Our dietary choices have enormous environmental impacts

In order to produce food for humanity, we have appropriated roughly 50 percent of all habitable land and 70 percent of the available fresh water. We harvest aquatic food from nearly every river, lake and ocean, pollute watersheds and coastal seas with excess nutrients and generate around 30 percent of all anthropogenic greenhouse gases. Like it or not, feeding humans puts enormous environmental pressure on our planet. 

In past studies, researchers have attempted to calculate the environmental impact of producing various different types of foods. By considering such factors as greenhouse gasses emitted during production, or the extent of water pollution, they have made some headway in quantifying the environmental consequences of food production per pound or kilogram. However, with industrialized farming and complex supply chains, it is difficult to assess the true environmental pressures of our global food system. 

“Everyone eats food, and more and more people are paying attention to the planetary consequences of what they eat,” said UC Santa Barbara marine ecologist Ben Halpern. However, as the world’s population increases decisions will need to be made about how to reduce the environmental footprint of food production in order to keep it sustainable, and this will necessitate a more comprehensive understanding of the various types of impacts. This proves to be a gargantuan task as there are so many different types of foods, produced in various ways and leading to a range of environmental pressures depending on the location of production. 

“The individual choice of eight billion people adds up,” said Halpern, “and we need to know the overall impact of total food production – not just per pound – especially when setting food policy.”

In a new study, Halpern and colleagues at UC Santa Barbara’s National Center for Ecological Analysis & Synthesis (NCEAS) have analyzed the greenhouse gas emissions, freshwater use, habitat disturbance and nutrient pollution (e.g., fertilizer runoff) generated by the production of 99 percent of all foods on Earth, including both aquatic and terrestrial foods. In addition, they combine these four pressures to map the estimated cumulative pressure, or ‘footprint,’ of food production globally, as well as in individual countries. Their research is published in the journal Nature Sustainability.

For Halpern, executive director at NCEAS and a professor at UCSB’s Bren School of Environmental Science & Management, understanding the impacts of food production along with the local context of these impacts has been a longstanding interest. By taking detailed data about greenhouse gas emissions, freshwater use, habitat disturbance and nutrient pollution generated by 99 percent of total reported production of aquatic and terrestrial foods in 2017, and mapping those impacts at high resolution, the researchers were able to create a more nuanced geospatial picture of the pressures – the inputs, processes and outputs – of global food production.

It turns out that the impacts of food production vary between countries, depending on the farming methods used and on environmental conditions prevalent at each locality. This leads to the unexpected situation that five countries contribute almost half of all environmental pressures arising from food production; these are India, China, the United States, Brazil and Pakistan.

In addition, the large proportion of the environmental footprint arising from terrestrial food production is generated from agricultural activities that take place over only 10 percent of the Earth’s surface. This means that, when looking at the cumulative pressure per unit of food production (efficiency), there are enormous variations between countries and it is not correct to assume, as has been the case previously, that the environmental footprint of production for any one food is the same in all locations. 

For example, thanks to technology that reduces greenhouse gases and increases yields, the United States – the world’s number one producer of soy – is more than twice as efficient as India (the fifth largest producer) at producing the crop, making American soy the more environmentally friendly choice.

“The environmental efficiency of producing a particular food type varies spatially, such that rankings of foods by efficiency differ sharply among countries, and this matters for guiding which foods we eat and from where,” said Halley Froehlich, assistant professor in environmental studies at UCSB and a co-author of the study.

The research also uncovers connections between land and sea that get missed when looking only at one or the other, and that result in significant environmental impacts. In some countries, raising pigs and chicken gives rise to an ocean footprint because they are fed meal made from marine fish such as herrings, anchovies and sardines. The converse is true for mariculture farms that make use of crop-based feeds and thus extend the environmental pressure caused by fish farms onto the land.

Assessing cumulative pressures can bring to light results that could not have been predicted by examining individual pressures alone. For instance, while raising cattle uses by far the most land for grazing, farming pigs produces a lot of pollution and uses more water. When comparing the two types of food production, the cumulative environmental pressures end up being slightly greater when raising pigs than when raising cattle. Measured by cumulative pressures, the five foods with the most severe environmental impacts are pigs, cows, rice, wheat and oil crops.

It is crucial to consider the cumulative effects on the environment of producing food to feed a growing global population. If we wish to reduce environmental degradation while still ensuring food security, we may need to rethink the way in which we produce food in general, say the researchers. In some cases, farming might need to improve efficiency; in other cases, consumers might need to change their food choices. Understanding the different environmental costs of food production in different countries will help to steer consumption towards lower-impact foods and ultimately to restructuring the food system such that we will be able to feed humanity in a sustainable manner. 

“We need this comprehensive information to make more accurate decisions about what we eat,” said Halpern, who modified his own food choices based on the results of this study.

“I became a pescatarian years ago because of wanting to reduce the environmental footprint of what I eat,” he said. “But then I thought, I’m a scientist, I should really use science to inform my decisions about what I eat. That’s actually why I started this research project. And now that we have the results, I see that from an environmental perspective, chicken is actually better than some seafood. And so I’ve shifted my diet to start including chicken again, while eliminating some high-pressure seafoods like bottom-trawl caught cod and haddock. I am actually eating my words.”

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By Alison Bosman, Earth.com Staff Writer

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