Full adoption of the most effective strategies to mitigate methane emissions by ruminants can help meet the 1.5 °C target by 2030 but not 2050

Abstract

To meet the 1.5 °C target, methane (CH4) from ruminants must be reduced by 11 to 30% by 2030 and 24 to 47% by 2050 compared to 2010 levels. A meta-analysis identified strategies to decrease product-based (PB; CH4 per unit meat or milk) and absolute (ABS) enteric CH4 emissions while maintaining or increasing animal productivity (AP; weight gain or milk yield). Next, the potential of different adoption rates of one PB or one ABS strategy to contribute to the 1.5 °C target was estimated. The database included findings from 430 peer-reviewed studies, which reported 98 mitigation strategies that can be classified into three categories: animal and feed management, diet formulation, and rumen manipulation. A random-effects meta-analysis weighted by inverse variance was carried out. Three PB strategies—namely, increasing feeding level, decreasing grass maturity, and decreasing dietary forage-to-concentrate ratio—decreased CH4 per unit meat or milk by on average 12% and increased AP by a median of 17%. Five ABS strategies—namely CH4 inhibitors, tanniferous forages, electron sinks, oils and fats, and oilseeds—decreased daily methane by on average 21%. Globally, only 100% adoption of the most effective PB and ABS strategies can meet the 1.5 °C target by 2030 but not 2050, because mitigation effects are offset by projected increases in CH4 due to increasing milk and meat demand. Notably, by 2030 and 2050, low- and middle-income countries may not meet their contribution to the 1.5 °C target for this same reason, whereas high-income countries could meet their contributions due to only a minor projected increase in enteric CH4 emissions.

Keywords: enteric; meta-analysis; methane; mitigation; ruminant.

Fig. 1.

Studied enteric methane mitigation strategies. For a complete list of strategies, see SI Appendix, Table S2.

Fig. 2.

Effective mitigation strategies and their effect on methane (CH₄) emissions (A) and animal performance metrics (B). CH₄I_M = CH₄ emission intensity for milk (g CH₄ kg of milk⁻¹); CH₄I_G = CH₄ emission intensity for weight gain (g CH₄ kg of weight gain for growing animals⁻¹); daily CH₄ = daily CH₄ emissions (g animal⁻¹ d⁻¹); digestibility = apparent digestibility of neutral detergent fiber (%); gain = average daily gain (kg d⁻¹); intake = dry matter intake (kg d⁻¹); milk = milk yield (kg d⁻¹); when numeric values are shown a significant effect was observed (adjusted P < 0.05) and no effect when adjusted P ≥ 0.05.

Fig. 3.

Projected change in enteric methane (CH₄) emissions between 2012 and 2030 without mitigation strategy under BAU and modeled mitigation scenarios (Product Based: adoption of one strategy that reduces product-based CH₄ emissions; Absolute: adoption of one strategy that reduces absolute CH₄ emissions; and Product Based & Absolute: adoption of one strategy that reduces product-based CH₄ emissions and one strategy that reduces absolute CH₄ emissions) for enteric CH₄ emission changes globally (A), in the African region (B), and in the European region (C). Error bars represent the average mitigation effect of the least and most effective mitigation strategy. Numbers in squares indicate the percentage of change from BAU.