The Second Law of Thermodynamics states that in any closed isolated system, available energy and matter are continuously and irrevocably degraded to the unavailable state. Since the global economy operates within an essentially closed system, the Second Law (the entropy law) is actually the ultimate regulator of economic activity.
- There is no equilibrium in the energy and material relationships between industrial economies and the biosphere;
- Sustainable development based on prevailing patterns of resource use is not even theoretically conceivable.
The thermodynamic interpretation of the economic process therefore suggests a new definition of sustainable development which contrasts radically with present practice: sustainable development is development that minimises resource use and the increase in global entropy.
Eco-systems, unlike economic systems, are driven by an external source of energy - the sun. The steady stream of solar energy sustains essentially all biological diversity and makes possible the diversity of life on earth. Through photosynthesis, living systems concentrate simple dispersed chemicals and use them to synthesise the most complex substances known. Thus, in contrast to economic systems, eco-systems steadily contribute to the accumulation of concentrated energy, matter and order within the biosphere. In thermodynamic terms, photosynthesis is the most important materially productive process on the planet and it is the ultimate source of all renewable resources used by the human economy. Moreover, since the flow of solar radiation is constant, steady and reliable, resource production in the ecological sector is potentially sustainable over any time scale relevant to humanity. Ecological productivity is limited, however, by the availability of nutrients, photosynthetic efficiency, and ultimately the rate of energy input (the 'solar flux') itself. Eco-systems therefore do not grow indefinitely. Unlike the economy, which expands through resource conversion and positive feedback, eco-systems are held in 'steady-state' or dynamic equilibrium by limiting factors and negative feedback.
This means that much of our wealth is illusion. We have simply drawn down one account (the biosphere) to add to another (material wealth). It might even be argued that we have been collectively impoverished in the process. Much potentially renewable ecological capital has been permanently converted into machinery, plant and possessions that will eventually wear out and have to be replaced at the cost of additional resources.
Heilbroner has noted that the origin of surplus in the era of industrial capitalism 'has gradually moved from trade through direct wage labour exploitation toward technological rents, and that modern-day profits consist of combinations of all three.' We can now add a fourth profit source to Heilbroner's list; the irreversible conversion of biological resources.
For human society, carrying capacity can be defined as the maximum rate of resource consumption and waste discharge that can be sustained indefinitely without progressively impairing ecological productivity and integrity. The corresponding maximum human population is therefore a function of per capita rates of resource consumption and waste production.
It should be understood that while human society depends on many ecological resources and functions for survival, carrying capacity is ultimately determined by the single vital resource or function in least supply. (On the global scale, loss of the ozone layer alone could conceivably lead to the extinction of the human species.)
Such considerations call seriously to question the Brundtland Commission's route to sustainable development through a five-to-ten-fold increase in industrial activity. Indeed, it forces a reconsideration of the entire material growth ethic, the central pillar of industrial society.
William E. Rees, Ph.D., Associate Professor of Planning and Resource Ecology, University of British Columbia, School of Community and Regional Planning, 6333 Memorial Road, Vancouver, BC, Canada V6T 1W5.