Which food is better for the planet?
Salmon or cod?
Knowing what to eat to minimize impact on the planet can feel like an impossible task: Eat locally? Skip meat? Opt for organic, free range, humanely raised?
But each of those choices, however Earth-friendly they may sound, come with environmental impact. And they can reverberate in unexpected ways, according to a recent study out of the National Center for Ecological Analysis and Synthesis, affecting not just the climate but water and wildlife habitats around the globe.
Consider the environmental footprints of some common dietary staples, including meat, fish, dairy and eggs and crops.
Greenhouse gas emissions
Raising cattle, for example, is so resource-intensive that it has a significant and well-known impact on greenhouse gas emissions, much greater than that of grains or vegetables. Think about it this way: it’s more efficient to grow plants for humans to eat than it is to use them for animal feed.
Red meat including beef and lamb also contribute to climate change by producing lots of methane, a greenhouse gas that is relatively short-lived in the atmosphere but is a more powerful trapper of heat than carbon dioxide.
And then there are sources of greenhouse gas emissions that are easier to overlook — such as certain methods for harvesting fish that live close to the sea floor, including flounder, cod and halibut. The use of bottom trawls, which drag nets along the ocean bottom, releases carbon stored in sediments.
Water use
But emissions aren’t the only way in which our food system is taking a toll on the planet. Another metric the researchers considered is the amount of water used to produce different food items. Agriculture is both a major cause and a casualty of water scarcity around the globe.
Rice is a particularly thirsty crop, but even so it requires less water per calorie than meat products such as pork and beef.
Nutrient pollution
Another environmental concern is nutrient pollution from fertilizers and animal waste. When excess nutrients including nitrogen and phosphorus wash into rivers, lakes or coastal waters, they can cause large growths of algae that eventually die and sink to the bottom. When they decompose, the process strips dissolved oxygen from the water, suffocating fish and other aquatic life.
Across the global food system, pig farming is the number one source of nutrient pollution.
Habitat disturbance
Finally, agriculture and fishing typically displace native animals and plants from their habitats. The new research quantifies this habitat disturbance, taking into account the degree to which some wildlife can coexist with different forms of farming or fishing.
One of the worst food groups for habitat disturbance are groundfish such as cod, haddock or halibut that dwell near the bottom of the sea. Almost a quarter of all wild-caught fish are collected through bottom trawling, which can destroy fragile ocean floor ecosystems.
Overall environmental impact
On balance, a total environmental footprint calculated by equally weighing all four of these types of ecological impacts confirms that plant-based foods cause less harms to the planet, on a per-calorie basis, than fish and meat production.
See how some of the more than 50 foods the researchers analyzed compare along four key metrics: contribution to global warming, water use, nutrient pollution and disturbances to wildlife habitats.
Some foods score poorly — or comparatively well — on all four tests, but in most cases the results are mixed.
Compare two foods of your choice
2.5x higher for beef
The data provides a more holistic way to evaluate how our meals shape the planet, said Ben Halpern, a professor at the University of California at Santa Barbara and the study’s lead author.
“When you do pay attention to these multiple pressures, things you thought weren’t bad get worse,” Halpern said. “Others you thought were bad aren’t as bad.”
Halpern already abstains from eating pork and beef to limit his personal environmental footprint. But the data also showed that some fish, for example, had greater consequences than he realized, while chicken scored “way better than I thought.”
The research also emphasizes how food production that may seem to have relatively low impacts still cause significant environmental shocks around the world.
Nuts such as almonds, for example, are a resource-intensive crop but aren’t produced on as large a scale as wheat, exacting less environmental damage. Wheat is cultivated across hundreds of millions of acres globally, causing a massive ecological footprint despite a relatively low per-calorie impact.
Crops like sugar cane and corn have similarly vast effects, mostly because of their ubiquity.
Impact per calorie and production
Meat Fish Dairy, eggs Crops
*Farmed **Wild caught
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Note: Chart uses a logarithmic scale.
The data helps us understand how food can be produced more efficiently, while maximizing the nutrition it offers, said Jim Leape, a professor at Stanford University and co-director of its Center for Ocean Solutions. The study showed that while about 1 percent of food production comes from oceans and other waterways, it accounts for close to 10 percent of the total global environmental impact.
“There are a lot of opportunities here to meet the challenges of building a food system that offers both healthy diet and a lower footprint," Leape said.