By Julie Cohen-UC Santa Barbara
Each kilo (about 2 pounds, 3 ounces) of homegrown veggies can cut greenhouse gas emissions by two kilograms, research shows.
For a new study published in the journal Landscape and Urban Planning, researchers modeled a vegetable garden based on converting an area of lawn to garden, replacing some conventionally produced purchased vegetables bought at the store with ones from the garden, and diverting some household organic waste and gray water from processing facilities for use as compost and water for the garden.
The researchers chose midrange numbers from a wide range of values in existing data and also conducted a sensitivity analysis to test how key components such as crop yield and managing household waste affected the model.
“We looked at high and low yields and found that they affected the emissions per kilogram of vegetable,” says David Cleveland, research professor in the environmental studies professor at the University of California, Santa Barbara.
“For every square meter of garden, if you get 10 times the amount of vegetables, then the amount of emissions per vegetable goes down, because you’re dividing more vegetables into the emissions per square meter.
Ironically, that makes the contribution of the garden less on a per-vegetable basis. However, for the garden as a whole, higher yield reduces the emissions because fewer vegetables are purchased.”
The way in which household organic waste is handled also influenced the outcome, Cleveland says. “There’s the potential for home composting to be either positive or negative for the climate. It takes a lot of attention to do it right.”
If optimal moisture and air conditions are not maintained, the waste becomes anaerobic and emits methane and nitrous oxide, powerful greenhouse gases, he says.
“We found that if household organic waste was exported to landfills that captured methane and burned it to generate electricity, households sending their organic waste to a central facility would reduce greenhouse gas emissions more than composting at home.
“This study shows that in terms of effect on the climate, small things matter. How much attention you pay to the garden matters. How efficiently the vegetables are produced and consumed matters.”
Home gardens are good, but Cleveland says it might be better for household or community gardeners to lobby for good centralized programs for organic waste management instead. The equipment and energy necessary to operate such an endeavor constitute a small portion of the total emissions. These could be offset by efficiency such as having trucks that come to pick up organic waste also deliver compost to people who want it for their gardens.
“It’s important not to get hung up on assumptions that small and local are always better,” Cleveland says. “They may not be. You have to keep your eye on the real goal and not get tripped up by intermediate steps.
“In addition to reducing greenhouse gas emissions, there are other potential environmental, social, psychological, and nutritional advantages to growing food yourself, whether in a household, community or school garden,” Cleveland says.
“However, the degree to which those benefits are realized can depend on small things. Our hope is that this research helps motivate households, communities, and policymakers to support vegetable gardens that can contribute to mitigating climate change.”
Source: UC Santa Barbara