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Urban agriculture has myriad benefits for those who participate in it, but it's not guaranteed to be more climate-friendly than conventional agriculture. That said, there are some very specific steps urban farmers can take to slash carbon emissions. [ABSTRACT FROM AUTHOR]

There is increasing interest in evaluating the environmental performance of urban agriculture (UA), primarily using life cycle assessment (LCA). However, LCA has been applied to UA inconsistently, making it difficult to confidently compare or draw conclusions from existing studies. This article outlines the key challenges of applying LCA to UA and recommends concrete steps to bring consistency and comprehensiveness to the topic. The research questions that LCA can address are framed before providing practical recommendations for performing LCAs of UA, considering several of its unique aspects that require special attention by practitioners. These include crop diversity, data availability, modeling compost, soil carbon sequestration, producing growing media, distribution of crops, and variability and uncertainty. Next, the article proposes future research areas that will benefit LCA generally and its application to UA, such as framing UA as urban green infrastructure, evaluating at the city scale, accounting for ecosystem services, and including social dimensions of UA. By following these recommendations, future LCAs of UA can be more consistent, comparable, and holistic, and will help build knowledge and inform policy-making and practices around UA. [Display omitted] • Life cycle assessment can address key societal issues relevant to urban agriculture. • Its application to urban agriculture raises multiple and unique challenges. • Handling of composts, crop distribution and growing media create large uncertainties. • Practical recommendations were derived to improve the reliability of LCAs. • Accounting for ecosystem services and social dimensions should be prioritized. [ABSTRACT FROM AUTHOR]

• Calculated environmental impacts of 8 urban farms/gardens using life cycle assessment. • Collected primary data and aimed for complete, transparent assessment. • Vertical, outdoor, professional farms had largest impacts by area; not by mass of crop. • Most impacts came from infrastructure, irrigation, compost, and peat from seedlings. • Results were highly sensitive to system modeling choices, such as compost parameters. Urban agriculture (UA) is often positioned as an environmentally sustainable food supply for cities. However, life cycle assessments (LCA) measuring environmental impacts of UA show mixed results, because of inconsistent application of LCA and reliance on hypothetical case studies. To address these shortcomings, we performed an LCA of eight urban farms and community gardens in Paris, France and San Francisco, California, USA. We collected primary data from sites representing diverse growing systems (low-intensity open-field to open-air hydroponics) and motivations (education, civic engagement, and commercial production). We found that medium-tech farms, with minimum social engagement had the lowest impacts using a kilogram-based functional unit, but socially-oriented farms had the lowest impacts with an area-based functional unit. Most impacts came from infrastructure (irrigation pipes, hydroponics structures), irrigation, compost, and peat for seedlings. Our findings can help LCA practitioners perform UA LCAs more completely/consistently, and help urban farmers/gardeners target high-environmental-impact practices to optimize. [ABSTRACT FROM AUTHOR]

Modern food systems incur many environmental impacts, which can be mitigated by the application of circular economy principles, such as the closing of material and energy loops and the upcycling of waste products. Mushroom farming provides a relevant case in this direction because organic waste can be used for substrate as an input in the cultivation process, which produces valuable outputs such as edible foodstuffs and soil amendment. Few studies evaluate the actual environmental impacts of circular food production systems and assess their efficacy with respect to more linear alternatives. To address this research gap, we quantified the environmental impacts of a circular, urban mushroom farm next to Paris, France. We used life cycle assessment to study the production of 1 kg of fresh oyster mushrooms (Pleurotus ostreatus), from the generation of substrate materials through delivery to the distribution center. Our goals were to quantify the environmental impacts of a novel type of food production system, to find the aspects of production that contribute most to these impacts, and to assess the advantages and disadvantages of circular economy for this case study. In terms of climate change impact, the product system emitted 2.99–3.18 kg CO2-eq./kg mushroom, and on-farm energy use was the top contributor to all impact categories except land use. Surprisingly, 31% of the climate change impacts came from transport throughout the supply chain, despite the local nature of the farm. Circular economy actions helped optimize the environmental performance by minimizing impacts from the use of materials, which were mostly upcycled. This suggests that further improvements could be made by reducing energy consumption on the farm or by making the transport schemes more efficient, rather than continuing to focus on the type and source of materials used. This circular, urban farm had similar climate change impacts to classical, more linear systems, but these impacts could be largely reduced by implementing appropriate actions. These were identified and discussed with the farmers, factoring in their feasibility. • Climate change impacts were 2.99–3.18 kg CO 2 eq. per kilogram of fresh mushroom. • A large portion of environmental impacts came from energy use on the farm. • Circularity led to low impacts from input materials, but high impacts from transport. • Improving sanitary measures to increase yield would greatly reduce impacts. • Impacts were similar to typical mushroom farms, but can be much lower if optimized. [ABSTRACT FROM AUTHOR]