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Issues of the Environment: A University of Michigan study of Urban Agriculture stirs controversy

Dr. Benjamin Goldstein, assistant professor at the University of Michigan School for Environment and Sustainability.
University of Michigan School for Environment and Sustainability
Dr. Benjamin Goldstein, assistant professor at the University of Michigan School for Environment and Sustainability.


  • A new University of Michigan-led international 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. “By assessing actual inputs and outputs on urban agriculture sites, we were able to assign climate change impacts to each serving of produce,” said study co-lead author Benjamin Goldstein, assistant professor at U-M’s School for Environment and Sustainability. “This dataset reveals that urban agriculture has higher carbon emissions per serving of fruit or vegetable than conventional agriculture—with a few exceptions.” (Source: *directly quoted* https://news.umich.edu/study-finds-that-urban-agriculture-must-be-carefully-planned-to-have-climate-benefits/)

  • Conventional farming relies on large plots of land maintained with pesticides, soil-additives and fertilizers, and sometimes supplemental irrigation to maximize crop yield. Conventional farmed crops are generally grown as a monoculture, with just one type of seed being cultivated in each plot. Beyond carbon footprint, according to the Rodale Institute, which studies the disparities between organic farming and conventional, some of the environmental downsides of  conventional farming include increased greenhouse gas emissions, soil erosion, water pollution, and threatens human health.”
  • Farmers and gardeners at urban agriculture sites in France, Germany, Poland, the United Kingdom and the United States were recruited as citizen scientists and used daily diary entries to record inputs and harvests from their food-growing sites throughout the 2019 season.
  • Inputs to the urban agriculture sites fell into three main categories: infrastructure (such as the raised beds in which food is grown, or pathways between plots), supplies (including compost, fertilizer, weed-blocking fabric and gasoline for machinery), and irrigation water. “Most of the climate impacts at urban farms are driven by the materials used to construct them—the infrastructure,” Goldstein said. “These farms typically only operate for a few years or a decade, so the greenhouse gases used to produce those materials are not used effectively.         

  • The researchers identified three best practices crucial to making low-tech urban agriculture more carbon-competitive with conventional agriculture:

    • Extend infrastructure lifetimes. Extend the lifetime of UA materials and structures such as raised beds, composting infrastructure and sheds. A raised bed used for five years will have approximately four times the environmental impact, per serving of food, as a raised bed used for 20 years. (Project Grow, an urban farming initiative that provides plots at sites throughout Washtenaw County, uses a revolving model where infrastructure remains and farmers rotate through over decades.)
    • Use urban wastes as UA inputs. Conserve carbon by engaging in “urban symbiosis,” which includes giving a second life to used materials, such as construction debris and demolition waste, that are unsuitable for new construction but potentially useful for UA. The most well-known symbiotic relationship between cities and UA is composting. The category also includes using rainwater and recycled grey water for irrigation.
    • Generate high levels of social benefits. In a survey conducted for the study, UA farmers and gardeners overwhelmingly reported improved mental health, diet and social networks. While increasing these “nonfood outputs” of UA does not reduce its carbon footprint, “growing spaces which maximize social benefits can outcompete conventional agriculture when UA benefits are considered holistically,” according to the study authors.

Additional resources: Links to some of the other papers to come out of the research project






David Fair: This is 89 one WEMU, and on today's edition of WEMU's Issues of the Environment, we're going to look at urban farming and gardening, specifically the carbon footprint these globally popular endeavors create. I'm David Fair, and I was certainly not alone in being surprised by part of what a University of Michigan study found 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. Now, that's certainly a headline that grabbed a lot of attention and has caused some pushback on the research on the U of M campus and among some homesteaders. That's why we wanted to go beyond the headline and gain a more well-rounded picture of the story. My guest today is Benjamin Goldstein. He is an assistant professor at the U of M School of Environment and Sustainability and is head of the Sustainable Urban Rural Futures Lab. He also served as co-lead author of the study. Thank you so much for making time for us today. I appreciate it.

Dr. Benjamin Goldstein: Happy to be here!

David Fair: Well, obviously, there was a very strong reaction, but was that more headline-driven or was that more content-driven?

Dr. Benjamin Goldstein: Probably a little bit of A and B. Coming into the study, we knew that the results could raise some eyebrows and would ruffle feathers. I have studied this in the past, so I had a feeling what type of results we would find and wasn't surprised myself personally when it came out. And we tried--I don't think we tried. We did provide a well-balanced discussion of urban agriculture in that article. First off, highlighting that it wasn't all farms that had higher carbon footprints than conventional agriculture, and in addition to that, we know that there are lots of other benefits to urban agriculture that are social and economic ecosystems driven. But, unfortunately, the way the media picked it up, and perhaps this is partially our fault because of the way the press release was worded by the University of Michigan, seemed like we were focused solely on trying to make urban agriculture look bad, which, certainly, was not the intent of the article.

David Fair: And, additionally, did that make it seem to some that, perhaps, the study and the publication were to serve as an endorsement of large-scale industrial farming?

Dr. Benjamin Goldstein: Oh, definitely not. If you look at my publication history, I have numerous articles that were very critical of large-scale conventional agriculture and all of its environmental and social depredations. Everyone on the study, and most of whom are actually urban farmers themselves or backyard gardeners, were all very critical of the conventional food system. And so, this was really supposed to be a sober appraisal, just looking at if you produce some food in urban settings versus if you produce it in conventional settings and in rural settings on large farms, what's the comparative carbon impact? And sometimes, for some fruits and vegetables, it can be higher in urban settings. It can also be lower in urban settings. But unfortunately, it was picked up--our article heavily. And a lot of people, at least a lot of journalist focused and some prominent journalists focused, just on the negative component that was comparing some of these farms and their carbon footprints to conventional agriculture and sort of using that as a way to either say that this article justified the practices of conventional agriculture, which is by no means weren't what we set out to do, and also that we, as authors, were calling for the banishment of urban farms and backyard gardeners, which, if you read the article, is exactly the opposite of what we say in the article. We actually said that urban agriculture needs more support from cities in specific ways, so that it can reduce its carbon impacts.

David Fair: You are listening to 89 one WEMU's Issues of the Environment, and we're talking with Benjamin Goldstein. He is an assistant professor at the U of M School of Environment and Sustainability and is head of the Sustainable Urban Rural Futures Lab. When the results came in from all the data collected, what do you attribute the greater carbon footprint?

Dr. Benjamin Goldstein: One thing we found is that a lot of these farms had a lot of carbon emissions embodied in the infrastructure used to build the farm. And just to clarify, we made sure that when we actually modeled that that those carbon emissions, for instance, if I build a raised bed and I buy wood and all of the carbon emissions related to producing that wood and transporting that wood, we made sure that all of those emissions were allocated across the lifetime of the farms. It's not like we just took all of that carbon and said, "Oh, it went to one year's worth of food produced at an urban farm." Now, we spread it out over ten, 20, 30, 50 years. We did different modeling approaches. So, it was really the infrastructure that was a majority of the carbon footprint for more than half of the farms.

David Fair: So, as we look to the future of urban agriculture, what is going to be the best practices that we can implement today to make that difference a decade and two decades down the line?

Dr. Benjamin Goldstein: Well, in the article, we outlined a few different things that farmers can do in order to help reduce their carbon footprint. So, not even just farmers, but also cities because, again, this article was not an indictment of urban farming itself. If we're critical of anything, it's the difficult environment that urban farmers have to live and exist within. So, one thing that farmers and cities can do is, well, this is more on the city side, they can make sure that they provide land tenure and stable spaces for our urban farmers to operate. Because when you build a farm for a couple of years, use a lot of materials to do that. And then, tear it down because maybe the cities kick you off of that plot because they think it's more valuable to redevelop it and sell it to real estate developers. That means that all of those carbon emissions went for basically producing only 1 or 2 years worth of crops, or maybe five years. And we found that if you can elongate the lifespan of farms, this has a very strong impact on reducing the carbon emissions. The second thing is that, where possible, farmers can choose to grow foods that are conventionally very carbon intensive to grow. So, these can be things like asparagus that are air freighted into cities, or tomatoes, which are grown traditionally in greenhouses, right? So, if we can supplant those types of crops, then that also means that it can have climate benefits for the urban food system as a whole. And then, the last thing: farmers can use recycled materials to build their farms. And we found that a lot of the farms that had a lower carbon footprint in our study, they tended to recycle building materials, to build raised beds, to build pathways, to build fences, to build little hoop houses on their properties.

David Fair: We're talking with U of M Assistant Professor Benjamin Goldstein on 89 one WEMU's Issues of the Environment. And let's talk about some of the other community benefits of urban farms and gardens. Access to fresh and healthy food, reduced local transportation needs, the social aspect of cooperation, camaraderie and community building--can the value of that be overstated?

Dr. Benjamin Goldstein: I don't think so. I think that these are really, really equally important reasons for performing urban agriculture and on par with growing and producing food in cities. All of those are worthwhile and something that we actually studied in this larger project that I was a part of. We actually published multiple papers that came out of that project that discussed the motivations and benefits of urban agriculture beyond just producing food. And so, I don't think that it can be overstated. And we were well aware in this project of how valuable all of this is. Our only goal was to hopefully align all of those great motivations and making sure that as this practice grows and becomes more popular, it also provides climate benefits on top of all of those other benefits.

David Fair: So, given the growing popularity of urban agriculture and the findings in your recently published study, which is much more broad than has been covered, it seems there is a lot more to study, a lot more to learn, and there will be greater research down the line. What is next for you and your colleagues?

Dr. Benjamin Goldstein: Well, we have been actually approached by different urban agriculture interest groups. Some of them are from student-led groups over here at the university. Also, some are broader coalitions of urban agriculture policy specialist study. And so, immediately in the short term, we're working with them to craft policy briefs that help explain the points of our study and what cities and also organizations that support urban agriculture can do to make sure that their actions help proliferate climate friendly urban agriculture. Other things, maybe more long-term, is working with different types of farms than the ones that we worked with on our project because we work only with what we called sort of local, low-tech urban agriculture--so, open air farms, community gardens, things like that, that were mostly managed by individuals and only a handful of which were managed by professional farmers. And one thing we did notice is that professional farmers, when they managed urban farming sites, they knew how to use the resources that they were putting into their food more efficiently, and that translated into lower carbon emissions. So, our plan is to hopefully work with some professional farmers and see is there a sort of a nice missing middle that we didn't really capture in our study, in terms of low tech, outdoor urban agriculture that can provide those benefits to communities and individuals, but also have climate-friendly food production. So, I think that's a really an interesting area to continue exploring.

David Fair: Well, I am looking forward to all of that as it becomes available, but I'd like to thank you for making time today and better explaining the research that you've done already. And, of course, we will include links to the full scope of the study on our website at wemu.org. Benjamin, thank you so much.

Dr. Benjamin Goldstein: You're welcome. Thanks for having me. And thanks for taking the time to dig below the headlines and give a more holistic take on this research.

David Fair: That is Benjamin Goldstein. He is an assistant professor in the University of Michigan's School of Environment and Sustainability and head of the Sustainable Urban Rural Futures Lab. He also served as co-lead author of the study on the carbon footprint of urban farming and gardening--part of a larger and broader look at that. For more information, again, go to wemu.org. Issues of the Environment is produced in partnership with the office of the Washtenaw County Water Resources Commissioner. And you hear it every Wednesday. I'm David Fair, and this is your community NPR station, 89 one WEMU FM, Ypsilanti.

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Contact David: dfair@emich.edu
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