Imagine a world where 100% of material resources—such as copper, lead, zinc, lithium—were recycled, all nitrogen, phosphorus and potassium fertilizer applied to crops was recovered, and all trees cut for timber were replanted. The fibers in clothing would be used again for new cloth, and the silicon in glass recovered to make new glass. About the only thing that would make a one-way pass through such an economy would be energy, which conceivably could be solar. This would be a circular economy—what I will call a closed green circle.
Resource use is measured in units of mass, whereas economic growth has a monetary value. In a closed green circle, we would strive to uncouple economic growth from material use by implementing technology that improves efficiency and resource capture.
We should strive to achieve the closed green circle as soon as possible, but it is unrealistic to think we will ever fully achieve it. First, it does not consider rising human numbers, who will demand and extract their portion of the resource flow from each turn of the circle and the existing human population that will certainly not want to see its share diminished. Sustainability is an elusive concept in a world of rising human population. Efficiency of resource use can lower demand, but not if the underlying population is growing and hoping to catch up in lifestyle. In recent years, the rate of carbon dioxide emissions per unit of economic output has declined, while overall carbon dioxide emissions have increased globally
Second, archeological deposits show that humans did not evolve in a culture of recycling, nor do we embrace it today without monetary incentives and punitive regulations. The closed green circle does not consider that the efficiencies of recycling decline as we attempt to recover the last smidgen of each resource for reuse. Some products are meant to be dispersed, and composite materials are often costly to separate. The green circle may be round, but a certain percentage of materials escapes recovery with each turn of the crank, so the circle will never close.
In the face of continuing human population growth, those who believe that we can transition to a sustainable world in which economic growth and material use are uncoupled need look no further than the weekly leavings for the trashman. These are often greatest in the most affluent societies.
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