Implementing an appropriate metric for the assessment of greenhouse gas emissions from livestock production: A national case study

Abstract

Livestock farming is of major economic relevance but also severely contributes to environmental impacts, especially greenhouse gas (GHG) emissions such as methane (CH4; particularly from ruminant production) and nitrous oxide (N2O; mainly from manure management and soil cultivated for feed production). In this study, we analyse the impact of GHG emissions from Austrian livestock production, using two metrics: a) the commonly used global warming potential (GWP) over 100 years (GWP100 in CO2-equivalents, CO2-e), and b) the recently introduced metric GWP*, which describes additional warming as a function of the timeline of short-lived GHG emissions (unit CO2 warming equivalents, CO2-we). We first compiled the sectoral (i.e. only direct emissions without upstream processes) GWP100 for different livestock categories with a focus on dairy cattle, beef cattle and pigs in Austria between 1990 and 2019. We also estimated product-related (i.e. per kg carcass weight or per litre of milk) GWP100 values, including upstream processes. We then calculated the corresponding GWP* metrics, both sectoral and product-related, and compared them with the GWP100 values. Decreasing livestock numbers and improved production efficiency were found to result in strong sectoral emission reductions from dairy production (–32 % of GWP100 from 1990 to 2019) and from pigs (–32 % CO2-e). This contrasts with low reductions from other livestock categories and even increases for cattle other than dairy cows (+3 % CO2-e), mainly due to rising suckler cow numbers. Allocated results per kg milk and kg body mass show quite similar results. Using the GWP* metric, the climate impacts of Austrian livestock production are less severe. When assuming constant management and emission intensity over a period of at least 20 years, the CO2-we (GWP*) is almost 50 % less than CO2-e (GWP100) per kg Austrian raw milk due to the different impacts of the short-lived CH4. A similar trend applies to an average cattle carcass (-40 % warming impact). The emission reductions of the shrinking Austrian livestock population represent an important contribution to a climate-neutral agriculture: The CH4 reductions of livestock production during the past 20 years reduce the current total Austrian CO2-we by 16 %. Continuous CH4 reduction, as we show it here for Austrian livestock, is an effective option to tackle the climate crisis in the short term. It shall be stressed that a relatively low GWP* should not be interpreted as a concession for further CH4 emissions but as an actual reduction of (additional) warming.