AGGREGATION ISSUES

Because of the importance of aggregation issues, both for data definition and for calculation of impacts, this topic will be dealt with in some detail. There are at least four dimensions of aggregation that play a role in impact assessments:

— Aggregation over technologies,

— A g g r e g a t i o n o v e r s i t e s ,

— Aggregation over time,

— Aggregation over social settings.

The most disaggregated studies done today are termed 'bottom-up' studies of a specific technology located at a specific site. Since the impacts will continue over the lifetime of the installation and possibly longer (radioactive contamination), there is certainly an aggregation over time involved in stating the impacts in compact form.

The better studies attempt to display impacts as a function of time, e.g. as short, medium and long term effects. However, even this approach may not catch important concerns, as it will typically aggregate over social settings, assuming them to be inert as a function of time. This is of course never the case in reality and, in recent centu-ries, the development of societies with time has been very rapid, entailing also rapid changes in social perceptions of a given impact. For example, the importance presently accorded to environmental damage was absent just a few decades ago, and there are bound to be issues about which society will be concerned over the next decades, but which currently are just considered as marginal by wide sections of society.

The item of aggregation over social settings also has a precise meaning at a given instance. For example, the impacts of a nuclear accident will greatly depend upon the response of the society. Will there be heroic firemen, as in Chernobyl, who will sacrifice their own lives in order to diminish the consequences of the accident?

Was the population properly informed about what to do in the case of an accident (going indoors, closing and opening windows at appropriate times, etc.)? Were there drills of evacuation procedures? The answers to these questions are " n o " for Russia and " y e s " for Sweden. A study making assumptions on accident mitigation effects must be in accordance with the make-up of the society for which the analysis is being performed.

Aggregation over sites implies that peculiarities in topography (leading perhaps to irregular dispersal of airborne pollutants) are not considered and that variations in population density around the energy installation studied will be

dis-regarded. This may be a sensible approach in the planning phase, where the actual location of the installation may not have been selected. It also gives more weight to the technologies themselves, making this approach suitable for generic planning choices between classes of technology (e.g. nuclear, fossil, renewable). Of course, once actual installations are to be built, new, site specific analyses may be invoked in order to determine the best location.

Aggregation over technologies would in most cases not make sense. However, in the particular case of assessing the existing stock of, for example, power plants in a region, something like technology aggregation may play a role. For example, one might use average technology for the impact analysis, rather than performing multiple calculations for specific installations involving both the most advanced tech-nology and the most outdated techtech-nology.

In a strict sense, aggregation is never allowed, because the impacts that play a role never depend linearly or in simple ways on assumptions of technology, topography, population distribution, and so on. One should in principle treat all installations individually and make the desired averages on the basis of the actual data. This may sound obvious, but it is also unachievable because only for some issues can the actual situations underlying the averages be addressed. As regards the preferences and concerns of future societies, or the future impacts of current releases (such as climate impacts), one will always have to do some indirect analysis, involving aggregation and assumptions on future societies (using, for example, the scenario method).

It can be concluded that some aggregation is always required, but that the level of aggregation must depend on the purpose of the assessment. The following pur-poses for impact assessments currently performed can be discerned:

— Licensing of particular installations,

— Energy system assessment,

— Energy planning and policy.

For licensing of a particular installation along a fuel chain or for a renewable energy system, clearly a site and technology specific analysis has to be performed, making use of actual data for physical pathways and populations at risk (as well as corresponding data for impacts on ecosystems, etc.). For the assessment of a particular energy system, the full chain — mining or extraction, refining, further treatment, transportation to and use in power plants, followed by transmission and final use — must be considered, and each step would typically involve different loca-tions. A complication in this respect is that, e.g. for a fuel based system, it is highly probable that, over the lifetime of the installation, fuel would be purchased from different vendors, and the fuel would often come from many geographical areas with widely differing extraction methods and impacts (e.g. Middle East versus North Sea oil or gas, German or Bolivian coal mines, open pit coal extraction in Australia, and so on). Future prices and environmental regulations will determine the change in fuel

mix over the lifetime of the installation, and any specific assumptions may turn out to be invalid.

For the planning type of assessment, it would be normal in most industrialized nations to consider only state of the art technology, although even in some advanced countries there is a reluctance to apply the available environmental cleaning options (currently for particle, S 02 and NOx emissions; in the future probably also for C 02

sequestering or other removal of greenhouse gases). In developing countries, there is a tendency to ignore available but costly options of environmental impact mitiga-tion. In some cases, the level of sophistication selected for a given technology depends on the intended site (e.g. near to or away from population centres). Another issue is maintenance policies. The lifetime of a given installation depends sensitively on the willingness to spend money on maintenance, and the level of spending opted for is a matter to be considered in the planning decisions.

Some of the issues involved [1] are listed below:

Technology and organization

— Type and scale of technology;

— Age of technology;

— Maintenance state and policy;

— Matching technology with the level of skills available;

— Management and control setup.

Natural setting

— Topography, vegetation, location of waterways, groundwater tables, etc.;

— Climatic regime: temperature, solar radiation, wind conditions, currents (if applicable), cloud cover, precipitation patterns, air stability, atmospheric particle content.

Social setting

— Scale and diversity of society;

— Development stage and goals;

— Types of Government, institutions and infrastructure.

Human setting

— Values and attitudes, goals of individuals;

— Level of participation, level of decentralization of decision making.

Impact assessments suitable for addressing these issues involve the con-struction of scenarios for future societies, in order to have a reference frame for discussion of social impacts. Because the scenario method is normative, it would in most cases be best to consider more than one scenario, covering important positions in the social debate of the society in question.

Another issue is the emergence of new technologies that may play a role over the planning period considered. Most scenarios for future societies do involve some assumption of new technologies coming into place, according to current research and development. However, the actual development is likely to involve new technologies that were not anticipated at the time of making the assessment. It is possible to analyse scenarios for sensitivity to such new technologies and sensitivity to possible errors in other scenario assumptions. This makes it possible to distinguish between those future scenarios which are resilient, i.e. those which do not become totally invalidated by changes in assumptions, and those which depend strongly on the assumptions made. In the case of energy technologies, it is equally important to consider the uncertainty of demand assumptions and assumptions on supply technolo-gies. The demand may vary according to social preferences and according to the emergence of new end use technologies that may provide better services with less energy input. It is therefore essential to consider the entire energy chain, not just to the energy delivered, but all the way to the service derived. No one demands energy, but people demand transportation, air conditioning, computing, entertainment, and so on.

The discussion of aggregation issues clearly points to the dilemma of impact analyses: Those answers that would be most useful in the political context are often answers that can be given only with large uncertainty. This places the final responsi-bility in the hands of the political decision maker, who has to weigh the impacts associated with different solutions and in that process to take into account uncertain-ties (e.g. choosing a more expensive solution because it has less uncertainty). But this is of course what decision making is about!