Carbon opportunity cost approach may result in double counting in environmental footprinting

Abstract Purpose Recently, carbon opportunity cost (COC) approach has been mentioned in the European Commission’s draft of the updates on the Product Environmental Footprint (PEF) method, yet the COC approach has several limitations. In this commentary article, we aim to highlight the methodological and practical challenges of using COC approach in product environmental footprinting with life cycle assessment (LCA). Methods The COC approach is typically based on the “foregone carbon sequestration” due to continued land use which postpones the natural regeneration. The foregone sequestration typically equals the difference in carbon stocks between current land use and the potential natural vegetation. In principle, the global warming potential (GWP) related to the transformation from historical land use (natural vegetation) to current land use overlaps with the GWP of the foregone sequestration. As an alternative to avoid double counting, we describe an additional COC approach. Results The COC approach includes a risk of double counting, if it is applied simultaneously with the land transformation approach in product environmental footprinting with LCA. Double counting leads to overestimation of anthropogenic environmental impacts and harms the LCA principle of additivity. Furthermore, the suitability of the COC approach in attributional LCA is limited, since it does not represent the anthropogenic environmental impacts compared with the non-anthropogenic natural baseline. Regardless of the benefits of the additional COC approach in terms of avoided double counting, any COC approach includes high uncertainties related to the estimation of historical carbon stock and potential natural vegetation carbon stocks. Furthermore, the additional COC approach only provides benefits if potential natural vegetation exceeds the historical carbon stock. Conclusions Overall, the COC approach based on foregone sequestration has a risk of double counting. Furthermore, any COC approach has high uncertainties and limited practical benefits, and therefore, we highly recommend keeping COC approaches apart from the European Commission’s PEF method.