25 January 2024

Agriculture developed in urban spaces can have six times the climate impact of traditional agriculture, explains a University of Michigan study. Some tricks, however, make it possible to solve the problem

by Matteo Cavallito

 

On average, urban agriculture products have six times the carbon footprint of conventionally grown products. But under certain conditions, by applying appropriate measures, the problem can be solved by realizing in crops characterized even by a lower climate impact in comparison with typical cropfields. This is suggested by research from the University of Michigan.

The study, published in the journal Nature Cities, looked at three different kind of spaces designated for city crops: professionally managed urban farms focused on food production, individual gardens administered by individual gardeners, and community gardens. For each of these sites, says a statement, the researchers calculated the greenhouse gas emissions associated with the farm’s materials and activities over its lifetime.

The impact of urban agriculture is six times greater

“Urban agriculture (UA) is a widely proposed strategy to make cities and urban food systems more sustainable,” the study notes. “Until now, we have lacked a comprehensive assessment of the environmental performance of UA relative to conventional agriculture, and results from earlier studies have been mixed.” To carry out the study, the first of its kind conducted on a large scale, the authors involved farmers and gardeners engaged in managing urban farming sites in France, Germany, Poland, the United Kingdom and the United States.

They were asked to compile daily records indicating all inputs and yields from their farming sites throughout the 2019 season.

The inputs, the authors recall, fall into three main categories: infrastructure, supplies (including compost, fertilizer, herbicides and gasoline for machinery) and water for irrigation. “Results – the research explains – reveal that the carbon footprint of food from UA is six times greater than conventional agriculture (420 gCO2e versus 70 gCO2e per serving).”

The critical factors

“Most of the climate impacts at urban farms are driven by the materials used to construct them—the infrastructure,” said Benjamin Goldstein, a professor in the School for Environment and Sustainability at the University of Michigan and co-author of the study.

“These farms typically only operate for a few years or a decade, so the greenhouse gases used to produce those materials are not used effectively. Conventional agriculture, on the other hand, is very efficient and hard to compete with.”

In addition, he Goldstein says, conventional farms often manage a single crop with the help of pesticides and fertilizers. In this way they can achieve higher yields and a smaller carbon footprint than urban enterprises.

The solutions

The research, however, brought out some contrarian data. “Some urban agriculture crops (for example, tomatoes) and sites (for example, 25% of individually managed gardens) outperform conventional agriculture,” the authors explain.

“These exceptions suggest that UA practitioners can reduce their climate impacts by cultivating crops that are typically greenhouse-grown or air-freighted, maintaining UA sites for many years, and using circularity (waste as inputs).”

According to the study, there are two main strategies to achieve this goal. First, the lifespan of materials and structures must be extended. In addition, it is necessary to use urban waste as inputs. Which means recovering used materials, enhancing organic waste through composting, and using recoverable rainwater and gray water for irrigation.