Reassessing the warming impact of methane emissions from Irish livestock using GWP*: historical trends and sustainable futures

Abstract

Methane from livestock production contributes significantly to Ireland’s greenhouse gas emissions. Methane emissions are generally expressed as carbon dioxide equivalents (CO2e) using the global warming potential (GWP) metric, but this conversion may result in an inaccurate assessment, because methane has a much shorter atmospheric lifespan than CO2. This study calculated the CO2e of methane emissions from Irish livestock using the GWP and GWP* metrics, the latter of which accounts for the short-lived nature of atmospheric methane. Methane emissions from all Irish livestock (1961–2020) were included and three projected scenarios to 2050 were hypothesised: increasing emissions, decreasing emissions and constant emissions. The CO2e of methane from Irish livestock was found to be influenced by changes in the rate of emission over the preceding decades. Using the GWP* metric, declining populations of donkeys and horses from 1961 to 2000 were shown to cause atmospheric removals of methane when expressed as CO2e. Increasing populations of swine and non-dairy cattle (in response to industrial changes and European Union [EU] regulations) saw significant increases in the CO2e of methane emissions from these sources. Milk quotas caused a significant reduction in the CO2e of methane emissions from dairy cows, and atmospheric removals were observed in the years 1990–2012. GWP* indicated that the constant and decreasing future emission scenarios gave more significant reductions in CO2e than the GWP. These results indicate the importance of the effect of emission rate on the CO2e of methane from Irish livestock, which is accounted for using GWP*, but not by the conventional GWP.