The Center on Food Security and the Environment is a joint effort of the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment.
To predict how agriculture will be affected by future climate change, scientists often rely on a single crop model – a computer simulation of how a specific crop’s yield responds to temperature changes. By combining 30 such models into a single study, and comparing each model against data from existing experimental wheat fields around the world, a team of researchers including Stanford professor David Lobell have developed a more powerful and accurate way to predict future wheat yields.
In a new analysis published in Nature Climate Change, the team’s results support previous work suggesting that wheat yields around the world are sensitive to rising temperatures. Using the new method of analysis, the team estimates an average six percent future yield loss for every one degree Celsius rise in global mean temperature.
“Combining 30 models gives us a much greater ability to predict future impacts and understand past impacts,” said Lobell. “This is a clear step forward.”
Lobell is professor of environmental earth system science in the School of Earth Science at Stanford and the deputy director of the Center on Food Security and the Environment. He is a senior fellow at the Stanford Woods Institute for the Environment and at the Freeman Spogli Institute for International Studies.
The estimated six percent yield loss for every degree increase is equivalent to about a quarter of the current volume of wheat traded globally in 2013. Yields at some sites, notably those in Mexico, Brazil, India and Sudan, show simulated wheat yield losses of more than 20 percent - in Sudan’s case, more than 50 percent - under a scenario in which global mean temperature rises by two degrees Celsius.
With higher temperatures also comes an increase in the variability of wheat yields, both by location and between years. More fluctuation in wheat yields could mean greater global price volatility for the staple crop.
Approximately 70 percent of the wheat produced today is grown either on irrigated plots or in rainy regions. The research team accounted for this factor by focusing its simulations on multiple regional-specific varieties of wheat that are commonly grown under these conditions.
The new paper includes several suggestions for avoiding some of the predicted yield losses. For example, some varieties of wheat are more heat tolerant than others, and farmers in the places hardest hit by rising temperatures could switch varieties to capitalize on this heat resistance. The effects of rising temperatures could also be managed, in part, by adjusting sowing and harvesting dates, or changing the way fertilizers are applied to crops.
Contact: David Lobell, dlobell@stanford.edu
Rosamond (Roz) Naylor has been named the first holder of the new William Wrigley Professorship in the School of Earth Sciences. Since 2006 Naylor has directed the Center on Food Security and the Environment, within the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. She is also associate professor, by courtesy, of Economics at Stanford.
"Professorships are the best way to recognize faculty for their superior leadership and commitment to research, teaching, service to the university and service to humanity," said Pamela Matson, dean of the School of Earth Sciences at Stanford. "Roz epitomizes these qualities - she is incredibly fitting as the inaugural holder of the William Wrigley Professorship."
Walter Falcon, professor (emeritus) of economics at Stanford and a longtime research collaborator of Naylor's, added: “All of Roz’s colleagues are delighted at her selection. She has long been a thought leader on food security issues, she has limitless energy, and she has an extraordinary capacity for bringing scholars together at Stanford and beyond.”
The new William Wrigley Professorship is supported by Mrs. Julie Ann Wrigley, AB '71 (Anthropology) and Ms. Alison Wrigley Rusack, AB '80 (Communication).
Naylor's research focuses on economic and biophysical dimensions of food security, and the environmental impacts of crop and animal production. She has been involved in many field-level research projects around the world and has published widely on issues related to intensive crop production, aquaculture and livestock systems, biofuels, climate change, food price volatility, and food policy analysis. At Stanford, Naylor teaches courses on the World Food Economy, Human-Environment Interactions, and Sustainable Agriculture.
Naylor currently serves on the Scientific Advisory Board for the Beijer Institute in Stockholm, is a Science Advisor for United Nation’s Secretary General Ban Ki-Moon’s initiative on Sustainable Development (Sustainable Agriculture section), and trustee of The Nature Conservancy California Chapter. Additionally, she serves on the editorial board of the journals Global Food Security and Journal on Food Security. Naylor received her B.A. in Economics and Environmental Studies from the University of Colorado, her M.Sc. in Economics from the London School of Economics, and her Ph.D. in applied economics from Stanford University.
The project is supported under the NSF Science, Engineering and Education for Sustainability Fellows (SEES Fellows) program, with the goal of helping to enable discoveries needed to inform actions that lead to environmental, energy and societal sustainability while creating the necessary workforce to address these challenges. Sustainability science is an emerging field that addresses the challenges of meeting human needs without harm to the environment, and without sacrificing the ability of future generations to meet their needs.
West Africa is highly vulnerable to climate hazards and better quantification and understanding of the impact of climate change on crop yields are urgently needed. Here we provide an assessment of near-term climate change impacts on sorghum yields in West Africa and account for uncertainties both in future climate scenarios and in crop models. Towards this goal, we use simulations of nine bias-corrected CMIP5 climate models and two crop models (SARRA-H and APSIM) to evaluate the robustness of projected crop yield impacts in this area. In broad agreement with the full CMIP5 ensemble, our subset of bias-corrected climate models projects a mean warming of +2.8 °C in the decades of 2031–2060 compared to a baseline of 1961–1990 and a robust change in rainfall in West Africa with less rain in the Western part of the Sahel (Senegal, South-West Mali) and more rain in Central Sahel (Burkina Faso, South-West Niger). Projected rainfall deficits are concentrated in early monsoon season in the Western part of the Sahel while positive rainfall changes are found in late monsoon season all over the Sahel, suggesting a shift in the seasonality of the monsoon. In response to such climate change, but without accounting for direct crop responses to CO2, mean crop yield decreases by about 16–20% and year-to-year variability increases in the Western part of the Sahel, while the eastern domain sees much milder impacts. Such differences in climate and impacts projections between the Western and Eastern parts of the Sahel are highly consistent across the climate and crop models used in this study. We investigate the robustness of impacts for different choices of cultivars, nutrient treatments, and crop responses to CO2. Adverse impacts on mean yield and yield variability are lowest for modern cultivars, as their short and nearly fixed growth cycle appears to be more resilient to the seasonality shift of the monsoon, thus suggesting shorter season varieties could be considered a potential adaptation to ongoing climate changes. Easing nitrogen stress via increasing fertilizer inputs would increase absolute yields, but also make the crops more responsive to climate stresses, thus enhancing the negative impacts of climate change in a relative sense. Finally, CO2 fertilization would significantly offset the negative climate impacts on sorghum yields by about 10%, with drier regions experiencing the largest benefits, though the net impacts of climate change remain negative even after accounting for CO2.
In a recent speech, Stanford professor Rosamond Naylor examined the wide range of challenges contributing to global food insecurity, which Naylor defined as a lack of plentiful, nutritious and affordable food. Naylor's lecture, titled "Feeding the World in the 21st Century," was part of the quarterly Earth Matters series sponsored by Stanford Continuing Studies and the Stanford School of Earth Sciences. Naylor, a professor of Environmental Earth System Science and director of the Center on Food Security and the Environment at Stanford, is also a professor (by courtesy) of Economics, and the William Wrigley Senior Fellow at the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment.
"One billion people go to bed day in and day out with chronic hunger," said Naylor. The problem of food insecurity, she explained, goes far beyond food supply. "We produce enough calories, just with cereal crops alone, to feed everyone on the planet," she said. Rather, food insecurity arises from a complex and interactive set of factors including poverty, malnutrition, disease, conflict, poor governance and volatile prices. Food supply depends on limited natural resources including water and energy, and food accessibility depends on government policies about land rights, biofuels, and food subsidies. Often, said Naylor, food policies in one country can impact food security in other parts of the world. Solutions to global hunger must account for this complexity, and for the "evolving" nature of food security.
As an example of this evolution, Naylor pointed to the success of China and India in reducing hunger rates from 70 percent to 15 percent within a single generation. Economic growth was key, as was the "Green Revolution," a series of advances in plant breeding, irrigation and agricultural technology that led to a doubling of global cereal crop production between 1970 and 2010. But Naylor warned that the success of the Green Revolution can lead to complacency about present-day food security challenges. China, for example, sharply reduced hunger as it underwent rapid economic growth, but now faces what Naylor described as a "second food security challenge" of micronutrient deficiency. Anemia, which is caused by a lack of dietary iron and which Naylor said is common in many rural areas of China, can permanently damage children's cognitive development and school performance, and eventually impede a country’s economic growth.
Although hunger is more prevalent in the developing world, food insecurity knows no geographic boundaries, said Naylor. Every country, including wealthy economies like the United States, struggles with problems of food availability, access, and nutrition. "Rather than think of this as 'their problem' that we don't need to deal with, really it's our problem too," Naylor said.
She pointed out that one in five children in the United States is chronically hungry, and 50 million Americans receive government food assistance. Many more millions go to soup kitchens every night, she added. "We are in a precarious position with our own food security, with big implications for public health and educational attainment," Naylor said. A major paradox of the United States' food security challenge is that hunger increasingly coexists with obesity. For the poorest Americans, cheap food offers abundant calories but low nutritional value. To improve the health and food security of millions of Americans, "linking policy in a way that can enhance the incomes of the poorest is really important, and it's the hard part,” she said.” It's not easy to fix the inequality issue."
When asked whether there were any "easy" decisions that the global community can agree to, Naylor responded, "What we need to do for a lot of these issues is pretty clear, but how we get after it is not always agreed upon." She added, "But I think we've seen quite a few success stories," including the growing research on climate resilient crops, new scientific tools such as plant genetics, improved modeling techniques for water and irrigation systems, and better knowledge about how to use fertilizer more efficiently. She also said that the growing body of agriculture-focused climate research was encouraging, and that Stanford is a leader on this front.
Naylor is the editor and co-author of The Evolving Sphere of Food Security, a new book from Oxford University Press. The book features a team of 19 faculty authors from 5 Stanford schools including Earth science, economics, law, engineering, medicine, political science, international relations, and biology. The all-Stanford lineup was intentional, Naylor said, because the university is committed to interdisciplinary research that addresses complex global issues like food security, and because "agriculture is incredibly dominated by policy, and Stanford has a long history of dealing with some of these policy elements. This is the glue that enables us to answer really challenging questions."