By Jason Daley

There's no way around it—everything in the grocery store, from nuts and kale to beef and apples, has an environmental impact. Fertilizer causes water pollution, farm fields can encroach on habitat, and a lot of carbon gets released when food is transported from one place to another. But it turns out not every stalk of broccoli or pound of Gouda has the same ecological footprint. A new study of food systems in the journal Science shows the same items sitting next to each other on the shelf can have radically different impacts.

Researchers Joseph Poore of the University of Oxford and Thomas Nemecek of the Swiss agricultural research institute Agroscope pored over 570 studies published in the last 20 years measuring food production across the globe. The food systems in the study represent about 90 percent of all the food produced on Earth, grown on roughly 570 million farms. Poore and Nemecek created a dataset covering 40,000 farms in 119 nations around the world producing 40 agricultural products. They then assessed the ecological impact of each commodity from "farm to fork," looking at its impact on land use, freshwater use, water pollution, air pollution and greenhouse gas emissions.

The results show that some crops are much more sustainable than others—for instance, bananas use a lot more land than onions—but also highlight the variability across producers of the same food product. The highest-impact beef has 12 times the emissions and uses 50 times the land of the most sustainably produced beef. Sustainable tomatoes can release almost no greenhouse gases, while high-impact producers can release six kilograms of CO2 per kilogram. High-impact coffee can release 1,000 percent more greenhouse gases than sustainable coffee. The same is true for almost every commodity studied.

Though Poore says that "geography plays a major role in determining all these environmental impacts," there is no one common thread explaining the huge disparities between producers. In rice-growing regions, for instance, some producers may flood their fields annually using long, deep floods that waste water and pollute lakes or rivers. Others may be more precise in their timing, using short shallow floods that have a much smaller impact. And the way rice is processed and whether it is kept as brown rice or milled down to white rice can make one bag 500 times more harmful to the environment than the other.

The fact that so many farms are using environmentally harmful methods is dismaying, but Craig Cox, senior vice president for agriculture and natural resources at the Environmental Working Group, sees things differently. "Actually, this is a good news story," he said. "What it tells us is we can change our huge environmental footprint by changing the practices farmers use. This is more confirmation that the way we farm and practice production have profoundly different effects."

The study highlights the fact that some difficult but modest changes could have huge impacts. According to the results, 25 percent of the world's food producers are creating 53 percent of the environmental burden. Focusing on that one quarter of farmers could have outsized environmental returns. Finding those solutions, however, will be on a case-by-case basis. "An approach to reduce environmental impacts or enhance productivity that is effective for one producer can be ineffective or create trade-offs for another," Poore said in a statement. "This is a sector where we require many different solutions delivered to many millions of different producers."

Most of the change needs to come at the level of agricultural policy and on the farms themselves. But Poore said consumers can make changes to reduce their impact. Animal products, he pointed out, make up the majority of agriculture's environmental burden, with farmed animal products using 83 percent of the world's farmland and producing 56 to 58 percent of agriculture's emissions. "Then you have the really ridiculous statistics, like high-impact beef creating 25,000 percent more greenhouse gases and using 11,000 percent more land per gram of protein than legumes," Poore said. "That's insane."

If we were all to collectively go vegan, Poore pointed out, it would take about 75 percent of all agricultural land out of production while still producing plenty of calories to feed the world. Since eggs, cheese and burgers are likely here to stay, reducing consumption of animal products by half and reforming the worst producers could still result in massive emissions reductions. "There are ways we could meet the demand for meat in more environmentally friendly ways," Cox said. "There's no way to get away from the fact that eating meat puts a lot of demand on the environment. But we could and should do it better."

Poore may have more insights about the global food system still to come. The analysis looked at studies published up to 2016, but in recent years, there have been about 300 more studies examining the impact of all sorts of agricultural systems that could be rolled into the analysis. That could lead to new policies and approaches. "There's a lot of room for mitigation in the system," he said. "We can target a small number of producers and create a lot of potential for change."

Reposted with permission from our media associate SIERRA magazine.