Replicating Nature: The Science of Carbon Circulation

CEWT | Engineering and ESG discussion paper | 8 November 2026 Nature has sustained life through the circulation of carbon among the atmosphere, plants, animals, soil, and oceans. The engineering question is whether industry can replace linear fossil-carbon extraction with carefully measured circular-carbon systems. 1. What Nature does with CO₂ Photosynthesis uses sunlight to convert carbon dioxide and water into energy-rich organic matter. Respiration uses oxygen to release biochemical energy and returns CO₂ and water. Digestion makes food nutrients available; cellular respiration is the primary CO₂-generating energy process. Photosynthesis: 6 CO₂ + 6 H₂O + sunlight → C₆H₁₂O₆ + 6 O₂ Cellular respiration: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy Carbon circulates, while energy enters the natural system principally from sunlight. Natural carbon cycling is not perfectly closed; geological storage and exchanges with oceans also matter. 2. Carbon cycling compared with CEWT CRT Figure 1. Conceptual analogy between photosynthesis/respiration and renewable-energy-driven methanation/trigeneration. For CRT, recovered CO₂ reacts with externally produced renewable hydrogen to regenerate methane. Combustion or other oxidation can then release energy, after which CO₂ must be captured again to close the intended carbon loop. Methanation: CO₂ + 4 H₂ → CH₄ + 2 H₂O Methane combustion: CH₄ + 2 O₂ → CO₂ + 2 H₂O 3. What changed with industrialisation? Fossil-fuel extraction transfers carbon stored in geological reservoirs over very long periods into the active atmosphere–ocean–biosphere cycle. Natural sinks absorb a substantial part of anthropogenic CO₂ emissions, but not all; the remaining accumulation increases atmospheric CO₂ and warms the climate through its greenhouse effect. 4. Can CRT stabilise atmospheric CO₂? Stabilising human-induced CO₂ warming requires global net CO₂ emissions to reach approximately zero. Reducing atmospheric CO₂ concentrations requires net removal. CRT may reduce demand for freshly extracted fossil carbon if it uses low-emissions energy, avoids leakage and achieves substantial capture and recycling; it does not by itself guarantee carbon neutrality or atmospheric CO₂ removal. Source of carbon Engineering implication CO₂ from existing exhaust May displace fossil-carbon inputs; residual and upstream emissions still count. CO₂ captured from air Draws on atmospheric carbon; substantial capture energy and cost must be included. 5. ESG by Design, Not by Declaration The meaningful metric is cumulative net greenhouse-gas emissions across the complete lifecycle, including embodied plant emissions, electricity imports, hydrogen production, methane leakage, CO₂ recovery losses, construction and decommissioning. Carbon conservation is not energy conservation: repeated fuel regeneration needs a continual external energy input, and irreversibilities cause losses. 6. CEWT proposition Replicating Nature — From Carbon Extraction to Carbon Circulation Industry can investigate a transition from extracting and releasing geological carbon to recovering and circulating carbon already in productive systems. CEWT’s CRT is one candidate pathway: recover CO₂, produce hydrogen using additional low-emissions power, synthesize reusable fuel, deliver electricity/heat/cooling, and recover the resulting CO₂. The environmental benefit must be demonstrated through complete mass, energy and lifecycle carbon balances, not assumed from the presence of recycling alone. Engineering tests before claiming climate benefit • Quantify all carbon entering, circulating within, and leaving the system boundary. • Measure renewable electricity imported for electrolysis, capture, compression and auxiliaries. • Verify CO₂ capture, methane leakage, recycle purity, conversion and purge losses. • Compare lifecycle emissions and fossil-carbon displacement with a credible reference system. Selected background references IPCC, AR6 Synthesis Report (2023): https://www.ipcc.ch/report/ar6/syr/ IEA, Putting CO₂ to Use (2019): https://www.iea.org/reports/putting-co2-to-use