climate change, (ii) assess the environmental and socioeconomic impacts of climate change, and (iii) formulate response strategies." The First Assessment Report of the IPCC was completed in August 1990 and served as the principal technical input to the negotiation of the United Nations Framework Convention on Climate Change, which was completed at the 1992 Earth Summit in Rio de Janeiro. The Framework Convention, which was signed in Rio by President George Bush and came into force in March 1994, after ratification by 164 nations (including ratification by the United States Senate), included a commitment by the industrialized countries to seek to reduce their emissions of carbon dioxide and other GHGs to 1990 levels by the year 2000. The Framework Convention is described in more detail in Box 1.1.

The IPCC followed up its 1990 "First Assessment" with supplemental assessments in 1992 and 1994 and a major "Second Assessment" completed in 1995 and published in 1996. (Altogether some 2,000 scientists and other specialists from more than 40 countries have served as authors and reviewers of the 17 volumes of exposition and analysis issued by the IPCC through 1996.) Among the principal findings of the 1995 assessment were that:

"the balance of evidence suggests a discernible human influence on global climate";

· the increase in mean global surface air temperature between 1990 and 2100 under a mid-range emissions scenario would probably fall between 2.2 and 6.5 degrees Fahrenheit;

• "regional temperature changes could differ substantially from the global mean value”;

· the warmer temperatures will lead to an increase in sea level (with a “best estimate" for the mid-range scenario of about one-and-a-half feet by 2100, continuing to increase thereafter), an "increase in the occurrence of extremely hot days and a decrease in the occurrence of extremely cold days”, and “a more vigorous hydrological cycle";

"climate change is likely to have wide-ranging and mostly adverse impacts on human health, with significant loss of life";

"boreal forests are likely to undergo irregular and large-scale losses of living trees because of the impacts of projected climate change";

See IPCC (1990,1992, 1994, 1996).

agricultural productivity "is projected to increase in some areas and decrease in others, especially the tropics and subtropics"; and

"climate change and the resulting sea-level rise can have a number of negative impacts on energy, industry, and transportation infrastructure; human settlements; the property insurance industry; tourism; and cultural systems and values".

The 1995 Assessment also emphasized that many uncertainties remain and called particular attention to the possibility of "surprises" arising from the nonlinear nature of the climate system. And it presented further analyses indicating, as previous IPCC assessments and the work of others have also done, that rapid reductions in the rate of increase of GHG concentrations in the atmosphere will be very difficult to achieve. This is because of the upward pressure of population growth and economic aspirations on energy demand, the large energy contribution and long turnover time (years to decades) of the fossil fuelburning equipment that produces the largest GHG emissions, and the long residence times of these gases (decades to centuries) in the atmosphere. (See Box 1.2.)

Box 1.1: The UN Framework Convention on Climate Change

The United Nations Framework Convention on Climate Change (UNFCCC) is the first binding, international legal instrument that deals directly with the threat of climate change. Since its enactment at the 1992 "Earth Summit" in Rio de Janeiro, the Convention has been signed by the United States and 164 other nations (plus the European Union). It came into force on 21 March 1994.

Signatory countries have agreed to take action to realize the goal outlined in Article 2 of the Convention, namely the "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system." To achieve this, all Parties to the Convention, both developed and developing, are committed under Article 4 to adopt national programs for mitigating climate change; to promote the sustainable management and conservation of GHG "sinks" (such as forests); to develop adaptation strategies; to take climate change into account when setting relevant social, economic, and environmental policies; to cooperate in technical, scientific, and educational matters; and to promote scientific research and exchange of information.

The UNFCCC also establishes more specific obligations for developed countries, which have agreed to seek to reduce their emissions of carbon dioxide and other greenhouse gases to 1990 levels by the year 2000. The OECD countries, in particular, are also committed to facilitate the transfer of financial and technological resources to developing countries, beyond that already available through existing development assistance. The Convention requires developed countries to take the lead in adopting measures to combat climate change, recognizing that they are mainly responsible for historic and current emissions of GHGs, and that developing countries will need assistance to meet the treaty's obligations.

A Conference of the Parties to the UNFCCC scheduled for Kyoto in December 1997 will attempt to reach agreement on a Protocol to the Convention codifying commitments for reductions in GHG emissions after the year 2000. The position on such reductions that will be taken at the Conference by the United States has not been settled at this writing

SOURCE: UNEP (1997).

Of course, the work of the IPCC to date will not be the last word on the issue of GHG-induced climate change. Some members of the research community think the IPCC's projections of future climate change and its consequences are too pessimistic, while others think they are too optimistic. Some contend that adaptation to climate change would be less difficult and less costly than trying to prevent the change; others argue that a strategy combining prevention and adaptation is likely to be both cheaper and safer than one relying on adaptation alone. Within the PCAST Energy R&D Panel there are significant differences of view on some of these questions.

What is more significant for the purposes of this report, however, is that the Panel is in complete agreement about the implications of the climate-change issue for energy R&D strategy, as follows:

because there is a significant possibility that governments will decide-in light of the perceived risks of GHG-induced climate change and the perceived benefits of a mixed prevention/adaptation strategy that emissions of greenhouse gases from energy systems should be reduced substantially and soon, prudence requires having in place an adequate energy R&D effort designed to expand the array of technological options relevant to accomplishing this at the lowest possible economic, environmental, and social cost;

because of the large role of fossil fuel technologies in the current U.S. and world energy systems, the technical difficulty and cost of modifying them to reduce carbon dioxide emissions, their long turnover times, their economic attractiveness compared to most of the currently available alternatives, and the long times typically required to develop new alternatives to the point of commercialization, this possible GHG-reduction mandate is the most demanding of all of the looming energy challenges in what it requires of national and international energy R&D efforts.

Of course, ameliorating the environmental problems caused by energy supply will be partly a matter, in many circumstances, of putting in place appropriate combinations of incentives and regulations that effectively incorporate environmental costs into the decision-making calculus of energy producers and consumers alike. But improvements in energy technology itself are an essential part of any sensible strategy for addressing environmental problems, providing a means to alleviate the economic burdens and inefficiencies that would be associated with imposition of stringent environmental regulations in the absence of technological advances.

This, then, is the wider environmental challenge to energy R&D: to provide energy options that can substantially ameliorate the local, regional, and global environmental risks and impacts of today's energysupply system, that can do so at affordable costs and without incurring new environmental (or political) risks as serious as those that have been ameliorated, and that are applicable to the needs and contexts of developing countries as well as industrialized ones (and the sooner the better). It is a big order.

Box 1.2: IPCC Emissions Scenarios and Their Implications

According to the IPCC, world emissions of carbon dioxide from fossil fuel burning amounted to about 6 billion metric tons (tonnes) of contained carbon per year in 1990. (It is customary to keep track of the emissions in terms of their carbon content rather than their total mass, in order to facilitate comparisons with other stocks and flows in the global carbon cycle in which the carbon may be in a variety of different chemical compounds.) The emissions of carbon dioxide from tropical deforestation amounted to about 1.5 billion tonnes per year, with an uncertainty of plus or minus a billion tonnes. The IPCC assumes that rates of tropical deforestation will gradually

decline over the next century, thus becoming even smaller in relative importance compared to the fossil fuel CO2 emissions.

Also taken into account in the IPCC analysis and its scenarios for future emissions possibilities are the other anthropogenic GHGs methane, tropospheric ozone, nitrous oxide, and halocarbons and anthropogenic particulate matter in the atmosphere that partly offsets the heat-trapping effect of the GHGs by screening out incoming sunlight. The IPCC found that, as of the mid-1990s, buildups of the non-CO2 GHGs had added about 75 percent to the heat-trapping effect that would have resulted by then from the buildup of CO2 alone; but the IPCC's best estimate of the effect of increasing particle concentrations was that these had approximately cancelled the effect of the increases in non-CO2 GHGs. In the IPCC "medium" scenario designated IS92a, increases in the effects of atmospheric particles over the next 100 years continue to roughly counterbalance the effects of increases in the non-CO, GHGs, so that the net increase in the heat-trapping effect over this period is about what would be expected from the CO2 buildup alone.

The IS92a scenario is based on a World Bank "medium" population forecast in which world population reaches 11.3 billion by the year 2100. The scenario assumes that real economic growth worldwide averages 2.9 percent per year from 1990 to 2025 and 2.0 percent per year from 2025 to 2100. It also assumes that the energy intensity of economic activity (energy per unit of real GDP) declines at 1.0 percent per year from 1990 to 2100 and that the carbon intensity of energy supply (kilograms of carbon emitted in CO2 per unit of energy supplied) decreases at 0.2 percent per year over this whole period. The result is that global carbon emissions increase from 7.4 billion tonnes per year in 1990 to 20 billion tonnes per year in 2100, and the cumulative carbon emissions between 1990 and 2100 amount to about 1500 billion tonnes.

The carbon content of the atmosphere in 2100 under the IPCC IS92a scenario would be some 1500 billion tonnes or about 715 parts per million of CO2 by volume (ppmv), two and a half times the preindustrial level, and still rising steeply. (Only about half of the 1500 billion tonnes of carbon added between 1990 and 2100 would have remained in the atmosphere, the rest having been taken up by the oceans and by vegetation according to the IPCC's carbon-cycle model.) This is the scenario for which the IPCC obtained the surface-temperature and sealevel-rise estimates mentioned in the text. Because of the thermal lag time of the oceans and the continuing melting of polar ice under warmer conditions, the IPCC noted, both temperature and sea level would continue to rise after 2100 even if the growth of atmospheric CO2 were halted at that point.

The magnitude of the challenge of stabilizing the CO2 content of the atmosphere, if society decides to do so, is illustrated in the IPCC 1995 Assessment by presentation of emissions trajectories that would be able to achieve stabilization at several different concentrations ranging from 450 to 1000 ppmv. (The preindustrial concentration was about 280 ppmv; today's is 365 ppmv.) These trajectories can be characterized by the cumulative emissions they entail between 1990 and 2100 (although of course what happens after that also matters). The results can be summarized as follows:

The IPCC's IS92a "medium" scenario, with cumulative emissions of 1500 billion tonnes of carbon between 1990 and 2100 and annual emissions of 20 billion tonnes of carbon per year in 2100, is clearly above even the highest of these stabilization trajectories.