|The North, the South and the Environment: Ecological Constraints and the Global Economy (UNU, 1995, 263 pages)|
Paul Ekins and Michael Jacobs
In the 20 years 1972-92, between the UN Conference on the Environment in Stockholm and that on Environment and Development (UNCED) in Rio de Janeiro, the scientific consensus has gradually hardened that the damage being inflicted by human activities on the natural environment render those activities unsustainable. It has become clear that the activities cannot be projected to continue into the future either because they will have destroyed the environmental conditions necessary for that continuation, or because their environmental effects will cause massive, unacceptable damage to human health and disruption of human ways of life.
This is not the place for a detailed review of the evidence that has led to the scientific consensus, but the now perceived seriousness of the problem can be illustrated by a number of quotations of the conclusions of reputable bodies which have conducted such a review. Thus the Business Council for Sustainable Development (BCSD) stated bluntly in its report to UNCED: 'We cannot continue in our present methods of using energy, managing forests, farming, protecting plant and animal species, managing urban growth and producing industrial goods.' (Schmidheiny 1992:5) The Brundtland Report, which initiated the process which led to UNCED, had formulated its perception of unsustainability in terms of a threat to survival: 'There are thresholds which cannot be crossed without endangering the basic integrity of the system. Today we are close to many of these thresholds; we must be ever mindful of the risk of endangering the survival of life on earth.' (WCED 1987:32-3)
The World Resources Institute (WRI),in collaboration with both the Development and Environment Programmes of the United Nations (UNDP and UNEP), concludes on the basis of one of the world's most extensive environmental databases that 'The world is not now headed toward a sustainable future, but rather toward a variety of potential human and environmental disasters' (WRI 1992:2). The World Bank, envisaging a 3.5 times increase in world economic output by 2030, acknowledged that 'If environmental pollution and degradation were to rise in step with such a rise in output, the result would be appalling environmental pollution and damage.' (World Bank 1992:9). The Fifth Action Programme of the European Community acknowledges that 'many current forms of activity and development are not environmentally sustainable' (CEC 1992a:4), as indicated by 'a slow but relentless deterioration of the environment of the Community, notwithstanding the measures taken over the last two decades' (CEC 1992b:3).
In its annual State of the World reports, the Worldwatch Institute has documented current environmental damage, concluding in 1993:
The environmentally destructive activities of recent decades are now showing up in reduced productivity of croplands,forests, grasslands and fiskeries; in the mounting cleanup costs of toxic waste sites; in rising health care costs for cancer, birth defects, allergies, emphysema, asthma and other respiratory diseases; and in the spread of hunger.
Brown et al 1993:4-5.
These trends mean: 'If we fail to convert our self-destructing economy into one that is environmentally sustainable, future generations will be overwhelmed by environmental degradation and social disintegration.' (ibid:21)
Little wonder, therefore, that in 1992 two of the world's most prestigious scientific institutions saw fit to issue a joint statement of warning:
Unrestrained resource consumption for energy production and other uses... could lead to catastrophic outcomes for the global environment. Some of the environmental changes may produce irreversible damage to the earth's capacity to sustain life.... The future of our planet is in the balance.
RS and NAS 1992:2,4
Unsustainability: the Symptoms
The concept of sustainability will be discussed and amplified further later in this chapter. For the present, an environmentally unsustainable activity is simply to be taken to be one which cannot be projected to continue into the future, because of its negative effect either on the environment or on the human condition of which it is a part. The main symptoms of unsustainability, with their principal causative agents and the geographical level to which they mainly apply, can be simply grouped as in Table 2.1.
Two immediate observations can be made about the symptoms of unsustainability. The first is the extent to which the problems are interlinked. The second is the fact that the most important problems are those of pollution and depletion of renewable resources.
Table 2.1 Symptoms of environmental unsustainability
|Greenhouse effect/ |
|Emissions of CO2, N2O, CH4 |
CFCs (and HFCs)
O3 (low level)
|Ozone depletion (global) |
|Emissions of CFCs |
Emissions of SO2, NOx, NH3
O3 (low level)
|Toxic pollution (continental)||SO2, NOx, O3, particulates |
Hydrocarbons, carbon monoxide
|Renewable Resource Depletion|
|Species extinction (global)||Land-use changes |
(eg development, deforestation)
Unsustainable harvest (eg over
Climate change (possible ozone
depletion in future)
|Deforestation (global, regional)||Land use
Unsustainable harvest (eg hardwoods)
Climate change (possible in future)
|Land degradation / |
loss of soil fertility
|Population pressure |
Climate change (possible in future)
|Water depletion ((bio) regional, |
|Unsustainable use |
Climate change (possible in future)
|Fisheries depletion (national, local)||Over-fishing, pollution
|Non-renewable resource depletion|
|Depletion of various |
resources, eg fossil fuels, minerals
|High levels of consumption|
|Other environmental problems|
|Congestion (national)||Waste disposal |
Unsustainability: The Evidence
Any survey of the evidence for environmental unsustainability which is serving only as an introduction to a paper is bound to be partial and simplified. At best, it can give a quantitative indication of the most important trends and processes and act as a preliminary overview, from which a more detailed exploration of the literature can be undertaken if desired. This survey draws heavily on two compendia of information: the biannual World Resources, produced by the World Resources Institute in collaboration with UNDP and UNEP, and the annual State of the World reports published by the Worldwakh Institute, which are in turn compiled from a wide range of primary datasets and research reports. It should be emphasized that uncertainty is a characteristic of much of the data, especially with reference to processes of global environmental change, which means that the effects of environmental unsustainability could be more or less serious than is currently believed likely to be the case.
Table 2.2 gives some best estimates of the contributions to global warming of the various greenhouse gases (GGs) and the reductions in GG emissions that are thought necessary to stabilize their atmospheric concentrations. Figure 2.1 shows the growth of emissions of carbon dioxide from fossil fuel burning since 1950 migrate or adapt to changed climatic conditions; loss of agricultural productivity where weather patterns become hotter, drier or more erratic than is agriculturally desirable; sea-level rise with inundation of coastal zones; a greater frequency of extreme weather conditions; and an increase in vector-borne diseases. The only possible benefits of global warming are enhanced agricultural productivity in some mid- and high-latitude areas, but there is no likelihood that this will significantly exceed agricultural losses elsewhere; and greater comfort in presently colder areas, which might be offset by the somewhat greater discomfort of higher temperatures in presently hotter areas.
The effects of failing to halt global warming are still highly uncertain.
Table 2.2 Greenhouse gases and the greenhouse effect
|Greenhouse gas||Main anthropogenic sources|
|Carbon dioxide (CO2)||Fossil fuel burning (77 per cent)|
|Deforestation (23 per cent)|
|Chlorofluorocarbons (CFCs)||Various industrial uses|
|Related gases (HFCs, HCFCs)||(eg refrigerators)|
|Methane (CH4)||Rice paddies, livestock
digestion, gas |
|Nitrous oxide (N2O)||Biomass and fossil fuel burning, |
fertilizer use, land use changes
|Other||Fossil fuel burning|
|% contribution to |
|IPCC rec. |
A sea-level rise of one metre, at the top of the IPCC (Intergovernmental Panel on Climate Change) range of uncertainty for the next century, would, according to the IPCC Impacts Working Group, 'displace populations, destroy low-lying urban infrastructure, inundate arable lands, contaminate freshwater supplies, and alter coastlines' (quoted in Woodwell 1990:128). The flooding of the deltas of Egypt and Bangladesh would deprive the former of 15 per cent of its arable land and the latter of 14 per cent of its net cropped area (Woodwell 1990:128). Worldwide, hundreds of millions of people could be displaced.
The IPCC's estimate of global warming was 3±1.5°C increase in average global temperatures over preindustrial levels for a doubling of atmospheric concentration of carbon dioxide equivalents. On current trends this doubling will be achieved by 2025. Cline (1991) has criticized such a short time horizon and projected that these trends imply a mean global warming of about 10°C over 250-300 years. Such an increase could multiply by several times IPCC estimates of damage, eg a sea-level rise of 4 metres would seem likely (Cline 1991:915).
Apart from CFCs, GG emissions derive from the burning of fossil fuels, deforestation and various agricultural practices. While a majority of the world's climate scientists as represented by the IPCC regard global warming as a serious present phenomenon, considerable uncertainties remain over the basic science, the extent of the likely damage and the costs of abating greenhouse gases. Beckerman (1991) and Solow (1991) have between them marshalled the doubts over both the science and the probable damage. Beckerman's reassuring conclusion is that the actual existence of the effect is far from certain, its probable damage is small and distant in time, therefore there is no urgency, and immediate action should concentrate on improving the knowledge base on the issue. This conclusion is broadly the same as that stemming from Nordhaus' benefit-cost analysis of the issue (Nordhaus 1991), which indicates, after phasing out CFCs, an optimal reduction of CO2 emissions (from baseline projections) of only 2 per cent.
Cline's 1992 benefit-cost analysis comes to a fundamentally different conclusion. Although his estimates of damage from global warming in the 21st century are similar to those of Nordhaus, they rise substantially thereafter, in the absence of abatement. He also factors in 20 per cent costless abatement to reflect currently unexploited no-cost energy-efficiency opportunities, and allows for risk aversion, to reflect the fact that, as Broome (1992:16) observes: 'Human-induced global warming, then, could possibly start a chain of events that could lead to the extinction of civilization or even of humanity. This is a remote possibility, but it exists.' These factors together cause him to arrive at a conclusion that: 'Using the central assumptions of this study, if there is weighting of outcomes to take account of risk aversion, the benefit-cost analysis finds that aggressive abatement action is warranted.' (Cline 1992:300) The 'aggressive abatement action' involves cutting CO2 emissions by 82 per cent from the baseline projection by 2100 to four gigatons of carbon annually, which is only about 60 per cent of emissions in 1990.
The global warming issue in its scope and uncertainties exemplifies many of the common characteristics of the modern environmental problematique and will be further discussed both later in this chapter and elsewhere in this book.
Production of CFCs peaked in 1988 and has since fallen by 46 per cent (Brown et al 1992a:62). Under the terms of the Montreal Protocol, most recently revised in November 1992, CFCs must be phased out in industrial countries by 1996 and in developing countries ten years later. However, it will be the year 2005 before stratospheric levels of chlorine, which is what damages the ozone layer, start to decline. Until then they will continue to increase, both because of the quantities of CFCs already produced that are not yet in the lower atmosphere and, once there, the length of time (10-15 years) it takes for them to reach the upper atmosphere (Meadows et al 1992:148). It will take a further 100 years for the chlorine to be cleansed from the stratosphere (ibid:160).
The 3 per cent loss of ozone noted in 1991 over the US and other temperate countries could cause as many as 12 million extra skin cancers in the US alone (WRI 1992:200). Another 3 per cent depletion, expected by the year 2000 (ibid:200), could cause a further 9-18 per cent increase in such cancers (Meadows et al 1992:). Measurements over Antarctica in September 1991 indicated a 50-60 per cent ozone loss (WRI 1992:200).
It seems from a recent study that ozone depletion in the upper atmosphere may cause global cooling, thus offsetting some of the greenhouse effect. It may be that this is a reason why observed global warming is less than that predicted by global climate models (ibid:200).
The principal effects of the deposition of acid atmospheric pollutants are the acidification of soils and water, and damage to forests, crops and buildings, and to human health (this is discussed below under toxic pollution). Water acidification results in a decline of fish and other aquatic life, which is now pronounced in several countries: more than 20 per cent of Sweden's 85,000 medium and large lakes are now acidified, with 4000 having suffered major biological damage; in Norway's four southernmost counties, fish stocks have been halved since 1940. The number of highly acidified lakes in New York's Adirondack mountains grew from 4 to 51 per cent between the 1930s and 1970s. Ninety per cent of the affected lakes had lost all their fish (McCormick 1989:37).
Symptoms of forest decline grew fast during the 1980s: by 1986 87 per cent of West Germany's firs were damaged, two thirds of them seriously (McCormick 1989:30). A study in 1990 concluded that 75 per cent of Europe's forests suffer damaging levels of sulphur deposition, and 60 per cent of them endure nitrogen deposition above their critical loads (WRI 1992:198). While there is considerable uncertainty over the actual figures, damage to crops and buildings is thought to be economically substantial: for example, $31 billion in 1983 to US wheat, corn, soybeans and peanuts; $500 million in eleven European countries in 1981 (McCormick 1989:40-41). The cost to Europe of corrosion of buildings has been estimated by the UN Economic Commission of Europe as $1.3-$6.5 billion pa.
Trends for global emissions of the principal acid gases, sulphur dioxide and
nitrogen oxide, are difficult to assess. In OECD countries sulphur dioxide
emissions fell by 25 per cent over the 1980s and by 38 per cent between 1970 and
the late 1980s, even while GDP grew by 30 per cent over the 1980s, and 77 per
cent from 1970. However, nitrogen oxide emissions grew by 12 per cent from
1970-87, largely because road traffic grew by 93
per cent, faster than GDP (OECD 1991b:21,23,53,61). The USSR and countries of Eastern Europe all had higher per capita sulphur emissions in 1989 than in Western Europe and North America (WRI 1992:64), though the restructuring of and, in some cases, reduction in economic activity since then may have reduced them. Nitrogen dioxide emissions, on the other hand, are more equal between the West and former Communist countries, reflecting the former's far higher rate of car ownership and use. While lack of data prevent any clear quantitative assessment of Third World trends in this area, it is clear that air pollution in rapidly industrializing countries is increasingly damaging both the environment and human health. In gross (as opposed to per capita) terms, China is already the third largest emitter of SO2 worldwide.
There are many pollutants which are injurious to health and only the briefest account of their scope and effects can be given here. The great majority of these pollutants are the products of industrial development, but two significant exceptions are pollution by sewage and from indoor fires. Indoor pollution, from cooking or heating by burning wood, straw or dung, adversely affects 400-700 million people and contributes to acute respiratory infections that kill up to four million children annually, permanently damaging the health of many more, children and adults (World Bank 1992:52). Sewage is the major cause of water contamination worldwide, with 1.7 billion people still not having access to adequate sanitation, a number that grew by 70 million during the 1980s. Sewage treatment is rarer still: in developing countries over 95 per cent is untreated before being discharged into surface waters (WRI 1992:167). Universal access to clean water and adequate sanitation would cut the incidence of Third World country disease dramatically: per year, two million fewer child deaths from diarrhoea, and 200 million fewer episodes of the illness; 300 million fewer people with roundworm; 150 million fewer with schistosomiasis (World Bank 1992:49). Needless to say, growing water scarcity (see below) and pollution from other sources are making access to clean water and adequate sanitation more difficult to provide.
Pollutants from industrialization are seriously degrading the quality of air, water and soils. Outdoor air pollution has three principal man-made sources -domestic energy use, vehicular emissions and industrial production - all of which increase with economic growth unless they are abated. The World Bank notes:
If the projected growth in demand for vehicular transport and electricity were to be met with the technologies currently in use, emissions of the main pollutants deriving from these sources would increase fivefold and elevenfold, respectively, by about 2030. Yet in the mid-1980s more than 1.3 billion people, mainly in the Third World, already lived in cities with air which did not meet WHO standards for SPM (suspended particulate matter), causing an estimate 300,000-700,000 premature deaths.
World Bank 1992:52
Lead is the other major pollutant in Third World cities, principally from car exhausts. Over half the newborns in Mexico City have blood lead levels high enough to impair their development (WRI 1992:51), while in Bangkok children have lost an average of four IQ points or more by age 7 because of lead pollution (World Bank 1992:53). How bad such situations can become is illustrated by Katowice in Poland, where lead levels in the soil reach about 50 times the permitted level. One study showed the difference in IQ between children with high and low blood lead levels to be 13 points, and indicated other profound health differences (WRI 1992:62).
Central and Eastern Europe provide many examples of the appalling damage uncontrolled industrializm can cause. Among 'serious environmental health hazards', WRI lists high levels of sulphur dioxide, oxides of nitrogen, lead and other hazardous chemicals in the ambient air...; contamination of groundwater and soil by nitrogenous fertilizers, pesticides and toxic metals; contamination of rivers by sewage and industrial waste; and a variety of chemical, physical, biological and psychosocial health hazards in the workplace.
In assessing the results of such a situation in Russia, the head of the Russian Academy of Medical Sciences shocked the world with his frankness: 'We have already doomed ourselves for the next 25 years.' Eleven per cent of Russian infants suffer from birth defects. 'With half of the drinking water and a tenth of the food supply contaminated, 55 per cent of school age children suffer health problems.' (Brown et al 1993:10).
Although in OECD countries the health impacts of pollution are much less severe, 'On a per capita basis, the OECD countries are overwhelmingly the world's major polluters, both within their own borders and in their contribution to global environmental degradation.' (WRI 1992:18) Their 16 per cent of the world's population consumed 43 per cent of 1989's global production of fossil fuels, most of its production of metals and well over a proportionate share of industrial materials and forest products. Per capita consumption of resources in OECD countries is often several times the global average. For example, OECD countries account for 78 per cent of all road vehicles (OECD 1991a:13). Because current technologies turn resources inexorably into wastes, the pollution emanating from these countries should come as no surprise: 40 per cent of global sulphur dioxide and 54 per cent of nitrogen oxides emissions; 68 per cent of industrial wastes by weight; 38 per cent of global potential warming impact from emissions of greenhouse gases (WRI 1992:17) OECD pollution may be killing fewer people than that from other regions, but its 'industrial residues - acidic materials, heavy metals, and toxic chemicals - degrade soils, damage plants, and endanger food supplies' (WRI 1992:18) just as unsustainably.
'When we consider just the numbers involved,' wrote Norman Myers in 1986, 'let alone the compressed time-frame of the episode,... we may suppose we are on the verge of one of the greatest extinction episodes to occur during the four billion years since the start of evolution.... The extinction spasm pending may well rank as the greatest impoverishment of Earth's species since the first flickerings of life.' (Myers 1986:4) Yet, as the World Bank notes, 'The complex web of interactions that sustains the vitality of ecosystems can unravel even if only a small number of key species disappear.' (World Bank 1992:59) On no issue of unsustainability is human ignorance so profound as in its understanding of biodiversity. Identified species are fewer than 1.5 million, but over 30 million, of which over 90 per cent are insects, are thought to exist (ibid:60). At such levels of ignorance, figures of extinction rates are little more than informed speculation. Harvard biologist Edward O Wilson puts the minimum loss of invertebrate species at 50,000 per year (Brown et al 1992b:9). More certain is that the tropical forests, covering 6-7 per cent of the Earth's land surface, contain 5090 per cent of all species. Myers places nearly 40 per cent of all species in the forests of Latin America outside Amazonia and those of Africa outside the Zaire basin (Myers 1986:12), most of which look likely to disappear by the early years of the next century. Myers writes: 'We are unconsciously conducting a superscale experiment with Earth's iotas. (ibid:2) Unfortunately it is an experiment conducted in almost total ignorance, and which can never be repeated. This is a strange way for an age which prides itself on rationality and scientific prowess to be proceeding.
It is estimated that the Earth's forest cover is now only two thirds of what it was in pre-agricultural times, but the amount of undisturbed, primary forest is only a quarter of that amount. Europe has practically no original forests; the US outside Alaska has only 5 per cent (Brown et al 1991:74). The large expanses of remaining primary temperate forests in Canada and the former Soviet Union, saved so far by their remoteness, are now also being felled, with Canada losing 200,000 hectares (ha) pa (Brown et al 1993:6).
In tropical countries only half the original area of forests remains, and over half of this has already been logged or degraded in some way (Brown et al 1991:74). Moreover, the rate of tropical deforestation accelerated markedly during the 1980s, reaching 17 million ha pa in 1991, compared to 11.3 million in the early 1980s, an increase of 50 per cent (WRI 1992:118). Some countries' deforestation has proceeded even faster than this. Thus Indonesia's rate has quadrupled since 1970, now destroying 1 million ha annually. Thailand's forest cover between 1961 and 1988 shrank from 55 per cent to 28 per cent (WRI 1992:47).
In the past 45 years 'about 11 per cent of the Earth's vegetated soils have become degraded to the point that their original biotic functions are damaged and reclamation may be costly or, in some cases, impossible' (WRI 1992:111). Since 1972, farmers have lost nearly 500 billion tons of topsoil (Brown et al 1993:4), a process that continues at a rate of 24 billion tons a year (ibid:12). Table 2.3 shows how 'moderate, severe and extreme' land degradation affects different regions.
Table 2.3 Land degradation by region
|Degraded area (DA) |
|DA as % of |
|Central America and Mexico||60.9||24.1|
Source: WRI 1992:112
Land degradation is caused by wind and water erosion and by chemical or physical factors, the former including salinization, acidification and pollution, the latter including compaction and waterlogging. The activities principally leading to land degradation are deforestation, overgrazing and agriculture.
The most obvious reason for water scarcity, of course, is drought: about 80 arid and semi-arid countries with some 40 per cent of the world's population experience periodic droughts (WRI 1992:160). Increasingly, however, burgeoning levels of water use are threatening water scarcity: global water use has risen by a factor of three, or by 50 per cent per capita, since 1950 (Brown et al 1993:22). Sixty-nine per cent of this is used for agriculture, 23 per cent for industry and 8 per cent for domestic uses. By the year 2000 water withdrawals for irrigation are expected to increase by 17 per cent and for industry by 61 per cent. Domestic use is also projected to rise sharply (WRI 1992:161). Such increases can only serve to exacerbate already severe trends in some places of falling water tables, depleted groundwater resources and inadequate supplies.
Thus in Beijing water tables have been falling 1-2 metres per year and a third of the wells have run dry, yet its total water demand in the year 2000 is projected to outstrip its current supply by 70 per cent (Brown et al 1993:26). The countries of the Middle East and North Africa face a situation of particular difficulty. Nearly all available supplies are being used, yet populations in some of the countries are projected to double over the next 25 years. The potential conflict in the situation is obvious, especially where water resources are shared. For example, 86 per cent of Egypt's water comes from the Nile, most of the waters of which originate in eight countries upstream.
Water withdrawn for industrial and domestic uses is largely returned to surface water systems after use, but often in a polluted condition, where it can degrade the water resource for other users or damage the environment.
In 1990 the total global fish catch declined for the first time in thirteen years. The following year the UN Food and Agriculture Organisation (FAO) reported that most traditional marine fish stocks have reached full exploitation. Although there was a record harvest in 1989, intensified fishing effort would only increase the catch by depleting fish populations. The FAO considers that four of its 17 major marine fishing areas are already overfished. Further evidence of a fish catch limit having been reached came from a 1990 US study, which showed that 18 per cent of US fish stocks are overexploited and 30 per cent of US fish stocks have declined since 1977 (WRI 1992:179). In July 1992 Canada reacted to dwindling catches off Nova Scotia and Labrador by banning all cod and haddock fishing in the area for two years, at a cost of $400 million in unemployment compensation and retraining (Brown 1993:8).
Perhaps even more threatening to fish stocks in the long term than overfishing is the ongoing pollution and destruction of coastal habitats where 90 per cent by weight of the world marine catch reproduces. Wetlands, mangroves and salt marshes are being rapidly cleared for urban, industrial and recreational uses: tropical countries have lost over 50 per cent of their mangroves and the US 50 per cent of its wetlands (WRI 1992:177) Most of the world's sewage still flows untreated into coastal waters (ibid:176), its pollution augmented by a variety of toxic chemicals, and further pollution from rivers. Thus a 1991 survey of 85 coastal watersheds in the US found that upstream sources, including agricultural and urban run-off, accounted for about 70 per cent of the nitrogen and 60 per cent of the phosphorus in the estuaries studied (WRI 1992:182). Such pollution can cause algal blooms, which have been reported from coastal areas around the world, and which can lead to mass kills of fish; or it can cut harvests, as in the US's Chesapeake Bay, which produced only one eighth the oyster catch of a century ago (Brown et al 1993:8); or it can render fish unfit for human consumption. These trends augur very badly for the future of tropical developing countries, many with fast-growing populations, 60 per cent of whom currently rely on fish for 40 per cent or more of their protein.
Non-renewable resource depletion
The depletion of non-renewable resources (eg minerals, fossil fuels) which caused much of the anxiety about unsustainability in the 1970s (see for example Meadows et al 1972), and which appears to be an unsustainable activity by definition, has declined dramatically in perceived importance. New discoveries and more efficient use of, and substitution away from, non-renewable resources has tended to keep constant, or even lengthen, their life-expectancies (defined as the known reserves/annual production, or R/P, ratio). As an example, the R/P ratio of oil and natural gas increased from 31 and 38 to 41 and 68 years respectively from 1970 to 1989 (Meadows et al 1992:68). Similarly Table 2.4 shows the R/P ratio for seven minerals in 1970, 1988 and 1990, using three different sources of data.
Table 2.4 World production, reserves and R/P ratios for various
minerals at various dates
|Minerals||World production||(million metric tons)||R/P ratios |
Although several of the 1990 R/P figures seem quite short periods of time, they are little changed from the 1970 figures. Some, indeed, have increased. Only lead and nickel appear to have become substantially more scarce, but the 1970 R/P ratio for nickel must be suspect, as it indicates a reserve level of the resource which must have been revised substantially downwards given the 1990 R/P ratio and interim production. The World Bank 500 year R/P ratio must be accounted doubtful in view of the other sources' estimates.
In one sense, any level of use of non-renewable resources is unsustainable, and, of course, new discoveries and the emergence of substitutes cannot be guaranteed. But the timescales involved in this depletion now seem much less pressing than for pollution and the depletion of renewable resources.
One of the most striking observations about the symptoms of unsustainability is the number of interlinkages between them, unfortunately usually tending to reinforce their negative effects. Some of these are specifically noted in Table 2.1 or in the evidence given above, but there are many others. Thus deforestation is a major cause of land degradation and increases in sedimentation and downstream nutrient enrichment of rivers and lakes worldwide (WRI 1992:169), as well as of species extinction and global warming. Acid deposition kills forests and pollutes water sources. Two of the most promising non-ozone-depleting potential substitutes for CFCs,
HFCs and HCFCs, are potent greenhouse gases. The extra W-B radiation reaching the Earth due to ozone depletion may damage fish larvae and juveniles and the phytoplankton at the base of the food web (WRI 1992:196), as well as cause damage to crops. Toxic pollution of freshwater increases its effective scarcity for human purposes. And, of course, practically all the problems are worsened, and the achievement of solutions to them rendered more difficult, by continuing population growth which adds over 90 million to human numbers each year.
This is the complex context within which environmental economic policy must be formulated. For some analysts, the evidence of environmental damage cited above is either not conclusive enough to warrant action, or they believe that the economy will react appropriately to emerging environmental scarcity without policy intervention (see for example Bernstam 1991). Others believe that active intervention is justified in order to achieve a 'sustainable development' that is compatible with continuing economic growth (see for example World Bank 1991). Others still believe that the environmental problems are evidence of limits to that growth (see for example Meadows et al 1992). The next section reviews these positions and focuses especially on the emerging concept of environmental sustainability.