Opinion: To Make a Real Impact on Climate Change, We Must Move Beyond the Carbon Footprint - Modern Farmer

Opinion: To Make a Real Impact on Climate Change, We Must Move Beyond the Carbon Footprint

Focusing on just one emissions metric minimizes all the other benefits of actions like urban agriculture.

Bluma Farm, a rooftop flower farm, on top of Cal student housing building.
Photography Submitted by Laney Siegner

As a researcher of urban agriculture, I was shocked to see a recent news article bearing the headline “Food from urban agriculture has a carbon footprint six times larger than conventional produce, study shows.” I had spent five years researching and publishing peer-reviewed articles and book chapters about urban agriculture during my Ph.D. with the Berkeley Food Institute, and this conclusion seemed to fly in the face of all that I’d read. How could this be? 

The researcher and passionate urban gardener in me couldn’t resist digging in deeper and working to illuminate a fuller “truth” around this recent result. Spoiler alert: Avoid carbon tunnel vision, as focusing on a single emissions metric misses the many other benefits that can get us out of the crisis we’re in. 

Back up a step: What is urban agriculture? Urban ag is any kind of food production space within a city, inclusive of commercial farms that grow and sell directly to consumers, non-profit farms that serve a broader mission, community gardens, school gardens and even vacant lots turned into thriving personal gardens or homesteads. 

Better yet, why do some researchers, farmers and activists prefer the term “urban agroecology?” From 2017 to 2019, my research team helped to define and elevate “urban agroecology” in the US as a better way of acknowledging the multifunctional benefits of urban green spaces. These farms and gardens are not “just” growing food, they are also building community, performing environmental services (think stormwater mitigation and reducing urban heat island effect), providing habitat for biodiversity and educating urban residents. It’s often one of the only ways kids and adults alike can interact with nature, see where their food comes from and witness the magic of a seed sprouting. Urban growing spaces are also often led by women and BIPOC farmers (more than 60 percent in my investigation of the East Bay in California’s Bay Area), serving as important grounds for empowerment, culturally relevant food production and healing of racialized patterns of agricultural work. 

Oxford Tract research farm at UC Berkeley. Photo submitted by Laney Siegner.

So, I had alarm bells going off when reading about this new study. The research from the University of Michigan-led study seems to show that fruit and vegetables grown in urban ag have a carbon footprint six times larger than that of “conventionally grown” food (meaning, on rural farmland). 

The choice to compare greenhouse gas intensity of soil-based urban agriculture systems with conventional farming systems brings up an inherently unfair comparison. When looking at conventional, large-scale farming systems, which are largely monocultures designed to maximize yield per acre via application of fossil-fuel based fertilizers, pesticides and other chemicals, we already have a large body of evidence that these are carbon-intensive production systems with a host of other detrimental environmental impacts (land, air and water pollution, soil degradation and erosion, habitat and biodiversity loss across billions of acres of “conventional farmland” globally). 

However, when you divide a large number (i.e., carbon emissions) by another large number (yield per acre), you get a small number of carbon emissions associated with each serving of lettuce, for example. When looking at urban community and school farms and gardens, we often see highly diversified plots that are more sparsely planted, with some weedy edges. They’re not exactly “yield-maximizing” practices on display. So, when you divide a relatively small number of carbon emissions, which the researchers in the study attributed to things such as garden infrastructure (raised beds, paved paths, tool sheds and others)—so, indirect emissions—and divide it by another very small number (yield per acre), you end up with a relatively larger number than your conventional allegory “lettuce serving.” The math here doesn’t point the finger towards the system that really needs changing in carbon and climate terms. 

This study disregards the far more pressing issue of the sheer quantity of emissions that come from conventional farming. Additionally, the conversations only circled back towards the end to include or acknowledge the many climate “benefits” of having spaces where city dwellers can connect with their food system and with nature in the city. These less quantifiable benefits are primary, not secondary; they are essential to bring into collective societal focus, rather than obscure behind a conclusion that sets up a feeling of confusion or uncertainty about whether urban ag is or is not a “climate solution.” Urban farms, especially when well managed and resourced with consistent staffing and city support, are critical pieces of the climate solutions puzzle. 

It brings me back to this unsettled feeling that the study is asking the wrong research question, if the conclusions and headlines point us towards some course of action around “fixing” urban farms so they can have a lower carbon footprint, while saying nothing about the carbon-intensive conventional farming system that urgently needs to change to address the overlapping climate and public health crisis. To quote one of the leaders of my urban ag research project, Dr. Timothy Bowles, a professor of Agroecology at U.C. Berkeley: 

“This is an issue with metrics… in this case, using efficiency as the metric (i.e., amount of food produced per unit of GHG emission). Efficiency metrics can be problematic for a number of reasons, and a number of studies have demonstrated more ‘efficient’ food production from conventional systems compared to various alternatives from a strictly GHG standpoint, largely due to higher yields, even if total emissions are high. In general, we need multifunctional perspectives for a more holistic systems comparison.” 

To be sure, we need conventional farming systems right now that create efficiency and economies of scale to grow and distribute large volumes of food to feed a growing population. There is no switching to diversified farming and regenerative agriculture overnight, just like there is no transition to purely solar and wind power for our electricity system without proper planning for this change. I’m not saying we can feed the entire city from the products of urban farms (although there have been researchers before me who modeled that this is theoretically possible, within a 50-mile radius, of a US midwestern city). What we need is for the conventional food system to change dramatically: to reduce reliance on fossil-fuel-based inputs, be more adaptive to climate extremes, adopt climate-friendly practices such as cover cropping and compost application, and in doing all this become a better source of healthy food. 

I’m also all for improving urban farms, increasing recycling of materials and waste streams in cities and resourcing them to be viable sites of food production, as the study authors point out as action items. I just find the impetus for doing so to be limited if we’re primarily talking about reducing the carbon footprint of these sites. Urban farms are capable of teaching the principles of photosynthesis, soil health and carbon sequestration even if they are not sequestering carbon in large quantities. And this knowledge is powerful. 

Where do we go from here as researchers, as eaters and producers of food? The food system of today is in crisis. It has prioritized cost and yield over all else. The result? It doesn’t work for farmers, it does not produce nutritious, healthy food for people and it is a disaster environmentally. However, the future of food can be diversified, abundant and rooted in soil health practices, fostering social equity and farmer well-being. I see that shift happening already on farms both urban and rural, big and small. It takes education, both farmer to farmer and farmer to consumer, as well as policy change to support the shifts already in motion. By reconnecting with food, with ecology, with living soil, we connect to climate solutions and help to reverse the damages of climate change.


Laney Siegner is founder and Co-director of Climate Farm School, with a Ph.D. from U.C. Berkeley Energy and Resources Group. 

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