Much research and thinking about sustainable development has focused on modifying economics to better integrate its operation with the workings and capacity of the environment, to reduce flows of waste and pollution. The full cost of a product, from raw material extraction to eventual disposal as waste, should be reflected in its market price, although in practice such a cradle to grave approach may prove troublesome for materials such as minerals. Many economists contend that a root cause of environmental degradation is the simple fact that many aspects of the environment are not properly valued in economic terms. Commonly owned resources, such as the air, oceans and fisheries, are particularly vulnerable to overexploitation for this reason, but when such things have proper price tags, it is argued that decisions can be made using cost-benefit analysis. Putting a price on environmental assets and services is one of the central aims of the discipline of environmental economics. This can be done by finding out how much people are willing to pay for an aspect of the environment or how much people would accept in compensation for the loss of an environmental asset. One of the justifications of environmental pricing is the fact that money is the language of government treasuries and big business, and thus it is appropriate to address environmental issues in terms that such influential bodies understand. There are problems with the approach, however. People's willingness to pay is heavily dependent on their awareness and knowledge of the resource and of the consequences of losing it. Information, when available, is open to manipulation by the media and other interest groups. In instances where the resource is unique in world terms -such as an endangered species, or a feature such as the Grand Canyon - who should be asked about willingness to pay? Should it be local people, national groups or an international audience? Our ignorance of how the environment works and the nature of the consequences of environmental change and degradation also present difficulties. In the case of climatic change due to human-induced atmospheric pollution, for example, all we know for sure is that the atmospheric concentrations of greenhouse gases have been rising and that human activity is most likely to be responsible. Forever, we do not know exactly ho the climate will change nor what effects any changes will have upon human society. We can only guess at the consequences, so we can only guess at the costs. Economists are undeterred by these types of problem: 'Valuation may be imperfect but, invariably; some valuation is better than none direct values, which are made up of non consumptive value use, option value, and existence value which, where they have been evaluated, appear to provide compelling arguments for the conservation and proper management of natural systems. For example, the value to the national economy of wilderness areas in Kenya, when consigned as National Parks, is estimated to be at least an order of magnitude greater per hectare than the land would yield if put to pastoral use, for example. However; differing values potentially derived from particular areas can be of benefit to different sectors of society. In the Kenyan example, management of the Masai Mara Reserve as a game park principally benefits the operators of tourist lodges and tours, while the pastoral Masai derive only 2 per cent or less of the accruing revenue. For the Masai, a mare financially worthwhile use of the research would be to open it up to pastoralism and /or for poaching ivory and other wildlife products. (Holdgate, 1991).

Other difficulties stem from the different ways groups perceive environmental value. Some groups may consider that certain parts of the environment lie outside the economists' realm. Adams (1993) gives the example of a mining company, which wanted to exploit a site in Australia's Kakadu National Park, an area which is sacred in Aboriginal culture. In this case, the application of cost-benefit analysis amounts to immorality: 'The aborigines say "It is sacred." The economist replies "How much?"' (Adams, 1993: 238). It is far these sorts of reasons that some people reject the economic approach to valuing and hence preserving the environment and biological diversity. They argue that economic criteria of value can change and are opportunistic in their practical application. The greed which underlies such systems will ultimately destroy them (e.g.Ehrenfeld, 1988).