Weak and strong sustainability

Weak and strong sustainability are terms that have emerged from the field of environmental economics and describe different approaches to sustainability, specifically in relation to natural resource management and economic development. Weak sustainability is applicable when certain natural and human capital assets are assessed as interchangeable, meaning that the use or loss of, for example, a reduction in natural capital can be considered sustainable if the simultaneous change in human capital meets or exceeds the value of the change in natural capital. It assumes that different types of capital can be measured and given value in the same way. Strong sustainability is applicable when a specific capital asset, typically a natural capital asset, is assessed as incommensurable or so valuable that it should be maintained or enhanced independently of changes in other, typically human-made, capitals. It particularly considers that certain natural assets have critical ecological functions that cannot be substituted by human-made alternatives. For example, according to weak sustainability, replacing a natural forest with a park or agricultural land can be considered sustainable if the recreational or economic value equal the value of the biodiversity lost and further environmental impact caused. According to strong sustainability, cutting down trees in a natural forest and planting new trees elsewhere might not be considered sustainable, when the value of biodiversity loss and wider ecological implications cannot be measured or offset. One of the first pieces of work to discuss these ideas was "Blueprint for a Green Economy" by Pearce, Markandya, and Barbier, published in 1989. This work laid the foundations for further discussion on the substitutability of natural capital (e.g., forests, water, and clean air) and human-made capital (e.g., buildings, machinery, and technology), and the implications for long-term ecological and economic health.

Origins and theory

Capital approach to sustainability and intergenerational equity To understand the concept of weak sustainability, it is first necessary to explore the capital approach to sustainability. This is key to the idea of intergenerational equity. This implies that a fair distribution of resources and assets between generations exists. Decision makers, both in theory and practice, need a concept that enables assessment in order to decide if intergenerational equity is achieved. The capital approach lends itself to this task. In this context we must distinguish between the different types of capital. Human capital (e.g. skills, knowledge) and natural capital (e.g. minerals, water) tend to be the most frequently cited examples. Within the concept it is believed that the amount of capital a generation has at its disposal is decisive for its development. A development is then called sustainable when it leaves the capital stock at least unchanged.

Sustainable development Although related, sustainable development and sustainability are two different concepts. Weak sustainability is an idea based upon the work of Nobel laureate Robert Solow, and John Hartwick. which states that 'human capital' can substitute 'natural capital'. The weak sustainability paradigm stems from the 1970s. It began as an extension of the neoclassical theory of economic growth, accounting for non-renewable natural resources as a factor of production. However, it only really came into the mainstream in the 1990s as the idea received more political attention as sustainable development discussions evolved in the late 1980s and early 1990s. A key landmark was the Rio Summit in 1992 where the vast majority of nation-states committed themselves to sustainable development. This commitment was demonstrated by the signing of Agenda 21, a global action plan on sustainable development. At its inception, sustainability was interpreted as a requirement to preserve, intact, the environment as we find it today in all its forms. The Brundtland Report, for example, stated that ‘The loss of plant and animal species can greatly limit the options of future generations. The result is that sustainable development requires the conservation of plant and animal species’.

Development of theory Wilfred Beckerman posits that the absolutist concept of sustainable development given above is morally repugnant. The largest part of the world's population live in acute poverty. Taking that as well as the acute degradation into account, one could justify using up vast resources in an attempt to preserve certain species from extinction. These species providing no real benefit for society other than a possible value for the knowledge of their continued existence. He argues that such a task would involve using resources that could have instead been devoted to more pressing world concerns. Examples include increasing access to clean drinking water or sanitation in the Third World. Many environmentalists shifted their attention to the idea of 'weak' sustainability. This allows for some natural resources to decrease as long as sufficient compensation is provided by increases in other resources. The result usually was an increase in human capital. This compensation is in the form of sustained human welfare. This is illustrated in a well-regarded definition by David Pearce, the author of numerous works on sustainability. He defines sustainability as implying something about maintaining the level of human welfare (or well-being) so that it may improve, but never declines (or, not more than temporarily). This implies sustainable development will not decrease over time. Inter-generational equity assumes each following generation has at least as much capital at its disposal as the preceding generation. The idea of leaving capital stock at least unchanged is widely accepted. The question arises, whether or not one form of capital may be substituted by another. This is the focus of the debate between 'weak' and 'strong' sustainability, and how intergenerational equity is to be achieved.

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