For all intents and purposes, climate change is not going to be good news for agriculture. Studies have shown that it will likely reduce crop yields, create a malnutrition crisis, and make large portions of the globe inhospitable to staple crops like maize or bananas.
But researchers from Brown and Tufts universities have a dire message for the world: studies linking climate change to a decrease in crop production might be underestimating the true impact of climate change on agriculture.
“The real missing pieces have been about peoples’ decision making,” Leah VanWey, professor of sociology at Brown and senior deputy director of the Institute at Brown for Environment and Society, told ThinkProgress. “This is not just about suitability. It’s not just about the climate. It’s farmers making decisions in real time.”
The study, published Monday in Nature Climate Change, looked at how climate change might affect crop production in the Brazilian state of Mato Grosso, a rapidly developing agricultural region of the country that produced 10 percent of the world’s soybeans in 2013.
But the study didn’t just look at crop yields, or the productivity of a certain crop per given unit of land. The study took a much broader approach, looking at how farmers might react to climate shocks — how much land farmers will put into rotation if the climate changes, and how many different crops a farmer might grow.
“These farmers, they’re operating on a razor’s edge,” Avery Cohn, assistant professor of environment and resource policy at Tufts, told ThinkProgress. “They need to get their crops in the ground as soon as they can, they are planting short cycle soy varieties that they need to harvest at the peak of the rainy season, and then they need to plant that corn at the peak of the rainy season, and then hope that the rainy season lasts long enough so the corn gets enough water.”
If climate change leads to decreasing yields, farmers might respond by taking a certain amount of their land out of rotation, because it’s no longer profitable. Or farmers might decide not to plant a second crop — a technique known as double cropping — and instead focus on getting the most out of their primary crop, another decision that could lead to reductions in overall agricultural yields.
“Our intuition was that this was a key margin of vulnerability,” Cohn said.
To understand how climate change could impact both double cropping and the overall amount of land in production, the researchers looked at satellite images of Mato Grosso’s fields over an eight year period. If a section of land turned green and then quickly brown, that meant that the parcel of land was being used for agricultural purposes (growing and then harvest). If there were two periods of green, that meant that the area was used for double cropping.
CREDIT: NASA/Stephanie Spera/Brown University
By combining historical climate data with this new data set created from the satellite imagery, the researchers concluded that a 1 degree Celsius increase in temperature was enough to reduce agricultural productivity in the region by nine to 13 percent. But perhaps more importantly, the researchers were able to discover that 70 percent of the total reduction in agricultural output in the region due to climate change could be attributed to both land changes and changes in double cropping. Crop yield, by contrast, only accounted for 30 percent of the overall reduction.
“Our estimates of the vulnerability of agriculture to climate change have mostly used yield as a proxy for output,” Cohn said. “In this region, we showed pretty clearly that yield is not a good proxy for output.”
What This Means For U.S. Farmers
Cohn said that conclusion is especially true for places like Mato Grosso, which don’t have the safety nets — the crop insurance or the subsidies — that farmers in the United States enjoy. To understand how climate shocks would impact farmer behavior, and larger agricultural output, in a place like the United States, more studies would need to be conducted — something that the researchers plan to pursue in the future. But Cohn speculated that for U.S. farmers, climate shocks might have a less pronounced impact on total crop area, but could still could lead farmers to not plant as many different kinds of crops.
“My best guess is that we’d see less of this stuff in the U.S.,” he said. “I can’t imagine farmers packing up and closing up shop quite as easily in the United States as in Brazil. But the question about planting one fewer crop, in response to climate change, is a question I’d like to look at.”
But VanWey notes that Mato Grosso is an especially interesting case study because it has undergone such rapid agricultural expansion in the last decade — something that the world will see more of as agricultural production is forced to expand to keep pace with increasing global population.
“[Mato Grosso] is a really good predictor of what’s going to happen in the rest of the world in the future,” she said. “I do think [the study] is applicable in the places we’re going to see agriculture expanding in the next 50 years.”