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Greenhouse Gases Emission from Urban vs. Conventional Produce Production

(Hypothetical) Report prepared for the Center for Integrated Agricultural Systems by:

Aida Ebrahimi, UW-Madison,
Jeremy Letournel, UW-Madison,
Adeline Wells, UW-Madison,


Scenario | Abstract | Introduction | Urban Practices | Results | Conclusion | Limitations and Constraints | Boundaries and Limitations | References | About the Authors

The scenario for this case study:

Photo: Center for Integrated Agricultural Systems

Looking ahead to the substantial impending effects of climate change, the University of Wisconsin-Madison’s Center for Integrated Agricultural Systems (CIAS) is curious to know whether or not produce grown conventionally or via urban agriculture results in fewer greenhouse gas emissions. They are interested in understanding whether or not it is more environmentally, economically, and socially sustainable for Madisonians to grow their own produce within city limits as opposed to buying it from Madison grocery stores such as Kwik Trip, Fresh Market, Capitol Centre Market, Trader Joes, etc. This committee has made it their goal to analyze data on production and transportation from both a conventional and an urban farm, resulting in a carbon footprint comparison between the two systems. The results of the case study will allow us to make recommendations to both the City of Madison and the University as to whether or not it would be beneficial to incorporate more urban agricultural systems into the city and campus layouts.


In regards to trends of rapid globalization and urbanization that have defined the past two centuries, increasingly high amounts of food are being imported into cities to meet the demands of their people. This importing of food from both domestic and international conventional farms results in high emissions of greenhouse gases via means of excessive fertilization, high amounts of energy used to run heavy machinery, processing, packaging, and transportation. Urban agriculture has garnered a lot of attention as being one way to combat food scarcity in urban populations, allowing city dwellers to be self-sustaining when it comes to providing produce for their families. However, the question as to whether the greenhouse gas emissions of produce grown in a city is lower than produce grown in the countryside still remains. This case study analyzed the greenhouse gas emissions of lettuce sold in Madison, Wisconsin; we took data from conventionally grown lettuce at Borg Produce in southern California, who provides to Fresh Market, as well as KP Simply Fresh Aquaponics Farm, who supplies the Willy Street Co-Op. While we recognize that KP Simply Fresh Aquaponics does not operate in Madison directly, the methods they use to grow their lettuce could easily be replicated on a smaller scale within city limits. Despite the constraints of this analysis, it can be inferred that lettuce grown via aquaponics has higher greenhouse gas emissions than lettuce grown conventionally. This study also analyzes the social aspects of urban agriculture.

What is urban agriculture?

The Environmental Protection Agency (EPA) defines urban agriculture as city and suburban agriculture taking the form of backyard, rooftop and balcony gardening, community gardening and vacant lots and parks, roadside urban fringe agriculture and livestock grazing in open space.

History of Urban Agriculture:

Urban agriculture became popular in North America during the 20th Century World Wars. The National War Garden Commission promoted the movement during World War I via the creation of posters, manuals, and cookbooks. This allowed American farmers to export to meet the needs of European Allies who were facing food shortages during the war. According to the NWGC, 3.5 million war gardens produced $350 million worth of food in 1917, and the number increased to 5.3 million gardens and $525 worth in 1918. “Victory Gardens” were a fad during World War II; they associated with national ideals of patriotism and societal responsibility. In 1944 Victory Gardens produced 40% of US produce. Since the end of World War II, the motives for domestic urban agriculture have been mainly grounded in principles of food security, self-sufficiency, and to support local producers while minimizing greenhouse gas emissions from transportation.

Current Motif and Social Aspects of Urban Agriculture

Many people do not know the source of their food; they don't know how much energy was put into growing that food, where it comes from, and who grew it. Sustainable food is not only food that has the lowest carbon footprint, but also food that supports the community and is socially just. Urban agriculture does not only allow the inner city residents to reconnect with their ecosystem, but it also gives the residents the ability to grow food in the soil, and perhaps one day become self-sufficient with the land available within cities. Urban agriculture also offers health, environmental and economic advantages to city residents. Farming in cities can provide increased access to healthy, affordable produce for urban residents, while lowering pollution impacts from transportation and waste products (Mukherji and Morales 2010).

Advocates of urban agriculture envision multiple benefits to cities, such as reducing the abundant supply of vacant, unproductive urban land under management by local governments; improving the public image of troubled neighborhoods; increasing the amount of neighborhood green space; supplying low-income residents with healthier and more nutritious food; developing more pride in self-sufficiency among inner-city residents who grow food for themselves and others; providing new, non-traditional program activities for community-based non-profit organizations; converting the food waste of supermarkets into compost and fertilizer used in food production; reducing food transportation through the greater availability of local produce; and supporting local and regional food systems in general (Kaufman 2000).

Different methods of Urban Agriculture

I) Community Gardens
Eagle Heights Community Gardens
Eagle Heights community Gardens. Photo: Aida Ebrahimi Eagle Heights community Gardens. Photo: Aida Ebrahimi Eagle Heights community Gardens. Photo: Aida Ebrahimi

One of the most common urban practices is community gardens. An area can be divided into smaller sections for families and individuals to practice gardening and grow their own food. Otherwise, the common area can be shared by the community and the neighborhood to collectively work towards growing food for everyone.

II) Raised Beds
Edible Landscapes Project rased beds
Edible Landscapes Project. Photo: Aaron Conradt Edible Landscapes Project. Photo: Aaron Conradt Edible Landscapes Project. Photo: Aaron Conradt

Raised beds are wooden or concrete blocks filled with topsoil and compost. They sit on top of the ground therefore the beds are usually transportable. Therefore plant roots do not disturb the urban infrastructures under the ground. Soil in a lot of the Urban areas is contaminated with heavy metals such as lead; raised beds are great alternatives if the soil is provided from a reliable source. Gardeners usually assume the soil is contaminated "because testing for heavy metals or trace minerals can be expensive" (Hendrickson and Porth, 2012).

III) Hydroponics
GreenHouse Learning Community Hydroponics. Photo:Tom Bryan GreenHouse Learning Community Hydroponics. Photo:Tom Bryan GreenHouse Learning Community Hydroponics. Photo:Bryce Richter

New forms of urban agriculture have become common among food producers. Hydroponics is a method of growing plants in a soilless media, perlite. The water in hydroponic system has fertilizers and nutrients for plants, as well as chemicals to stabilize the pH. Depending on the hydroponic system, the water use is considerably low. Hydroponics are improving to become more practical in urban settings; examples of these improvements are vertical, window hydroponics (Schnitzler 2013).

IV) Aquaponics
Growing Power Milwaukee. Photo: Aida Ebrahimi Home Aquaponics Setup. Photo:Waleed Alzuhair Growing Power Milwaukee. Photo: Aida Ebrahimi

Often confused by hydroponics, aquaponics is a combined system of growing plants hydroponically and culturing fish in closed system. The waste water form fish is used to irrigate plants. The fish waste has enough nutrients for the plants to grow without any additional hormones or nutrient inputs (Rokocy et al. 2006). The only chemicals added to water is to maintain a steady pH. The water from fish is filtered through a bed of pallets, gravel, or perlite where bacteria breaks down the ammonia from the fish to nutrients plants can use. The excess water from plants goes back into the fish tank as a source of food.

Examples of  Successful Uses of Urban Agriculture

I) London, UK. 

Table 1:Potential production of fruit and vegetable in London
 Land Type  Land Area in Hectares  % Used for urban Agriculture
 Agricultural land  13,566   50% 
 Other greenbelt land  40,034   20%
 Allotments  831   100%
 City farms  51   25%
 Community gardens  20   25%
 Public open space  14,617   5%
 Derelict/vacant land  1,388   1%
 Gardens  38,014   14%
 Total  108,521   20%

The estimated proportion of various types of land, combined with the estimated "average yield/ha" gives a rough indication of the potential production. This is calculated only for fruits and vegetable production, if another agricultural  production would be used, the results would be different. Using a productivity level of 10.7 t/ha, London could produce 232,000 ton of fruit and vegetable, which would supply Londoners with 18% of their intake if we calculate with the World Health Organization recommendation to 0.5 kg of vegetable and fruit a day. This table also shows that when the land is used on a more private settling, such as an allotment, the public is more likely to use such a space for urban agriculture to produce some fruits and vegetable that they will be able to bring back to their own home, sell or donate to friends and family, or even sell for some profit at a farmers market. Although food sold from an allotment might be sold for profit, there is a need to understand that the land is not being used as a city farm since the it is not the owner of the allotment's primary job, but rather a hobby or a way to earn some cash to his/her revenue. 

Table 2: Comparison of the global warming potential of food commodities supplied through the community farms in Sutton(UK) and the conventional food supply system 
 Commodity Community Farm GWP (kg CO2e kg−1 product) Conventional Food Supply GWP (kg CO2e kg−1 product)Relative GWP savings (%) 
 Lettuce (spring) 0.34 1.59 81
 Carrot 0.37 0.49 24
 Spinach 0.21 2.38 91
 Beans (spring) 0.11 10.44 99

These results integrate the data from the production and transport stages, and are shown per kilogram of ready-to-buy product at the point of retail. Proponents argue that reduced food miles will result in fewer emissions by reducing transportation costs (Paxton 1994). But in some circumstances, urban agriculture may lead to a net increase in carbon emissions through additional energy and fertilizer inputs for plant growth in unfavorable environments, such as with tomatoes grown in Spain and transported to the UK versus tomatoes grown in heated greenhouses in the UK (DEFRA 2008). In fact in the  United States, the only comprehensive LCA to date for an entire food system revealed that food miles account for a mere 4 % of the greenhouse gas emissions of the USA’s food system, which led to the conclusion that buying local has negligible impact on reducing greenhouse gas emissions and may indeed lead to an increase given the significant contribution of the production phase (Weber and Matthews 2008).

forms of urban ag
Figure 1: This figure shows what urban growers do with the fruits and vegetables in the cities of Columbia, Kansas City and St. Louis, Missouri. (Hendrickson 2012)

II) Columbia, Kansas City, and St.Louis in Missouri

Figure 1 shows what forms of urban agriculture currently exists in Columbia, Kansas City and St. Louis, through education, assistance or policies. This data was gathered by students at the University of Missouri, from surveying the urban residents within the cities and shows what people do with the produce they grow. However, we do not know how many people currently use land within the city limits for urban agriculture, or which method they use to grow their food. Urban agriculture can be used for many different reasons whether it be for personal consumption of the produce, sharing with friends, or it can be marketed and sold for profit. Though there are currently many ways to produce fruits and vegetables in Columbia, Kansas City and St. Louis, there is a vast distribution of what is being done with the fresh product from urban agriculture. The population of Columbia, Kansas City and St. Louis currently has access to many different types of urban agriculture area: community gardens, vegetable gardens, Community Supported Agriculture (CSA), greenhouse agriculture, kitchen gardens, edible landscape, greenbelt agriculture, etc. 

In general, Missouri’s urban agriculturalists face similar issues to those in the nation as a whole. It is clear that urban agriculture quickly involves the larger food system for most practitioners. For example, improving food access, addressing obesity issues, removing the disconnect between consumers and the food they eat, encouraging farm-to-school programs, and re-localizing the food supply are all food system issues identified in the hearings that often transcend metropolitan boundaries. In addition, certain production and marketing issues, including organic and food safety certification as well as access to markets and food distribution, transcend urban-rural boundaries and are largely a matter of farm scale and profitability. However, specific concerns about soil remediation in contaminated areas and brownfields, cost of and access to water, and land tenure and long-term security on improved urban farms remain strong barriers in Missouri’s cities and may provide opportunities for change (Hendrickson 2012). 

Photo: KP Simply Fresh Aquaponics
KP Simply Fresh Aquaponics Farm:

One example of sustainable urban agriculture is the Willy Street Co-Op’s lettuce supplier of KP Simply Fresh Aquaponics Farm, located in North Freedom, WI, along the Baraboo River; approximately 40 miles north-east of Madison. Though KP’s fish are not certified organic, KP operates by circulating water: it goes from their tilapia tank to a filtering system, and then the nutrient-rich water goes to the greenhouse via a PVC pipe system, which allows for little evaporation. According to Donna, one of the farm’s four managers, an average farmer would require 100 gallons of water to produce the amount of lettuce they do, whereas they circulate 4 gallons. In a hydroponics system, sufficient amounts of nutrients must be added to the water system allow for plant growth, whereas fish supply the majority of nutrients in an aquaponics system; the only additions KP makes are calcium and potassium, in order to maintain a PH between 6.5 and 7.

The largest source of greenhouse gas emissions at KP Simply Fresh comes from the grow lights, which are on 18-19 hours per day from October to March. Their grow lights are traditional 1000-watt bulbs; the farm has had trouble finding the correct LED to allow for high growth rates. The combination of the high-wattage bulbs with long hours of use results in a monthly electricity bill of $3,500 for the farm. However, the lights are not used at all from April 10th until October 1st, when the brightness of the sun is enough for the plants to grow. The family-owned business supplies between 800 and 900 heads of lettuce per week to a variety of stores, restaurants, nursing homes, and hospitals, all of which are within a 60-mile radius from the farm. Furthermore, there is no middle-man within this operation; the business does all of the growing, harvesting, and delivery themselves, resulting in face-to-face transactions. KP Simply Fresh Farm is a local example of sustainable agriculture that could be replicated within city limits on a smaller scale.

Using the information KP Simply Fresh provided us, we calculated the carbon footprint of their electricity use. Knowing the duration of the time the lights are being used and their monthly electricity bill, we found that they use 60 light bulbs. The carbon footprint of electricity per heads of lettuce ends up to 3.18 kg CO2e. To obtain this number, we calculated the total CO2e of total energy use from light bulbs using 0.66 kgCO2e per kWh. This conversion is the average total footprint of energy consumed from the US grid according to Mike Berners-Lee's How Bad Are Bananas? (2011).

Indianapolis Fruit:

Indianapolis fruit is the current distributor of Iceberg lettuce for the Fresh Madison Market. After talking to Paul Hasenberg, the Produce Manager, he mentioned that the store was currently receiving their Iceberg lettuce from California through a company called Indianapolis Fruit. According to the Agricultural Marketing Resource Center, lettuce production occurs year-round throughout the United States, through a sequence of production in Arizona and California, as well as commercial greenhouse hydroponic facilities. The majority of production from April through October occurs in the Salinas Valley of California, while production from November through March occurs in Yuma, Arizona, and California’s Imperial Valley  (ERS 2006). 

Similarly to most large distributors, Indianapolis Fruit buys their lettuce from California from a company called Borg Produce. They source their produce from their own farms but also from select contracted growers from all over the world. They have a wide variety of fruits, vegetables and tropical produces. Borg Produce and it's companies manage a large network of cold storages, shipping points and a fleet of over 60 large trucks (Borg Produce Sales 2015). 

According to the Journal of Sustainable Agriculture, a head of lettuce grown in a conventional farm produces on average 0.192 kg CO2e per kilogram of lettuce. To find the average weight of an iceberg lettuce, we went to Fresh Madison Market and weighed 10 randomly picked heads and found an average of 30.75 ounces per head which equals to 0.87 kg. Let's assume a head of lettuce takes up about a cubic foot in a truck. A typical trailer in the US is 48x8x13 feet, or about 5000 cubic feet, so we can fit 5000 heads of lettuce per truck (J. Klonowski 2011). Using Google maps, we calculated that the total distance from Borg Produce, through Indianapolis to Madison is a total of 2372 miles. According to the United States Environmental Protection Agency, a truck has an emission average of 0.297 kg CO2e per Ton-mile. So a truck traveling from California to Madison would then emit a total of 704.484 kg CO2e per Ton. If a truck carries approximately 5000 heads of iceberg lettuce, that would mean the truck is carrying approximately 4350 kg of iceberg lettuce which equals to 4.8 short tons. The total emissions from the production of 4350 kg of iceberg lettuce is 835.2 kg CO2e. With the emissions from production and the transportation, the total emissions from bringing the lettuce to Madison is 4216.72 kg CO2e which equals to 0.843 kg CO2e per head of lettuce. This number is already very high and does not take in consideration the refrigeration of the lettuce for the entire trip, which if made non-stop would take 34 hours.


After analyzing the data of lettuce grown by KP Simply Fresh Farm and Borg Produce, it can be concluded that more locally grown lettuce via aquaponics has higher greenhouse gas emissions than conventionally grown lettuce. While we recognize that our data for aquaponic grown lettuce is lacking in regards fish food and transportation, the high usage of electricity was offsets the emissions used to grow and transport lettuce from California farms. These calculations were done by us using the information we gained by phone interviews, peer-reviewed articles, and food providers' webpages. However, this study focuses on the social issues of locally grown food as well as the greenhouse gas emissions of lettuce production. urban agriculture systems provide citizens with a sense of food security, self-sustenance, and community building. Should education increase, making the practices more feasible and accessible to city dwellers, urban agriculture will be a good way to combat food scarcity in cities in the 21st Century. Through urban agriculture, people can connect to the source of their food and understand the process of growing food. This understanding raises an awareness of how much input is required to grow fresh produce and ensures food justice by influencing the choices one makes while purchasing food.

Limitations and Constraints of Urban Practicing

Even though urban agriculture does have great potential, it also has many constraints. In 2000, Jerry Kaufman and Martin Bailkey, who is also part of the Department of Urban and Regional Planning at the University of Wisconsin-Madison, interviewed over 120 people from a very diverse group: community development corporations, neighborhood organizations, social service organizations, university extension services, and private sector business, in order to understand the perspective of those who are skeptical about urban agriculture. They found that some inner-city vacant lands are too contaminated by past uses to grow food safely without incurring prohibitively high remediation costs. Testing the soil to ensure its safety and healthiness is expensive (Deelstra 2000). Replacing the previous media with healthy soil and compost can be expensive as well. Few fundings sources exist for urban agriculture projects initiated by resource-strapped non-profit organizations. Key federal agencies, such as the United States Department of Agriculture (USDA), and the Department of Housing and Urban Development (HUD), are only remotely attuned to the idea of urban agriculture. Most city based neighborhoods or community development organizations lack the interest and knowledge to grow food. Organizations with an interest in and capacity for urban agriculture would encounter significant difficulties that would impede their efforts, such as vandalism, a lack of market for selling their products, or a shortage of staff with the necessary technical knowledge to be urban food producers. Support for urban agriculture from city official is sparse; the difficulties experienced by project initiators in accessing city-owned vacant parcels is noteworthy. Finally, a lack of consensus exists among participants and observers over what constitutes successful urban agriculture projects. Each individual has a different vision and technique for growing food, which initiates a dispute.

To maintain the nutrients in the soil, compost can help to improve the quality and provides nutrients for plants. Producing one's compost can be challenging, and may arise problems in the urban area. Creating compost in large quantities in urban neighborhoods may disturb the residents with the odor it creates. This challenge may decrease the interest of people in urban agriculture. One of the biggest setbacks for urban agriculture is space availability. For people who live in dense and populated cities, space is an issue. Many people who live in apartments and high rises do not have the space and sunlight to grow edible plants. However, recently many studies and experiments are taking place to develope hydroponics techniques to grow food vertically (Mok 2013). Lastly, season changes and extreme weather patterns prohibits urban residents to grow food all year. The lack indoor space and access to greenhouses limits food producers to grow food continually. Season change and extreme cold in Wisconsin, for example, limits the availability of fresh produce during winters.

Boundaries and Limitations of this Study

This study was conducted by interviewing KP Simply Fresh, a local food supplier in Madison, WI, and Indianapolis Fruits, Supplier of Fresh Madison Market and a national food distributor in Indianapolis, IN. These providers were not able to provide us with accurate numbers therefore the information we could receive from these suppliers were limited to approximations. Using peer-reviewed articles, we were able to use these approximations and calculate the carbon footprint of these suppliers. These numbers are only an approximation and does not encompass the complete food supply chain, such as the carbon footprint of calcium and potassium used by KP Simply Fresh.


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About the Authors:

projectphoto Aida Ebrahimi: Aida is a sophomore at UW-Madison studying Environmental Science and Computer Science. Aida was born in Iran and moved to Minnesota when she was 15. She is one of the garden assistants with FH King Students for Sustainable Agriculture. Aida likes to garden and lake jump in her free time.

Jeremy Letournel: Jeremy is a senior at UW-Madison studying Biological Aspects of Conservation and Environmental Studies. Jeremy likes to spend time outside of the house especially when the weather permits it. Over the summer, you would most likely find him at the Union Terrace, playing ultimate Frisbee or playing volleyball at Edward Klief park. Jeremy has been in a lot of places in the world, but still would like to travel to Australia and Japan. and he is a  D.C. Posse Scholar. 

Adeline Wells: Adeline is a sophomore at UW-Madison studying Environmental Studies, Political Science, and Global Health. She is particularly interested in environmental politics both domestically and internationally, especially in regards to clean water. Adeline is also involved with Amnesty International-UW Students, the Sierra Student Coalition, and the UW Sustainability Council. On her free time she likes to hula hoop.

Keywordssustainability, urban agriculture, conventional, food systems, food security, small scale, garden, cities, carbon footprint, community, greenhouse gas emissions   Doc ID48423
OwnerKate A.GroupFood Production Systems &
Created2015-03-05 16:40:29Updated2021-06-04 08:36:56
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