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Wind turbine



Sustainable systems


Nature shows us how to be sustainable. Natural cycles re-use wastes and recycle resources.

Lines and loops

Many human activities have processes that form a straight line. Resources are used up and wastes are produced. This is not sustainable.

To be truly sustainable, processes should be modified into loops that do not generate wastes or use limited resources.

This can prove expensive. Unless people are willing and able to pay more, it may mean that it is difficult to achieve economic sustainability.



Recycling glass to make new bottles is a sustainable loop process.

Roll over the image to see an example of a more sustainable loop.

The Natural Step Framework

The Natural Step Framework looks at how to make human activities more sustainable. It views four systems and describes the conditions that they must meet for a sustainable activity.


System Description Sustainable condition


Resources from the earth's crust.

Resources such as minerals, metals and carbon from fossil fuels should not be removed from the Earth at a quicker rate than they are deposited naturally.
E.g. carbon-neutral processes like the carbon-cycle.


Man-made, synthetic materials that do not occur naturally.

Synthetic compounds may not be biodegradable. They should not be allowed to accumulate in nature.
E.g. polymers should not simply be left to accumulate in landfill.

productivity and biodiversity

All biological life on the Earth.

Human activities should not diminish the sustainability of plant and animal resources.
E.g. over-fishing has depleted marine fish stocks.

Human needs

The social interaction of humans and how their needs are met.

The Earth's resources should be used efficiently and responsibly to meet the needs of all people; in the present and for the future.
E.g. access to healthcare, clean drinking water and sanitation as a bare minimum for all.