A July 2014 research paper co-authored by FSE deputy director David Lobell is one of 25 articles selected by the editors of the scientific journal Environmental Research Letters to be featured in the journal's Highlights of 2014 collection. The Editorial Board also recognized the paper as 'Highly Commended' during the vote for ERL's 'Best Article' for 2014.

In "Getting caught with our plants down: the risk of a global crop yield slowdown from climate trends in the next two decades," Lobell and co-author Claudia Tebaldi, a senior researcher at the National Center for Atmospheric Research, find that the chance of a worldwide slowdown in yield growth for wheat and corn in the next 20 years is significantly higher due to global warming. With only natural climate variability the odds of a 10 percent yield drop over two decades - equivalent to a halving of the yield growth rate - are one in two hundred for wheat and corn. But under a scenario of human-induced climate change, the likelihood rises to one in ten for corn and one in twenty for wheat.

Lobell said these results are of particular interest to organizations working toward global food security and related issues that would be strongly impacted by falling crop yields in the next 20 years. 

“The people asking these questions are accustomed to planning for scenarios with much less than a 10 percent chance of happening, so it will be interesting to see whether this study has any effect on how they operate," Lobell said. “As scientists, we might prefer to work on time scales in which the answers are clearer, but we also want to be responsive to the actual concerns and questions that decision makers have.”

Lobell is associate professor of Environmental Earth System Science at Stanford and associate director of the Center on Food Security and the Environment. He is also a senior fellow at theStanford Woods Institute for the Environment and the Freeman Spogli Institute for International Studies.

The European Union led the world in wheat production and exports in 2014-15. Yet Europe is also the region where productivity has slowed the most. Yields of major crops have not increased as much as would be expected over the past 20 years, based on past productivity increases and innovations in agriculture.

Finding the causes of that stagnation is key to understanding the trajectory of the global food supply.

Logically, it would seem that climate change would affect crops. But in the overall picture of agriculture, it's hard to figure out how much. European farming is a complex venture, and other possible stagnating factors include changes in government policy. For example, farm subsidies are no longer based on productivity and the use of fertilizer is now controlled to reduce runoff into water supplies. Ongoing positive factors include improvements in farm management practices and advances in crop genetics.

Historically, scientists relied on models to estimate the effects of climate change. Now Stanford's Frances C. Moore has for the first time statistically quantified the relative importance of climate in the stagnation of European crops. She found that warming and precipitation trends are affecting European grain harvests. Moore is a PhD candidate in the Emmett Interdisciplinary Program in Environment and Resources.

"This study is sobering in that it shows climate drags on some of the crops in this region," said David Lobell, co-author of the paper. "Yet this new approach to looking at the problem will help us understand more quickly what impacts require more attention, and that can only be positive in the long term." Lobell is an associate professor of environmental Earth system science and the deputy director of the Center on Food Security and the Environment at Stanford. He is also a senior fellow in the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. He studies ways to improve crop yields in major agricultural regions, with emphasis on adaptation to climate change.

"This is a major step in using quantitative analysis to disentangle the effect of climate change in a complicated system," said Dáithí Stone, a pioneer in comparing actual seasonal weather forecasts with what those forecasts would have been if human activities had not emitted greenhouse gases. "It demonstrates that the signal has become large enough that we may see the effect of climate change in a complicated system like agriculture." Stone is a research scientist in the Computational Chemistry, Materials and Climate Group of Berkeley Lab.

How wheat and corn and barley grow

Moore considered two factors in the study: actual crop yields and expected crop yields given historic temperature and precipitation trends. She applied statistical analyses to look for patterns in regional maps of actual European yields of wheat, maize (known in the United States as corn), barley and sugar beets, from 1989 to 2009.

The study found that climate trends can explain 10 percent of the slowdown in wheat and barley yields, with changes in government policy and agriculture likely responsible for the remainder of the stagnation. Moore found evidence that long-term temperature and precipitation trends since 1989 reduced overall European yields of wheat by 2.5 percent and barley by 3.8 percent, while slightly increasing maize and sugar beet yields.

Moore also wanted to find out to what extent farmers had adapted their practices to accommodate changing conditions. She applied power analysis, a statistical tool to test the effect of adaptation. But she discovered the test was not effective in the context of this study.

"We think farmers have been hurt already by warming and drying trends in Italy," Moore said. Undaunted by the limits of statistical analysis to measure farmer adaptation, she is planning another way to find out. "I have been doing this work in front of a computer – in the future I would like to go to Italy," she said. "It would be interesting to talk to the farmers."

Leslie Willoughby is an intern at Stanford News Service.

Media Contact

Frances C. Moore, Emmett Interdisciplinary Program in Environment and Resources: (617) 233-3380, fcmoore@stanford.edu

Dan Stober, Stanford News Service: (650) 721-6965, dstober@stanford.edu

In a lecture to the Stanford community Tuesday night, Professor Sir Gordon Conway argued that sustainably intensifying agriculture, especially in Africa, is the only way to feed a growing global population without greatly expanding the amount of land used for farming. Sir Gordon is an agricultural ecologist and was an early pioneer of sustainable agriculture while working in Malaysia in the 1960s. He is now a professor of international development at Imperial College London and the director of Agriculture for Impact, a project funded by the Bill and Melinda Gates Foundation.

Sir Gordon's lecture, "Can Sustainable Intensification Feed the World?" was the second installment of the Food and Nutrition Policy Symposium Series sponsored by the Center on Food Security and the Environment.

Sir Gordon described three major challenges to ensuring future global food security: food prices are higher and more volatile, one billion people are malnourished (including 1 in 5 children), and rising demand means that 60 to 100 percent more food will be needed to feed the world by 2050. Solving the food security crisis will mean improving both the quantity and the nutrition of food, at stable and affordable prices, in the face of major challenges.

These challenges include factors on the demand side of the global food economy, such as population growth, changing diets, and the use of crops for biofuels. Supply side factors like high fertilizer prices, climate change, and scarcity of land and water put even more pressure on the food system. 

The solution, Sir Gordon said, is agricultural intensification, a set of practices that allow farmers to produce more food with existing land and water. Sustainability is a key component, so that intensification does not also raise greenhouse gas emissions, deplete soil quality, or damage the resilience of farming systems. Sustainable intensification will be especially important in Africa, said Sir Gordon, where population growth and dietary changes will be most dramatic, and where currently crop yields are far below most other areas of the world.

 Farmers, scientists and policymakers can take several approaches to sustainable intensification. An ecological approach includes practices that safeguard environmental resources and reduce farmers’ dependence on chemicals like herbicides and pesticides, such as through organic farming, integrated pest management, agroforestry or conservation agriculture. A genetic intensification approach includes developing better plant varieties, with traits that promote more sustainable agriculture by resisting pests and diseases, or that provide more nutrition. A third approach is socio-economic intensification of agriculture, through the development of farmers’ cooperatives, better links between farmers and markets, and improved access by farmers to insurance and credit.

The goal, Sir Gordon said, is to help farmers “build resilient livelihoods” that will withstand economic and environmental shocks in the coming decades. Good science is important, but strong political leadership, especially within Africa, will be just as crucial.