Analysts usually estimate a crop’s carbon footprint based on country-level factors. But that formulation isn’t adequate, according to a new analysis of soy exports from Brazil. Published in Global Environmental Change, the study tracked soy from specific production sites in Brazil to its final destinations across the world and found that the carbon footprint of the crop varied widely depending on its origin within the country.
“There’s not an average footprint for Brazilian soy, or even Brazilian soy from one particular state,” says agricultural engineer Neus Escobar, a postdoctoral researcher at the University of Bonn in Germany who led the study. “It really depends on deforestation and the spot where the soybean was planted.”
Earlier calculations of soy’s carbon footprint were largely based on the damage caused by rainforest clearance in the central-western Brazilian state of Mato Grosso. Over the last two decades, Brazil—the world’s largest exporter of soy—implemented various environmental policies to mitigate the damage caused by soy cultivation. Many of these laws aimed to prevent further deforestation in the Amazon basin. But as a result, soy cultivation shifted to another biodiverse region known as the Cerrado, a savannah-like biome that spans Brazil’s central plateaus. Estimates of the crop’s environmental impacts didn’t account for this shift.
In the new study, Escobar and her colleagues combined two methods to acquire a fine-scale view of soy cultivation. They performed a life-cycle analysis to see where soy products ended up in the world and combined this with data on land-use change, crop management practices, and domestic transport at the municipality level. They tracked soy, protein cakes used as cattle feed, and soybean oil from their sources on farms through industrial processing and international shipping to their destinations. The analyses spanned all soy cultivation across Brazil from 2010 to 2015 and represented nearly 90,000 different supply chains. This level of detailed quantification is “quite new,” says environmental scientist Eric Lambin of Stanford University, who was not involved with the study. “There have been some studies focusing on land use and others on processing, etc. But putting all the pieces together to get this detailed picture is quite innovative.”
The researchers found that the emissions per unit of product from four central states, known collectively as MATOPIBA (Maranhão, Tocantins, Piauí, and Bahia), were six times higher than the national average. These states span newly cleared agricultural regions in the Cerrado, where soy cultivation is directly linked to the loss of natural grasslands.
The results uncover an unintended consequence of conservation policies, says ecologist Marcia Macedo of the Woods Hole Research Center in Massachusetts, who was not involved with the study. “Efforts to remove Amazon deforestation from soybean supply chains were relatively successful, but they created the conditions for expansion to occur in the Cerrado,” Macedo says. As a result, importers still buy carbon emissions in the region, although they may not be contributing to rainforest destruction. Domestic transport, especially among Brazil’s land-locked central and western states, was the second greatest contributor to emissions, accounting for nearly 25% of the country’s soy-linked emissions.
The data also revealed that other nations had significant differences in the carbon footprint of their imports. China is the largest importer of Brazilian soy, receiving 118 metric tons each year, but only about a quarter of that was a product of deforestation. The European Union, on the other hand, imported soy that led to about 67.6 metric tons of CO2 emissions, but nearly half of this carbon footprint represented the loss of native vegetation.
Future studies could employ similar approaches to better understand the carbon footprint of other commodities such as beef, timber, and palm oil. At least in the case of soy, simply changing where a country sources its product is not a solution, Lambin says, because changing sources could lead to a rise in emissions from domestic transport. “Changing the sourcing of one country or region such as the EU would not solve the problem, just displace it,” he says. “It’s like a puzzle where you move one piece and then all the others change as well.”
But the results could help from a global trade perspective, as they help governments decide where and how to work with producers to improve sustainability, according to Escobar. In Brazil, soy growers are exploring new sustainable cropping systems that would minimize the need for more land—the best way to reduce a crop’s carbon footprint. “It takes decades of small mitigation measures just to repay the carbon debt created by initially converting land for agriculture,” Lambin says. “Everything else is only marginal by comparison.”