In places such as New York and Boston, the appeal of the self-sustaining rooftop farm is irresistible. If only enough unused space were converted to fertile fields, the thinking goes, local kale and spinach for the masses could be a reality, even in the most crowded neighborhoods.
Proponents claim that city vegetable gardens are a solution to nearly every urban woe, providing access to healthy foods in neighborhoods that lack it, as well as economic stimulation, community engagement, and significant reductions in greenhouse gas emissions. But a new study published in the journal Environmental Science & Technology says that in colder climates such as the Northeast's, the emissions reductions are minimal.
"Urban farming advocates tend to focus on the distance from farm to fork, equating local food with environmentally sustainable food, oversimplifying the complexity of food sustainability to a single aspect," the researchers write. In reality, the carbon reductions made possible by urban farming are much smaller than many had assumed. In the best case scenario, urban farming would only reduce a Northeastern's city's food-related carbon footprint by 2.9 percent, the study found.
The study's authors used Boston to prove their point.
They first established the city's food-related environmental impact baseline by combining publicly available dietary information with data on the burden required to supply that food. Next, they determined the space available for urban farming, including both ground lots and usable rooftop space. Finally, they used data from several farms in Boston and New York to understand the resources used, including fossil fuel-based power, the vegetables they yield, and their overall environmental impact. Ultimately, the researchers found the environmental gains from urban farming to be "marginal."
The reason is that while city-grown vegetables can have a slightly lower environmental impact than those grown thousands of miles away, horticulture has never been the real problem. It's not apples and tomatoes that are responsible for most of the diet's greenhouse gas emissions; it's animals. Meat and dairy products contribute 54 percent of the American diet's potential impact on climate change. If city residents really want to lower their carbon footprints, they should become vegan. For bonus points, they can turn their roofs into solar gardens instead of vegetable ones.
There are many reasons to embrace urban agriculture. Greater access to produce could help improve the diet of city residents, and replacing pavement with soil could help abate water runoff, for example. But slowing climate change isn't one of them. The potential economic benefits of urban farming are also less promising than proponents had hoped, the study found. Even if Boston-grown vegetables were sold within the larger metropolitan area, the value would still be less than .5 percent of regional gross domestic product. And while some of that growth would go to low-income neighborhoods, the majority would flow to areas with poverty rates below 25 percent.
"I am positive about urban agriculture," says Benjamin Goldstein, of the Technical University of Denmark and the lead author of the study. "I just want to make sure it's done for the right reasons."