The circular economy differs from a linear economy because the output of one process is the input of another.
The available outputs of the food production are uneaten vegetable matter and sewage from which we can harvest nutrients, energy, water and solid waste. Natural ecosystems are circular in that plants and animals accumulate nutrients and grow during their life, and then release those nutrients back to the environment as they excrete, or when they die.
An ecosystem is a circular economy built of component linear processes. An ant nest organizes and concentrates nutrients that form a valuable supply for nearby trees or scavenging beetles. A tree accumulates resources and stores them in the form of timber.
A specific ecology may also rely on external cycles. A rainforest, for example, relies on a larger circular system for its water. The water cycle injects water into the rainforest which releases it to the sea. The rainforest is also a net user of energy. Sunlight powers the growth of the forest, and is the primary source of energy for all other life forms.
Of course, sunlight also powers the water cycle, evaporating water and driving the winds that move clouds around the earth. Our fossil fuels come from ancient forests. The only sources of energy on earth that are not derived from sunlight are the gravitational pull of the tides and the geothermal energy from our molten core.
When planning a circular economy, it is critical that we take note of this net use of energy, and the reliance on larger cycles, so that we do not cripple each component of the ecosystem with artificial constraints. Linear processes can participate in a circular economy if their waste provides valuable inputs to other areas of the economy.
Read earlier articles in this series