Reisinger, A., Ledgard, S.F., Falconer, S.J. 2017. Sensitivity of the carbon footprint of New Zealand milk to greenhouse gasmetrics. Ecological Indicators 81, 74–82.
Highlights

The carbon footprint of milk depends on the choice of GHG metric.
GHG metrics that emphasise long-lived gases tend to favour low-input systems.
Differences in footprint among farms are greater if long-lived gases are emphasised.
Ranking is robust for most farms but differences are significant in some instances.
Transparency in the choice of GHG metrics would support more robust policy outcomes.

Read more  (external website, may be paid access)