Serageldin, Ismail, Herman Daly and Robert Goodland. 1994. "The Concept of Environmental Sustainability." Chapter for the Institute for Environment and Systems Analysis's (ed.) Principles of Sustainable Development. Amsterdam, Netherlands.

Summary: The paper is divided into four sections as follows:

Natural capital and sustainability (see p. 2-5):

Natural capital is "the stock of environmentally provided assetswhich provide a flow of useful goods or services" (p. 2). It is scarcity of natural capital which limits economic development.

Sustainability has four levels: weak, sensible, strong and absurdly strong.

According to the authors, economic logic requires investment in the limiting factors, natural and human-made capital. They argue, "operationally, this translates into: encouraging the growth of natural capital by reducing our level of current exploitation; investing in projects to relieve pressure on natural capital stocks; and by increasing the end-use efficiency of products" (p. 4). See Figure 1: Comparison of Social, Economic and Environmental Sustainability (p. 5)

Criteria for environmental sustainability (see p. 6-15): See Figure 2: Rules-of-thumb for Environmental Sustainability (p. 6).

Output Rule: Waste emissions from a project should be within the assimilative capacity of the local environment to absorb without unacceptable degradation of its future waste absorptive capacity or other important services.

Input Rule: (a) Renewables: harvest rates of renewable resource inputs would be within regenerative capacity of the natural system that generates them; and (b) Non-renewables: depletion rates of nonrenewable resource inputs should be equal to the rate at which renewable substitutes are developed by human invention and investment.

Ehrlich and Holdren's (1974) model for human carrying capacity says that impact (I) is equal to population (P) times affluence (A) times technology (T). Population is human numbers. Affluence is consumption per capita and technology refers to environmental impact per unit of output.

A dynamic formulation: from sustainability to sustainable development. The authors present three questions which monitor progress toward sustainability (see p. 16-19):

Given the political unreality of a voluntary decline in the overall affluence of industrial countries, how is the "pattern" of this affluence shifting?

What is the trend in the consumption of natural resources per unit of output?

To what extent is the pollution impact per unit of economic activity declining? See Figure 5: Economic Activity and the Environment (p. 17).

World Bank progress towards sustainable development (see p. 20-4): The agenda includes:

Assisting borrowing countries in promoting environmental stewardship.

Assessing and mitigating whatever adverse impacts are associated with Bank-financed projects.

Building on the positive synergies between development and the environment (often called "win-win" strategies.

Addressing the global environmental challenges.

Keywords: environmental sustainability, natural capital, The World Bank