Usually, increasing agricultural productivity depends on adding something, such as fertilizer or water. A new Stanford University-led study reveals that removing one thing in particular – a common air pollutant – could lead to dramatic gains in crop yields. The analysis, published June 1 in Science Advances, uses satellite images to reveal for the first time how nitrogen oxides – gases found in car exhaust and industrial emissions – affect crop productivity. Its findings have important implications for increasing agricultural output and analyzing climate change mitigation costs and benefits around the world.

“Nitrogen oxides are invisible to humans, but new satellites have been able to map them with incredibly high precision. Since we can also measure crop production from space, this opened up the chance to rapidly improve our knowledge of how these gases affect agriculture in different regions,” said study lead author David Lobell, the Gloria and Richard Kushel Director of Stanford’s Center on Food Security and the Environment.

A NOx-ious problem

Nitrogen oxides, or NOx, are among the most widely emitted pollutants in the world. These gases can directly damage crop cells and indirectly affect them through their role as precursors to formation of ozone, an airborne toxin known to reduce crop yields, and particulate matter aerosols that can absorb and scatter sunlight away from crops.

While scientists have long had a general understanding of nitrogen oxides’ potential for damage, little is known about their actual impacts on agricultural productivity. Past research has been limited by a lack of overlap between air monitoring stations and agricultural areas, and confounding effects of different pollutants, among other challenges to ground-based analysis.

To avoid these limitations, Lobell and his colleagues combined satellite measures of crop greenness and nitrogen dioxide levels for 2018-2020. Nitrogen dioxide is the primary form of NOx and a good measure of total NOx. Although NOx is invisible to humans, nitrogen dioxide has a distinct interaction with ultraviolet light that has enabled satellite measurements of the gas at a much higher spatial and temporal resolution than for any other air pollutant.

“In addition to being more easily measured than other pollutants, nitrogen dioxide has the nice feature of being a primary pollutant, meaning it is directly emitted rather than formed in the atmosphere,” said study co-author Jennifer Burney, an associate professor of environmental science at the University of California, San Diego. “That means relating emissions to impacts is much more straightforward than for other pollutants.”

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Calculating crop impacts

Based on their observations, the researchers estimated that reducing NOx emissions by about half in each region would improve yields by about 25% for winter crops and 15% for summer crops in China, nearly 10% for both winter and summer crops in Western Europe, and roughly 8% for summer crops and 6% for winter crops in India. North and South America generally had the lowest NOx exposures. Overall, the effects seemed most negative in seasons and locations where NOx likely drives ozone formation.

“The actions you would take to reduce NOx, such as vehicle electrification, overlap closely with the types of energy transformations needed to slow climate change and improve local air quality for human health,” said Burney. “The main take-home from this study is that the agricultural benefits of these actions could be really substantial, enough to help ease the challenge of feeding a growing population.”

Previous research by Lobell and Burney estimated reductions in ozone, particulate matter, nitrogen dioxide, and sulfur dioxide between 1999 and 2019 contributed to about 20% of the increase in U.S. corn and soybean yield gains during that period – an amount worth about $5 billion per year.

Future analysis could incorporate other satellite observations, including photosynthetic activity measured through solar-induced fluorescence, to better understand nitrogen dioxide’s effects on crops’ varying degrees of sensitivity to the gas throughout the growing season, according to the researchers. Similarly, more detailed examination of other pollutants, such as sulfur dioxide and ammonia, as well as meteorological variables, such as drought and heat, could help to explain why nitrogen dioxide affects crops differently across different regions, years, and seasons.

“It’s really exciting how many different things can be measured from satellites now, much of it coming from new European satellites,” said study coauthor Stefania Di Tommaso, a research data analyst at Stanford’s Center on Food Security and the Environment. “As the data keep improving, it really drives us to be more ambitious and creative as scientists in the types of questions we ask.”
 

Lobell is also a professor of Earth system science in Stanford’s School of Earth, Energy & Environmental Sciences, 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 and the Stanford Institute for Economic Policy Research. Burney also holds the Marshall Saunders Chancellor’s Endowed Chair in Global Climate Policy and Research at UC San Diego and is a research affiliate at UC San Diego’s Policy Design and Evaluation Laboratory, a fellow at the Stanford Center on Food Security and the Environment, and head of the Science Policy Fellows Program at UC San Diego.

When David Relman learned in April that he was elected to the American Academy of Arts and Sciences, he was humbled – and a bit surprised. 

Relman is a senior fellow at the Center for International Security and Cooperation and the Thomas C. and Joan M. Merigan Professor and a professor of medicine and of microbiology & immunology. AAA&S honors exceptional scholars, leaders, artists, and innovators engaged in advancing the public good. 

When he received notification, Relman went to the organization’s web site to check on the discipline area and specialty with which he was affiliated. 

“I looked at the areas and specialties that pertained to my background and expertise (medical sciences, microbiology and immunology, other aspects of the biological sciences), but I could not find my name,” he said. “I thought that maybe the notification was in error.” Then he looked more closely at AAA&S’s letter, and found that his nominators had proposed the “public affairs and public policy section.” 

Arguably that distinction truly reflects Relman’s wide-ranging and serious policy impact in biosecurity, as well as his groundbreaking career work on the nature of the human indigenous microbiota (microbiome). AAA&S’ section of 220 policy luminaries includes former President Barack Obama, former Secretary of Labor Robert Reich, and former Secretary of State Madeleine Albright. Indeed, Relman’s extensive knowledge in microbiology and immunology has played key roles on several critical U.S. and international policy fronts – most recently, the pandemic. 

 Boundless curiosity 

“When you consider the history of the academy and its origins in 1780 during the American Revolution by John Adams and John Hancock, it’s really quite awe-inspiring. You’re joining those who follow in that history,” said Relman, who received an S.B. (Biology) from MIT, M.D. from Harvard Medical School, and joined the faculty at Stanford in 1994. 

Relman’s scholarship is characterized by boundless curiosity – he asks the deeper questions about the pandemic, about human-microbial relationships – both beneficial and harmful, and what they portend for humanity and the future of life on Earth. With grace and diligence, he’s explored the assembly, diversity, stability, and resilience of human microbial communities, while collaborating with other scholars and policy makers on issues paramount to humanity. 

“When I step back and think about the pandemic, it’s clear that it is about much more than just the virus, but also about the social, political, and environmental factors that contribute to the emergence and impact of such pathogens,” said Relman, currently director of a Biosecurity and Global Health initiative at FSI. 

Why do pandemics and more localized outbreaks arise, and how do they uniquely manifest themselves, he ponders. 

“What are the factors that underlie these events, and can we anticipate them better? We much consider three categories of factors: One, is the microbes themselves – and microbes evolve and find ways to do new things. The second category is the hosts – humans, plants, and animals. And humans are undertaking new activities as individuals and as populations that tend to make us more vulnerable, such as immune suppressing ourselves to treat cancer and autoimmune disorders and crowding ourselves into megacities. The third is environmental, and that relates to climate change, and our changing use of land, such as deforestation, intrusion into previously isolated habitats, and other factors,” Relman said. 

Intrusion into new habitats, making contact with animal hosts such as bats that harbor potential disease-causing microbes and viruses, and then bringing these potential pathogens into a lab where we manipulate and alter these agents can lead to human error and accidents, not without grave consequence. “The choices we make in an effort to understand the world around us all come with risk,” he said. 

As far as the microbes and viruses go, “transmissibility is the key,” Relman said. The COVID pandemic reinforced this view for him. 

“When you see what happens when a virus can travel around the globe so quickly, transmissibility has to be viewed as the critical attribute. Viruses evolve and can outrun anything that we might throw in their way, even when we’re already prepared. So, we have to be agile, quick, and shrewd, and we desperately need a far better public health system across the globe that can respond and implement needed measures much more quickly.” 

It’s not just drugs and vaccines and science when it comes to tackling a pandemic. “It’s the social factors, the political factors, and the willingness of humans to work together, and trust, respect and believing in each other. We’ve learned the hard way that this is a tall order. Sometimes we really don’t work together very well,” he said. 

Long-view perspectives 

Relman quotes Joshua Lederberg, a Nobel Prize-winning geneticist and Stanford professor on this age-old war between humanity and viruses: 

“The future of humanity and microbes likely will unfold as episodes of a suspense thriller that could be titled, ‘Our Wits Versus Their Genes,’” Lederberg wrote in an essay, “Infectious History,” in 2000. 

That perspective inspires Relman, who considers this suspense thriller with open eyes and an open mind – digging deeply into complex scientific challenges while understanding long-view perspectives. 

“If you step back in time and consider the history of this planet,” he said, “realize the Earth is about 4.6 billion years old. The earliest life forms we know of were microscopic organisms (microbes) that left signs of their presence in rocks at least 3.7 billion years ago. They have had literally billions of years to diversify, adapt, and secure niches – including on and in animals.” 

On the other hand, modern humans (homo sapiens) have been around for only 200,000 years. “So, we’ve basically been here for the last 3 or 4 seconds of a 24-hour period that started with the formation of Earth. Compare this to microbial life, which has been here for more than 19 hours of this 24-hour period, and will be continue to persist and evolve on this planet for far longer than humanity,” Relman said. 

Relman contemplates and studies the intricacies of the human-microbe relationship, and delves into the issue of how do “favorable” relationships become established, whose interests do they serve, and how can they be supported or restored? 

“This is fundamental to my laboratory work. And why do those relationships sometimes go off the rails? What causes an unusual turn of events such as pandemics? And in what ways and for what reasons do humans mess with these storylines and relationships with these microbes? Those are the puzzles and mysteries that intrigue me,” he said. 

Health equity is a major concern for Relman. Pandemics and public health crises invariably result in harsher consequences for underserved populations than more privileged ones. Many of these communities lack ready access to vaccines, treatments and safeguards, and suffer more disproportionate economic and social turmoil. This is true regardless of how a pandemic arises, including and especially those that might arise because of irresponsible or deliberately malevolent human activities. 

“Subsequent generations are going to be looking at how we’ve handled this pandemic across society, especially for the underserved,” Relman said. “We need to, and can do, much better on this front.” 

Relman was a long-time volunteer for the Rock Medicine program organized by the Haight Ashbury Free Clinics, a free health care service provider serving more than 34,000 people who need access to quality medical care. He served as the chief medical officer for the program for more than a decade. In the 1990s he was featured on MTV for his work providing free medical care at concerts through the program. “Don’t get me started on the dangers of mosh pits,” he once said. 

Scientific truth-telling 

A pioneer in his field, Relman’s research paper on bacillary angiomatosis and a method for the discovery of new pathogens was selected as “one of the 50 most important publications of the 

past century” by the American Society for Microbiology. In other research, ecological theory and predictions are tested in clinical studies with multiple approaches for characterizing the human microbiome. His work has led to the development of molecular methods for identifying novel microbial pathogens, and the subsequent identification of several historically important microbial disease agents. He was one of the first to characterize microbial diversity in the human body using modern molecular methods. Relman is also the Chief of Infectious Diseases at the Veterans Affairs Palo Alto Health Care System in Palo Alto, California, and served as science co-director at CISAC from 2013-2017. 

During the pandemic, scientific knowledge has been expressed in many ways – but political polarization in the U.S. has sometimes worked against crafting sound policy. 

Relman said, “All good scientists know what they’re good at. You need to be very mindful about what you know and what you don’t know. While people are pretty quick to say what they know, they’re not terribly quick to admit what they don’t know. This goes to the issue of ‘lanes’ and the roles of scientists in policy formulation.” 

Many scientists, he added, may think that scientific information alone determines the ultimate public policy. “But it’s only a piece of it. Lots of other factors go into policy, such as social, cultural, political, and economic considerations,” he said. 

National security policy 

Relman served as vice-chair of the National Academy of Sciences Committee that reviewed the science performed as part of the FBI investigation of the 2001 “Anthrax Letters.” He’s also been a member of the National Science Advisory Board on Biosecurity, and was president of the Infectious Diseases Society of America. He is currently a member of the Intelligence Community Studies Board and the Committee on Emerging Infectious Diseases and 21st Century Health Threats, both at the National Academies of Science, as well as the Science and Security Board of the Bulletin of Atomic Scientists and the Defense Science Board at the Pentagon. He received an NIH Pioneer Award, an NIH Transformative Research Award, and was elected a member of the National Academy of Medicine in 2011. 

He also chaired and led the work on the National Academies of Science 2020 report on “Havana syndrome,” cases of unexplained health disorders – aka, “anomalous health incidents” – among U.S. government personnel and their families at overseas embassies. Their findings pointed to a “plausible role of directed, pulsed radiofrequency energy,” though “no hypothesis has been proven, and the circumstances remain unclear.” 

Relman said, “I think that we’re going to be facing challenges like this one, that is, complex poorly-explained health problems at the interface of emerging science and national security, more frequently, and that’s what I’ve told our national leadership.” In the report, the scientists wrote, “We as a nation need to address these specific cases as well as the possibility of future cases with a concerted, coordinated, and comprehensive approach.” 

Megan Palmer, the executive director of the Bio Policy & Leadership Initiatives and Relman’s longtime colleague, said, “David is an exceptional scientist, mentor, colleague and friend. He is deeply thoughtful, especially about the role of science and scientists in society, and he is committed to work with integrity for the service of others. He is compelled to tackle the most difficult problems with great care, and he inspires others to follow suit. I am so grateful for his mentorship; he believes in and brings out the best in people.”