The concept of chain of causalities

With the aim to use a systemic approach to environmental issues, encompassing all the environmental impacts and all the potential objectives of an environmental policy, we propose to enlarge the pressure-state-impact structure or the midpoint / endpoint structure to the concept of process or chain of causalities between a cause and a final impact, with possibly a succession of coupled cause-impact. A good example is the greenhouse effect with greenhouse gas emissions (GHG) as a first cause, which by physical phenomenon increases the infrared radiative forcing, which increases the average earth temperature, which modifies the global and local climates, then with impacts on the agriculture, sea level, with final impacts on all the biocenosis including the humans. If an initial pressure can be easily detected (GHG emissions), there are afterwards a lot of intermediate states and impacts.

Another advantage of the concept of process or chain of causalities is to be much wider than a stock or flow problem inspired by physics: any process can be taken into account, as cultural, psychological, psycho-physical, biological effect, and of course physical.

The concept of chain of causality is one option to interpret the concept of 'environmental mechanism' defined within Life cycle impact assessment framework by a 'system of physical, chemical and biological processes for a given impact category, linking the life cycle inventory analysis results to category indicators and to category endpoints' (ISO 14040, 2006: see section 6.2.2.2).

The chains of causalities have to describe all the impacts on the environment, but at the same time to avoid redundancy: a same process should not be part of two chains. For instance, if we consider the chain "odours" or a chain "health effects of photochemical pollution" (chains resp. 9 and 13 described in Annex 6), we can not consider a chain "health effects of air pollution", because the well-being is part of health as defined by the WHO and because photochemical pollution is part of air pollution. It the reason why we defined a chain called "direct restricted effects on human health of air pollutants" (chain 11): "Direct" excludes secondary pollutants, and "restricted"

excludes well-being.

A chain of causalities can be described through:

• The element(s) of a field of human activity (the transport system or any other sector), which is at the beginning of the process, taking into account a life cycle perspective, i.e. considering all the processes needed for the considered activity all over its life cycle. When considering only the environmental impacts of the system under study (and not the economic or social effects), life cycle assessment or LCA follows typically this approach.

LCA is a process to evaluate the environmental burdens associated with a

product system or activity, by identifying and quantitatively describing the energy and materials used, and wastes released to the environment, and to assess the impacts of those energy and material uses and releases to the environment. The assessment includes the entire life cycle of the product or activity, encompassing extracting and processing raw materials, manufacturing, distribution, use, re-use, maintenance, recycling and final disposal, and all transport involved. LCA addresses environmental impacts of the system under study in the areas of ecological systems, human health and resource depletion (Fullana et al., 2009; see section 6.2.2).

Transport consists of three main subsystems, including infrastructure, energy used, and vehicle. For each of them there are five types of activities, including production, existence, use, maintenance, and destruction. All together, there are 13 subsystems-activities, as the use of the infrastructure, final energy and vehicle is considered common to the three subsystems (i.e. the traffic): See Table 9. The 13 subsystems can be simplified into four, as coloured in Table 9 and used in Annex 5, by considering the three main subsystems but extracting the traffic. These transport subsystems do not cover all the materials used as made within the Life cycle approach, but the main ones. Thus the elements in the table are not necessarily absolute or final in this form, but provide an overview of the main elements at the source of the impacts on the environment.

Table 9. Typology of the main transport subsystems Building (1) Final electricity Traffic = infrastructure - final energy - vehicle use (13)

• The final targets: Goger (2006a) and Goger and Joumard (2007) consider three targets (nature, humans, man-made heritage) and a pseudo-target, the earth. In addition the Eco-indicator approach (Brand et al., 1998;

Goedkoop and Spriemsma, 2001) includes three types of endpoint damages: resources, ecosystem quality, and human health. The two first are subdivisions of the target "nature". The (human) health is defined by World Health Organisation (WHO, 1946) as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity". Therefore it is useful to distinguish health in a restricted meaning (absence of disease or infirmity) and the complement so-called human well-being, because the processes are often very different. Finally we get the target structure presented Table 10, with six targets: the resources, the

ecosystems (both together the nature), the human health in a restricted meaning, the human well-being (both together the humans or the human health as defined by WHO), the man-made heritage, and the earth.

• The in-between elements, i.e. the chain of causalities between the human activity (as the transport system) and the final targets, to be described in detail. To design impact indicators, it is important to know the scientific milieu able to understand the process, and therefore to give the scientific disciplines involved. We propose a first and simple science structure:

physics, chemistry, biology, psychology / sociology. This structure corresponds to the general university scheme, where the environment issues are usually treated per discipline, in worlds coming close but ignoring each other most of the time: world of the physico-chemists (photochemical smog), world of atmosphere physicists (greenhouse), world of biologists (health impacts), world of engineers and energy specialists (emissions), world of psychologists (sensitive pollution, annoyance), limited world of sociologists or environment historians, etc. It is important also to know if the process is linear or not, and if the human activity characteristics are major or minor explanation parameters, in order to know how these characteristics can be used for indicator building. Finally the reversibility is a major parameter from the sustainability point of view (see section 2.2.5), where we have to distinguish the reversibility for individuals and for species: The accidents have irreversible impacts for the humans who die, but for the society it is a reversible impact. The distance and time scales indicate who is concerned, if it is a local or global, short, medium or long term impact.

Table 10. Typology of the targets of the impacts on the environment

Targets Pseudo-target

health as defined by the WHO Human well-being Man-made heritage

With a distinction is made between common and historic buildings

Earth

The concept of chain of causalities allows us also to give a precise definition to the expressions 'environmental impact' or 'impact on the environment'. The environment is defined by the targets (Table 10): the humans, the nature and the man-made heritage. Any modification of these targets due to one of the transport subsystems presented Table 9 is an environmental impact due to transport.

A chain of causalities can thus be defined as an "homogeneous process between the transport system and a final target of the impacts on the environment".