A living system is sustainable if it can continue to draw inputs from its environment at the rate needed for it to thrive.  Until a maximum point of availability of inputs is reached it is possible for a system to thrive and to grow simultaneously.  Once the maximum rate at which inputs can be obtained is reached the system can no longer thrive and grow at the same time – it can thrive only if it constrains future growth and it can grow only at the expense of quality of life.  Should inputs decline, then the system itself must contract in order to preserve quality of life, and a failure to do so will threaten the health or very existence of the system.

This description is, of course an over-simplification, because it does not take into account efficiencies in the transformation processes to inputs within the system, which may allow the system to use less of a particular input to produce the same output which was previously obtained under less-efficient conditions.  Nevertheless there is only so much that can be achieved by technology and efficiency in the face of a world of geometrically expanding consumption.

A system need not collapse at the point that it immediately overshoots its level of sustainability; rather overshooting (and a temporary illusory image of thriving) seems to occur rather commonly in nature prior to collapse.

Intelligent systems contain feedback loops which serve to regulate activity by slowing or shutting down a process temporarily if it overshoots a safe level.

The WWF Living Planet Survey attempts to provide a measure of global sustainability by comparing both the global ecological footprint (consumption) of humankind against the biocapacity (ability to provide inputs and absorb by-product outputs) of the planet.  The footprints of individual nations as well as their biocapacities have also been calculated. The latest available report is for 2010 using 2007 data. Figures in square brackets indicate the previous most recent figures i.e. from the 2008 Report using 2005 data.

The WWF model assumes a total of 11.9 billion global hectares [13.6] (gha -  a hectare of global average ability to produce resources and absorb wastes) are available on the planet.  Whilst this figure is not fixed – it can be changed upwards for instance, by changes in technology to allow for greater productivity and more productive waste handling, or by the introduction of other more sustainable resource-management practices (or downwards by opposite factors) it is the least flexible and changing of the factors under consideration, the other two being population growth and rates of consumption.  The looming threat of climate change however represents a very real threat, and may lead to a long-term lowering of the planet's biocapacity. The figure of 11.9 gha divided by the estimated global population in 2007 results in a global per capita figure of 1.8 gha [2.1]. In other words, the combined effects of increasec levels of consumption, environmental degradation and population growth have led to a 14% reduction in per capita bio-capacity in the short period of two years.

The 2010 Living Planet Survey indicates that the global footprint in 2007 was 2.7 gha or an overshoot of 0.9 gha [0.6] per person more than was available.  If the 2005 global figures are re-aggregated into High-, Middle- and Low-Income countries, stark differences can be seen (6.4, 2.2 & 1.0 gha respectively). At individual nation level the UAE had the worst per capita footprint (9.5) closely followed by the USA (9.4). When population is taken into account however one can see that the USA had a national footprint of 2.8 billion gha (21% of the global total) whereas the UAE has a national footprint of 43 million gha (0.3% of the global total). The EU component of Europe had a per capita footprint of 4.7 and a total footprint of 2.3 billion gha (17% of global total). China has a per capita footprint of 2.1 and India a per capita footprint of only 0.9 but because of their large populations produce significant national footprints of 2.8 billion gha and 993 million gha respectively. South Africa's per capita footprint was listed as 2.1 with a national footprint of 100 million gha. At the lowest end of the scale are the Congo Republic, Haiti, Afghanistan and Malawi with per capita footprints of 0.5 and national footprints of 2 million, 4.3 million, 15 million and 6.5 million gha respectively. The USA national footprint in 2005 (produced by 298 million people) exceeded the footprint produced by the 2,4 billion people in the world's poorest countries by some 430 million gha or 18%.

Along with per capita and national footprint sizes, the third element considered in the Living Planet Survey is the Biocapacity of countries. By comparing a country's per capita footprint with its per capita biocapacity it can be determined whether a country is living within or beyond its biocapacity and therefore whether it is a debtor or creditor nation from an ecological point of view. To see a table, based on the 2005 data, of selected countries, including South Africa click here. To view an interactive graphic of national data based on the latest 2007 data click here.

Most nations are living beyond their geo-political biocapacities, some grossly so. Based on 2007 figures, we have already considerably overshot the planet's bio-capacity, and we needed almost 1.5 planet earths in order to maintain human activities sustainably. With rapidly growing populations in China and India in particular, and aspirations to achieve a 'western consumerist lifestyle' the picture is much bleaker. Indeed if everyone on the planet were to live like a typical US consumer we would require 4.4 planet earths to maintain this consumption at sustainable levels.

As we only have one earth, and have reached or are imminently reaching a peak state for the supply of most natural resources our only solutions to the sustainability equation must lie with the population and consumption elements of the equation.

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