Rasul Kajwan, Bruckner Martin, Mempel Finn, Trsek Stefan, Hertwich Edgar G
Industrial Ecology Programme, Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim 7034, Norway.
Institute for Ecological Economics, Department of Socioeconomics, Vienna University of Economics and Business, Vienna 1020, Austria.
PNAS Nexus. 2024 Dec 17;3(12):pgae524. doi: 10.1093/pnasnexus/pgae524. eCollection 2024 Dec.
Biomass was the principal energy source in preindustrial societies; their agriculture provided more energy than it required. Thus, the energy return on energy investment (EROEI) needed to be >1. Recent studies have indicated that this may not be the case for modern industrialized agrifood systems (AFSs). Although the green revolution radically improved agricultural yields, it came at the expense of increased energy inputs, mainly in the form of fossil fuels. AFSs relying on external energy pose a food security risk, an economic issue for agricultural producers, and an environmental issue for all. Previous EROEI studies investigated mainly certain groups of commodities, typically at the local or national level. Here, a comprehensive global analysis shows that current AFSs have a lower EROEI than previously estimated. Globally, EROEI has increased from 0.68 in 1995 to 0.91 in 2019. In low-income regions, AFSs are still energy sources, but their EROEI has declined with increasing wealth, reflecting the growing utilization of fossil fuels. AFSs of high-income regions are energy sinks, although their EROEI has improved. Food processing is responsible for 40% of the total energy use in the global AFS, notably larger than fertilizer, which accounts for 17%. More than half of the energy use in food processing is for livestock products that also require disproportionate energy input through their inefficient conversion of (human-edible) feed. Livestock products use 60% of energy inputs while delivering <20% of food calories.
生物质是工业化前社会的主要能源；当时的农业提供的能源超过了其自身所需。因此，能源投资的能量回报率（EROEI）需要大于1。最近的研究表明，现代工业化农业食品系统（AFS）可能并非如此。尽管绿色革命极大地提高了农业产量，但这是以能源投入增加为代价的，主要形式是化石燃料。依赖外部能源的农业食品系统带来了粮食安全风险，对农业生产者来说是一个经济问题，对所有人来说则是一个环境问题。以往关于能源投资的能量回报率的研究主要调查某些商品类别，通常是在地方或国家层面。在此，一项全面的全球分析表明，当前的农业食品系统的能源投资的能量回报率低于先前的估计。在全球范围内，能源投资的能量回报率已从1995年的0.68增至2019年的0.91。在低收入地区，农业食品系统仍是能源来源，但随着财富增加，其能源投资的能量回报率有所下降，这反映出化石燃料使用的增加。高收入地区的农业食品系统是能源消耗者，尽管其能源投资的能量回报率有所改善。食品加工占全球农业食品系统总能源使用量的40%，明显高于占17%的化肥。食品加工中一半以上的能源用于畜产品，而畜产品通过低效转化（人类可食用的）饲料还需要不成比例的能源投入。畜产品消耗60%的能源投入，而提供的食物热量却不到20%。
