A recent Global Perspective by Wartenberg et al. in Environmental Science & Technology Letters sheds much-needed light on the complex environmental impacts of cannabis cultivation.(1) Among the pathways identified by their ambitious review—land cover change, water use, pesticide use, energy use, air pollution, and water pollution—energy use may prove to be the most significant. Cannabis factory farming involves energy-intensive lighting, space conditioning, dehumidification, artificial CO₂ fertilization, water reclamation, and other processes to boost yields while maintaining year-round tropical indoor conditions irrespective of the outdoor climate. The authors do a service by bringing further attention to the role of energy in indoor cultivation, as the literature focuses largely on outdoor practices.(2,3) The Global Perspective exemplifies the accounting and methodological complexities in cannabis energy analysis. The authors suggest that my estimate (Mills(4)) of 20 TWh-y (10¹² Wh-y) electricity consumption for legal and illicit indoor cannabis cultivation in the U.S. may not be plausible, equating it to the 1.7 quads (10¹⁵ BTU) site energy use for all U.S. agriculture.(5) However, the energy equivalent of 20 TWh is only 0.068 quads (4% of U.S. agriculture). The authors inadvertently cite a grey literature estimate of national energy use for indoor cannabis cultivation (New Frontier Data(6)) as 4.2 MWh-y (10⁶ Wh-y), lower than Mills(4) by more than six orders of magnitude. However, the source document reports 4.2 million MWh-y (10¹² Wh-y), admittedly a peculiar phrasing of units. The authors also restate that source’s estimated greenhouse gas emissions only for legal cultivation, one-quarter of the total presented therein. The remaining factor-of-three difference between these two estimates is non-trivial and merits examination. Mills(4) models energy intensity ((kWh/gram of finished flower produced)), while the New Frontier Data study(6) utilizes limited field measurements. Both studies extrapolate intensities to estimate national energy demand and emissions. Importantly, the studies’ boundary conditions and findings are not directly comparable, notably that off-grid and transportation energy are not counted in the New Frontier Data study,(6) which also excluded direct fossil-fuel use within the facilities and did not explicitly include small-scale operations which may be more energy intensive than larger professionally operated facilities. Greenhouse gas emissions differ even more, as the New Frontier Data study(6) excluded manufactured CO₂ used to enhance plant growth, transportation energy, and off-grid electricity typically produced by inefficient diesel generators. The New Frontier Data study(6) also utilized a proprietary, nonrandomized, self-reported sample of cultivation sites heavily representative of milder climates with cleaner grids (California and Oregon). While various data are presented for 81 benchmark sites, only 24 (from seven states) yielded the intensity metric underlying their national estimate. The sample also likely represented atypical adoption of efficiency features (e.g., 20% of the sites had LED lighting, which was rarely deemed cost effective at the time(7)). Lastly, the manner and extent to which strain choice (a significant factor),(8,9) crop drying, cold storage, and particularly carbon-intensive black-market operations were addressed is not documented. Wartenberg et al.(1) caution about the unavailability of accurate energy-use data from individual cultivators. Fortunately, such information is increasingly found in the literature,(8−12) which supports model validation, as are market-level data,(2,10,12−15) which support estimates of aggregate energy demand. While they note an absence of data on cultivation area and planting densities, these are not inputs to either study’s methodology. While others arrive at similar or higher measured energy intensities(9,15) and shares of total regional electricity demand(15,16) as in Mills(4), the authors note that energy efficiencies likely improved during the six-year interval between the two studies. That said, during this period, there were major transformations in the industry (and increasing cannabis consumption(17)) that could have driven energy use either up (e.g., larger facility volumes) or down (e.g., more greenhouses, which average 25% lower energy intensity(6)). One data set(8) indicates a trend toward larger facilities, which could elevate energy intensities. It is thus critical to track efficiencies as well as aggregate demand metrics that can trend in opposite directions. Meanwhile, a recent and exhaustive peer-reviewed, model-based assessment(18) identifies a carbon-intensity range bracketing the value in Mills(4), and demonstrates the strong influence of climate and electric generation mix on carbon emissions. The New Frontier Data study(6) is a significant outlier (Figure 1) among the other studies in terms of its very high yield density (grams/m²-y, twice the average of a large meta-analysis(8)) and correspondingly low energy intensity (one quarter to one seventh that of other studies(4,9,18)). Many pre- and post-cultivation energy uses must also be quantified. These include energy embodied in inputs such as growing media, fertilizer, water supply and treatment; postcultivation processing, extractions, and preparations; refrigerated storage; retail operations; and transportation. Other energy-accounting considerations include energy embodied in failed and interdicted (black-market) crops or those destroyed due to unacceptable lab-test results. Energy use in this industry is a largely unattended issue among policymakers.(13) Yet, at energy intensities of ∼6 kWh/gram,(4) indoor cannabis cultivation is 500 times more energy intensive than aluminum smelting,(19) and energy per unit floor area is 50–100 times that of homes and offices.(13) Wartenberg et al.(1) outline traditional policy recommendations, including performance standards, incentives for energy efficiency, and data disclosure. While such measures yield large savings in other contexts, a confounding factor exists in the case of indoor cannabis. Consider one planned 55-acre [22 ha] windowless industrial park in the California desert which includes a dedicated natural-gas power plant that could power 90,000 average(20) all-electric homes.(13) To instead employ solar electricity would require photovoltaic arrays spanning 25 times the roof area, or roughly 1400 acres [567 ha], far more than outdoor cultivation would require for the same yield. This draws into question the potential for sustainabile indoor cannabis cultivation, where “best practices” promise only to optimize the suboptimal. Meanwhile, the alternative—virtually zero-energy outdoor cultivation, which would require only 0.01% of U.S. agricultural lands(13) to meet current demand—receives no financial or policy inducements and indeed is banned in many jurisdictions, rendering it at a competitive disadvantage to indoor practices eligible for market-distorting subsidies (utility rebates)(21) to finance costly measures like LED lighting. Notably, some indirect nonenergy impacts identified by Wartenberg et al.(1) may prove as or more severe for indoor than outdoor cultivation. These include land use (energy extraction, infrastructure), water use (evaporation during electricity generation), water pollution (hydroponic systems shunting pollutants into wastewater treatment systems), indoor/outdoor air pollution (VOC emissions in urban air basins), and solid waste production (soil and artificial growing media landfilled after each cropping cycle at intervals as short as 40 days,(14) while frequently replaced high-pressure sodium and metal-halide grow lights contain mercury).(13) In sum, indoor cannabis production is a particularly complex and fast-growing driver of energy demand and greenhouse gas emissions and yet is far less studied than other comparable uses of energy. In particular, despite the passage of a quarter century since cannabis was first legalized for medical use, U.S. energy and environmental agencies have conducted no known technical or policy research on associated energy impacts. Even leading states have only recently begun considering it.(22) There remains a pressing need for more analysis, particularly given that legalization of indoor cannabis cultivation by the incoming Biden Administration would directly undermine its ambitious climate goals. The author declares no competing financial interest. The author declares no competing financial interest.
This article references 22 other publications.

中文翻译：

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评论“大麻与环境：科学告诉我们什么以及我们仍然需要知道什么”

Wartenberg 等人最近的全球视角。在《环境科学与技术快报》中，我们迫切需要了解大麻种植对环境的复杂影响。(1) 在他们雄心勃勃的审查中确定的途径中——土地覆盖变化、水的使用、杀虫剂的使用、能源的使用、空气污染和水污染——能源使用可能被证明是最重要的。大麻工厂化养殖涉及能源密集型照明、空间调节、除湿、人工 CO ₂施肥、水回收和其他过程，以提高产量，同时保持全年热带室内条件，无论室外气候如何。作者通过进一步关注能量在室内种植中的作用来提供服务，因为文献主要关注户外实践。 (2,3) 全球视角举例说明了大麻能量分析中的会计和方法复杂性。作者建议，我对美国合法和非法室内大麻种植的 20 TWh-y (10 ¹² Wh-y) 电力消耗的估计 (Mills(4))可能不合理，将其等同于 1.7 quads (10 ¹⁵ Wh-y)BTU) 用于所有美国农业的现场能源使用。(5) 然而，20 TWh 的能源当量仅为 0.068 quads（美国农业的 4%）。作者无意中引用了一项关于室内大麻种植国家能源使用的灰色文献估计（New Frontier Data(6)）为 4.2 MWh-y (10 ⁶ Wh-y)，比 Mills(4) 低六个数量级以上. 然而，源文件报告了 420万兆瓦时-年 (10 ¹²Wh-y)，不可否认的是单位的特殊措辞。作者还重申了该来源估计的温室气体排放量仅用于合法种植，占其中提出的总量的四分之一。这两个估计值之间剩余的三分之一差异是重要的，值得检查。Mills(4) 模拟能源强度（（千瓦时/克生产的成品花）），而新前沿数据研究 (6) 使用有限的现场测量。两项研究都推断强度以估计国家能源需求和排放。重要的是，这些研究的边界条件和结果没有直接可比性，特别是离网和运输能源不计入新前沿数据研究，(6) 它还排除了设施内直接使用化石燃料，并且没有明确包括可能比专业运营的大型设施更耗能的小规模运营。温室气体排放差异更大，因为 New Frontier Data 研究 (6) 排除了制造的 CO₂用于促进植物生长、运输能源和通常由低效柴油发电机产生的离网电力。New Frontier Data 研究 (6) 还利用了一个专有的、非随机的、自我报告的种植地点样本，这些样本在很大程度上代表了具有更清洁网格的温和气候（加利福尼亚和俄勒冈）。虽然提供了 81 个基准站点的各种数据，但只有 24 个（来自七个州）产生了作为其国家估计基础的强度指标。该样本还可能代表了对效率特性的非典型采用（例如，20% 的站点具有 LED 照明，这在当时很少被认为具有成本效益 (7)）。最后，没有记录解决菌株选择（一个重要因素）、（8,9）作物干燥、冷藏，特别是碳密集型黑市操作的方式和程度。Wartenberg 等人 (1) 对无法获得来自个体耕种者的准确能源使用数据持谨慎态度。幸运的是，此类信息越来越多地出现在支持模型验证的文献 (8-12) 中，以及支持总能源需求估计的市场级数据 (2,10,12-15)。虽然他们注意到缺乏种植面积和种植密度的数据，但这些都不是对任何一项研究方法的投入。而其他人则达到相似或更高的测量能量强度 (9,15) 和总能量的份额 虽然他们注意到缺乏种植面积和种植密度的数据，但这些都不是对任何一项研究方法的投入。而其他人则达到相似或更高的测量能量强度 (9,15) 和总能量的份额 虽然他们注意到缺乏种植面积和种植密度的数据，但这些都不是对任何一项研究方法的投入。而其他人则达到相似或更高的测量能量强度 (9,15) 和总能量的份额地区电力需求 (15,16) 与 Mills(4) 一样，作者指出，在两项研究之间的六年间隔期间，能源效率可能有所提高。也就是说，在此期间，该行业发生了重大变革（以及大麻消费量的增加 (17)），这可能会推动能源使用量增加（例如，更大的设施数量）或减少（例如，更多的温室，平均 25%较低的能源强度(6))。一个数据集 (8) 表明了向更大设施发展的趋势，这可能会提高能源强度。因此，跟踪效率和汇总数据至关重要可以向相反方向发展的需求指标。同时，最近一项详尽的同行评审、基于模型的评估 (18) 确定了包含 Mills (4) 值的碳强度范围，并证明了气候和发电组合对碳排放的强烈影响。New Frontier Data 研究 (6) 是其他研究中的一个重要异常值（图 1），因为它的产量密度非常高（克/米²-y，是大型荟萃分析平均值的两倍 (8)) 和相应的低能量强度（其他研究 (4,9,18) 的四分之一到七分之一）。许多种植前和种植后的能源使用也必须量化。其中包括包含在生长介质、肥料、供水和处理等投入中的能源；培养后加工、提取和制备；冷藏；零售业务；和运输。其他能源会计考虑因素包括包含在失败和被禁止的（黑市）作物中的能量，或那些由于不可接受的实验室测试结果而被破坏的能量。该行业的能源使用在很大程度上是政策制定者未关注的问题。 (13) 然而，在约 6 千瓦时/克的能源强度下，(4) 室内大麻种植的能源强度是铝冶炼的 500 倍，(19) 每单位建筑面积的能源是家庭和办公室的 50-100 倍。(13) Wartenberg 等人 (1) 概述了传统的政策建议，包括绩效标准、能效激励措施和数据披露。虽然这些措施在其他情况下会产生大量节省，但室内大麻的情况存在一个混杂因素。考虑在加利福尼亚沙漠中规划一个占地 55 英亩 [22 公顷] 的无窗工业园区，其中包括一个专用的天然气发电厂，可为 90,000 个普通 (20) 全电动家庭供电。(13) 代替使用太阳能将需要光伏阵列跨越屋顶面积的 25 倍，或大约 1400 英亩 [567 公顷]，远远超过相同产量所需的户外种植。这引起了人们对可持续室内大麻种植潜力的质疑，其中“最佳实践”承诺只优化次优。与此同时，替代方案——几乎零能耗的户外种植，只需要 0.01% 的美国农业用地 (13) 即可满足当前需求——没有收到任何财政或政策诱因，实际上在许多司法管辖区被禁止，使其处于竞争劣势有资格获得扭曲市场补贴（公用事业回扣）(21) 的室内实践，以资助昂贵的措施，如 LED 照明。值得注意的是，Wartenberg 等人 (1) 确定的一些间接非能源影响可能证明室内种植比室外种植更严重。这些包括土地使用（能源开采、基础设施）、用水（发电过程中的蒸发）、水污染（水培系统将污染物分流到废水处理系统中）、室内/室外空气污染（城市空气流域的 VOC 排放）和固体废物生产（在每个种植周期后以短至 40 天的间隔填埋的土壤和人工生长介质，(14) 同时频繁更换高压钠和金属-卤化物生长灯含有汞。(13) 总之，室内大麻生产是能源需求和温室气体排放的一个特别复杂和快速增长的驱动因素，但与其他类似的能源用途相比，研究较少。特别是，尽管大麻首次被合法用于医疗用途已经过去了四分之一个世纪，但美国能源和环境机构尚未就相关的能源影响进行任何已知的技术或政策研究。甚至主要国家最近才开始考虑它。 (22) 仍然迫切需要更多的分析，特别是考虑到即将上任的拜登政府将室内大麻种植合法化将直接破坏其雄心勃勃的气候目标。作者声明没有竞争性经济利益。作者声明没有竞争性经济利益。
本文引用了 22 篇其他出版物。