FSE associate director David Lobell delivers a lecture on "Understanding the limits of crops (and models) under extreme heat" as part of UC Davis' Climate-Smart Agriculture conference. Special Session - #7. Lobell's talk begins at 51:00.
David Lobell is the Benjamin M. Page Professor at Stanford University in the Department of Earth System Science and the Gloria and Richard Kushel Director of the Center on Food Security and the Environment. He is also the William Wrigley Senior Fellow at the Stanford Woods Institute for the Environment, and a senior fellow at the Freeman Spogli Institute for International Studies (FSI) and the Stanford Institute for Economic Policy and Research (SIEPR).
Lobell's research focuses on agriculture and food security, specifically on generating and using unique datasets to study rural areas throughout the world. His early research focused on climate change risks and adaptations in cropping systems, and he served on the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report as lead author for the food chapter and core writing team member for the Summary for Policymakers. More recent work has developed new techniques to measure progress on sustainable development goals and study the impacts of climate-smart practices in agriculture. His work has been recognized with various awards, including the Macelwane Medal from the American Geophysical Union (2010), a Macarthur Fellowship (2013), the National Academy of Sciences Prize in Food and Agriculture Sciences (2022) and election to the National Academy of Sciences (2023).
Prior to his Stanford appointment, Lobell was a Lawrence Post-doctoral Fellow at Lawrence Livermore National Laboratory. He holds a PhD in Geological and Environmental Sciences from Stanford University and a Sc.B. in Applied Mathematics from Brown University.
Lobell Lab
A project to advance the science that guides investment in food security and crop productivity, and to effectively communicate this science to a broad audience.
G-FEED: Global Food, Environment and Economic Dynamics
An interdisciplinary group working cooperatively to understand the relationship between society and the environment by examining regional and global scale phenomena using statistical analyses of real world data.
Households depend upon food prices, incomes, and disease burdens that impact the ability to use consumed food. Climate change and extreme temperatures impact all of these factors. In this talk, David Lobell focuses on the impact of heat in growing regions that are important for food prices. He reviews recent research on heat impacts and discusses whether crop yields are becoming more or less sensitive to heat.
Stanford experts from a range of disciplines will discuss the interconnections and interactions among humanity’s need for and use of energy, food, water, and environmental resources. Drawing on their own research, each speaker will illustrate and evaluate some of the ways in which decisions in one resource area can lead to trade-offs or co-benefits in other areas. Stanford students and faculty will lead interactive breakout sessions to explore a range of challenges associated with energy transitioning to a sustainable system.
Featured videos:
Energy and Food Nexus: David Lobell, Assistant Professor of Environmental Earth System Science
Plenary Discussion: The Way Forward
Moderated by Margot Gerritsen, Associate Professor of Energy Resources Engineering; Director, Institute for Computational and Mathematical Engineering
Donald Kennedy, President, Emeritus, Stanford University; Bing Professor of Environmental Science, Emeritus
Rosamond Naylor, Professor of Environmental Earth System Science; Director, Center on Food Security and the Environment
Adam Brandt, Assistant Professor of Energy Resources Engineering
Donald Kennedy is the editor-in-chief of Science, the journal of the American Association for the Advancement of Science, and a CESP senior fellow by courtesy. His present research program entails policy on such trans-boundary environmental problems as: major land-use changes; economically-driven alterations in agricultural practice; global climate change; and the development of regulatory policies.
Kennedy has served on the faculty of Stanford University from 1960 to the present. From 1980 to 1992 he served as President of Stanford University. He was Commissioner of the US Food and Drug Administration from 1977-79. Previously at Stanford, he was as director of the Program in Human Biology from 1973-1977 and chair of the Department of Biology from 1964-1972.
Kennedy is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society. He served on the National Commission for Public Service and the Carnegie Commission on Science, Technology and Government, and as a founding director of the Health Effects Institute. He currently serves as a director of the Carnegie Endowment for International Peace, and as co-chair of the National Academies' Project on Science, Technology and Law. Kennedy received AB and PhD degrees in biology from Harvard University.
David Lobell is the Benjamin M. Page Professor at Stanford University in the Department of Earth System Science and the Gloria and Richard Kushel Director of the Center on Food Security and the Environment. He is also the William Wrigley Senior Fellow at the Stanford Woods Institute for the Environment, and a senior fellow at the Freeman Spogli Institute for International Studies (FSI) and the Stanford Institute for Economic Policy and Research (SIEPR).
Lobell's research focuses on agriculture and food security, specifically on generating and using unique datasets to study rural areas throughout the world. His early research focused on climate change risks and adaptations in cropping systems, and he served on the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report as lead author for the food chapter and core writing team member for the Summary for Policymakers. More recent work has developed new techniques to measure progress on sustainable development goals and study the impacts of climate-smart practices in agriculture. His work has been recognized with various awards, including the Macelwane Medal from the American Geophysical Union (2010), a Macarthur Fellowship (2013), the National Academy of Sciences Prize in Food and Agriculture Sciences (2022) and election to the National Academy of Sciences (2023).
Prior to his Stanford appointment, Lobell was a Lawrence Post-doctoral Fellow at Lawrence Livermore National Laboratory. He holds a PhD in Geological and Environmental Sciences from Stanford University and a Sc.B. in Applied Mathematics from Brown University.
Lobell Lab
A project to advance the science that guides investment in food security and crop productivity, and to effectively communicate this science to a broad audience.
G-FEED: Global Food, Environment and Economic Dynamics
An interdisciplinary group working cooperatively to understand the relationship between society and the environment by examining regional and global scale phenomena using statistical analyses of real world data.
Rosamond Naylor is the William Wrigley Professor in Earth System Science, a Senior Fellow at Stanford Woods Institute and the Freeman Spogli Institute for International Studies, the founding Director at the Center on Food Security and the Environment, and Professor of Economics (by courtesy) at Stanford University. She 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. Her research focuses on policies and practices to improve global food security and protect the environment on land and at sea. She works with her students in many locations around the world. 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. In addition to her many peer-reviewed papers, Naylor has published two books on her work: The Evolving Sphere of Food Security (Naylor, ed., 2014), and The Tropical Oil Crops Revolution: Food, Farmers, Fuels, and Forests (Byerlee, Falcon, and Naylor, 2017).
She is a Fellow of the Ecological Society of America, a Pew Marine Fellow, a Leopold Leadership Fellow, a Fellow of the Beijer Institute for Ecological Economics, a member of Sigma Xi, and the co-Chair of the Blue Food Assessment. Naylor serves as the President of the Board of Directors for Aspen Global Change Institute, is a member of the Scientific Advisory Committee for Oceana and is a member of the Forest Advisory Panel for Cargill. At Stanford, Naylor teaches courses on the World Food Economy, Human-Environment Interactions, and Food and Security.
Although weather data are widely acknowledged to contain measurement errors, the implications of these errors for models that relate weather to yields have not been adequately examined. From statistical theory and applications in many other fields, it is clear that measurement error in a single predictor variable can lead to bias in estimating the effects of that variable, as well as any other correlated predictors. Of particular concern for statistical crop models is that errors in measuring precipitation can lead to bias in inferences about yield responses to both temperature and precipitation. In this study, simulation extrapolation (SIMEX) is used to gauge the importance of measurement error for two recent studies that employed statistical crop models. In both cases, estimates of yield responses to temperature were only slightly changed when considering measurement errors. However, yield responses to precipitation were significantly larger when assuming that precipitation is measured with 30% error, compared to the common assumption of error-free measurements. Thus, results indicate that studies that ignore measurement errors are unlikely to be biased for estimating T sensitivity of yields, but can easily underestimate P sensitivity by a factor of two or more. More work is needed to test effects of measurement errors in other cases, as well as to better quantify the magnitudes of errors in weather measurements for cropped regions. As a rough substitute for detailed measurement error analysis, sensitivity tests that double the yield response to precipitation are advised when applying statistical crop models to projections from climate ensembles. Depending on the magnitude of precipitation projections, which in turn depend on the spatial and temporal scale of analysis, the conclusions of a study may or may not be altered by considering the effects of measurement errors.
We have read the headline a number of times now warning us that increasing temperatures are threatening global crop production. One need only to recall the drought and heat wave that hit the mid-western United States last summer, damaging corn and soybean production. Higher temperatures are certainly part of the problem, but a new study led by FSE associate director David Lobell finds its impacts in the U.S. are more indirect. Water stress may be the main culprit.
To validate this hypothesis and to help differentiate the different mechanisms impacting crop yields at higher temperatures, the research team used a model known as an Agricultural Production Systems Simulator (APSIM). High temperatures had a strong negative effect on corn yield response in the United States, in agreement with the data, but the predominate effect of heat in the model was via increased water stress.
As temperatures increase, plants transpire more water into the atmosphere, just as people sweat more on hotter days. With more hot days, the corn plant finds it harder to maintain growth rates, and at the same time loses more water, which sets up the risk of even more drought stress later in the season.
“APSIM computes daily water stress as the ratio of water supply to demand, and during the critical month of July this ratio is three times more responsive to 2 ºC warming than to a 20 percent precipitation reduction,” writes Lobell and co-authors in a new paper published in Nature Climate Change. “Water stress during July is particularly important for overall biomass growth and final yield, with July being the month with the most total biomass growth.”
Direct heat stress on the plant, such as happens on extremely hot days, played a more minor role in determining final yield. The study suggests that increased CO2 may reduce crop sensitivity to extreme heat by increasing water use efficiency, but gains are likely to be no more than 25 percent.
“The APSIM model has been valuable in its ability to discriminate the importance of these factors,” said Lobell. “Models like these are useful for guiding efforts to develop crops with greater tolerance to increased temperatures, an important component of most adaptation strategies in agriculture, and helping to identify which processes are critical for modeling efforts to consider when projecting climate change impacts.”
The researchers project sensitivity to extreme heat will remain a severe constraint to crop production in the foreseeable future, especially as the region warms. They are now using the models to evaluate different strategies for developing new varieties of corn that can better handle the heat.
Statistical studies of rainfed maize yields in the United States and elsewhere have indicated two clear features: a strong negative yield response to accumulation of temperatures above 30°C (or extreme degree days (EDD)), and a relatively weak response to seasonal rainfall. Here we show that the process-based Agricultural Production Systems Simulator (APSIM) is able to reproduce both of these relationships in the Midwestern United States and provide insight into underlying mechanisms. The predominant effects of EDD in APSIM are associated with increased vapour pressure deficit, which contributes to water stress in two ways: by increasing demand for soil water to sustain a given rate of carbon assimilation, and by reducing future supply of soil water by raising transpiration rates. APSIM computes daily water stress as the ratio of water supply to demand, and during the critical month of July this ratio is three times more responsive to 2°C warming than to a 20% precipitation reduction. The results suggest a relatively minor role for direct heat stress on reproductive organs at present temperatures in this region. Effects of elevated CO2 on transpiration efficiency should reduce yield sensitivity to EDD in the coming decades, but at most by 25%.
Sugarcane area is currently expanding in Brazil, largely in response to domestic and international demand for sugar-based ethanol. To investigate the potential hydroclimatic impacts of future expansion, a regional climate model is used to simulate 5 years of a scenario in which cerrado and cropland areas (~1.1E6 km2) within south-central Brazil are converted to sugarcane. Results indicate a cooling of up to ~1.0°C during the peak of the growing season, mainly as a result of increased albedo of sugarcane relative to the previous landscape. After harvest, warming of similar magnitude occurs from a significant decline in evapotranspiration and a repartitioning toward greater sensible heating. Overall, annual temperature changes from large-scale conversion are expected to be small because of offsetting reductions in net radiation absorption and evapotranspiration. The decline in net water flux from land to the atmosphere implies a reduction in regional precipitation, which is consistent with progressively decreasing simulated average rainfall for the study period, upon conversion to sugarcane. However, rainfall changes were not robust across three ensemble members. The results suggest that sugarcane expansion will not drastically alter the regional energy or water balance, but could result in important local and seasonal effects.
