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Sustainable development and its implications for chemical engineering Roland Clift Centre for Environmental Strategy, University of Surrey, Guildford, Surrey GU2 7XH, UK Received 4 October 2005; received in revised form 4 October 2005; accepted 11 October 2005

Abstract Sustainable development presents us all with the challenge of living in ways which are compatible with the long-term constraints imposed by the finite carrying capacity of the closed system which is Planet Earth. The chemical engineering approach to the management of complex systems involving material and energy flows will be essential in meeting the challenge. System-based tools for environmental management already embody chemical engineering principles, albeit applied to broader systems than those which chemical engineering conventionally covers. Clean technology is an approach to process selection, design and operation which combines conventional chemical engineering with some of these system-based environmental management tools; it represents an interesting new direction in the application of chemical engineering to develop more sustainable processes. Less conventional applications of chemical engineering lie in public sector decisions, using the approach known as post-normal science. These applications require chemical engineers to take on a significantly different role, using their professional expertise to work with people from other disciplines and with the lay public. The contribution of chemical engineering to the formation of UK energy policy provides an example of the importance of this role. Recognising the role of engineers as agents of social change implies the need for a different set of skills, which just might make the profession more attractive to potential new recruits. 䉷 2005 Published by Elsevier Ltd. Keywords: Sustainable development

1. Introduction Rather than summarising or reviewing an area of established chemical engineering science, this contribution sets out to explore a relatively new and—at least in the author’s view—essential way in which the skills of the chemical engineer need to be deployed. The need is to find solutions to a set of global challenges which are grouped under the heading of sustainable development. The argument in this paper builds on previous discussions of the role of engineering in general and chemical engineering in particular in sustainable development (e.g., Clift, 1998; Mitchell et al., 2004), to explore some of the research challenges introduced by sustainable development and identify some of the disciplines with which chemical engineers will have to work to develop this agenda.

E-mail address: [email protected]. 0009-2509/$ - see front matter 䉷 2005 Published by Elsevier Ltd. doi:10.1016/j.ces.2005.10.017

There is growing acceptance in professional engineering bodies that engineers carry a responsibility to the whole of society, not just to their employers or clients. In a process initiated under John Bridgwater’s presidency, the Institution of Chemical Engineers has played a major role in developing a declaration whose most recent form is The Melbourne Communiqué (IChemE, 2003), signed by a number of institutions representing the profession around the world and including the injunction “We will use our talents, knowledge and organisational skills for the continued betterment of humanity to protect the public welfare”. In a similar vein, the Code of Professional Ethics of the American Institute of Chemical Engineers enjoins its members to “hold paramount the safety, health and welfare of the public in the performance of their professional duties”. Before discussing the implications of this new emphasis in chemical engineering, the reasons for the developing paradigm will be reviewed. Mankind as a whole is facing something new: the realisation that what we can do with and on planet Earth is constrained; there are no new geographical horizons to cross; the capacity

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Fig. 1. The human economy—schematic (from Clift, 1995).

of the planet to provide resources and absorb the emissions and impacts of human activities is finite; and in many geographical and industrial areas we have already exceeded the carrying capacity of the planet (see e.g., Perdan, 2004). To reconcile human activities with the carrying capacity of the planet will require major changes in patterns of consumption as well as in industrial systems. Particularly in the consumer-oriented world, gains in industrial efficiency have a tendency to be offset by changes in consumer behaviour. This phenomenon is known as “rebound”; e.g., improvements in the fuel efficiency of vehicles are offset by demand for larger cars with more fittings and devices; improvements in home insulation are taken up by increasing the indoor temperature; etc. (Jackson, 1996). Finding the path of sustainable development therefore cannot be an enterprise for any one academic discipline: it requires active collaboration between engineers, scientists, social scientists, economists, philosophers, lawyers, etc. Although the field is trans-disciplinary, the engineering contribution is essential and chemical engineering in particular must be central. Understanding the problems posed by sustainable development requires an understanding of the way in which complex systems behave and can be managed (e.g., Clayton and Radcliffe, 1996). Whereas the idea that civil engineering, for example, should include elements of system thinking is novel (e.g., Jowitt, 2004), the systems approach has been central to chemical engineering since its inception as a distinct discipline: although George E. Davis did not use the terminology of system theory, it is clear that he recognised that unit operations were to be studied as the elements which are assembled to form a process; i.e., a system which displays emergent properties, arising from the co-functioning of the elements of the system. Fig. 1 shows the complex system of human activities reduced to its barest minimum.1 Human society requires food and also relies on some natural products which are provided by agricultural activities, and goods and services provided by industrial 1 For further discussion of the significance of Fig. 1, see Clift (1998) and Mitchell et al. (2004).

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activities. Waste is regarded as part of the economy—material is only lost when it is dispersed into water bodies or the atmosphere. Until the agricultural and industrial revolution, most of the energy needed to drive the transformations in the system came from the sun, via wind- or water-mills or biomass fuels. One of the changes brought about by the industrial revolution was a switch to non-renewable resources, particularly for energy. Energy use provides an example of the constraints on human activities, and is explored later in this paper. The availability of carbon-based fossil fuels is one constraint. However, the ability of the planet to accommodate the emissions is another constraint, particularly the effect of carbon dioxide emissions in altering global climatic patterns with potentially catastrophic results (see, e.g., RCEP, 2000). Which of the two constraints will become active first? The economic system can deal with resource constraints; as resources become more scarce, the price goes up so that other resources become “economic”. Hydrocarbon fuels give a clear example of this. Increasing energy prices have made exploitation of oil sands not just economic but profitable, notably in Alberta (and this is the motivation behind the work of Zholkovskij and Masliyah (2005) reported in this set of papers). Given the range of carbonbased fuels on the planet, the resource constraint is flexible. However, the emission constraint is not. Although the effect of increasing carbon dioxide levels in the atmosphere is uncertain (and probably not predictable in the deterministic sense, given that the global climatic system is complex and dynamic with positive feedback effects so that it is chaotic; see RCEP, 2000), it is ostrich-like to pretend that there will be no consequences, a point which is also made by Batterham (2005) in his contribution. So the emission constraint will “bite” before the resource constraint: we already know the whereabouts of more carbon-based fuel then we can burn without serious risk of catastrophic damage to the biosphere. Whereas the economic system can cope with scarcity of supply, economic devices to cope with scarcity of emission capacity have to be devised. Carbon-trading is one such device. Whether or not this particular economic device proves to be effective, the imperative of reducing the carbon intensity of developed and developing economies represents a major engineering challenge. It also leads to a new role for engineers, as essential participants in political and social processes, which is part of the theme of this paper.

2. System-based environmental management 2.1. Analytical tools Given that chemical engineering is concerned with complex systems, it is no accident that many of the developments which underpin the new system-based approach to managing environmental performance (Wrisberg and Udo de haes, 2002) recognisably derive from chemical engineering. However, they involve a fusion of chemical engineering with other disciplines including environmental sciences, toxicology and economics. Three of the principal tools are introduced here.

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2.1.1. Material flow accounting (MFA) MFA is defined as the “quantitative accounting of material inputs and outputs of process in a chain perspective” (Bringezu and Moriguchi, 2002). MFA is a form of material balance analysis, typically applied to one material or group of materials (such as iron/steel or paper) passing through a geographical area or an industrial sector. MFA is applied to obtain estimates for resource consumption, or of waste arisings so that recycling rates can be estimated and activities to improve waste recovery and recycling can be planned (e.g., Melo, 1999; van Schaik and Reuter, 2004; Verhoef et al., 2004; Dahlström et al., 2004). Where the material in question is incorporated in products with significant service lives, it is necessary to allow for the distribution of residence times in the economy using what amounts to an application of residence time theory (e.g., Melo, 1999; van Schaik and Reuter, 2004). By tracking the values of materials as well as their flow rates—a form of value chain analysis—this kind of accounting can show where value as well as material is lost (Dahlström et al., 2004). Extended forms of material flow accounting can show, for example, the results of incomplete material separation in waste streams and the implications of the fact that many metals are obtained from mixed ores and therefore do not enter the economy as separate streams (Verhoef et al., 2004).

2.1.2. Life cycle assessment (LCA) LCA is defined as studying “the environmental aspects and potential impacts of a product or process or service throughout its life, from raw material acquisition through production, use and disposal” (ISO, 1997). Whereas MFA applies mass balance approaches to a sector or area, LCA starts by compiling mass balances over the complete supply chain providing a service or product extending from the “cradle” of primary resources—metal ores or fossil fuel deposits for example—through to the “grave” of recycling or safe disposal; the term “life cycle” is used in this context to describe the supply chain, but it includes the service life of a product or process. In the sequence of steps conventionally followed in carrying out an LCA (see Baumann and Tillman, 2004), compiling the material and energy balance is termed the Inventory phase. Apart from the extended system boundary, inventory analysis differs from conventional material and energy balance analysis by the need to include trace flows of species whose environmental significance is large, for example because they have high human or eco-toxicity. Inventory analysis typically produces a body of detailed numerical information which rarely reveals the most important environmental impacts. The next phase in carrying out an LCA is life cycle impact assessment (LCIA) which aims to estimate the magnitude and significance of the potential impacts arising from the whole life cycle. The general approach is to define a manageable set of environmental impact categories—greenhouse warming, photochemical oxidant formation and resource depletion for example—and to estimate the contribution of each of the flows into and out of the system to each of the impact categories (for summaries of the LCIA

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approach see Clift, 2001 or Azapagic, 2004; for a full account see Baumann and Tillman, 2004). The LCIA approach of expressing impacts in terms of contributions to a set of environmental categories forms the basis of the “Environmental Burden” approach, originally developed by ICI for setting targets and reporting on company environmental performance (Wright et al., 1997) and subsequently incorporated into the sustainability metrics promoted by the Institution of Chemical Engineers (IChemE, 2004). Some LCA practitioners advocate a further step, known as valuation, in which the disparate environmental impacts are aggregated into a singly metric, usually expressed in economic terms, for example as a total damage cost (see Baumann and Tillman, 2004). For reason outlined later in this paper, valuation is not generally recommended: aggregation across environmental impacts obscures information.

2.1.3. Industrial ecology Fig. 1 emphasised that materials and energy are only lost from the economy when they are dispersed, so that one general approach to improving the resource efficiency of human activities is to use materials and energy as many times as possible. This approach is increasingly known as “Industrial Ecology” (see e.g., Graedel and Allenby, 1995; Ayres and Ayres, 1996), based on a loose—and arguably misleading—analogy with living ecosystems. One form of industrial ecology is “industrial symbiosis”: a form of collaboration between neighbouring plants so that wastes and emissions from one are used as inputs to others. The classic case of industrial symbiosis is the Kalundborg eco-park in Denmark. At a purely technological level, Kalundborg shows only the kind of process integration which a chemical engineer would naturally expect. The interest is therefore more in the way the relationships between different organisations have developed to enable mutually beneficial interdependence (Ehrenfeld and Gertler, 1997). Thus, understanding and promoting the development of industrial ecologies must be a collaborative endeavour between chemical engineering, social science and business management. Another form of industrial ecology entails systematic use and re-use of materials and components in a series of different applications. This is shown in general form in Fig. 2. Products may be re-used in the same application, as exemplified by refillable containers. The material might be reprocessed for recycling into the same application, or it might be down-cycled into an application with lower performance characteristics so that it can pass through a succession or “cascade” of different uses. Such systems are more complex than the single supply chains which are the province of LCA and typically require decisions on the relative environmental and economic comparisons between different routings. However, they are no more complex than process systems with multiple recycle loops. The kind of industrial ecology in Fig. 2 can be modelled for decision support by combining LCA with approaches used in process systems engineering, representing a further new application of relatively routine chemical engineering (e.g., Allen, 2004; Mellor et al., 2002). It is possible to incorporate logistics—both

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Fig. 2. Industrial ecology (from Mellor et al., 2002).

distribution of products and collection of materials at the end of their service lives—within the same framework. Further insights into the sustainability of product systems can be obtained by examining the distribution of economic benefits and added value along the supply chain (Clift and Wright, 2000; Clift, 2003). Typically what emerges is a highly skewed distribution, with primary resource industries apparently responsible for major environmental impacts but achieving limited added economic value and with the later stages of the supply chain, including retailing, characterised by high added value with much less environmental impact; in other words, global trade can act to export unsustainability from the consuming country to countries whose economies are dominated by primary industries. This raises further questions over whether it is appropriate to describe the sustainability of a company or economic sector (or a country) in terms of its direct impacts or in terms of its consumption. This point is revisited below.

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ENVIRONMENTAL IMPACT Fig. 3. Clean-up and clean technology (from Clift and Longley, 1995).

2.2. Clean-up vs. clean technology The system-based approach to environmental management has also led to a change in emphasis in process engineering over the last two decades, away from “clean-up” or “end-of-pipe” approaches to pollution abatement towards “clean technology” or “pollution prevention” (Clift and Longley, 1995; Allen and Rosselot, 1997; Clift, 2001; Allen and Shonnard, 2002). Fig. 3 illustrates the idea. Any general technology can be translated into specific designs by trading off cost against environmental impact. Adding pollution abatement to a process, i.e., the cleanup approach, can reduce its environmental impact but necessarily at increased cost. The clean technology approach is to look for a “win–win” solution whose performance is improved in both economic and environmental terms. In order to ensure that

the improved environmental performance is real and does not merely represent shifting environmental impacts to some other point in the material and energy supply chains, it is essential to evaluate the environmental impacts on a life cycle basis. Approaches to combining process analysis and design with LCA as tools to guide process selection, design and operation have been developed as part of the contribution of chemical engineering to sustainable development (e.g., Azapagic and Clift, 1999; Clift and Azapagic, 1999). If environmental performance is measured in terms of contribution to general impact categories rather than being aggregated into a single metric, then there are a number of “environmental impact” axes corresponding to the different categories. Thus, Fig. 3 is really a

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3. Engineering as a normative discipline

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Fig. 4. Process selection, design and operation.

two-dimensional projection or simplification of an ndimensional surface. Decisions over process selection, design and operation necessarily involve trade-offs between cost and the different environmental impacts. The problem in terms of process design is shown schematically in Fig. 4, in the two-dimensional simplification of trading off cost against one measure of environmental performance. The performances of technologies 1–3 are each represented by a space in Fig. 4 which represents the possible range of performance. For each technology, there is a decision frontier which represents the set of designs for which it is impossible to improve one performance parameter without making the other parameter worse.2 Technology 4 is clearly less effective than technologies 1–3, and is therefore considered no further. The overall decision envelope is tangential to the decision frontiers representing the individual technologies. The optimal design point lies on the decision envelope but at a point determined by the trade-off between economic and environmental performance (or, in the general case, between different measures of environmental performance). For example, if technology 2 of Fig. 4 is selected, the design point would be at point B. The negative gradient of the tangent at B gives the marginal cost of abating the environmental impact, and thus helps in selection of the preferred design. The Pollution Prevention and Control regime, brought in by the European Directive on Integrated Pollution Prevention and Control (IPPC) and intended to act as a driver to promote cleaner technologies, requires explicit trade-offs between different categories of environmental impact assessed on a lifecycle basis (Nicholas et al., 2000). In some European member states, IPPC is interpreted in a way which is equivalent to the approach shown schematically in Fig. 3 (Emmott and Haigh, 1996; Geldermann et al., 1999). 2 In the economics literature, these are termed “Pareto surfaces” and a design which lies on the decision frontier is said to be “Pareto optimal”. In the business management literature, the overall decision frontier is sometimes termed the “data envelope”.

The preceding section reviewed some environmental management tools which may not be widely known amongst chemical engineers but are nevertheless clearly rooted in chemical engineering science. However, it is a theme of this paper that sustainable development requires not just new tools but a new role. Those with engineering expertise need to contribute at an early stage in the framing of problems, not just in problemsolving; i.e., engineers should have a normative role as well as their more familiar analytical role. This concept of engineering adopting (or returning to) a normative role can be understood by examining the kinds of decisions in which professional engineers may be involved. Fig. 5 shows a useful classification of decisions, adapted from the literature on multi-objective optimisation (Cohon, 1978; Azapagic and Clift, 1999) with the terminology aligned with that used in environmental system analysis (e.g., Wrisberg and Udo de haes, 2002). The first distinction is whether the objectives or criteria to be used in the decision have been made in advance. Within a commercial organisation there usually will have been prior agreement on objectives, for example in terms of economic performance (including reputation and share value) which depend in turn on environmental performance and on the broader concept of corporate social responsibility (including the aspects covered by the IChemE’s Sustainability Metrics). Within the broad class of decisions on the left in Fig. 5, there are two sub-classes depending on whether the objectives have been aggregated into a single performance metric. For example, environmental impacts are sometimes evaluated as damage costs—“externalities” in the vocabulary of economics—so that they can be combined with conventional economic cost in a single “ecometric”. This corresponds to assigning weights or preferences to the criteria in advance. “Valuation” in LCA is an example of this kind of aggregation. An engineering decision then reduces to selection or optimisation on the basis of this single metric. This familiar approach may be appropriate for decisions which are routine with limited significance—selecting an item of equipment to form part of a process plant, for example. However, even within a commercial organisation, for strategic decisions with greater significance—such as a decision on whether to invest in the new plant—it is usually considered

Decisions

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Fig. 5. A taxonomy of decisions (after Cohon, 1978).

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preferable to examine the trade-offs explicitly rather than losing information by aggregating into a single metric (see Petrie et al., 2004). The account of clean technology summarised in the preceding section is an example of the analysis needed to support this kind of decision. The role of the engineer in such a decision process is to ensure that all the necessary information is presented as clearly as possible, with uncertainty ranges made explicit. The normative role for engineers comes in for decisions in the other class, on the right in Fig. 5, where developing the objectives or criteria forms part of the decision process. Substantive decisions in the public domain typically fall within this class. Examples include setting environmental standards (RCEP, 1998), use of land, and more mundane but nevertheless essential and potentially contentious decisions such as road planning and waste management strategy. Given that the criteria have not been determined a priori, it is clearly pointless to try to aggregate impacts to a single metric. In fact, attempts to apply cost/benefit analysis, which is an extreme form of aggregation, to decisions in this category can be seen to lead to political disturbances, for example over road construction in the UK. Balancing the techno-economic, environmental and social dimensions of sustainable development makes this kind of decision increasingly important. Therefore, engineers in general and chemical engineers in particular must expect to be involved in this kind of decision process.

3.2. Risk, uncertainty and acceptance in decisions Although “decisions without agreed criteria” are unavoidable in engineering for sustainable development, they represent something unfamiliar to most engineers. Decisions in this category typically affect a broad range of people and organisations, so these stakeholders should be involved in the decision process. Different stakeholders will typically have different views about the criteria defining a desirable outcome. Decisions must often be made in the face of missing information and uncertainty about the confidence which can be placed on the available information; it can be argued that engineering design has always required decisions to be made based on incomplete information, but the involvement of stakeholders with different objectives makes this kind of decision different. Furthermore, the systems about which decisions must be made may be so complex that their behaviour is not predictable, while the consequences of the decision may be highly significant. This kind of decision problem has become known as the domain of “post-normal science”. The concept is shown schematically in Fig. 6. Decisions with low uncertainty and decision stakes are the conventional province of the engineer. When the stakes or uncertainty are higher, specialist skill and judgement are needed—i.e., professional consultancy may be required. When the risks arising from high stakes and/or uncertainty are high, we are in the realm of post-normal science. Here “the contribution of all the stakeholders. . . is not merely a matter of broader democratic participation. . . . Quality depends on open dialogue between all those affected. This we call an ‘extended

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Fig. 6. Post-normal science (after Ravetz, 1993).

peer community’, consisting not merely of persons with some form. . . of institutional accreditation, but rather of all those with a desire to participate in the resolution of the issue” (Funtowicz et al., 1999). The idea of a peer community is familiar enough. The notion of an extended peer community, recognising that the knowledge needed to reach an accepted decision does not reside solely with technical experts, is less familiar (and may be seen as anathema by some in the engineering profession!). However, if sustainability leads inevitably to decisions without agreed criteria, then it is also inevitable that some form of extended peer community will be needed if decisions are to be accepted in the face of uncertainty and risk.3 The problem for the engineer is then to recognise that the role of the technical expert in this kind of decision is different; it is to “act as Honest Broker, to ensure that the scientific and technical information is presented clearly and without bias” (Mitchell et al., 2004). But then the decision process needs to be structured carefully. Fig. 7 shows a model for deliberative decision processes, originally proposed as a way of setting environmental standards but much broader in its potential applications (RCEP, 1998). The key feature is that specialist assessment with interaction between specialist disciplines lies at the core of the process, but people’s values must inform recognition and definition of the problem and the objectives and decision criteria, and also the synthesis of different technical assessments to arrive at an accepted decision. Funtowicz et al. (1999) described this model as “as a sort of manual for post-normal science”.

3 For a discussion of the role of the “lay expert” in this kind of decision, see Irwin (2003).

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Fig. 7. A model of deliberative decision processes (RCEP, 1998).

3.3. An example: energy policy and climate change The role of engineering expertise in a problem falling into the realm of post-normal science can be illustrated by an influential study by the UK Royal Commission on Environmental Pollution (RCEP, 2000) on global climate change and energy policy. The RCEP is a body of independent experts which has maintained a tradition of freedom from political intervention; its deliberations, therefore, correspond to the multidisciplinary analysis at the centre of Fig. 7. However, the issues which the Commission addresses are framed by public concerns, and the ways in which its conclusions are applied are determined by political processes. In this sense, the RCEP’s work approximates to the model of Fig. 7. The key aspect of the Royal Commission’s analysis concerned targets for carbon dioxide emissions from the UK in the year 2050. The report starts with an analysis of the evidence that emissions of climate-forcing “greenhouse gases” from human activities are causing changes in the global climate and regional weather patterns. In effect, it endorses the conclusions of the UN Intergovernmental Panel on Climate Change (IPCC). To quote the RCEP report, the world is now faced with a radical challenge of a totally new kind which requires an urgent response. . . By the time the effects of human activities on the global climate are clear and unambiguous it would be too late to take preventive measures. This statement may not be news to the scientific community, but was necessary at the time of publication (2000) to underpin the Commission’s recommendations; although the UK government now stresses its belief that climate change represents a real and serious threat, this commitment has emerged since publication of the RCEP report. The statement also identifies this as a problem in post-normal science: high uncertainty but very high stakes. The analysis which followed had three principal steps in which the key disciplines were respectively climate science, moral philosophy and engineering: 1. The risk of serious global climate change increases with increasing carbon dioxide concentration in the atmosphere.

Therefore, the ecological constraint (in the sense introduced at the beginning of this paper) was framed in terms of preventing runaway rise in carbon dioxide concentration. Although there is no threshold at which the stability of the global climate becomes “unsafe”, the RCEP recommended the target of stabilising CO2 concentration at about 550 ppmv, about double the pre-industrial level. Even at this level, major climate impacts and rise in sea level must be expected. However, the implications of the constraint for limiting emissions are not very sensitive to its level: stabilisation at any level below 750 ppmv requires global emissions to be reduced below projections on a “business as usual” basis. The 550 ppmv cap requires total global emissions to be stabilised roughly at current values. 2. Working back from the tolerable emissions, RCEP argued that an effective, enduring and equitable climate protocol will eventually require emission quotas to be allocated to nations on a simple and equal per capita basis. This is known as the “contract and converge” principle: it requires the developed economies to reduce their emissions to converge on the global constraint. Dividing the tolerable emissions by projected global population in 2050 gave the per capita target. Multiplying by the UK population gave the target for the UK: about 40% of emissions in 1997. 3. The normative engineering input came in the third step of the analysis, by developing representative scenarios to show how the target of 60% reduction in UK CO2 emissions by 2050 might be achieved. This was an application of foresighting, as distinct from forecasting. Forecasting is the process of predicting how a system—in this case, the energy supply system in the UK—is likely to develop. Foresighting uses a different approach: projecting possible future scenarios, usually over a time-scale—50 years in the case of the RCEP energy study—longer than that which can be covered by forecasting. Foresighting can lead on to backcasting, the process of investigating what must be done now to invalidate simplistic “business-as-usual” forecasts and improve the chances of reaching a desirable future scenario (Robinson, 2003). The use of scenarios in energy planning

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and policy is well established (e.g., Darton, 2004). In the case of the RCEP’s analysis, the scenarios enabled the cost of changing course to achieve the 60% reduction to be estimated. The answer was “about 2% of annual GDP”, at a time when GDP growth was still projected as 4% per annum; i.e., the costs are substantial but not impossible (and arguably much lower than the economic and social costs of runaway climate change). The strength of the RCEP argument derived from this multidisciplinary analysis, in which the engineering input was necessary but not sufficient. Arguably the engineering component will be even more essential in bringing about the changes in the energy system needed to meet the 60% target, but this is within the more familiar role of the engineer. Based on this analysis, it was possible for the RCEP to say In this report we illustrate ways in which the UK could cut its carbon dioxide emissions by 60% by 2050. Achieving this will require vision, leadership and action which begin now. About 2 21 years after publication of the RCEP report, the recommendation was accepted in a White Paper setting out UK energy policy. This was one of the first political admissions that the targets agreed under the Kyoto protocol are nowhere near enough to prevent gross climate change. The target has since been adopted by some governments in addition to the UK. 3.4. A caution against optimism Of course, declaration of policy by the government of one industrialised country gives very limited reassurance. Achieving the goal of stabilising atmospheric CO2 concentration will require a lot more, including adoption of low-carbon energy economies in the developing countries, so there remains much to be done by engineers acting in their more conventional roles. Also, a further difficult problem is starting to emerge. The question was raised earlier: should the sustainability of a country be assessed in terms of its direct impacts or its consumption? In principle, it is possible for a country to export its unsustainability by consuming goods and materials with high environmental impact which are produced elsewhere in the world. For example, greenhouse warming emissions from the UK have reduced measurably as a result of the migration of energy-intensive industries such as primary metal production (see Dahlström et al., 2004), but this does not mean that UK society has reduced its real contribution to climate change. Finding ways to address the problem of inequitable consumption will be even harder than reducing national carbon emissions, but it is clear that the process must involve environmental system analysis—particularly LCA—and therefore that chemical engineering must have a key role. 4. Conclusions One of the features of the discipline of chemical engineering is its concern with managing complex systems, particularly systems involving flows of materials and energy. The concept of sustainable development introduces a concern for the be-

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haviour of complex systems which makes the chemical engineering approach all the more essential. The development and use of system-based tools for managing the environmental performance of human activities already represents a new but relatively straightforward extension of chemical engineering. The approaches known as clean technology and industrial ecology already require a fusion of chemical engineering with other disciplines including natural science, toxicology, economics and business management. The field for possible applications of chemical engineering becomes even broader when it is recognised that sustainable development requires increasing emphasis on decisions in which the objectives of the decision and the criteria by which success is to be judged must be formulated as part of the decision process. Typically, the uncertainties and the risks of the decision are high. This kind of problem is known as post-normal science. The field is generally less familiar to chemical engineers, and requires working with more alien groups including social scientists, philosophers and the non-expert “lay” public. However, this kind of analysis and decision structuring will be of increasing importance; it is illustrated by the essential input from engineering, alongside climate science and moral philosophy, into the analysis which successfully changed the UK government’s policy towards energy and climate change. Post-normal science introduces or reinforces the role of the technical specialist as an agent of social as well as technological change. Such a normative role will be unfamiliar, and probably uncomfortable, to many practising engineers. However it can also be seen as a way of enriching professional practice. If presented right, it could make engineering in general and chemical engineering in particular more attractive to potential new recruits, and thereby help to overcome the problem of declining recruitment to the profession which is apparent in many parts of the world. References Allen, D.T., 2004. An industrial ecology: material flows and engineering design. In: Azapagic, A., Perdan, S., Clift, R. (Eds.), Sustainable Development in Practice—Case Studies for Engineers and Scientists. Wiley, Chichester, pp. 281–300 (Chapter 8). Allen, D.T., Rosselot, K.S., 1997. Pollution Prevention for Chemical Processes. Wiley, New York. Allen, D.T., Shonnard, D.R., 2002. Green Engineering: Environmentally Conscious Design of Chemical Processes. Prentice-Hall, Upper Saddle River, NJ. Ayres, R.U., Ayres, L.W., 1996. Industrial Ecology: Towards Closing the Material Cycles. Edward Elgar, Cheltenham. Azapagic, A., 2004. Life cycle thinking and life cycle assessment (LCA). In: Azapagic, A., Perdan, S., Clift, R. (Eds.), Sustainable Development in Practice—Case Studies for Engineers and Scientists. Wiley, Chichester, pp. 426–437 (Appendix). Azapagic, A., Clift, R., 1999. The application of life cycle assessment to process optimisation. Computers and Chemical Engineering 23, 1509–1526. Batterham, R.J., 2005. Sustainability—the next chapter. Chemical Engineering Science, this volume, doi: 10.1016/j.ces.2005.10.016. Baumann, H., Tillman, A.-M., 2004. The Hitch-hiker’s Guide to LCA. Studentlitteratur, Lund, Sweden. Bringezu, S., Moriguchi, 2002. Material flow analysis. In: Ayres, R., Ayres, L.W. (Eds.), A Handbook of Industrial Ecology. Edward Elgar, Cheltenham.

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ISO, 1997. Environmental management—life cycle assessment—principles and framework. ISO 14040, International Organisation for Standardisation, Geneva. Jackson, T., 1996. Material Concerns—Pollution, Profit and Quality of Life. Routledge, London. Jowitt, P.W., 2004. Systems and sustainability: sustainable development, civil engineering and the formation of the civil engineer. Proceedings of ICE: Engineering Sustainability no. 157, pp. 1–11. Mellor, W., Wright, E., Clift, R., Azapagic, A., Stevens, G., 2002. A mathematical model and decision-support framework for material recovery, recycling and cascaded use. Chemical Engineering Science 57, 4697–4713. Melo, M.T., 1999. Statistical analysis of metal scrap generation: the case of aluminium in Germany. Resources, Conservation and Recycling 26, 91–113. Mitchell, C.A., Carew, A.L., Clift, R., 2004. The role of the professional engineer and scientist in sustainable development. In: Azapagic, A., Perdan, S., Clift, R. (Eds.), Sustainable Development in Practice—Case Studies for Engineers and Scientists. Wiley, Chichester, pp. 29–55 (Chapter 2). Nicholas, M.J., Clift, R., Azapagic, A., Walker, F.C., Porter, D.E., 2000. Determination of ‘Best Available Techniques’ for integrated pollution prevention and control: a life cycle approach. Transactions of Institution of Chemical Engineers Part B 78 (3), 193–203. Perdan, S., 2004. Introduction to sustainable development. In: Azapagic, A., Perdan, S., Clift, R. (Eds.), Sustainable Development in Practice—Case Studies for Engineers and Scientists. Wiley, Chichester, pp. 3–28 (Chapter 1). Petrie, J., Basson, L., Notten, P., Stewart, M., 2004. Multi-criteria decision analysis: the case of power generation in South Africa. In: Azapagic, A., Perdan, S., Clift, R. (Eds.), Sustainable Development in Practice—Case Studies for Engineers and Scientists. Wiley, Chichester, pp. 367–396 (Chapter 12). Ravetz, J.R., 1993. Science for the post-normal age. Futures 25, 735–755. RCEP, 1998. Setting environmental standards. 21st Report of the Royal Commission on Environmental Pollution, The Stationery Office, London. RCEP, 2000. Energy: the changing climate. 22nd Report of the Royal Commission on Environmental Pollution, The Stationery Office, London. Robinson, J., 2003. Future subjunctive: backcasting as social learning. Futures 35, 839–856. van Schaik, A., Reuter, M.A., 2004. The time-varying factors influencing the recycling rate of products. Resources, Conservation and Recycling 40, 301–328. Verhoef, E.V., Dijkema, G.P.J., Reuter, M.A., 2004. Process knowledge, system dynamics and metal ecology. Journal of Industrial Ecology 8, 23–43. Wright, M., Allen, D.T., Clift, R., Sas, H., 1997. Measuring corporate environmental performance: the ICI environmental burden system. Journal of Industrial Ecology 2, 117–127. Wrisberg, N., Udo de haes, H.A. (Eds.), 2002. Analytical Tools for Environmental Design and Management in a Systems Perspective. Kluwer, Dordrecht. Zholkovskij, E.K., Masliyah, J.H., 2005. Influence of cross-section geometry on band broadening in plug-flow microchannels. Chemical Engineering Science, this volume, doi: 10.1016/j.ces.2005.10.020.