Research: Urban Agriculture’s Carbon Footprint 6X Larger Than Traditional Farming

“Most of the climate impacts at urban farms are driven by the materials used to construct them-the infrastructure,”

Co-authors of the Nature Cities paper are from McGill University in Canada, University Paris-Saclay and the Agroecology and Environmental Research Unit in France, the University of Kent in the United Kingdom, ILS Research in Germany, City University of New York and Adam Mickiewicz University in Poland. 2024

Excerpt:

A new University of Michigan-led international study finds that fruits and vegetables grown in urban farms and gardens have a carbon footprint that is, on average, six times greater than conventionally grown produce.

However, a few city-grown crops equaled or outperformed conventional agriculture under certain conditions. Tomatoes grown in the soil of open-air urban plots had a lower carbon intensity than tomatoes grown in conventional greenhouses, while the emissions difference between conventional and urban agriculture vanished for air-freighted crops like asparagus.

“The exceptions revealed by our study suggest that urban agriculture practitioners can reduce their climate impacts by cultivating crops that are typically greenhouse-grown or air-freighted, in addition to making changes in site design and management,” said study co-lead author Jason Hawes, a doctoral student at U-M’s School for Environment and Sustainability.

“Urban agriculture offers a variety of social, nutritional and place-based environmental benefits, which make it an appealing feature of future sustainable cities. This work shines light on ways to ensure that urban agriculture benefits the climate, as well as the people and places it serves.”

Urban garden in Nantes, France. Image credit: Baptiste Grard.
Urban agriculture, the practice of farming within the confines of a city, is becoming increasingly popular worldwide and is touted as a way to make cities and urban food systems more sustainable. By some estimates, between 20% and 30% of the global urban population engages in some form of urban agriculture.

The researchers identified three best practices crucial to making low-tech urban agriculture more carbon-competitive with conventional agriculture:

Extend infrastructure lifetimes. Extend the lifetime of UA materials and structures such as raised beds, composting infrastructure and sheds. A raised bed used for five years will have approximately four times the environmental impact, per serving of food, as a raised bed used for 20 years.

Use urban wastes as UA inputs. Conserve carbon by engaging in “urban symbiosis,” which includes giving a second life to used materials, such as construction debris and demolition waste, that are unsuitable for new construction but potentially useful for UA. The most well-known symbiotic relationship between cities and UA is composting. The category also includes using rainwater and recycled grey water for irrigation.

Generate high levels of social benefits. In a survey conducted for the study, UA farmers and gardeners overwhelmingly reported improved mental health, diet and social networks. While increasing these “nonfood outputs” of UA does not reduce its carbon footprint, “growing spaces which maximize social benefits can outcompete conventional agriculture when UA benefits are considered holistically,” according to the study authors.

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