When fossil feedstock is used, the fossil-based embedded carbon contained in chemicals and materials is emitted to the atmosphere at their end of life, assuming complete oxidation (e.g. through combustion or (bio)degradation).

When using CCU-based feedstock to replace the fossil feedstock, at the end of life, no additional carbon (or CO₂, respectively) is emitted to the air because it was captured from the air (or from point sources) before through carbon capture. Only the electricity demand for CCU-based feedstock production causes CO₂ emissions.

At end of life, carbon embedded in chemicals and derived materials is released to the atmosphere as CO_₂. In the case of fossil-based feedstock, this contributes to global warming. For CCU-based feedstock this is not the case, since all carbon embedded in these products was captured from the air (or from point sources) before through carbon capture. In a simplified model, additional emissions only electricity production for causes emissions for CCU-based feedstock production. Only the use of renewable energy can save emissions.
The GHG emissions of CCU-based methanol could be 67 to 77 % lower compared to emissions from releasing embedded carbon of fossil fuels, when using current energy supply based on photovoltaics. With improvements in renewable energy production, the reduction could increase to levels between 96 and 100 %.