Though scientists have long known that Africa is a major contributor to rising levels of atmospheric methane, the primary culprit has been a mystery: emissions from the typical sources, such as wetlands and landfills, couldn’t account for the total measured by planes and satellites. This lack of clarity has complicated efforts to reduce emissions of the potent greenhouse gas, a step central to slowing near-term climate change because methane, despite a relatively short lifespan, traps 80 times more heat than carbon dioxide (CO2) during its first 20 years in the atmosphere.
In early 2023, Robert Stavins, the Meyer professor of energy and economic development at Harvard Kennedy School, asked whether anyone had looked at emissions from rice cultivation. Since the 2007-2008 global food price crisis, African countries have increasingly shifted to growing rice domestically, rather than importing it, to feed their growing populations more inexpensively. Were researchers accounting for this new reality?
Vasco McCoy Family professor of atmospheric chemistry Daniel Jacob and others working with him began to do some calculations. Previous analyses had not accounted for the proliferation of rice paddies on the continent, nor the higher methane emissions per acre resulting from factors such as expanded irrigation. After adjusting for these variables, the team found that African rice cultivation now accounts for 7 percent of global methane emissions, much more than previously thought. How, then, could policymakers resolve the tension between two critical goals: curbing climate change and promoting food security, especially in the developing world?
The latter takes precedence, says Zichong Chen, a research associate working with Jacob and an author of the study: “Food security is a bigger priority than greenhouse gases and global warming. If we starve, then we don’t care about climate change at all.” But there are ways to reduce emissions without cutting rice production—whether by requiring other emitters, such as oil and gas companies, to reduce more aggressively, or by adapting rice cultivation techniques to produce less methane. These steps will be essential to mitigate climate change during the next few decades, Jacob says: “If you want to maintain warming below a certain level, you need to act now.”
The findings don’t imply that African countries have to—or should—reduce the amount of rice they produce. While other sources of methane, such as livestock, inevitably produce emissions, “by improving practices in rice agriculture, we can cut emissions to basically zero,” he continues. To explain how, he outlines the process by which rice cultivation produces methane. Microbes that break down dead vegetation typically rely on oxygen for the decomposition reaction and produce CO2 as a byproduct—much the way humans inhale oxygen and exhale CO2. But farmers often flood rice paddies with water to suppress weed growth, manage pests, and create optimal conditions for the semi-aquatic plant. This flooding prevents oxygen from penetrating the paddies, causing microbes to switch to anaerobic reactions that produce methane instead. As a result, a flooded rice paddy “behaves like a wetland on steroids,” Jacob explains. “You have a lot of vegetation that is being decomposed.”
But rice cultivation doesn’t require flooding paddies. One easy way to eliminate emissions is by switching to upland rice, which is cultivated in non-flooded conditions and therefore doesn’t produce methane. There is a drawback, however: upland rice produces smaller yields. “I don’t think we’ll convince farmers to switch to rice that has a lower yield unless there’s regulation to that effect, and I don’t see that coming,” Jacob says. Researchers are therefore studying how to increase upland rice yields; Jacob hopes that, eventually, these varieties will rival the productivity of flooded rice.
It’s also possible to reduce methane emissions by flooding paddies only when necessary. “You can have patterns of wetting and drying,” Jacob explains, “and those tend to be very efficient at reducing methane emissions.” The challenge becomes sharing these best practices with small farmers scattered across the continent—a more difficult feat than disseminating information through a centralized government or corporation. Jacob hopes that framing these changes as economically beneficial to farmers can encourage them to adapt: less frequent flooding may require more labor, but also uses less water. He and his research collaborators have partnered with the United Nations and the International Rice Research Institute in attempts to encourage farmers to change their methods.
Genetically modifying upland rice and communicating with farmers will take time. In the interim, other sectors—such as waste management and energy production—will have to reduce emissions more aggressively. But Chen and Jacob remain optimistic that collaboration with growers will eventually make rice cultivation more climate friendly, too. “It’s very important to let them know: if you reduce methane emissions, you’ll also benefit,” Chen says. “Right now, communication is the most important gap.”
