Conventional farms often grow a single crop with the help of pesticides and fertilizers, resulting in larger harvests and a reduced carbon footprint, but less healthy food. A critic pointed out that climate alarmists who are shutting down farmers are likely to go after urban farmers and gardeners, too.

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 U-M-led study, published online Jan. 22 in the journal Nature Cities, 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).

For each site, the researchers calculated the climate-altering greenhouse gas emissions associated with on-farm materials and activities over the lifetime of the farm. The emissions, expressed in kilograms of carbon dioxide equivalents per serving of food, were then compared to foods raised by conventional methods.