2023 March Board Book

Pressman et al.

10.3389/fsufs.2022.1072805

FIGURE 7 Mechanisms of decreasing CH 4 emissions since 2008 include decreasing dairy herd size, increasing per capita production, and manure management CH 4 reductions programs. In (A–C) , the x -axis shows years; in (A) the entire historical time series is shown (1950–2017), while in (B, C) , only 2008–2017 are shown. In (A, B) , the y -axis is annual total dairy CH 4 emissions, but in (B) the y -axis does not begin at zero in order to provide a close-up view of CH 4 dynamics from 2008 to 2017. In (A) , the right y axis shows per capita milk production and cattle population. (B) Shows hypothetical estimates of annual CH 4 reductions due to DDRDP and AMMP program implementation, which has been added to historical CH 4 emissions to plot putative emissions without these programs. The y -axis of (C) shows cattle population and the right y axis shows per capita milk production.

agricultural sectors, including Australian beef feedlots (Ridoutt et al., 2022), Australian sheep meat production (Ridoutt, 2021a), Australian livestock production (Ridoutt, 2021b), and Austrian dairy production (Hörtenhuber et al., 2022). Similar to reductions scenarios in our study, Ridoutt and coauthors found larger potential GHG reduction benefits from supplementing Australian beef steers with enteric CH 4 -inhibiting macroalgae Asparagopsis taxiformis when emissions were assessed using GWP ∗ rather than GWP (Ridoutt et al., 2022). Similarly to our study, Hörtenhuber and coauthors found that decreasing lactating dairy cattle population due to improved production efficiency resulted in strong sectoral emission reductions from dairy production, which were greater when assessed with GWP ∗

than with GWP 100 (Hörtenhuber et al., 2022). In Australian livestock industries where CH 4 emissions increased from 1990 to 2018 (beef, pork, and dairy production), emissions from the beef cattle, pig meat and milk production industries assessed using GWP ∗ contributed to climate warming less than when assessed with the GWP 100 climate metric (Ridoutt, 2021b). While increasing background emissions in Australia from 1990 to 2018 are similar to our “historical” scenario, we found that under increasing background emissions, GWP ∗ - based emissions estimates were greater than those given by GWP. This discrepancy may be because the authors used total GHG emissions, not only CH 4 , in their analysis. It may also result from annual Australian CH 4 emissions increasing

Frontiers in Sustainable Food Systems

14

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