Locavore or vegetarian? What's the best way to reduce climate impact of food?

This year’s Thanksgiving feast falls only a few days before the start of the global climate summit in Paris. Although the connections are not always obvious, the topic of food – and what you choose to eat – has a lot to do with climate change.

Our global agriculture system puts food on the table but it also puts greenhouse gases (GHG) in the air, which represent a huge portion of global emissions. GHG emissions come directly from farms such as methane from cows and nitrous oxide from fertilized fields, while other emissions come from the industries that support agriculture, such as fertilizer factories that consume fossil fuels.

Still other emissions come from natural lands, which have massive stocks of natural carbon stored in plants and soils. When natural lands are cleared to make room for more food production, the carbon in those natural pools is emitted to the atmosphere as carbon dioxide.

Adding all these emissions together makes agriculture responsible for between roughly one fifth and one third of all global anthropogenic, or mandmade, greenhouse gas emissions.

How can these emissions be reduced? My own research through the University of California Global Food Initiative has focused on evaluating a wide range of factors from biofuels to local food systems.

Undoubtedly, broad emissions reductions must come from political action and industry commitments. Nevertheless, an enlightened consumer can also help achieve meaningful reductions in GHG emissions, particularly for the case of food. The trick is to understanding what food means for your personal carbon footprint and how to effectively shrink this footprint.

On par with electricity

Zooming in from the global picture on emissions to a single home reveals how important our personal food choices are for climate change. You can use carbon footprint calculators, such as the University of California CoolClimate Tool, to get an idea of how important food is in relation to choices we make about commuting, air travel, home energy use, and consumption of other goods and services.

For the average U.S. household, food consumption will be responsible for about the same GHG emissions as home electricity consumption for the average US household.

Measuring the greenhouse gas impact of different foods is complex but in general, it’s commonly agreed that plant-based diets have a lower carbon footprint.davidwoliver/flickr, CC BY-NC

That’s a significant portion of an individual’s GHG footprint but it could be seen as a blessing in disguise. While you may be stuck with your home or your vehicle for some time and their associated GHG emissions, food is something we purchase with great frequency. And every trip to the grocery store or farmer’s market is another opportunity for an action that has a significant and lasting impact on our climate.

Making concrete decisions, though, is not always straight-forward. Many consumers are faced with a perplexing array of options from organic to conventional foods, supermarkets to farmers markets, and genetically modified organisms to more traditional varieties.

And in truth, the carbon footprint of many food options is disputed in the scientific literature. Despite the need for more research, there appears to be a very clear advantage for individuals to chose a more plant-based diet. A meat-intensive diet has more than twice the emissions of a vegan diet. Reducing the quantity of meat (particularly red meat) and dairy on the table can go a long way to reducing the carbon footprint of your food.

Food miles and water recycling

Local food systems are popularly thought to reduce GHG emissions through decreased food transport or food miles. But in many cases food miles turn out to be a meaningful but small piece of the overall GHG emissions from food.

For example, a broad analysis of the US food supply suggests that food miles may be responsible for less than 10% of the GHG emissions associated with food. This general trend suggests that where you get your food from is much less important than first-order issues, such as shifting to a more plant-based diet. A little-appreciated way of reducing the carbon footprint of food is to recycle nearby water rather than pump it long distances. The Pajaro Valley Water Management Agency (PVWMA) Water Resources Center in California sanitizes wastewater for direct use or blending with ground (well) water.US Department of Agriculture, CC BY

Where, then, does this leave a rapidly emerging local food movement?

For starters, there are some cases where food miles have greater importance. For example, food miles can play a big part in the carbon footprint of foods when airplanes or refrigeration are required during transport.

There is, however, untapped potential for locally produced food to deliver carbon savings around water and fertilizers.

When water is pumped long distances, it can add to food’s carbon footprint. Re-use of purified urban wastewater for irrigating crops represents one strategy for addressing this challenge but is only economically and environmentally feasible when food production is in close proximity to cities.

Using fossil fuels to produce fertilizers, such as ammonia, can also be a big piece of the carbon footprint of food. Nutrients in reclaimed wastewater and urban compost may provide a low-carbon alternative to fossil fuel-based fertilizers. But similar to water re-use, reusing nutrients is most easily done when there is a short distance between food production and consumption.

To be sure, buying local food doesn’t imply that food or nutrient recycling has happened. But developing local food systems could certainly be a first step towards exploring how to close the water and nutrient loop.

Elliott Campbell receives research funding from the National Science Foundation, U.S. Department of Agriculture, and the U.S. Department of Energy.