Elsevier

Landscape and Urban Planning

Volume 157, January 2017, Pages 365-374
Landscape and Urban Planning

The potential for urban household vegetable gardens to reduce greenhouse gas emissions

https://doi.org/10.1016/j.landurbplan.2016.07.008Get rights and content

Highlights

  • We modeled greenhouse gas emission reductions due to household vegetable gardens.

  • Model gardens replaced lawn, & used household greywater & composted organic waste.

  • Gardens had 2 kg lower emissions per kg of vegetable than purchased vegetables.

  • Results were sensitive to yield and method of processing household organic waste.

  • Gardens could make major contributions to official climate change mitigation targets.

Abstract

We carried out a life cycle assessment to model the potential for alternative household vegetable gardens (AHHVGs) to mitigate global climate change by reducing greenhouse gas emissions (GHGE) for Santa Barbara County, California, USA. Our model included changes in GHGE due to the effect of creating an AHHVG for five components: reduction of lawn area due to replacement by the AHHVG; reduction of vegetables purchased from the conventional agrifood system due to replacement by vegetables produced in the AHHVG; reduction in amount of greywater exported to treatment facilities due to diversion to irrigate the AHHVG; reduction in amount of household organic waste exported to treatment facilities due to diversion to composting at the household level for application to the AHHVG; and composting organic household waste for use in the AHHVG. We found that AHHVGs could reduce emissions by over 2 kg CO2e kg−1 vegetable, but that results were sensitive to the range of values for the key variables of yield and alternative methods for processing household organic waste. In our baseline scenario (50% of single-family households with an 18.7 m2 AHHVG, providing 50% of their vegetable consumption), AHHVGs contributed 3.3% of the GHGE reduction goals of unincorporated Santa Barbara County for 2020, 0.5% of the goals for the City of Santa Barbara for 2050, and by extrapolation, 7.8% of the goals for California for 2020. Our results could provide an incentive for governments to include support of AHHVG as part of climate mitigation strategies, and for households to grow vegetables in AHHVGs to address climate change.

Introduction

Urban food production, comprising urban agriculture, community gardens, allotment gardens, and household gardens, is an important component of urban ecosystems. There is growing interest in urban gardens as part of what the local food movement sees as an alternative to the mainstream food system, based on the assumption that they cannot only contribute to improving human physical, psychological and social health, but to environmental health as well (Alaimo, Packnett, Miles, & Kruger, 2008; Cameron et al., 2012, Litt et al., 2011, Talukder et al., 2010; Waliczek, Zajicek, & Lineberger, 2005).

Urban food gardens in the US have been a response to environmental problems, as well as to economic and social problems, since at least the end of the 19th century (Lawson, 2005). Today climate change is the most critical environmental problem, and as the proportion of the global population living in cities continues to increase beyond the 50% reached in 2009, urban ecosystems are having an increasing effect on climate, which means an increasing potential to contribute to mitigating climate change (Lal, 2012).

Urban food production could reduce net greenhouse gas emissions (GHGE) compared with the conventional food system because of its potential to produce food with lower intensity of transportation (Kulak, Graves, & Chatterton, 2013; Lee, Lee, & Lee, 2015), energy use, and packaging (Kulak et al., 2013), and greater carbon sequestration (Fisher & Karunanithi, 2014). More indirect ways in which gardening might reduce GHGE include reducing or replacing urban lawn (Fisher & Karunanithi, 2014), and reducing energy consumption for air-conditioning, computers or driving due to more time spent outside (Okvat & Zautra, 2011). However, food production in general is not included in quantified GHGE reduction targets in the US because of lack of documented potential and monitoring methods (Dinar, Larson, & Frisbie, 2012).

To date, no research has estimated the potential contribution of household vegetable gardens (HHVG) to reduce GHGE and contribute to mitigation targets, and in general, household gardens have been neglected in food and urban policy compared with community gardens, though they likely often comprise a much larger area (Taylor and Lovell, 2012, Taylor and Lovell, 2015). Our research addresses this gap for the case of Santa Barbara County, California, USA (SBC) (see Section SM 1.1). The purpose of our paper is to present a method for estimating the climate change mitigation potential of household food gardens, including identifying key variables via sensitivity analysis, to provide an example of using this method for one county in California, with extrapolation to the state, and to test the hypothesis that AHHVG can be an important means of reducing GHGE. We used a life cycle assessment (LCA) approach to asses this potential for alternative household vegetable gardens (AHHVGs) defined as HHVGs designed to minimize GHGE. We estimated changes in GHGE kg−1 vegetable for five components of our model AHHVG in comparison with the baseline with no AHHVG. We also carried out a sensitivity analysis for several key variables. We then compared the total reduction in GHGE from AHHVGs to climate mitigation targets for unincorporated SBC and the City of Santa Barbara, and also extrapolated results to California. Results supported the hypothesis that AHHVGs could make meaningful contributions to meeting climate change mitigation goals.

While motivating households to create and maintain food gardens would be a major challenge to realizing the climate mitigation potential of AHHVGs, the increasing recognition of the need to mitigate climate change in the short term, and the additional personal and community benefits of gardening could together provide major motivation.

Section snippets

Methods

Our research design is illustrated in Fig. 1. In Section 2.1 we describe our model, and in Sections 2.2–2.6 we briefly describe the methods used for calculating each component of the model. We also provide additional detail for methods and results, including formulae, in the Supplementary material (Sections SM 2.1–2.5).

The potential impact of AHHVGs on GHGE

We found a net difference in emissions for AHHVG of −2.10 kg CO2e kg−1 vegetables yr−1 for our model (Eq. (1)) in the baseline scenario as shown in the first column of Table 1. In our model the components contributing most to the reduction in GHGE due to the AHHVG were exporting OW (47%), and purchased conventional vegetables (37%), followed by lawn replacement (13%) and greywater (3%). Composting OW for the AHHVG offset 17% of the reduction.

Sensitivity analysis

The scenarios for high and low values of GHGE for yield,

Implications for home and community gardeners

While the potential of urban food production to reduce GHGE has been promoted, especially in terms of carbon sequestration (Lal, 2012), very little research has been done, especially on household gardens. While there will be differences among all gardens, we know of no data showing consistent differences between types of urban food production, for example between urban farms, community gardens, and household gardens, that would effect GHGE.

Kulak et al. estimated the GHGE for 16 vegetable and

Conclusion

The goals of our research reported here are to motivate greater discussion of the potential of urban food gardens to contribute to climate change mitigation, to suggest a model by which this potential can be evaluated, and to provide an example of applying this model. Our results supported our hypothesis that AHHVGs can be an important means of reducing GHGE, and could therefore contribute to meeting climate mitigation targets. However, because of the large contribution of yield and OW

Acknowledgments

We thank Matt Fore, Kyle Meisterling, Jeff Onsted, and Daniela Soleri for comments on a draft of this paper; Deborah Allen, Jeanine Bentley, Patrick Canning, Jeff Claren, Steve Clark, Anette Clauson, Stephen Fisher, Matt Fore, Carlyle Johnston, Eric Lohela, Jeffrey Hunt, Jennifer King, Biing-Hwan Lin, Jeffrey Morris, Barbara Shelton, Rose Hayden-Smith, Travis Spier, Christopher Weber, and Bob Wilkinson for information and/or discussion; and three anonymous reviewers.

David A. Cleveland is Research Professor of sustainable food and agriculture in the Environmental Studies Program and in the Department of Geography at the University of California, Santa Barbara. His research and teaching focus on small-scale, sustainable food systems, and he has worked with farmers around the world, including in Ghana, Mexico, Zuni, Hopi, Pakistan, and the United States. His current focus is the potential contributions of diet change and food system localization to climate

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    David A. Cleveland is Research Professor of sustainable food and agriculture in the Environmental Studies Program and in the Department of Geography at the University of California, Santa Barbara. His research and teaching focus on small-scale, sustainable food systems, and he has worked with farmers around the world, including in Ghana, Mexico, Zuni, Hopi, Pakistan, and the United States. His current focus is the potential contributions of diet change and food system localization to climate change mitigation, improved nutrition, and food sovereignty. His 2014 book, Balancing on a Planet: The future of food and agriculture, is an interdisciplinary primer on critical thinking and effective action for the future of our global agrifood systems, based on an understanding of their biological and sociocultural roots. The other authors were graduate and undergraduate students at the University of California, Santa Barbara, at the time the research was carried out.

    1

    These authors contributed equally.

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