Life cycle emissions of greenhouse gas emissions

Life cycle assessment (LCA) of greenhouse gas emissions has been developed for analyzing environmental burdens and impacts of products “from cradle to grave”: from resource extraction to waste disposal. Life cycle assessments of greenhouse gas emissions are often part of wider environmental assessments, which also cover other environmental burdens or impacts. Such wider-ranging assessments allow for considering “trade-offs” between reduction of greenhouse gas emissions and other environmental impacts and co-benefits of reduced greenhouse gas emissions. Data about greenhouse gas emissions used as input in assessments of current product life cycles do allow for substantial uncertainties in life cycle emission estimates. Estimates of life cycle greenhouse gas emissions linked to new processes and products are subject to even greater data-linked uncertainty. Variability in outcomes of life cycle assessments of greenhouse gas emissions may originate in different choices regarding system boundaries, time horizons, and the allocation of emissions to outputs in multi-output processes. Life cycle assessments can include other interventions than the emission of well-mixed greenhouse gases, which can affect climate such as changes in tropospheric ozone and aerosol concentrations, changes in albedo, and the generation of contrails and cirrus clouds.

Life cycle assessments may be useful in the identification of life cycle stages that are major contributors to life cycle greenhouse gas emissions and of major reduction options, in the verification of alleged climate benefits, and to establish major differences between competing products.

Main findings from available life cycle assessments of greenhouse gas emissions are summarized for products ranging from buildings to unconventional fossil fuels, and from food to vehicles. Guidance for reducing greenhouse gas emissions is presented. Future directions in developing life cycle assessment and its application are indicated. These include better handling of indirect effects, of uncertainty, and of changes in ecosystem carbon stocks and improved comprehensiveness in dealing with climate change by including, where appropriate, climate effects of changes in albedo, tropospheric ozone, and aerosols and the generation of contrails and cirrus clouds.