A new study looking into the dynamics between climate change and agricultural output found that only a third of production loss seen in Mato Grosso, Brazil over the last few years can be attributed to lower crop yields. The paper, written by Brown and Tufts university researchers suggests that we've been overlooking how two key human responses to climate -- the total area farmed and the number of crops planted -- will impact food production in the future.
The paper, published in Nature Climate Change, focused on the Brazilian state of Mato Grosso, an emerging agricultural region that produced 10% of the global supply of soybeans as of 2013. By analyzing temperature and precipitation data from this area over an eight-year time period, the team calculated how sensitive the agricultural industry of the region is to climate change. Basing on these estimates, they projected that an increase of 1 degree Celsius will cause a 9 to 13 percent reduction in soy and corn output in Mato Grosso.
"This is worrisome given that the temperature in the study region is predicted to rise by as much as 2 degrees by midcentury under the range of plausible greenhouse gas emissions scenarios," said Avery Cohn, aassistant professor of environment and resource policy at Tufts, who led the work while he was a visiting researcher at Brown.
The accuracy of these figures hinges of course on the assumption that patterns observed in the past will hold true in the future. But study's most alarming find however doesn't come from crop yields alone, but from the mechanisms that drive changes in agricultural output.
Most similar studies only look at how changes in a region's climate influence crop yield, i.e. how much food is harvested from a unit of agricultural land. But if you only focus on this single variable you'll miss the critical dynamics that affect overall output says Leah VanWey, professor of sociology at Brown and senior deputy director of the Institute at Brown for the Study of Environment and Society (IBES).
"If you look at yields alone, you're not looking at all of the information because there are economic and social changes going on as well," VanWay, one of the study's senior authors, said.
"You're not taking into account farmers' reactions to climate shocks."
If yields decrease, farmers may be less inclined to farm the same area as it's just not profitable anymore -- a decrease in production per square meter means lower profits at harvest, but the farmer's cost while growing the crop stays the same.
Another factor that plays a part in decreasing overall production is be the reduction of number of crops per season. The planting of two successive crops on the same land in a growing season -- known as double-cropping -- is a common practice in Mato Grosso. If climate takes a shift for the worse and crops don't grow, farmers may be inclined to save their money and effort for better times by not planting a second crop.
For this study the team analyzed not only crop yield figures in the region, but also the yearly variation in field area and double cropping. Cohn and VanWey worked with Brown University Professor of earth, environmental and planetary sciences Jack Mustard and graduate student Stephanie Spera, who gathered satellite images of the Mato Grosso region from NASA's MODIS satellite -- which is used to monitor land cover and use around the world. They were able to identify cropland on these images as they turn green during the growing season but then quickly become brown as the plants are harvested. Two green stages in the same growing season was indicative of double-cropping.
"The changes in cropping that we quantified with remotely sensed data were stunning," Mustard said.
"We can use those satellite data to better understand what's happening from a climate, economic, and sociological standpoint."
Image credits NASA/Brown University.
The team found that an increase of 1 degree Celsius led to substantial decreases in total farmed area and in double cropping incidence. In fact, more than 70 percent of the overall loss in production can be attributed to these two factors, the paper concludes. Only the remaining 30 percent is attributable to lower crop yields.
"Had we looked at yield alone, as most studies do, we would have missed the production losses associated with these other variables," VanWey said.
Cohn believes that the results suggest more traditional studies "may be underestimating the magnitude of the link between climate and agricultural production."
This hold true especially in countries that invest little in agricultural subsidies, such as Brazil. Here farmers are more dependent on the profitability of their crops and if yields drop, they just don't have the money to farm the same area of land.
"This is an agricultural frontier in the tropics in a middle-income country," VanWey said. "This is where the vast majority of agricultural development is going to happen in the next 30 to 50 years. So understanding how people respond in this kind of environment is going to be really important."
VanWey said the next step might be to repeat this study it in the U.S. to see if increased subsidies or insurance help to guard against climate shocks. If so, it might inform policy decisions in emerging agricultural regions like Mato Grosso.
"We may need to figure out a way to create incentives -- credit products or insurance -- that can reduce farmers' responses to climate shocks," VanWey said.
