Abstract

Environmentalists generally argue that ecological damage will (eventually) lead to declines in human well-being. From this perspective, the recent introduction of the “environmentalist's paradox” in BioScience by Raudsepp-Hearne and colleagues (2010) is particularly significant. In essence, Raudsepp-Hearne and colleagues (2010) claimed that although ecosystem services have been degraded, human well-being—paradoxically—has increased. In this article, we show that this debate is in fact rooted in a broader discussion on weak sustainability versus strong sustainability (the substitutability of human-made capital for natural capital). We warn against the reductive nature of focusing only on a stock–flow framework in which a natural-capital stock produces ecosystem services. Concretely, we recommend a holistic approach in which the complexity, irreversibility, uncertainty, and ethical predicaments intrinsic to the natural environment and its connections to humanity are also considered.

Since the publication of Our Common Future by the World Commission on Environment and Development (WCED) in 1987, the notion of sustainable development has come to the fore in political discussions. The WCED advised a “development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs” (WCED 1987, p. 43). This widely accepted description of sustainable development (Kates et al. 2005) takes human well-being as a central concept. Although this definition implies a focus on both intragenerational and intergenerational equity, we will only consider the latter in this article. The concept of nondeclining human well-being will therefore be our main concern with regard to sustainable development.

Environmentalists generally assume that ecological deterioration will (eventually) lead to declines in human well-being. In this light, the recent introduction of the “environmentalist's paradox” by Raudsepp-Hearne and colleagues (2010) in BioScience is all the more remarkable. Essentially, they claimed that although ecosystem services (i.e., benefits of ecosystems flowing to people) have been degraded, human well-being has (paradoxically) increased. Of course, such a controversial statement provoked several responses (Duraiappah 2011, Nelson 2011), which were refuted by Raudsepp-Hearne and colleagues (2011).

Economists have studied the relationship between nature and human well-being throughout history (Perman et al. 2003, Common and Stagl 2005). In 1798, the classical economist Thomas Malthus doubted in his Essay on the Principle of Population that economic growth would be everlasting in the presence of natural constraints. Assuming a fixed stock of land, he argued that population would increase exponentially while food supply could only grow linearly. This might cause a long-term decrease of unit output per capita over time. The eventual number of living people would be driven down to a stationary-state subsistence level. Later, as a result of the vast improvements in living standards during the Industrial Revolution, the pessimistic Malthusian outlook was replaced by the more optimistic neoclassical economic theories. Neoclassical economists considered scarcity a relative issue rather than an absolute one. As a result, they believed that nature does not put any absolute limits on the improvement of well-being. Only in the 1970s did the environment reclaim a prominent role in economic analysis. On one hand, natural-resource economists study the economic activity–induced flow of natural resources from the environment to the economy (Callan and Thomas 2000). With their theories, they mainly search for the economically efficient and optimal depletion of natural resources. On the other hand, environmental economists generally study the flow of residuals coming from the economy to the environment (Callan and Thomas 2000). Basically, they concentrate on residuals that have undesired effects on the environment. To put it simply, natural-resource and environmental economists consider natural resources important determinants for an economy. Nevertheless, both natural-resource economics and environmental economics are still conceptually in line with neoclassical theories, because in these fields, it is argued that the economy and the natural environment are distinct entities (Common and Stagl 2005).

Ecological economists perceive connections between nature and economics as essential. They do not deny the importance of monetarily valuing pollution and natural resources, as did the neoclassical economists. Their starting point, however, is the acknowledgement that the economy is a subsystem within the environment (Common and Stagl 2005). Ecological economics arises out of the understanding that since the 1970s, human economic activities appear to have had such a negative impact on nature that future generations could be made economically worse off. The main objective of this relatively new field is to tackle these problems (Perman et al. 2003), and ecological economists usually agree with environmentalists that the natural environment could put limits on the improvement of human well-being.

Because most environmentalists (and ecological economists) on one hand and neoclassical economists on the other hand ultimately share the WCED goal of the improvement of human well-being, both groups view the problem of environmental degradation from an anthropocentric perspective (Jamieson 1998). However, this dichotomy of academic traditions yielded a fundamental disagreement about the relationship between nature and human well-being. Since the upswing of ecological economics in the middle of the 1990s, a serious debate on the link between environmental damage and well-being has been conducted in formalized, economic terms. The dispute essentially boils down to the belief in the ability of natural capital (natural resources such as crude oil, gas, forests, and fisheries) and human-made capital (e.g., production plants, equipment and infrastructure, but also the stock of learned and disembodied skills and knowledge) to be substituted for one another. Whereas weak sustainability (WS) supporters (primarily natural-resource and environmental economists) are more optimistic concerning the interchangeability of natural and human-made capital, strong sustainability (SS) adherents (chiefly ecological economists and environmentalists) are more pessimistic about this possibility (Perman et al. 2003, Neumayer 2010).

We argue that the concepts used in the discussion on ecosystem services and their inherent problems are clearly rooted in the WS–SS debate. Our major goal in this article is therefore to establish the link between the environmentalist's paradox and the broader WS–SS debate. Moreover, we will argue that this apparent paradox may indicate a conceptual deficiency of discussing the relationship between human beings and nature only by means of capital substitutability and ecosystem services. Finally, we formulate several future research tracks in light of these findings.

The environmentalist's paradox

The statement of the environmentalist's paradox by Raudsepp-Hearne and colleagues (2010) is based on the (2005) findings of the Millennium Ecosystem Assessment (MA). Out of 24 provisioning (e.g., fishery supplies and timber), regulating (e.g., climate regulation and erosion control), and cultural ecosystem services (e.g., ecotourism and aesthetic values), the MA reported 15 ecosystem services that were being degraded or used unsustainably at the global scale (table 1). Moreover, the demand of ecosystem services has, in general, increased in the past 50 years (only fuel wood, capture fisheries, and wild foods showed mixed or declining trends in demand). In addition, the MA (2005) simultaneously identified a steady improvement of human well-being measured in terms of the Human Development Index (HDI; a weighted average of life expectancy, literacy, educational attainment, and gross domestic product [GDP] per capita). Raudsepp-Hearne and colleagues (2010) therefore argued that the results of the MA (2005) contradicted the expectation of environmentalists in the sense that the destruction of ecosystem services seems to not have led to declines in human well-being.

Table 1.

Trends in supply for ecosystem services (adapted from Raudsepp-Hearne and colleagues 2010).

TrendProvisioning ecosystem servicesRegulating ecosystem servicesCultural ecosystem services
Declining supply Fuel wood, genetic resources, biochemical, freshwater, capture fisheries, wild foods Local climate regulation, erosion control, water quality regulation, pest control, pollination, natural hazard regulation Spiritual and religious values, aesthetic values 
Increasing supply Crops, livestock, aquaculture Global climate regulation  
Mixed trends in supply Timber, cotton Water flow regulation, disease control Recreation and ecotourism 
TrendProvisioning ecosystem servicesRegulating ecosystem servicesCultural ecosystem services
Declining supply Fuel wood, genetic resources, biochemical, freshwater, capture fisheries, wild foods Local climate regulation, erosion control, water quality regulation, pest control, pollination, natural hazard regulation Spiritual and religious values, aesthetic values 
Increasing supply Crops, livestock, aquaculture Global climate regulation  
Mixed trends in supply Timber, cotton Water flow regulation, disease control Recreation and ecotourism 
Table 1.

Trends in supply for ecosystem services (adapted from Raudsepp-Hearne and colleagues 2010).

TrendProvisioning ecosystem servicesRegulating ecosystem servicesCultural ecosystem services
Declining supply Fuel wood, genetic resources, biochemical, freshwater, capture fisheries, wild foods Local climate regulation, erosion control, water quality regulation, pest control, pollination, natural hazard regulation Spiritual and religious values, aesthetic values 
Increasing supply Crops, livestock, aquaculture Global climate regulation  
Mixed trends in supply Timber, cotton Water flow regulation, disease control Recreation and ecotourism 
TrendProvisioning ecosystem servicesRegulating ecosystem servicesCultural ecosystem services
Declining supply Fuel wood, genetic resources, biochemical, freshwater, capture fisheries, wild foods Local climate regulation, erosion control, water quality regulation, pest control, pollination, natural hazard regulation Spiritual and religious values, aesthetic values 
Increasing supply Crops, livestock, aquaculture Global climate regulation  
Mixed trends in supply Timber, cotton Water flow regulation, disease control Recreation and ecotourism 

Weak versus strong sustainability

One could observe the relationship between man and nature through the lens of natural-capital stock yielding ecosystem services, which eventually affects human well-being. Capital is seen as a key concept in ensuring well-being and should therefore not decline over time. Capital is “the stock that possesses the capacity of giving rise to flows of goods and/or services” (Ekins et al. 2003, p. 166). Natural capital represents the ecosystem structures and processes that provide ecosystem functions (regulation, habitat, production, and information), which yield several natural goods and ecosystem services (de Groot et al. 2002). The WS–SS debate since the 1990s has held a focus on the substitutability of natural capital. We elaborate on the notions of WS and SS below. Subsequently, we illustrate the main criticisms of the WS–SS discussion as a whole.

Weak sustainability.

Supporters of WS suggest that natural capital and human-made capital are, in general, interchangeable with respect to well-being improvement (Dietz and Neumayer 2007). This means that depletion of one form of capital can be compensated by a surplus of the other one. The WS concept originates in the 1970s as a by-product of neoclassical economic theories used in the search for an optimal extraction path for nonrenewable natural resources. Dasgupta and Heal (1974) claimed that because of a positive utility-discount rate and the scarce nature of nonrenewable resources, consumption would fall to zero in the long run. In order to avoid this undesirable outcome and instead to achieve sustained well-being over time, Solow (1974) asserted that early generations may extract exhaustible resources in an optimal way, as long as they add optimally to the stock of reproducible capital. Hartwick (1977) refined this statement and proposed the savings investment rule (now known as the Hartwick rule). According to this rule, the rents (defined as the difference between the price at which one can sell the concerned resources and all associated costs) from exhaustible-resource depletion should be saved and reinvested in produced capital in order to achieve nondeclining consumption. The Hartwick rule is in fact the statement of WS: If resources are optimally extracted, reinvestment may offset these losses so that the total capital stock will not fall over time. As a result, natural capital and human-made capital are generally substitutes for each other from the WS perspective. For WS advocates, monetary valuation of natural resources, ecosystem services and future environmental damage is the most important objective. The WS paradigm supposes that sufficient technological progress can improve human well-being despite environmental damage.

The initial strong-sustainability stance: Maintaining the economic value of natural capital.

The SS paradigm originates as a countermovement to the neoclassical WS paradigm. Adherents of SS argue that natural and human-made capital may be regarded as substitutes for each other in an “empty” world in which human-made capital is limiting and natural capital superabundant. However, in the current “full” world, natural and human-made capital should be regarded as complements, because natural capital is becoming the limiting factor and human-made capital the superabundant one. Therefore, from the perspective of SS supporters, natural capital should be maintained (Daly 1995). Contrary to the WS advocates, SS adherents are generally pessimistic with regard to the possibility of technological progress. Daly (1995) furthermore argued that SS does not mean that “no species could ever go extinct, nor any nonrenewable resource should ever be taken from the ground, no matter how many people are starving,” and dismissed this idea as “absurdly strong sustainability” (p. 49). SS refers to the separate protection of the different natural capital forms. From this perspective, the value of natural capital should not decline. Unlimited replacements within natural capital are assumed possible. The rents from oil extraction could, for example, be partly invested in future energy provision. (Dietz and Neumayer 2007). As in the case of WS, natural capital should then be measured in monetary terms (Hanley 2000).

Strong sustainability through the determination of critical natural capital.

The two paradigms described above have in common that they take an economic perspective with respect to natural capital, in the sense that it could be monetarily valued. This perspective is, however, increasingly contested. According to Douai (2009), two implicit assumptions could prove troublesome. First, monetary valuation of the environment presumes commensurability of environmental values (i.e., all different kinds of human wants can be translated into monodimensional utility). Second, one supposes the commodification of natural resources (i.e., this utility can be transformed into monetary values). For these two reasons, several authors have advocated the noncompensability of the environment (e.g., Munda 1997, Spash 1999, Trainor 2006). This line of reasoning constitutes another strand within ecological economics that puts a particular emphasis on discussing natural capital in physical instead of in monetary terms (Özkaynak et al. 2004). This interpretation of SS implies that an essential physical subset of natural capital must be preserved, because this critical natural capital (CNC) cannot be substituted for by any form of human-made capital (de Groot et al. 2002, Chiesura and de Groot 2003). Consequently, neither substitutions between natural capital and human-made capital nor substitutions among different forms of CNC are permitted under this point of view. This viewpoint of SS therefore allows for environmental damage only if environmental functions irreplaceable by human-made capital are not affected.

Problems in the weak–strong sustainability debate.

The WS–SS debate is discussed by means of the notion of capital. However, several authors have expressed doubt about whether the capital perspective is a suitable approach to adequately describe the complex characteristics of the natural world. Jamieson (1998) argued that natural capital implicitly draws on the idea of human transformation and use. Nature is only regarded as natural capital if it serves human needs, whereas the difference between natural and human-made capital is difficult to determine in many cases. Cultivated natural capital (i.e., capital that cannot be fully claimed by either nature or humans, such as agricultural land and planted forests) plays a particularly ambiguous role under this point of view (Holland 1997, Åkerman 2003). Although this issue is raised by environmental philosophers, ecologists intuitively categorize all living matter (and therefore agricultural land) as natural capital, since it is integrated into the ecosystem. In this light, the MA (2005) perceived food-provisioning services as ecosystem services yielded from natural capital. Ecosystem services should therefore be regarded not only as parts of nature that ought to be protected but also as components of nature that could be actively (and artificially) improved.

Another important concept in the WS–SS discussion is the substitutability of capital forms. This economic notion also shows several conceptual problems. Holland (1997) offered a linguistic insight in this regard by postulating two ambiguities concerning substitution: purpose and degree. The substitutability of an object largely depends on its purpose: According to its purpose, human beings decide whether the substitute is adequate. If one is interested in nutritional value, one may, for example, substitute one apple for another. However, if one is concerned about the specific flavor, the latter apple may not be a perfect substitute. In addition, this example shows that an object is often neither completely substitutable nor fully complementary: The degree of substitutability may vary. As a consequence, (the degree of) substitutability is, to a significant extent, context dependent.

The real world, with its complexities, moreover poses many more problems for the question of substitutability. We find it striking that many SS supporters who recognize the inherent complexity of the ecosystem draw on very simple examples to prove their points. Daly (1995) claimed, for example, that fisheries are complementary to fishing boats, whereas Jacobs (1995) argued that the value of the ozone layer cannot be substituted for by sunscreen creams. Next to the contextual caveat described above, these two examples share the feature of having a clear link between the environmental function (yielding ecosystem services useful for human beings) and the environmental structure (i.e., what is physically needed to provide the environmental function; Daly and Farley 2011). In the former example, the fisheries offer a food-provisioning function, whereas the fishing boats are alleged to be complementary to this environmental function. In the latter example, both the ozone layer and sunscreen creams are connected with the reduction of UV rays. However, such a relationship is often not straightforward. Imagine, for example, that some sort of human-made capital can substitute for the environmental function of climate regulation. What environmental structure does it then concretely substitute for—an amalgam of land, trees, other vegetation, atmospheric gas mixture, humidity, and so on? Moreover, trees, which are essential for climate regulation, contribute to several other environmental functions, such as erosion control, shading, and food provision. To put it in a general way, the WS–SS discussion may be too limited to describe the complexity and overlap of environmental functions and environmental structures.

In this light, Georgescu-Roegen (1971) interestingly made a distinction between stock flows and fund-service resources. Stock–flow resources can be transformed to products serving human needs and are, as a result, physically used up (e.g., oil reserves). Fund-service resources are not materially used up, can only be used at a certain rate, and are therefore worn out (e.g., water resources). Note that many ecosystem services by definition belong to the latter category. Although the stock–flow framework is appropriate for provisional services, it may be less suitable for regulating and cultural services. The inability to use many ecosystem services at the preferred rate and the fact that large disruptions thereof may irreversibly cause environmental disasters that lead to a complete collapse of human well-being means that although the stock–flow framework is often used to discuss ecosystem services, it is, in fact, often unsuitable (Daly and Farley 2011).

Furthermore, the capital view of nature seems to bypass any ethical arguments. The WS–SS discussion basically takes an anthropological, needs-based perspective. Jamieson (1998) suggested that SS adherents may confuse a normative claim with a descriptive claim. According to Jamieson (1998), SS supporters may be more concerned with the ethical obligation that natural capital ought to be nonsubstitutable than they are with whether it actually is. When Daly (2005) stated that “as the world becomes full of us and our stuff, it becomes empty of what was here before” (p. 100), this indeed exclaims a fear of decline of the natural world rather than of human well-being. This may be one of the reasons that the SS paradigm has shifted toward arguments in favor of preserving CNCs with more certain nonsubstitutability characteristics. However, with discussion of the relationship between nature and human beings only through the lens of capital substitution, this debate may be narrowed down to the sole consideration of its feasibility and not its moral desirability. Jamieson (1998) therefore saw the question of whether nature is a force of good as indispensable. A negative answer to this question would mean the acceptance of the hypothetical possibility of a world full of stuff without nature. Beckerman (1994, 1995) seemed to support this stance, since he found the attribution of an independent intrinsic value to nature doubtful. Conversely, an affirmative answer would protect all nature without exception. This stance has the disadvantage of allowing for the very real possibility that human well-being could decline. The complete prohibition of environmental degradation—even if it would substantially improve human well-being—may be unreasonable in light of current trends of rising world-population pressure. Nevertheless, human actions often strongly—and above all, irreversibly—affect the natural world, so that current natural destruction could leave future generations with no possibility of an ethical choice at all. This imposes a questionable situation for future generations in which there are ever-changing and plausibly disruptive relationships between humanity and nature. Consequently, we fully agree with the following moderate conclusion of Holland (1997): “On the one hand… the ‘crisis’—the rate and extent of the loss of the natural world—is not (just) an economic crisis, and on the other hand… the loss of ‘nature’ is not (just) the loss of a romantic ideal, but the loss of our own history and that of the community of life to which we belong” (p. 133). In the needs-based perspective of the capital approach, a social contract with future generations is missing. In this light, the shift toward a rights-based view of sustainable development may be more suitable (Redclift 2005, Vucetich and Nelson 2010).

Ultimately, even if the WS–SS debate is a valid one that does not have to pass any ethical test, the fundamental problem remains that it is very difficult to test which sustainability paradigm is more correct. Neumayer (2010) maintained that both WS and SS supporters make assumptions and claims about the distant future that are dogmatic and uncontestable. Because predictions concerning the future are intrinsically subject to uncertainty and risk, the SS perspective is more cautious (Figge 2005). Nonetheless, the debate essentially boils down to a belief (WS supporters) or disbelief (SS adherents) in the value of technological progress (Perman et al. 2003).

Linking the environmentalist's paradox to the debate on weak versus strong sustainability

The debate on the environmentalist's paradox is embedded in a broader discussion on the substitutability of natural and human-made capital or, in other words, the WS–SS discussion. If the environmentalist's paradox indeed holds, the SS supporters will have suffered a crushing defeat. Because natural and human-made capital are essentially nonsubstitutable for each other according to the SS paradigm, destruction of the natural-capital stock would lead to declining ecosystem services and, eventually, to a decline in human well-being. Despite indications of declining ecosystem services (and therefore a deterioration of the natural-capital stock), the MA (2005) claimed that human well-being is improving.

Raudsepp-Hearne and colleagues (2010) suggested four possible explanations of the environmentalist's paradox. First, the measurement of well-being could be inaccurate, because the relevant variables could have been badly chosen or the data aggregation of the HDI could mask declines in well-being. There are large discrepancies between rural and urban areas, but life expectancy, literacy, educational attainment, and GDP have, however, increased steadily. Moreover, these dimensions of well-being correlate strongly with other dimensions. Raudsepp-Hearne and colleagues (2010) therefore rejected this hypothesis. Duraiappah (2011), however, questioned this suggested rejection. Concretely, he argued that aggregate human well-being measures, such as the HDI and the per capita gross net product, do not capture other essential components of well-being, such as social relations, security, and freedom of choice. In addition, the well-being measures that directly include natural capital do show declines of well-being, which moreover could be attributed to the deterioration of ecosystem services. According to Duraiappah (2011), multidimensional indicators might be more suitable for evaluating well-being.

Both WS and SS supporters reject the possibility that GDP would be a good proxy of human well-being. For WS advocates, the main problem with GDP is that it does not take into account environmental and human-made damage, which diminishes actual human well-being. Therefore, they subtract the concerned depreciations from the original well-being measure. Well-known examples are green GDP (Repetto 1989) and genuine savings (Pearce and Atkinson 1993). On top of these concerns, SS followers also criticize the fact that several other negative externalities are counted as positive contributions to GDP (in addition to environmental damage—e.g., defense expenditure and costs of income inequality). Considering these issues, Daly and Cobb (1992) developed the Index of Sustainable Economic Welfare in which they calculate the “real” consumption possibilities. Ironically, this measure introduced by SS supporters presumes substitutability of the capital forms and therefore adheres in fact to the WS paradigm (Dietz and Neumayer 2007). Duraiappah (2011) correctly identified a problem of circular reasoning when one applies such aggregate measures to assess human well-being. Since one presumes ex ante that environmental (and other) damage diminishes current human well-being, one cannot validate the environmentalist's paradox. Note that internalizing externalities, as was suggested by Nelson (2011), therefore also faces this problem. In addition, the use of multidimensional measures may be interesting, but these thwart the possibility of comparability. In other words, it is then difficult to determine whether human well-being has improved or declined.

Second, it is plausible that only provisioning ecosystem services (in particular, food production) play an important role for human well-being. As is indicated in table 1, the production of crops, livestock, and aquaculture has grown, which contrasts the mostly decreasing regulating and cultural ecosystem services. Although Raudsepp-Hearne and colleagues (2010) argued that earlier studies indicated a strong correlation between the trends in HDI and food-provisioning services, they did not find a clear positive impact of nonfood services on the HDI. Consequently, they argued that the benefits of food services outweigh the costs of nonfood services. Nevertheless, they did recognize that there is considerable evidence that the decline of several nonfood services can harm human well-being at the regional level and indirectly through damage of food services due to environmental degradation.

In the previous section, we illustrated that one of the strands of the SS paradigm emphasized the importance of physically preserving a subset of CNC. This CNC is seen as a nonsubstitutable natural-capital stock that is essential to human well-being. Therefore, one might question whether the ecosystem services from the MA (2005) are “critical” ecosystem services in the sense that they adhere to the CNC framework. One could argue that an affirmative answer would support the WS stance, since there would then be evidence that CNC is not that critical after all to the improvement of human well-being. It is tempting to follow this reasoning; the connection between food production and human well-being is clear. The answer is, however, not clear cut, because the border between CNC and natural capital seems to be so blurry (Ekins 2003) that the two terms are used interchangeably: The ecosystem services described by the MA (2005), de Groot and colleagues (2002), and Ekins and colleagues (2003) are very similar, although the second and third study involved natural capital and CNC, respectively. In practice, ecological complexity seems therefore to have led to an enlargement of the list of critical ecosystem services to the extent that there is no use anymore in calling it “critical.” However, this is a result of the ecosystem's being so interdependent—that it is impossible to compile a short list of a small amount of critical services. Norgaard (2010) asserted that a discussion about sustainability by way of ecosystem services would be insufficient. He maintains that the capital perspective of ecosystem services ignores many ecological facets, such as population dynamics, food webs, and coevolutionary processes.

The third possible solution to the environmentalist's paradox suggested by Raudsepp-Hearne and colleagues (2010) is founded on the hypothesis of the delinking of human well-being from ecosystem deterioration by means of ample technical and innovative progress. Despite rising efficiencies with regard to the use of ecosystem services, Raudsepp-Hearne and colleagues postulated, following the MA (2005), that both the use of ecosystem services itself and the demand for them increase in most cases. As a result, technical progress is achieved primarily at the supply side and not at the demand side. Interestingly, Raudsepp-Hearne and colleagues (2010) also framed technological progress as an issue of substitution: Deteriorating ecosystem services can be compensated for by improved engineering services. They claimed, for example, that the introduction of fertilizers has improved human well-being noticeably, with only a very small additional amount of ecosystem services' being used. Nonetheless, the track record of technology replacing ecosystem services is rather mixed. Raudsepp-Hearne and colleagues (2010) concluded that there is no convincing evidence of the decoupling of society's well-being from ecosystems.

This argument lies at the heart of the WS–SS discussion. WS supporters believe in productivity-improving processes with regard to natural resources and the environment à laSolow (1974) that may offset resource scarcity and other environmental problems. In addition, they assert that ecosystem services can be interchanged with human-made services. As was mentioned in the discussion of the previous argument of Raudsepp-Hearne and colleagues (2010), we should beware that ecosystem services that do not have a direct use for humanity can still be essential in terms of general ecosystem resilience. Next to the fact that declining ecosystem services in conjunction with improving human well-being do not argue in favor of the SS paradigm, the repudiation of these two points in the study of Raudsepp-Hearne and colleagues (2010) therefore also erodes the validity of the WS stance.

As a fourth explanation, Raudsepp-Hearne and colleagues (2010) suggested that there could be a time lag between the ecosystem-service damage and the impact on human well-being. According to Raudsepp-Hearne and colleagues (2010), this hypothesis is very difficult to test because of the high uncertainty involved in determining its duration, strength, and generality. At the local level, there is weak empirical support for this hypothesis, according to Raudsepp-Hearne and colleagues (2010). However, they claimed that this confirmation is not clear cut at all at the global level. However, Raudsepp-Hearne and colleagues (2010) recognized the danger of an accumulation of local disturbances of ecosystem services leading to large disruptions at the global scale if the tipping point is exceeded. The human capacity to adapt to such changes in ecosystem services is also highly uncertain. In conclusion, Raudsepp-Hearne and colleagues (2010) argued that the evidence of a time lag is mixed. Nelson (2011) put forward that making a distinction between resource flows and resource stocks may help untangle the environmentalist's paradox. Although the former is assessed per unit of time, the latter lacks such a time dimension. Ecosystem services are flows, since they are the streams that can be yielded from the natural-capital stock. However, the natural-capital stock could be declining in such a way that the stream of ecosystem services also declines, which would eventually lead to a decline in human well-being.

The distinction between stocks and flows is indeed crucial from the capital perspective. However, we do not agree with Nelson (2011) that this distinction helps explain the environmentalist's paradox. Note that—strictly speaking—the stock–flow framework does not imply time lags between the deterioration of ecosystem services and a decline in human well-being, although it may suggest time lags between declining capital stock and declining human well-being. Following this framework, declining natural-capital stock is expected to eventually decrease ecosystem services. Because ecosystem services are assumed to be directly linked to human well-being, their degradation would affect human well-being immediately if they cannot be substituted by human-made services. Even taking into account the possibility of time lags, the declining trend of ecosystem services, in combination with the improving human well-being shown in the MA (2005) as a result, does not argue in favor of the validation of the stock–flow framework. Consequently, although a time lag may separate the environmental deterioration from the complete collapse of the ecosystem feared by Duraiappah (2011), the stock–flow framework seems to be inadequate in this light.

Supporters of SS postulate that natural-capital stock ought to be protected in order to preserve human well-being. From this perspective, the finding of Raudsepp-Hearne and colleagues (2010) that human well-being improved in spite of declining ecosystem services does not support the SS stance. WS adherents argue that human well-being can still improve in cases of declining ecosystem services, as long as technological progress sufficiently increases efficiency with regard to natural resource use or environmental damage or decreasing ecosystem services are compensated for by enhanced human-made services. Since Raudsepp-Hearne and colleagues (2010) illustrated that these two WS conditions are not sufficiently satisfied, the WS paradigm cannot be considered validated either. It is possible that not all ecosystem services play an important role with respect to human well-being. However, making a simple short list of ecosystem services that directly benefit human beings would fundamentally undermine the interdependent character of ecosystems. Several ecosystems can be damaged in such way that other ecosystems can also be affected. Furthermore, a time factor may play a key role: If environmental pressure exceeds the tipping point, ecosystems can collapse completely, which would result in severe effects on human well-being.

Neither the WS nor the SS paradigm can therefore be validated by means of the environmentalist's paradox. Because the WS–SS discussion builds on the stock–flow framework, this means that the concept of a natural-capital stock yielding ecosystem services is likely to be inaccurate. Concretely, this discussion and the “Problems in the weak–strong sustainability debate” section reveal that the underlying implicit stock–flow framework considerably simplifies the complex relationship between human well-being and nature.

Conclusions

Environmentalists and ecologists generally adapt economic metaphors to describe the multifaceted relationship between the environment and human well-being. Nature is essentially perceived as a capital stock that provides utility streams to humanity in the form of ecosystem services. This framework has the merit of disseminating the debate on environmental issues to a wide target audience. Environmental, natural-resources and ecological economists, ecologists, and environmentalists have all been able to contribute to this important discussion. Since the 1990s, there has been an ardent debate on the substitutability between natural and human-made capital. Although WS supporters mainly believe that these two types of capital are substitutable for one another, SS followers generally contest the possibility of interchangeability.

We have linked the environmentalist's paradox initiated by Raudsepp-Hearne and colleagues (2010) and discussed by Duraiappah (2011), Nelson (2011), and Raudsepp-Hearne and colleagues (2011) with this WS–SS debate. Basically, the environmentalist's paradox states that ecosystem services seem to decline in general, whereas human well-being seems to improve. Because of the economic roots of the WS–SS debate, very similar argumentations are used in discussing the environmentalist's paradox. The debate on the environmentalist's paradox, however, clarifies that it also simultaneously stumbles on the same boundaries as the WS–SS discussion.

The underlying stock–flow framework of the environmentalist's paradox should, in our opinion, be treated with scrutiny. Although the reductive perspective on nature expressed in terms of ecosystem services offers a lucid framework for reasoning, an exclusive focus on this perspective would heavily erode the debate on the relationship between human beings and nature. Embracing complexity is no trivial task in sustainable development. On one hand, academia is becoming more and more specialized, inducing professional isolation and highly technical jargon. On the other hand, because this problem is increasingly acknowledged, it has led to more intense interdisciplinary collaboration. Although this cooperation is definitely needed, we should avoid sacrificing intricate subtleties for metaphors that, although they are easy to understand for all participants of the debate, severely simplify the complex reality.

Recommendations for future research.

Our criticism on the WS and SS paradigms does not mean that we deem the concerns of WS and SS supporters irrelevant. A focus on technological progress without seriously interfering with ecosystems, while being realistic about the ability to decouple environmental degradation from human well-being, seems a sensible yardstick. This “cautious positivism” should entail a truly transdisciplinary approach not only in which nature is seen as a natural-capital stock yielding ecosystem services but in which the complexity, irreversibility, uncertainty, and ethical predicaments intrinsic to the natural environment and its connections to humanity are also taken into account. We will make specific recommendations for economists, as well as biologists, ecologists, and agronomists in this regard.

We believe that economists interested in sustainable development should consider the nonlinear and interdependent character of ecological systems in their models. In mainstream neoclassical economics, this issue is unfortunately rarely taken into account. The recently emerged concept of sustainability economics within the ecological-economics community, which “is ethically founded in the idea of efficiency—that is, nonwastefulness—in the use of scarce resources for achieving the two normative goals of (1) the satisfaction of the needs and wants of individual humans and (2) justice, including justice between humans of present and future generations and justice toward nature, in the setting of human–nature relationships over the long-term and inherently uncertain future” (Baumgärtner and Quaas 2010, p. 447, emphasis in the original) may present such insights.

Biologists, ecologists, and agronomists concerned with sustainable development should, in our opinion, focus on approaches that enhance human well-being in view of a limited amount of natural resources and ecological interdependency. We concretely suggest three tracks of ongoing research that deserve particular attention.

First, one should concentrate on food production. Climate change shifts and will continue to shift our way of dealing with agriculture. Therefore, we recommend further elaborated research on improving the output of crops and livestock in face of this tremendous challenge. The resilience of agricultural production will depend to a large extent on the success of biotechnological innovations tailored to drought resistance (Blum 2011) and the willingness of farmers to adopt new technologies and to grow novel crops that show high productivity in changing climatic circumstances (Kenny 2011). This means that both technical and socioeconomic factors should be taken into consideration. Along with substantially increasing agricultural production, one should cope with the risks associated with climate change regarding agricultural yields. Smallholders in the developing world might therefore invest in mixed crop–livestock systems in which they can use animals as some sort of insurance in times of drought (Herrero et al. 2010). One should focus not only on adaptation to global warming but also on mitigation: An increase of 2 instead of 4 degrees Celsius is hypothesized to halve the impact of climate change (Warren 2011). Improving carbon sinks by means of, for example, soil-based sequestration (Glenk and Colombo 2011) and considerable reduction of carbon sources through, for example, a smart choice of technology or crops (Vergé et al. 2007) might decrease the rate of climate change.

Second, one should find a solution for the increases in energy demand due to a combination of significant population growth and exhaustion of fossil fuels. Although standard economics teaches us that high oil prices will drive us toward other energy sources, one must make sure that these energy alternatives are in fact available. Substitution by biofuels may play an essential role because of their nonexhaustibility. There remains, however, a fundamental hurdle in the sense that classical agricultural production (Hertel et al. 2010), as well as the combustion of biofuels (Gustafsson et al. 2009), may cause higher greenhouse gas emissions. Furthermore, biofuel crops directly compete for land with crops intended for food production (Harvey and Pilgrim 2011). Nevertheless, recent research developments give cause for hope: Microalgae potentially have a yield per hectare per year 7–31 times as high as the next-best crop, oil palm (Demirbas 2011). Although microalgae research is currently still at the initial stage, it seems promising to constitute at least a part of the solution to the energy problem (Scott et al. 2010).

Third, vulnerable species (either directly or indirectly) linked to human well-being should be conserved in the face of anthropogenic changes. Although we do not argue that every species should be protected without exception, we do believe that the list of species of concern will be very long, given the enormous complexity of ecosystems. The difficulty for ecologists is consequently that although only a few species directly contribute to human well-being, many more contribute indirectly by influencing the ecological equilibrium. Therefore, Rands and colleagues (2010) suggested that the implicit costs of biodiversity losses should be internalized in well-being measures. Furthermore, budget constraints complicate the process of choosing which species deserve conservation preference. There are some recent interesting studies in which this selection is made in a more systematic way. Wilson and colleagues (2011) suggested that giving priority to the most endangered species almost never results in a long-term optimum outcome. They claimed that it might be more beneficial to allocate resources to preventive conservation. Another innovative idea is to replace underperforming protected areas instead of directly augmenting current protected areas (Fuller et al. 2010).

These recommendations suggest that future human well-being will be determined by our success in dealing with the competing uses of land in a world full of complex interdependencies. Food production, biofuels, and species conservation are all important for human well-being, but there is clearly a space constraint. The (arguably) first ecological economist Kenneth Boulding (1966) seemed to be right: Our unlimited “cowboy economy” is indeed rapidly becoming a limited “spaceman economy.”

Acknowledgments

We thank three anonymous reviewers for their helpful comments. This article has benefited considerably from interesting discussions (especially with Liesbet Vranken) at the 13th Belgian PhD Symposium of Agricultural and Natural Resource Economics, Brussels, on 27 April 2011. We are grateful for the financial support of the European Fund for Regional Development project 475, Closing the Circle.

References cited

Åkerman
M
.
2003
.
What does ‘natural capital’ do? The role of metaphor in economic understanding of the environment
.
Environmental Values
12
:
431
448
.

Baumgärtner
S
Quaas
MF
.
2010
.
What is sustainability economics?
Ecological Economics
69
:
445
450
.

Beckerman
W
.
1994
.
‘Sustainable development’: Is it a useful concept?
Environmental Values
3
:
191
209
.

Beckerman
W
.
1995
.
How would you like your ‘sustainability’, sir? Weak or strong? A reply to my critics
.
Environmental Values
4
:
169
179
.

Blum
A
.
2011
.
Plant Breeding For Water-Limited Environments
.
Springer
.

Boulding
KE
.
1966
.
The economics of the coming Spaceship Earth
. Pages
3
14
in
Jarrett
H
, ed.
Environmental Quality in a Growing Economy
.
Resources for the Future/Johns Hopkins University Press
.

Callan
SJ
Thomas
JM
.
2000
.
Environmental Economics and Management: Theory, Policy, and Applications
.
Dryden Press
.

Chiesura
A
de Groot
R[S]
.
2003
.
Critical natural capital: A socio-cultural perspective
.
Ecological Economics
44
:
219
231
.

Common
M
Stagl
S
.
2005
.
Ecological Economics: An Introduction
.
Cambridge University Press
.

Daly
HE
.
1995
.
On Wilfred Beckerman's Critique of Sustainable Development
.
Environmental Values
4
:
49
55
.

Daly
HE
.
2005
.
Economics in a full world
.
Scientific American
3
:
100
107
.

Daly
HE
Cobb
JB
Jr
.
1992
.
For the Common Good: Redirecting the Economy toward Community, the Environment, and a Sustainable Future
.
Beacon Press
.

Daly
HE
Farley
J
.
2011
.
Ecological Economics: Principles and Applications
, 2nd ed.
Island Press
.

Dasgupta
P
Heal
G
.
1974
.
The optimal depletion of exhaustible resources
.
Review of Economic Studies
41
:
3
28
.

De Groot
RS
Wilson
MA
Boumans
RMJ
.
2002
.
A typology for the classification, description and valuation of ecosystem functions, goods and services
.
Ecological Economics
41
:
393
408
.

Demirbas
MF
.
2011
.
Biofuels from algae for sustainable development
.
Applied Energy
88
:
3473
3480
.

Dietz
S
Neumayer
E
.
2007
.
Weak and strong sustainability in the SEEA: Concepts and measurement
.
Ecological Economics
61
:
617
626
.

Douai
A
.
2009
.
Value theory in ecological economics: The contribution of a political economy of wealth
.
Environmental Values
18
:
257
284
.

Duraiappah
AK
.
2011
.
Ecosystem services and human well-being: Do global findings make any sense?
BioScience
61
:
7
8
.

Ekins
P
.
2003
.
Identifying critical natural capital: Conclusions about critical natural capital
.
Ecological Economics
44
:
277
292
.

Ekins
P
Simon
S
Deutsch
L
Folke
C
de Groot
R[S]
.
2003
.
A framework for the practical application of the concepts of critical natural capital and strong sustainability
.
Ecological Economics
44
:
165
185
.

Figge
F
.
2005
.
Capital substitutability and weak sustainability revisited: The conditions for capital substitution in the presence of risk
.
Environmental Values
14
:
185
201
.

Fuller
RA
McDonald-Madden
E
Wilson
KA
Carwardine
J
Grantham
HS
Watson
JEM
Klein
CJ
Green
DC
Possingham
HP
.
2010
.
Replacing underperforming protected areas achieves better conservation outcomes
.
Nature
466
:
365
367
.

Georgescu-Roegen
N
.
1971
.
The Entropy Law and the Economic Process
.
Harvard University Press
.

Glenk
K
Colombo
S
.
2011
.
Designing policies to mitigate the agricultural contribution to climate change: An assessment of soil based carbon sequestration and its ancillary effects
.
Climatic Change
105
:
43
66
.

Gustafsson
Ö
Kruså
M
Zencak
Z
Sheesley
RJ
Granat
L
Engström
E
Praveen
PS
Rao
PSP
Leck
C
Rodhe
H
.
2009
.
Brown clouds over South Asia: Biomass or fossil fuel combustion?
Science
323
:
495
498
.

Hanley
N
.
2000
.
Macroeconomic measures of ‘sustainability
.’
Journal of Economic Surveys
14
:
1
30
.

Hartwick
JM
.
1977
.
Intergenerational equity and investing of rents from exhaustible resources
.
American Economic Review
67
:
972
974
.

Harvey
M
Pilgrim
S
.
2011
.
The new competition for land: Food, energy, and climate change
.
Food Policy
36
(
suppl.
):
S40
S51
.

Herrero
M
et al. .
2010
.
Smart investments in sustainable food production: Revisiting mixed crop-livestock systems
.
Science
327
:
822
825
.

Hertel
TW
Golub
AA
Jones
AD
O'Hare
M
Plevin
RJ
Kammen
DM
.
2010
.
Effects of US maize ethanol on global land use and greenhouse gas emissions: Estimating market-mediated responses
.
BioScience
60
:
223
231
.

Holland
A
.
1997
.
Substitutability: Why strong sustainability is weak and absurdly strong sustainability is not absurd
. Pages
119
134
in
Foster
J
, ed.
Valuing Nature? Economics, Ethics and Environment
.
Routledge
.

Jacobs
M
.
1995
.
Sustainable development, capital substitution and economic humility: A response to Beckerman
.
Environmental Values
4
:
57
68
.

Jamieson
D
.
1998
.
Sustainability and beyond
.
Ecological Economics
24
:
183
192
.

Kates
RW
Parris
TM
Leiserowitz
AA
.
2005
.
What is sustainable development? Goals, indicators, values, and practice
.
Environment
47
:
8
21
.

Kenny
G
.
2011
.
Adaptation in agriculture: Lessons for resilience from eastern regions of New Zealand
.
Climatic Change
106
:
441
462
.

[MA] Millennium Ecosystem Assessment
.
2005
.
Ecosystems and Human Well-being: Synthesis
.
Island Press
.

Malthus
TR
.
1798
.
An Essay on the Principle of Population, as It Affects the Future Improvement of Society
.
With Remarks on the Speculations of Mr. Godwin, Mr. Condorcet, and Other Writers. (www.esp.org/books/malthus/population/malthus.pdf; 5 January 2012)

Munda
G
.
1997
.
Environmental Economics, Ecological Economics, and the Concept of Sustainable Development
.
Environmental Values
6
:
213
233
.

Nelson
GC
.
2011
.
Untangling the environmentalist's paradox: Better data, better accounting, and better technology will help
.
BioScience
61
:
9
10
.

Neumayer
E
.
2010
.
Weak versus Strong Sustainability: Exploring the Limits of Two Opposing Paradigms
, 2nd ed.
Edward Elgar
.

Norgaard
RB
.
2010
.
Ecosystem services: From eye-opening metaphor to complexity blinder
.
Ecological Economics
69
:
1219
1227
.

Özkaynak
B
Devine
P
Rigby
D
.
2004
.
Operationalising strong sustainability: Definitions, methodologies and outcomes
.
Environmental Values
13
:
279
303
.

Pearce
DW
Atkinson
GD
.
1993
.
Capital theory and the measurement of sustainable development: An indicator of “weak” sustainability
.
Ecological Economics
8
:
103
108
.

Perman
R
Ma
Y
Common
M
Maddison
D
Mcgilvray
J
.
2003
.
Natural Resource and Environmental Economics
.
Pearson Education
.

Rands
MRW
et al. .
2010
.
Biodiversity conservation: Challenges beyond 2010
.
Science
329
:
1298
1303
.

Raudsepp-Hearne
C
Peterson
GD
Tengö
M
Bennett
EM
Holland
T
Benessaiah
K
Macdonald
GK
Pfeifer
L
.
2010
.
Untangling the environmentalist's paradox: Why is human well-being increasing as ecosystem services degrade?
BioScience
60
:
576
589
.

Raudsepp-Hearne
C
Peterson
GD
Tengö
M
Bennett
EM
.
2011
.
The paradox persists: How to resolve it?
BioScience
61
:
11
12
.

Redclift
M
.
2005
.
Sustainable development (1987–2005): An oxymoron comes of age
.
Sustainable Development
13
:
212
227
.

Repetto
R
.
1989
.
Renewable resources and population growth: Past experiences and future prospects
.
Population and Environment
10
:
221
236
.

Scott
SA
Davey
MP
Dennis
JS
Horst
I
Howe
CJ
Lea-Smith
DJ
Smith
AG
.
2010
.
Biodiesel from algae: Challenges and prospects
.
Current Opinion in Biotechnology
21
:
277
286
.

Solow
RM
.
1974
.
Intergenerational equity and exhaustible resources
.
Review of Economic Studies
41
:
29
45
.

Spash
CL
.
1999
.
The development of environmental thinking in economics
.
Environmental Values
8
:
413
435
.

Trainor
SF
.
2006
.
Realms of value: Conflicting natural resource values and incommensurability
.
Environmental Values
15
:
3
29
.

Vergé
XPC
De Kimpe
C
Desjardins
RL
.
2007
.
Agricultural production, greenhouse gas emissions and mitigation potential
.
Agricultural and Forest Meteorology
142
:
255
269
.

Vucetich
JA
Nelson
MP
.
2010
.
Sustainability: Virtuous or vulgar?
BioScience
60
:
539
544
.

Warren
R
.
2011
.
The role of interactions in a world implementing adaptation and mitigation solutions to climate change
.
Philosophical Transactions of the Royal Society A
369
:
217
241
.

[WCED] World Commission on Environment Development
.
1987
.
Our Common Future
.
Oxford University Press
.

Wilson
HB
Joseph
LN
Moore
AL
Possingham
HP
.
2011
.
When should we save the most endangered species?
Ecology Letters
14
:
886
890
.

Author notes

Frederic Ang (frederic.ang@uhasselt.be) is a researcher and Steven Van Passel is an assistant professor in the Department of Business Economics at Hasselt University, in Diepenbeek, Belgium. They study problems with regard to the environment and natural resources from an economic perspective.