Key issues and options in accounting for carbon sequestration and temporary storage in life cycle assessment and carbon footprinting

Biological sequestration can increase the carbon stocks of non-atmospheric reservoirs (e.g. land and land-based products). Since this contained carbon is sequestered from, and retained outside, the atmosphere for a period of time, the concentration of CO2 in the atmosphere is temporarily reduced and some radiative forcing is avoided. Carbon removal from the atmosphere and storage in the biosphere or anthroposphere, therefore, has the potential to mitigate climate change, even if the carbon storage and associated benefits might be temporary. Life cycle assessment (LCA) and carbon footprinting (CF) are increasingly popular tools for the environmental assessment of products, that take into account their entire life cycle. There have been significant efforts to develop robust methods to account for the benefits, if any, of sequestration and temporary storage and release of biogenic carbon. However, there is still no overall consensus on the most appropriate ways of considering and quantifying it. This paper reviews and discusses six available methods for accounting for the potential climate impacts of carbon sequestration and temporary storage or release of biogenic carbon in LCA and CF. Several viewpoints and approaches are presented in a structured manner to help decision-makers in their selection of an option from competing approaches for dealing with timing issues, including delayed emissions of fossil carbon. Key issues identified are that the benefits of temporary carbon removals depend on the time horizon adopted when assessing climate change impacts and are therefore not purely science-based but include value judgments. We therefore did not recommend a preferred option out of the six alternatives presented here. Further work is needed to combine aspects of scientific and socio-economic understanding with value judgements and ethical considerations.