Apples from New-Zealand, Avocados from California, steaks from Argentina, to name just a few examples - agricultural goods are transported all around the globe across all distances to provide citizens with nourishment. “Already, this comes with an enormous ‘food-print’ and we know that a growing world population not only means growing urban infrastructures but also growing resource consumption and greenhouse gas emissions,” co-author Prajal Pradhan says. “That’s why we asked ourselves: What would happen if cities source their food from local agriculture in areas surrounding them? How many people could be nourished, how much CO2 could be avoided by reduced transport needs? And last: would unmitigated global warming change the picture?”
About 35 percent of urban residents could be nourished by utilizing local land resources, the researcher's analysis reveals, but the situation is quite diverse on a global scale. Regions like Southern Asia with countries such as India could benefit a lot from local agricultural production - they could nourish actually more than 80 percent of their city population. However, if climate change, urban population growth and lifestyle changes keep on accelerating, this could completely change the picture and take the option off the table.
The researchers identified urban growth as the factor that will have the strongest impact on future urban food demand, followed by dietary changes, e.g. toward more meat consumption. Finally, climate change could reduce options by harming agricultural production. While in South Asia urban growth might reduce the local nourishment potential by about 30 percent in 2050, in Northern Africa it is climate change that reduces the potential by about 30 percent in 2050. In regions like Northern America or Western Europe the situation will, according to the study, not change that much.
When it comes to consumption patterns, cities are not only characterized by administrative boundaries, but rather as functional units including the urban hinterland. The researchers focused on city clusters, like twin cities or regions with several smaller cities close to each other, with a population of more than 100.000 people and examined 4121 of these clusters around the globe. The advantage of this approach is that close urban administrative entities are considered as one functional urban area. Therefore, New York comprises more than 1.000 administrative entities on the east coast of the USA, while the largest city clusters in terms of inhabitants were areas around megacities like Guangzhou, Tokyo and Mexico-City with a population of up to 40 million people each. Using this approach the researchers analyzed the impact of and for 2.5 billion urban residents - this equals about 70 percent of urban population in 2010.
"Cities are at the heart of the climate problem"
Using a new Urban Assessment Model developed at PIK, the scientists analyzed the nourishment potential of local agriculture on land surrounding the cities and investigated food transport in order to show how optimizations would reduce the environmental „food-print" of urban areas. "Of course, feeding our cities by local agriculture is not a switch we could simply flip, and self-sufficient cities would not be able to just duplicate what's on our plates today," lead-author Steffen Kriewald explains. "Regional agriculture would not be able to produce all foods on our menu in a globalized food world, however, nutrition requirements could be met in many regions of the world, our study shows."
"Cities are at the heart of the climate problem and pivotal for sustainable future development," co-author Juergen Kropp concludes, he is co-chair of PIK's Climate Resilience Research Department. "Our study provides the first global analysis on the global potential of local agriculture and combines it with other relevant effects. We're able to show that an optimized local production would decrease emissions from food transport by a factor of ten – about 4 percent of global CO2 emissions could hence be reduced this way. This is a conservative number, as for instance air transport was not yet considered due of the lack of available data. Local production therefore would reduce the dependence on global food production chains, while in contrast further uncontrolled urban growth, climate and dietary changes would reverse this effect. We show that producing food locally could act as a kind of adaptation as it ensures local food security, can close local nutrient cycles and therefore would help to protect the climate."
Article: Steffen Kriewald, Prajal Pradhan, Luis Costa, Anselmo Garcia Cantu Ros, Jürgen Kropp (2019): Hungry Cities: how local food self-sufficiency relates to climate change, diets, and urbanization. Environmental Research Letters. [DOI 10.1088/1748-9326/ab2d56]
Weblink to the article: https://doi.org/10.1088/1748-9326/ab2d56
Weblink to a brief video explainer: https://youtu.be/j-yZIN87OzU
More studies recently published by the PIK team of city researchers:
Haroldo V. Ribeiro, Diego Rybski, Jürgen P. Kropp (2019): Effects of changing population or density on urban carbon dioxide emission. Nature Communications. [DOI 10.1038/s41467-019-11184-y]
Weblink to the article: https://www.nature.com/articles/s41467-019-11184-y
Linda Krummenauer, Boris. F. Prahl, Luís Costa, Anne Holsten, Carsten Walther, Jürgen P. Kropp (2019): Global drivers of minimum mortality temperatures in cities. Science of the Total Environment. [DOI 10.1016/j.scitotenv.2019.07.366]
Weblink to the article: https://www.sciencedirect.com/science/article/pii/S0048969719334801
Martin Behnisch, Martin Schorcht, Steffen Kriewald, Diego Rybski (2019): Settlement percolation: A study of building connectivity and poles of inaccessibility. Landscape and Urban Planning. [DOI: 10.1016/j.landurbplan.2019.103631]
Weblink to the article: https://www.sciencedirect.com/science/article/pii/S0169204618310661
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