Urban agriculture is a form of food production that has the potential to change consumption patterns and transform people's relationship with the land and the way they eat, but like all activities it is also responsible for emitting carbon dioxide. carbon (CO2) and other related gases Global Warming. A new study evaluated emissions from different types of urban agriculture and concluded that, on average, this activity produces six times more carbon dioxide than conventional agriculture.
the jobpublished in the new magazine Nature citiesIt calls for ways to make urban agriculture more sustainable.
Jason Howes, a PhD student in the School of Environment and Agriculture, said: “Urban agriculture provides a range of local social, food and environmental benefits, making it an attractive feature for sustainable cities of the future.” Sustainability From the University of Michigan in the United States, and the first author of the article, according to a statement from that institution.
The statement said that between 20 and 30 percent of the world's urban population engages in some activities related to urban agriculture, according to some estimates. “This work helps show ways to ensure that urban agriculture benefits the community climateAnd so are the people and places it serves,” Jason Howes said.
The research evaluated 73 urban agricultural farms in five different countries: Germany, the United States, France, Poland and the United Kingdom. Of the 73 farms, nine were urban collective gardens (shared spaces, managed by a group of gardeners), seven were urban farms (professionally managed and with the main aim of producing food), and 55 were individual gardens. Two of the farms did not fall into any of the three categories mentioned above. The work had input from citizen scientists to collect data.
According to the results, the sources of carbon emissions are linked to three dimensions of agricultural work in the urban context: emissions Greenhouse gases In the production and transportation of materials used in construction Infrastructure, such as raised beds and sheds; Consumables such as fertilizers, fabric used to cover the soil and prevent other weeds from growing, and gasoline when using machinery; and irrigation water which, if supplied from the grid or wells, may require energy transmission.
Taking these emissions sources into account, the research team calculated that urban agriculture, on average, emits 0.42 kilograms of carbon dioxide equivalent per serving (this unit represents the amount of grams of each type of food needed for one person in one day, according to the Dietary Guidelines ), while conventional agriculture releases 0.07 kg of carbon dioxide equivalent – that is, it emits six times less.
“Most climate impacts on urban farms are caused by the materials used to build them — the infrastructure,” Benjamin Goldstein, a professor at the University of Michigan School of Environment and Sustainability, said in the same statement. “These farms usually only operate for a few years or a decade, so the greenhouse gases emitted to produce these materials are not used effectively. On the other hand, conventional agriculture is very efficient and difficult to compete with.
If the life of these farms can be extended, the weight of emissions emitted in the production of materials used in infrastructure can be reduced. The article points out that another way to avoid this effect is to use materials used in building infrastructure. This method is part of an idea Circular economy Or “urban symbiosis,” as the article puts it, at the center of which urban agriculture may be.
The authors defend Fertilization From discarded organic matter in the city as natural fertilizer for urban farms and gardens, as well as rainwater and treated water as a way to reduce greenhouse gas emissions associated with traditional water sources.
Tomatoes are exceptions
Although urban farming on average releases more CO2 equivalent – and this is according to the countries analyzed – there are many differences between the type of farm and even depending on the agricultural crops. Urban farms, which are more dense, have emissions similar to conventional agriculture, for example.
On the other hand, tomatoes grown naturally on a plot of land in the middle of the city are much less polluting than those grown in greenhouses. Furthermore, in the case of food flown in by air, even though it is conventionally produced, it has more emissions associated with it than the same food produced in an urban garden, which is located in a nearby context.
“The exceptions revealed by our study suggest that urban agriculture practitioners can reduce climate impact by growing crops that are typically grown in greenhouses or transported by air,” Jason Howes said.
There is also an important point about the personal well-being and social importance that urban agriculture promotes that is important to include in the greenhouse gas emissions equation, the authors say.
“A cost-benefit analysis of a community garden in the UK estimated that social benefits, such as improved learning and reduced hospital admissions, accounted for 99.4% of the total value generated economically at that site,” the article states. “Because the distribution of emissions often follows the generation of economic value, growing spaces that maximize social benefits can outperform conventional agriculture when the benefits of urban agriculture are considered holistically.”
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