A new University of Michigan-led 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.
Study co-lead author Jason Hawes, a doctoral student at U of M's School for Environment and Sustainability, acknowledged the results may be surprising to many people involved in raising food in cities.
"Urban agriculture has a climate change problem, right? It's clear that it is not what maybe people would assume just because it's local," Hawes said.
Hawes said the short-term use of infrastructure is responsible for most of the higher carbon footprint of urban-grown produce.
Since such farms often are in operation for less than a decade, the greenhouse gases used to produce farm materials are used inefficiently — in other words, the emissions are not spread out over a long period of time, which would mitigate their impact.
Hawes said more recycling and reuse of farm and garden materials would help, as would maximizing the considerable social benefits of urban farming.
For example, people involved in collective or individual gardens in urban areas, or working on the urban farms, tend to eat less meat than other people. And meat has a far higher carbon footprint than fruits and vegetables.
"So if we can simultaneously improve the footprint of urban agriculture, and get people that participate to eat less meat, then that's a win-win," Hawes said.
Another way to shrink the carbon footprint of urban farms is to focus on crops that are otherwise typically grown in higher-carbon environments — tomatoes, for example, which use less resources when grown in open beds than in greenhouses, and asparagus, which is frequently flown by plane to markets.
The study was published in the January 22 issue of the journal Nature Cities.
It used data from 73 urban farms and gardens in five countries. Researchers said it's the largest published study to compare the carbon footprints of urban and conventional agriculture.
