Nature’s nutrient cycles exemplify circular design. These are essential nutrients for life on earth that often play multiple roles.

Carbon, a fundamental element, forms the basis of life. Photosynthesis, aided by sunlight and water, converts carbon dioxide (CO2) gas into plant growth. Humans and animals consume plants, and the return CO2 to the atmosphere through respiration, decomposition, and decay. 

Notably, only about 1% of carbon on Earth resides in the atmosphere as CO2, while 99% is stored in the Earth’s core in various forms. Despite its low concentration (pre-industrial: ~280-ppm, less than 0.03%), CO2’s role as a “greenhouse gas” is significant. Unlike oxygen and nitrogen, CO2 can retain heat, keeping the Earth warm. The earth’s natural temperature fluctuations correlate well with CO2 concentrations.

Unfortunately, industrial development has increased fossil fuel use, releasing carbon dioxide (CO2) from the Earth’s core and causing atmospheric CO2 levels to rise steadily, now exceeding 420-ppm, a 50% increase from pre-industrial levels. This disruption of the natural process has led to global warming, climate change, arctic ice melt, ocean level rise, forest fires, and other issues.

Nitrogen, the most abundant atmospheric component (78%), is another essential nutrient for life. Nitrogen gas is relatively inert and must be transformed by microorganisms through processes like fixation and nitration to be available for life. Microorganisms also allow denitrification to convert fixed nitrogen back to gas and return it to the atmosphere, completing the cycle. Nitrogen also maintains atmospheric pressure, provides inertness, and increases biodiversity.

Human activities have altered the global nitrogen cycle. Massive use of synthetic nitrogen fertilizers has doubled global fixation rates. About 60% of nitrogen in applied fertilizer is wasted, polluting aquatic systems and causing acidification, toxic blooms, and animal death. Other issues include terrestrial nutrient imbalance and biodiversity decline.

The phosphorus cycle is another crucial nutrient cycle. Phosphorus helps biological energy transfer, genetic material, and cell membrane composition. Synthetic fertilizers containing phosphorus are mostly wasted, causing severe ecological pollution and aquatic death. Significant biodiversity loss threatens the phosphorus cycle.

Other ecological cycles like the water and sulfur cycles transfer nutrients and energy to living organisms and return them to the environment. Human activities have disrupted most of these cycles.

To address these issues, implementing circular design is essential. It involves maximizing recycling and reuse to eliminate waste and pollution, regenerating resources, and not depleting them. These concepts are most effective in early product or process design. Techniques like complete Life Cycle Analyses (LCAs) ensure continuous improvement by identifying and rectifying shortcomings in the early design phases.