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A sunshine limit to growth

The following is a brief extract from a much longer article, entitled 'The Ecology of Sustainable Development' by William Rees, which appeared in Volume 20, No 1, of  the Ecologist (L3, or L18 subscription, from Worthyvale Manor, Camelford, Cornwall, PL32 9TT, tel 0840 212711).

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.

'Any form of economic activity dependent on material resources therefore contributes to a constant increase in global net entropy'


All modern economies are dependent on fixed stocks of non-renewable material and energy resources. The Second Law therefore declares that they necessarily consume and degrade the very resource base which sustains them. Our material economies treat other components of the biosphere as resources, and all the products of economic activity (that is both the by-products of manufacturing and the final consumer goods) are eventually returned to the biosphere as waste. Thus, while we like to think of our economies as dynamic, productive systems, the Second Law states that in thermodynamic terms, all material economic 'production' is in fact 'consumption'. Any form of economic activity dependent on material resources therefore contributes to a constant increase in global net entropy (disorder), through the continuous dissipation of available energy and matter. It follows that contrary to the assumptions of neo-classical theory: - 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.

'Eco-systems, unlike economic systems, are driven by an external source of energy - the sun'


The consumption of ecological resources everywhere has begun to exceed sustainable rates of biological production. Nearly 40 per cent of terrestrial net primary productivity (photosynthesis) is already being used or co-opted by humans, one species among millions, and the fraction is steadily increasing.

'Biosphere resources are becoming increasingly scarce and there are no substitutes'


At present, markets do not even recognise such factors as nutrient recycling, soil building, atmosphere maintenance and climate stabilisation as resources. Thus, while market economics can usually price the scarce material inputs to manufacturing, it is virtually silent on the value of biosphere processes. Not surprisingly, it is these more critical resources that are becoming increasingly scarce and there are no substitutes.

'Any human activity cannot be sustained indefinitely if it uses not only the annual production of the biosphere (the 'interest') but also cuts into the standing stock (the 'capital')'


Clearly, any human activity dependent on the consumptive use of ecological resources (forestry, fisheries, agriculture, waste disposal, urban sprawl onto agricultural land) cannot be sustained indefinitely if it uses not only the annual production of the biosphere (the 'interest') but also cuts into the standing stock (the 'capital'). Herein lies the essence of our environmental crisis. Persistent trends in key ecological variables indicate that we have not only been living off the interest but also con-suming our ecological capital. This is the inevitable consequence of exponential material growth in a finite environment. In short, the global economy is cannibalising the biosphere.

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.

'Hence we are within one population doubling of the 'sunshine limit' to growth and at present rates will reach that limit in 35 years'


Through a thermodynamic analysis of food production, Bryson has estimated that about 900 square metres of cropland are required to produce the average per capita food energy requirements assuming year round cropping. With an average growing season of only 180 days, each hectare of agricultural land will theoretically support about 5.5 people. The present world population density is about 3 persons per arable hectare. Hence we are within one population doubling of the 'sunshine limit' to growth and at present rates will reach that limit in 35 years. 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.

Editorial Notes: Date of original publication unknown.

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