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,” says Jason Hawes, a doctoral student at the University of Michigan’s School for Environment and Sustainability and co-lead author of the study in the journal Nature Cities.

“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 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.

Despite strong evidence of the social and nutritional benefits of urban agriculture, its carbon footprint remains understudied. Most previously published studies have focused on high-tech, energy-intensive forms of UA—such as vertical farms and rooftop greenhouses—even though the vast majority of urban farms are decidedly low-tech: crops grown in soil on open-air plots.

The new study aimed to fill some of the knowledge gaps by comparing the carbon footprints of food produced at low-tech urban agriculture sites to conventional crops. It used data from 73 urban farms and gardens in five countries and is the largest published study to compare the carbon footprints of urban and conventional agriculture.

Three types of urban agriculture sites were analyzed: urban farms (professionally managed and focused on food production), individual gardens (small plots managed by single gardeners), and collective gardens (communal spaces managed by groups of gardeners).

Read the full article about urban farms and carbon footprints by Jim Erickson at Futurity.