Study calls for people to grow their own food for many years to come, despite finding higher carbon footprint compared to conventional agriculture

To meet global food challenges, such as increases in overall food demand alongside decreases in the natural resources needed for food production, urban agriculture is expected to play a critical role in the coming decades^[1]. Because of the significant potential for transport carbon emissions reductions when food is grown close to the point of consumption^[2], as opposed to in rural areas far away, there is the assumption that urban agriculture can be much less carbon intensive than conventional agriculture.

As more scientific studies are performed, we gain more insight into urban agriculture’s full carbon footprint. Hawes et al. (2024) (“the Hawes study”) added more context to this topic by examining life cycle impacts of low-tech approaches in their new study published on 22 Jan. 2024. But what they found was unexpected: individual gardens are about five times more carbon intensive per serving of fruit or vegetables than conventional farming.

The study was covered in an article in the Telegraph online, which started a wave of misrepresentation on social media. The Telegraph headline “Carbon footprint of homegrown food five times greater than those grown conventionally” was screenshotted and shared widely in multiple unique posts (such as this and this) alongside the general claim that the study implies urban agriculture is bad for the climate and, therefore, may be banned.

One example from a Facebook group with 237 thousand followers has the caption: “Now will they come for your backyard veggie garden? #Reason #GlobalWarming”. Another example from a Facebook group with over one million followers asked: “Which country will be the first to declare home gardens a climate crime? This is absolute lunacy”. Joe Rogan (18.6 million Instagram followers) shared the Telegraph headline with the caption “Anyone that discourages people from growing their own food is not your friend” (over 410 thousand likes).

As explained below, the claim that the study’s findings were meant to discourage and stop people from growing their own food misrepresents the original study. The claim is also unsupported within the context of the wider scientific community’s interest in promoting the multiple ecological and social benefits of urban agriculture, regardless of carbon related considerations^[3-5]. These benefits were explicitly emphasized in the Hawes study, and again in their explainer article in The Conversation published on the same day, but they were not discussed in the Telegraph’s widely shared article. The Telegraph article also failed to mention that a quarter of home gardens studied outperformed conventional agriculture, which is clearly stated in the study’s publicly visible abstract.

No statements against urban agriculture, home gardens, or citizen rights

In the Hawes study, there are no statements nor calls against the use of urban agriculture or home gardens. There is also no indication whatsoever that people should not grow their own food. The carbon footprint of food produced using urban agriculture was found to be six times greater than conventional agriculture on average (see below for details). Even with their unexpected findings, the authors highlighted the situations where low-tech urban agriculture outperforms conventional agriculture from a carbon footprint perspective. They suggested best practices to keep low-tech urban farms, individual gardens and collective gardens as long-term fixtures in cities by making them more carbon-competitive.

The Hawes study is emphatically not a call to discourage, limit, or criminalize people growing their own food. In an email with Science Feedback, lead and corresponding author Jason Hawes (School for Environment and Sustainability, University of Michigan) reiterated:

“We did not call for a ban on urban farming and gardening…our team has more than a century of experience studying the many personal and community benefits that these urban food-growing sites produce…none of our recommendations involved banning the practice – in fact, we suggested that one key [best] practice would be to ensure long-term land tenure for urban agriculture sites.”

In the study’s abstract, the authors clearly call for “maintaining [urban agriculture] sites for many years”. In the study’s conclusion, the authors stressed that because of urban agriculture’s many social, nutritional, and environmental benefits (explored below), it is likely to “have a key role to play in future sustainable cities”.

There is no evidence that this study has been or will be used in any way, in policies or laws for example, to limit citizen rights to have home gardens as a new strategy to mitigate climate change. The claim that the study’s main finding, as headlined in the Telegraph, is meant as propaganda to discourage urban gardening and stop people from growing their own food is inaccurate.

What did the study do, find, and propose?

By partnering with individual gardeners, community garden volunteers and urban farm managers at 73 sites across five countries in North America and Europe, Hawes and colleagues tested the assumption that low-tech urban agriculture is less intensive than conventional agriculture. This assumption is mainly based on the fact that transportation emissions, which are very significant for conventional agriculture, are drastically and in some cases entirely reduced in urban agriculture.

The study aimed to clarify previous uncertainties from earlier studies, and provide the first large-scale, comprehensive assessment of the full life cycle carbon footprint of different types of low-tech urban agriculture compared to conventional agriculture. Food product emissions were quantified from three types: urban farms (professionally managed, focused on food production), individual gardens (small plots managed by single gardeners) and collective gardens (communal spaces managed by groups of gardeners). For each country, the study included food produced using conventional agriculture both domestically and abroad, considering on-farm impacts, processing and transportation to the city. High-tech urban agriculture was not considered.

The carbon footprint of food produced using urban agriculture on average (all three categories) was found to be six times greater than conventional agriculture (420 grams of carbon dioxide emissions equivalent (gCO2e) versus 70 gCO2e per serving), with the individual gardens category being about five times more carbon intensive (340 gCO2e, hence the Telegraph headline highlighting the term “homegrown food”).

The main reason why urban agriculture was found to be more carbon intensive than conventional agriculture was the emissions associated with its infrastructure. This includes using raised beds, concrete walkways, small shelters like sheds, and so on, all of which add emissions that are not necessarily comparable to the wide-open fields of conventional farms which can produce food at-scale.

In addition, only urban grown tomatoes and asparagus were less carbon intensive than conventionally grown versions among the crops considered. This is likely because conventional tomatoes are already very carbon intensive when grown (i.e., industrial greenhouses) and still need to be transported to the city, meaning urban grown versions are carbon-competitive^[6]. Conventionally grown asparagus often requires air-freight importation and when this is factored in “the statistical difference between individual gardens and conventional agriculture vanishes”.

Grouping all urban agriculture categories together, 17 of the 73 sites (23%) had less emissions than conventional agriculture, which helped the authors identify best practices to ensure the longevity and sustainability of urban farms, individual gardens and collective gardens in cities, contrary to the claims made on social media. They suggested that practitioners of urban agriculture and policy makers should:

1. maximize the lifespan of farm infrastructure;
2. promote urban waste streams as inputs, and,
3. use farms as sites for education, leisure and community building.

Based on the results and expertise of the authors, the Hawes study is in reality a call for people who grow their own food to explore how they can reduce their carbon footprint “by cultivating crops that are typically greenhouse-grown or air-freighted, maintaining [urban agriculture] sites for many years, and leveraging circularity (waste as inputs).”

Scientists continue to research and call for more urban agriculture

Urban agriculture, farming, and gardening refers to food production in urban areas, including animal husbandry, aquaculture, beekeeping, and horticulture. By enhancing vegetation cover in cities, which increases shade, evapotranspiration, and creates an urban cooling effect, urban agriculture is an internationally recognized option for climate change adaptation (e.g., featured since 2016 in the European Climate Adaptation Platform Climate-ADAPT). Hawes and colleagues are part of the wider scientific community investigating how to minimize the potential costs and maximize the already significant benefits of urban agriculture, especially low-tech approaches and home gardens.

Senior researcher Dr. Johannes Langemeyer of the Integrated System Analysis of Urban Vegetation and Agriculture (URBAG) project provided Science Feedback with some insight into the wider context surrounding studies like the one by Hawes and colleagues, in relation to the unique functions of home gardens aside from food production. Based at the Institute of Environmental Science and Technology of Universitat Autònoma de Barcelona (ICTA – UAB), Dr. Langemeyer explained:

“Commercial agriculture is primarily optimized for maximizing production yields. In contrast, urban gardening – distinct from urban agriculture – often does not prioritize food production as its primary goal, especially in regions like Europe, the US, and the UK. Urban gardening typically serves multifunctional purposes, such as fostering a connection to nature, providing educational opportunities, and facilitating leisure activities. Therefore, comparing CO2 emissions on the basis of production yield can be misleading, as the objectives of commercial agriculture and urban gardening are fundamentally different.

A hypothetical reversal of this comparison might illustrate this point more clearly. For instance, if one were to compare commercial agriculture with urban gardening based on the leisure hours each provides, and possibly the CO2 emissions associated with these leisure hours, the contrast in objectives and outcomes would become more apparent. This perspective highlights the importance of considering the specific goals and functions of different agricultural practices when making such comparisons.”

Scientists have been increasingly studying the role of different forms of urban agriculture, like urban community gardens, in driving sustainable development in cities (Fig. 1). There have been at least over 200 independent scientific studies exploring the different sustainable development aspects of urban gardens, with a drastic increase in recent years as scientists have recognized that “promoting urban gardens could be a relevant urban policy directed towards sustainable development”, as concluded by Ribeiro et al. (2023) following a comprehensive bibliometric analysis^[7].

Figure 1. Visual overview of the Ribeiro et al. (2023) bibliometric analysis of the scientific literature on urban gardens as tools to promote sustainable development in cities, assessed using the triple-bottom-line framework (see reference [8]).Top: Publications meeting the analysis criteria according to the year of publication (x-axis), demonstrating growth in interest (number of publications indicated in the y-axis). Bottom: The cluster analysis of the publications selected with the most citations, based on the triple-bottom-line sustainable development pyramid.

Urban farming can address 13 out of the 17 United Nations Sustainable Development Goals across economic, social and ecological vectors, as demonstrated by some of the outputs of the international GROOF (Greenhouses to reduce CO2 on Roofs) project. Although carbon emissions are a legitimate concern that must be quantified, just as Hawes and colleagues performed for low-tech approaches, urban gardens have been documented across different socio-cultural contexts to do more than just provide food. They also provide public spaces for citizens’ well-being, and serve as meeting places and as places of learning, especially in recent years during the COVID-19 global pandemic^[9].

Scientists have even undertaken efforts to encourage the world’s youth to know about and participate in urban agriculture, for example with the article “The Important Roles of Urban Agriculture” published in the journal Frontiers for Young Minds^[10]. Opinion articles with titles like “Urban gardening has taken root, and it’s time for cities to encourage new growth” by urban planning experts outside of traditional academia demonstrate the widespread support of urban agriculture as a permanent fixture in urban life, contrary to the claim on social media that studies like Hawes et al. (2024) imply experts want the opposite. The United Nations University even hosts a video series on the role of urban gardens in biodiversity conservation and sustainable development.

But just like from the carbon footprint perspective, the social and community aspects of urban agriculture has both benefits and limitations (see here for an overview within the US context, including 40 references of studies by scientists exploring the critical value of urban agriculture). The growth in research interest in urban agriculture and the scientific debate surrounding potential risks and benefits were also outlined in a Global Sustainable Development Report brief in 2015. Overall, as far as we are aware at Science Feedback, there is no evidence of scientists making any efforts related to restricting urban agriculture, home gardens, and citizen rights to growing their own food by citing climate change related concerns.

Conclusion

Although low-tech urban agriculture is expected to be a central component of sustainable cities in the future due to its many social, ecological, and nutritional benefits, Hawes and colleagues found it is not necessarily less carbon intensive than conventional agriculture as is commonly assumed. There are multiple ways to reduce the carbon footprint of different kinds of urban agriculture to make them more carbon-competitive with conventional agriculture, such as reusing the same infrastructure year-after-year. The claim that the study and article headline chosen by the Telegraph is meant to discourage and stop people from growing their own food has no support in reality. The study has been misrepresented on social media; there are no statements nor calls against the use of urban agriculture or home gardens within the study or anywhere else among the wider scientific community. On the contrary, Hawes and colleagues clearly call for “maintaining [urban agriculture] sites for many years”, and they concluded that urban agriculture will “have a key role to play in future sustainable cities”.

REFERENCES

• 1 – Nicholls et al. (2020) The contribution of small-scale food production in urban areas to the sustainable development goals: A review and case study. Sustainability Science.
• 2 – Lee et al. (2015) Greenhouse gas emission reduction effect in the transportation sector by urban agriculture in Seoul, Korea. Landscape and Urban Planning.
• 3 – Azunre et al. (2019) A review of the role of urban agriculture in the sustainable city discourse. Cities.
• 4 – Appolloni et al. (2021) The global rise of urban rooftop agriculture: A review of worldwide cases. Journal of Cleaner Production.
• 5 – Goldstein et al. (2017) Contributions of local farming to urban sustainability in the Northeast United States. Environmental Science & Technology.
• 6 – Maureira et al. (2022) Evaluating tomato production in open-field and high-tech greenhouse systems. Journal of Cleaner Production.
• 7 – Ribeiro et al. (2023) Evidence on how urban gardens help citizens and cities to enhance sustainable development. Review and bibliometric analysis. Landscape and Urban Planning.
• 8 – Hacking & Guthrie (2008) A framework for clarifying the meaning of Triple Bottom-Line, Integrated, and Sustainability Assessment. Environmental Impact Assessment Review.
• 9 – Ikeda et al. (2023) The Role of Urban Gardening in Global Cities: Three Case Studies in Berlin, Rome and Tokyo. In Sustainable Health Through Food, Nutrition, and Lifestyle. Springer Nature.
• 10 – Orsini & D’Ostuni (2022) The Important Roles of Urban Agriculture. Frontiers for Young Minds.