A Stanford-led team has discovered how to estimate crop yields with more accuracy than ever before with satellites that measure a special form of light emitted by plants. This breakthrough will help scientists study how crops respond to climate change. 

As Earth's population grows toward a projected 9 billion by 2050 and climate change puts growing pressure on the world's agriculture, researchers are turning to technology to help safeguard the global food supply.

A research team, led by Kaiyu Guan, a postdoctoral fellow in Earth system science at Stanford's School of Earth, Energy, & Environmental Sciences, has developed a method to estimate crop yields using satellites that can measure solar-induced fluorescence, a light emitted by growing plants. The team published its results in the journal Global Change Biology.

Scientists have used satellites to collect agricultural data since 1972, when the National Aeronautics and Space Administration (NASA) pioneered the practice of using the color – or "greenness" – of reflected sunlight to map plant cover over the entire globe.

"This was an amazing breakthrough that fundamentally changed the way we view our planet," said Joe Berry, professor of global ecology at the Carnegie Institution for Science and a co-author of the study. "However, these vegetation maps are not ideal predictors of crop productivity. What we need to know is growth rate rather than greenness.

The growth rate can tell researchers what size yield to expect from crops by the end of the growing season. The higher the growth rate of a soybean plant or stalk of corn, for instance, the greater the harvest from a mature plant.

"What we need to measure is flux – the carbon dioxide that is exchanged between plants and the atmosphere – to understand photosynthesis and plant growth," Guan said. "How do you use color to infer flux? That's a big gap."  
 

Solar-induced fluorescence

Recently, researchers at NASA and several European institutes discovered how to measure this flux, called solar-induced fluorescence, from satellites that were originally designed for measuring ozone and other gases in the atmosphere.

A plant uses most of the energy it absorbs from the sun to grow via photosynthesis, and dissipates unused energy as heat. It also passively releases between 1 and 2 percent of the original solar energy absorbed by the plant back into the atmosphere as fluorescent light. Guan's team worked out how to distinguish the tiny flow of specific fluorescence from the abundance of reflected sunlight that also arrives at the satellite.

"I think of it like crumbs falling to the ground as people are eating. It's a very small trail," said co-author David Lobell, associate professor of Earth system science at Stanford's School of Earth, Energy, & Environmental Science. "This glow that plants have seems to be very proportional to how fast they're growing. So the more they're growing, the more photosynthesis they're doing, and the brighter they're fluorescing." Lobell is also deputy director of the Center on Food Security and the Environment.

The research team saw an opportunity to use this new data to close the knowledge gap about crop growth, beginning with a major corn- and soybean-producing region of the U.S. Midwest.

"With the fluorescence breakthrough, we can start to directly measure photosynthesis instead of color," Guan said.

The fact that fluorescence can now be detected from space allows researchers to measure plant growth across much larger areas and over long periods of time, giving a much clearer picture of how yields fluctuate under changing weather conditions.

"One of the really cool things about fluorescence is that it opens up a whole new set of questions that we can ask about vegetation, and often times it's these new measurements that drive the science forward," Lobell said.  
 

Next steps

The research team has already identified a number of potential uses of this approach by agricultural scientists, farmers, crop insurance providers and government agencies concerned with agricultural productivity.

If there is a day when the plant is really stressed, the fluorescence will drop significantly, Lobell said. Capturing these short-term responses to environmental changes will help scientists understand what factors plants are responding to on the daily time scale.

"That helps us, for example, figure out what we need to worry about in terms of stresses that crops are responding to," Lobell said. "What should we really be focusing on in terms of the next generation of cropping systems? What should they be able to withstand that the current crops can't withstand?"

At this early stage, fluorescence measurements are relatively low-resolution (a single measurement covers about 50 square kilometers) and because it is only collected once per day, cloudy skies can interfere with the fluorescence signal. For now, researchers have to supplement the data with other information and with on-the-ground observations to refine the measurements.

"Now that we have demonstrated the concept, we hope to soon be orbiting some new satellites specifically designed to make fluorescence measurements with better spatial and temporal resolution," Berry said.

The team plans to continue its research on U.S. crop yields while expanding measurements to other parts of the world.

"In the future, we hope to directly use this technology to monitor global food production, for example in China or Brazil, or even in your backyard," Guan said.

David Lobell is also deputy director of the Center on Food Security and the Environment, and William Wrigley Senior Fellow at the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment. The study was also co-authored by Youngguan Zhang of the International Institute for Earth System Sciences at Nanjing University and the German Research Center for Geosciences (GFZ); Joanna Joiner of the NASA Goddard Space Flight Center Laboratory for Atmospheric Chemistry and Dynamics; Luis Guanter of GFZ; and Grayson Badgley of Stanford's Department of Earth System Science and Department of Global Ecology at the Carnegie Institution for Science.

CONTACTS:   
 

p> Kaiyu Guan, Stanford School of Earth, Energy, & Environmental Sciences: kaiyug@stanford.edu

Laura Seaman, Stanford's Center on Food Security and the Environment: lseaman@stanford.edu, (650) 723-4920

Stanford students belong to the first generation that could witness the end of extreme global poverty — in what would be one of humankind's greatest achievements — the head of the World Bank said during a recent talk on campus.

But their generation, he said, is also likely to experience the first global pandemic since the 1918 influenza that killed more than 50 million people.

Jim Yong Kim, president of the World Bank, said innovations in health, education and finance are behind the World Bank's twin goals of ending extreme poverty and boosting shared prosperity for the bottom 40 percent of the global population.

Speaking at the inaugural conference of the Stanford Global Development and Poverty Initiative on Oct. 29, Kim lauded faculty and students for their multidisciplinary approach in tackling poverty and improving public health. He is an infectious disease physician who oversaw World Health Organization initiatives on HIV/AIDS.

"Seeking transformative solutions to challenges of development and poverty that are necessarily cross-disciplinary is exactly what a great university should be doing," Kim said in his speech at Stanford.

The World Bank announced last month that the number of people living on less than $1.90 a day is expected to drop to 9.6 percent of the global population by the end of the year. That is down from 36 percent in 1990.

The bank has pledged to cut that rate to 3 percent by 2030.

"We expect the extreme poverty rate to drop below 10 percent for the first time in human history," he said. "This is the best news in the world today. And this is the first generation in human history that has been able to see that potential outcome." 

Promoting prosperity

One of the co-founders of Partners in Health, Kim was the keynote speaker at the daylong conference, "Shared Prosperity and Health," which drew together Stanford faculty and researchers, plus government and NGO officials from around the world.

Stanford's global development and poverty effort is a university-wide initiative of the Stanford Institute for Innovation in Developing Economies, known as Stanford Seed, and the Freeman Spogli Institute for International Studies. The conference was held at Stanford's Graduate School of Business, which was a partner in the event.

Kim's talk was optimistic about the newly adopted U.N. Sustainable Development Goals, with an ambitious agenda to end poverty and hunger, ensure healthy lives, empower women and girls and attain quality education for all children by 2030.

While those goals seem lofty, Kim pointed to the accomplishment of bringing down extreme poverty to 10 percent, a figure many had once said was impossible.

Ninety-one percent of children in developing countries now attend primary school, up from 83 percent in 2000, he said. And the number of people on antiretroviral drugs for treatment of HIV in sub-Saharan Africa has increased eightfold in the last decade.

"But we're humbled by the challenges ahead," Kim said. "Rising global temperatures will have devastating impacts on poor countries and poor people – and, as we saw with Ebola, major pandemics are likely to disproportionately affect the poor."

Pandemic threats

Kim said that most virologists and infectious disease experts are certain a pandemic will sweep the world in the next 30 years. He said that would lead to more than 30 million deaths and anywhere from 5 to 10 percent of lost GDP.

He blasted the global community for taking eight months to respond to the Ebola crisis in West Africa, noting that Guinea, Sierra Leone and Liberia had among the fastest growing economies in Africa before the outbreak killed more than 11,000 people – most of whom were poor.

In an effort to speed up financial aid the next time such an outbreak occurs, the World Bank is developing the Pandemic Emergency Facility, which would disburse funding immediately to national governments and responding agencies.

Rajiv Shah, the administrator for the U.S. Agency for International Development from 2010-2015, spoke earlier at the conference about his work leading the U.S. efforts to contain Ebola.

"Three small countries with total population of maybe 30 million people had such weak health systems with so little domestic investment – in one country $6 per capita health investment per year – that when Ebola became a crisis there was no first-line of defense," he said.

By October 2014, the U.S. was pouring hundreds of millions of dollars into containment efforts, including the establishment of a 2,500-personnel military deployment to hit Ebola on the ground. Shah said President Obama "stayed extraordinarily true to the science" of containment at the source.

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Stunted children 

Moving beyond containment of epidemics, Kim said the most important investment developing countries could make in their people starts when a woman becomes pregnant. Using a combination of health, nutrition and education will have lifelong benefits for each child, as well as for the country in which each prospers.

The World Bank estimates that 26 percent of all children under age 5 in developing countries are stunted, which means they are malnourished and under-stimulated, risking a loss of cognitive abilities that lasts a lifetime. The number climbs to 36 percent in sub-Saharan Africa, giving those children limited prospects in life."This is a disgrace, a global scandal and, in my view, akin to a medical emergency," Kim said. "Children who are stunted by age 5 will not have an equal opportunity in life. If your brain won't let you learn and adapt in a fast-changing world, you won't prosper and, neither will society. All of us lose."

From 2001 to 2013, the World Bank invested $3.3 billion in early childhood development programs in poor countries. Kim said innovative policymaking and financial tools allowed the bank to help Peru cut its rate of child stunting in half to 14 percent in just eight years.

"Progress is possible – and it can happen quickly. But we must do even more,"he said.

Kim said the world set a target in 2012 to reduce stunting in children by 40 percent. But that would still leave 100 million children malnourished and undereducated. The bank and world leaders should pledge to end stunting for all children by 2030, he said.

"With partners like the Global Development and Poverty Initiative and the entire Stanford community, I'm full of hope that we can indeed be the first generation in human history to end extreme poverty and create a more just and prosperous world for everyone on the planet."

Read more here about another innovation to improve health in the developing world.