On average, urban farms have a carbon footprint that is six times greater than conventional farms, says a surprising recent study. However, the new dataset also showed that individually, many urban farms are better for the planet than conventional agriculture, because their farmers have taken certain steps that, if widely applied, could turn urban farming into an overall force for good. 

Crucially, the new research “is not calling for an end to urban gardening,” cautions Jason Hawes, a researcher in resource policy and behavior at the University of Michigan School for Environment and Sustainability, and lead researcher of the new findings. “Instead, we wanted to provide quantitative evidence for the carbon footprint of urban agriculture, which in turn allows us to identify ways to reduce the impact on the climate.”

Urban farms (which can include everything from home gardens to commercial city farms) are typically celebrated for their diversity, low rates of fertilizers and pesticide use, and reduced food transport emissions. They’re often seen as a hopeful counter to the resource-intensive monoculture model of conventional farms, where food is typically farmed miles away from the populations it ultimately feeds. 

Because environmental sustainability is the primary motivation urban gardeners cite for growing food, the researchers felt the need to really test these sustainability credentials out.

To do so, they worked with citizen scientists to gather data from 73 urban farms, which were spread across five countries: France, Germany, Poland, the US and the UK. This sample incorporated a range of farm types, from small home plots and community gardens where participants grow food for personal consumption, to city farms where food is grown for commercial gain. For each, the researchers tallied up the carbon emissions of different inputs, ranging from the materials used to make raised beds, to fertilizers, and compost. The overall footprint of each farm was then expressed as a measure per standard serving of fruit and veg, and then compared with the same measure on conventional farms. 

The study’s geographical scope and number of farms it included made it the first large-scale study to examine urban farming sustainability. Across the sample of 73 sites, they found that on average, the carbon footprint of urban farms was greater than conventional farms, by up to six times: that amounted to 420 grams of CO2 equivalent per serving of food from urban agriculture, versus 70 grams per serving produced from conventional farms.

In that figure, the source of most carbon was something of a surprise: it derived from the infrastructure required to establish urban farms—such as raised beds, compost sheds, and landscaping, which may frequently be turned over due to the comparatively shorter lifespan of urban farms. “This is partially down to the relative transience of urban agriculture. But it also just emerges from the nature of urban food growing sites: there’s a lot more new wood and stone invested in a typical urban garden than in your average big open field in the countryside,” Hawes explains. 

However, while most urban farms showed this higher footprint, within the sample there was a huge amount of variation. In fact, in a handful of farms—17 out of the 73—the footprint was notably lower than that of conventional farms. The researchers also noticed that in some cases this shrunken footprint aligned with particular crops such as open-air tomatoes, which were much more sustainably grown, compared to those from conventional farms where they’re often raised in resource-intensive greenhouses and transported over long distances to cities. The same trend appeared for some crops of urban-grown asparagus, when compared to commercial asparagus that’s air-freighted in from remote farms.

These nuanced findings mean it would be unwise to write off urban farming. In fact using “lessons learned on those climate-friendly sites,” says Hawes, they suggest some best practices that could turn urban farms into a much-needed force for climate good.

First up, farmers could tackle the biggest source of emissions in infrastructure. What would help, the study suggests, is improved tenure conditions so that urban farmers aren’t driven off the land and forced to relocate, which is a common feature of city farms in metropolises around the world. One striking stat from the study showed that a raised vegetable bed that lasted only five years had a carbon footprint four times higher than one that remained in state for 20 years. “In addition to extending the lifetimes of urban farms and gardens, we note that food growers can save carbon by using reclaimed materials to build their infrastructure,” Hawes says. 

Smart crop selection is another way to bring down carbon emissions, perhaps by focusing urban farms to specialize in crops that typically travel long distances or are greenhouse-grown, producing them locally with reduced inputs instead. Recycling urban waste streams into compost is another way to offset carbon costs, the study suggests. 

Ultimately, urban farming has real potential as conventional agriculture’s greener cousin, if we do it right, says Hawkes. “Urban agriculture has a lot of benefits for cities and for the folks who participate in it,” he emphasizes. But “we have to understand its carbon dynamics and how to design for more carbon-efficient urban food production.”

Hawes et. al. “Comparing the carbon footprints of urban and conventional agriculture.” Nature Cities. 2024.

Image: AI-generated

Source: anthropocenemagazine.org