Background/Question/Methods Urban agriculture (UA) – producing food in and around the city – can help green cities, feed urbanites, strengthen communities, and improve human well-being. UA also shortens the distance from farm to fork and typically uses fewer agrochemicals than conventional agriculture. Because of this, UA is often touted as environmentally superior to conventional food chains. There is limited empirical work, however, testing this assertion. Case studies, typically of only one or a few urban farms, show that in terms of resource intensity and carbon emissions, UA can be better than, similar to, or even considerably worse than conventional agriculture. To better clarify to what extent UA is environmentally preferable to conventional farming, we performed the most comprehensive study of UA to date. Through site visits and electronic surveys, we used a citizen-science approach to monitor resource use and production at 74 urban food producers in cities in France, Germany, Poland, the United Kingdom, and the United States during the 2019 growing season. We input the collected data into a life cycle assessment model to estimate the embodied and direct carbon emissions, energy use, water use, and nutrient inputs need to support fruit and vegetable production using UA.
Environmental impacts varied significantly across our sample. When we grouped farms as either collective gardens, urban farms, or individual gardens, and compared these groups to produce available in our five countries, we found that collective gardens and individual gardens are statistically more carbon intensive (p< 0.05) than conventional agriculture. Urban farms, which are often more carbon intensive than the other two UA forms, are indistinguishable from conventional farms. When looking at the sources of environmental impacts in UA, we found that infrastructure, such as growing beds, buildings, irrigation systems, and fencing, account for more than 50% of the impacts for most of our cases. Using statistical models, we determined that infrastructure must have a minimum lifespan of 10 years for an urban farm to have similar environmental impacts to a conventional farm. This suggests that UA cannot be a transitional land use, as it sometimes is, if it is going to be a sustainable supplement to conventional farming. Policy makers and urban farmers should judiciously choose the types of farms they support and ensure long-term land tenure ( >10 years) when promoting UA for environmental reasons.