Challenges for the balanced attribution of livestock’s environmental impacts: the art of conveying simple messages around complex realities

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🔬研究者:LCA研究者は、GWP指標の限界と代替指標の開発に関する議論を参考にできる。

🏢実務担当者:サステナビリティ担当者は、畜産製品の環境フットプリント報告における指標選択の透明性を高めるための示唆を得られる。

🏛政策担当者:政策立案者は、農業部門の排出削減目標設定における指標の影響を考慮する必要がある。

Meat production is often listed among the largest contributors to climate change, and is usually associated with biodiversity damage, feed-food competition, and water scarcity. This assumption is largely based on the biogenic methane (CH4) emissions of the global herd of ruminants and its occupation of land. Environmental assessments of the livestock sector are all too frequently stated in simplistic terms, making use of a myopic selection of metrics, and overlooking underlying heterogeneity and complexities. One example of such oversimplification is the comparison of the warming effect of different greenhouse gases (CO2, CH4, and N2O), which are associated with a series of challenges due to their own heterogeneous atmospheric ‘behavior’. Whilst useful for certain research questions, standardizations such as the commonly used GWP100 hide many complex issues. These issues include considering different emission profiles of production systems (e.g., low-methane porcine vs. high-methane ruminant), the need to factor in CO2 and CH4 sinks, the different atmospheric lifetimes of each gas and subsequent atmospheric warming potential, and compensatory background emissions in alternative rewilding scenarios. Whilst poorly managed land negatively affects biodiversity, well-managed land strategies, including those pertaining to livestock production, can lead to favorable outcomes (e.g., biodiverse swards that encourage pollination and beneficial microfauna). Similarly, the assessment of water wastage and land use requires contextualized approaches. This highlights the importance of addressing agricultural heterogeneity in systems analysis, including Life Cycle Assessment (LCA). To further reflect the food-environment nexus, nutritional LCA (nLCA) incorporates considerations of food. optimizing e.g. nutritional sustenance and reducing, in theory, the amount of food we consume through meal-level assessment - rather than focusing on a single product.• Being more recent than the wider LCA ‘umbrella’ (e.g., Life Cycle Cost Analyses), one current drawback of nLCA is that it can be easily manipulated to favour one product over another, whether plant- or animal sourced, by singling out specific nutrients (e.g., fiber or vitamin C vs. vitamin B12 or digestible amino acid balanced protein). When considering the value of livestock products against their environmental impact, a holistic assessment is needed using balanced metrics and avoiding tunnel vision. Besides factoring in nutrition and co-product benefits, other natural capitals, and societal assets that result from well-managed farm enterprises need to be acknowledged, even if no empirical metric can currently fully account for their true value. Examples include: biodiversity, soil health, land stewardship, and rural community support; especially in a time of extreme variability due to climate, social unrest, and economic crises. A major challenge for the scientific community has been the development of balanced metrics to evaluate the environmental, social, and economic impacts of livestock production systems, which enable feasible policy action scenarios that balance the protection of natural capital with food security. For instance, the difficulty of robustly assessing the relative impact of various livestock-associated greenhouse gases (GHGs) on the climate provides a clear example, especially given the vast differences in behavior and variable lifetimes in the atmosphere of the individual GHGs, and how this relates to short- and long-lived climate agents. For industries such as ruminant agriculture, where the primary emissions are non-CO2 (i.e., methane, CH4, and nitrous oxide, N2O), the way these metrics equate to CO2-equivalents (CO2-eq) has overly simplified their impacts on global warming, compared to industries that primarily emit fossil fuel-sourced CO2. Other environmental impacts, such as the degree to which livestock production uses water, which subsequently is not available for other human uses, or the effects that land use has on cropland scarcity or biodiversity, have suffered from similar issues of misrepresentation through oversimplification. In tandem with the aforementioned complexities of sustainability assessments, identifying metrics that represent a food’s nutritional value vs. just using units of mass, protein or energy have been developed to better elucidate the true nutrition-environment nexus. The goal of this paper, therefore, is to outline current issues related to the quantification of livestock’s impacts on the environment, briefly describing alternative metrics for more transparent, and holistic impact accounting. Furthermore, it is argued that accounting for single environmental impacts ignores the broader value of livestock, and other agricultural commodities for that matter, as part of a circular food system that contributes to social resilience beyond one major anthropogenically driven challenge, such as climate change. Keeping these other aspects out of the scope of consideration will likely invite unexpected and highly negative consequences that would then backfire on any progress otherwise made. With respect to climate change, carbon footprints’ impact assessments usually adopt GWP100 characterization factors (i.e., global warming potential over a 100-year time horizon), thus standardizing the atmospheric effects of all GHGs to CO2-eq. It is typically claimed under GWP100 that CH4 is a GHG 28 times more potent than CO2. The origin of this number is the Intergovernmental Panel on Climate Change’s (IPCC) Assessment Report (AR) 5 published in 2013 (IPCC, 2013). In the IPCC AR 6 (IPCC, 2021), which replaced AR 5, the number was refined to 27.2 for biogenic CH4 sources of non-fossil origin. IPCC (2021) now explicitly recommends sensitivity analyses of timeframes considered to better represent the complexities of various GHG’s atmospheric behavior. For instance, if calculated under a 20-year timeframe (GWP20), a CH4 (non-fossil) is considered to have a GWP 80.8 times more potent than CO2, whilst over 500 years (GWP500), it is 7.3 times more potent than CO2. These IPCC precise published values (to 1 decimal place) suggest an accuracy of understanding of atmospheric dynamics, which in reality is not available. However, the more recent standardization factors and impact assessment advice published under AR 6 (IPCC, 2021) do provide recommendations for the calculation of CO2 uptake, taking a step forward in acknowledging carbon cycling response (formally referred to as carbon feedback), both positive and negative depending on the system under investigation. If reported accurately and transparently, this is one way of mitigating subjective decision-making related to sustainability assessments (as will be elucidated in the next section). When converting the greenhouse effect of various GHGs to CO2-eq, complexities emerge due to differences in their decomposition or removal (sink) characteristics from the atmosphere. In brief, CH4 decomposes mostly to CO2 and H2O in the atmosphere within a few years (Lelieveld et al., 2016). This decomposition happens primarily through reaction with hydroxyl (OH-) radicals (Li et al., 2008), often nicknamed the detergent of the atmosphere because they also react with a number of other atmospheric gases and thus “clean” the atmosphere of otherwise damaging buildups of various chemical elements. This creates a highly complex chemical reaction scheme, which is as yet insufficiently understood by the atmospheric sciences. In contrast to CH4, CO2 is highly inert and reacts minimally in the atmosphere. It thus requires terrestrial and aquatic sinks to be removed, which function predominately through photosynthesis, or dissolution in oceans (causing increased acidification). Since both the photosynthetic and oceanic capture cycles are in long-term equilibrium, additional injections of CO2 from fossil fuel sources outside of these cycles gradually accumulate and deposit in the atmosphere without the prospect of dissolution within human-relevant timescales. N2O, a potent GHG emitted from agricultural systems, not discussed in detail here, would behave as a long-lived gas in the context of a GWP100 metric. However, for the purpose of this discussion, its behavior would be intermediate between CO2 and CH4. The different atmospheric dynamics of these GHG’s, CO2, N2O, and CH4, need to be reflected in climate change considerations, a practice rarely conducted by sustainability analysts (Lynch, 2019), particularly when policymaking in relation to agricultural climate action. As with all models, climate change models are prone to uncertainties through the inherent simplification of complex biochemical processes. Despite GHG measurements and subsequent calculations becoming more sophisticated as technology improves, such models still suffer from a lack of granular primary data on the one side, and a tendency of complex systems (e.g., the carbon cycle) to reach tipping points where system dynamics undergo rapid changes (e.g., change of albedo following ice cap melting) on the other. With these challenges in mind, predicting the true effect of complex nutrient cycles (carbon in this case) on the atmosphere becomes a daunting task. However, until more primary data becomes available to improve existing characterization factors related to metrics such as GWP100, there are some measures scientists and sustainability assessors can take to increase transparency related to the effect of their subjective decisions (e.g., choosing one GHG impact assessment over another). For example, when reporting GWP100 values, it is prudent to also report impacts under GWP20 and GWP500. In it is particularly when using the carbon to the of emission factors that the amount of GHGs in a given whether or in the (e.g., CH4 as under IPCC and emission factors which how is to the as or N2O, for Furthermore, acknowledging both the likely sinks of CH4 and its more

• openalex https://doi.org/10.1093/af/vfac096first seen 2026-08-02 16:50:54