Sensitivity of the carbon footprint of New Zealand milk to greenhouse gas metrics

摘要: Abstract Milk production is responsible for emitting a range of greenhouse gases (GHGs), mainly carbon dioxide (CO 2 ), nitrous oxide (N O) and methane (CH 4 ). In Life Cycle Assessments (LCA), the Global Warming Potential with time horizon 100 years (GWP100) used almost universally to aggregate emissions individual into so-called CO -equivalent that are calculate overall footprint milk production. However, there growing awareness that, depending on purpose LCA, metrics other than GWP100 could be justified some would give very different weighting short-lived gas CH relative long-lived N O when calculating footprint. Pastoral dairy systems at levels intensification differ in balance short- GHGs associated on- off-farm emissions. Differences therefore highly sensitive choice GHG metric. Here we explore extent which alternative metric choices alter New Zealand national, regional farm scales compared selected European countries. We find ranking farms terms their relatively robust against metric, despite significant differences utilisation pastures versus supplementary feed, fertiliser use energy consumption various stages operations. instances where fundamentally change conclusions LCA systems, including whether move towards higher or lower input increase decrease average Zealand. Greater transparency about implications often inadvertent implicit value judgements embedded these metrics, help ensure policy decisions consumer based indeed deliver climate outcomes intended by end-users.