Results from log-log regressions.

Beef production accounts for the largest share of global livestock greenhouse gas emissions and is an important target for climate mitigation efforts. Most life-cycle assessments comparing the carbon footprint of beef production systems have been limited to production emissions. None also consider potential carbon sequestration due to grazing and alternate uses of land used for production. We assess the carbon footprint of 100 beef production systems in 16 countries, including production emissions, soil carbon sequestration from grazing, and carbon opportunity cost—the potential carbon sequestration that could occur on land if it were not used for production. We conduct a pairwise comparison of pasture-finished operations in which cattle almost exclusively consume grasses and forage, and grain-finished operations in which cattle are first grazed and then fed a grain-based diet. We find that pasture-finished operations have 20% higher production emissions and 42% higher carbon footprint than grain-finished systems. We also find that more land-intensive operations generally have higher carbon footprints. Regression analysis indicates that a 10% increase in land-use intensity is associated with a 4.8% increase in production emissions, but a 9.0% increase in carbon footprint, including production emissions, soil carbon sequestration and carbon opportunity cost. The carbon opportunity cost of operations was, on average, 130% larger than production emissions. These results point to the importance of accounting for carbon opportunity cost in assessing the sustainability of beef production systems and developing climate mitigation strategies.

牛肉生产占全球畜禽温室气体排放的最大份额，是气候减缓行动的核心目标之一。当前绝大多数比较牛肉生产系统碳足迹（carbon footprint）的生命周期评估，均仅局限于生产环节的温室气体排放，未考虑因放牧及生产用地的替代用途所产生的潜在碳固存。本研究对16个国家的100个牛肉生产系统的碳足迹进行了全面评估，涵盖生产排放、放牧带来的土壤碳固存，以及碳机会成本（carbon opportunity cost）——即若某块土地不用于牛肉生产时，其可实现的潜在碳固存总量。本研究对两种典型育肥模式开展了配对比较：一种为放牧育肥模式，牛群几乎仅以牧草和饲草为食；另一种为谷饲育肥模式，牛群先进行放牧，随后饲喂谷物日粮。研究结果显示，放牧育肥系统的生产排放较谷饲系统高出20%，总碳足迹则高出42%。此外，土地利用强度更高的养殖系统通常碳足迹也更高。回归分析结果表明，土地利用强度每提升10%，生产排放将增加4.8%，而综合生产排放、土壤碳固存与碳机会成本的总碳足迹则会增加9.0%。各养殖系统的碳机会成本平均较生产排放高出130%。上述研究结果凸显了在评估牛肉生产系统可持续性、制定气候减缓策略时，纳入碳机会成本考量的重要性。