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    Ancient Amazonians intentionally created fertile “dark earth”

    The Amazon river basin is known for its immense and lush tropical forests, so one might assume that the Amazon’s land is equally rich. In fact, the soils underlying the forested vegetation, particularly in the hilly uplands, are surprisingly infertile. Much of the Amazon’s soil is acidic and low in nutrients, making it notoriously difficult to farm.

    But over the years, archaeologists have dug up mysteriously black and fertile patches of ancient soils in hundreds of sites across the Amazon. This “dark earth” has been found in and around human settlements dating back hundreds to thousands of years. And it has been a matter of some debate as to whether the super-rich soil was purposefully created or a coincidental byproduct of these ancient cultures.

    Now, a study led by researchers at MIT, the University of Florida, and in Brazil aims to settle the debate over dark earth’s origins. The team has pieced together results from soil analyses, ethnographic observations, and interviews with modern Indigenous communities, to show that dark earth was intentionally produced by ancient Amazonians as a way to improve the soil and sustain large and complex societies.

    “If you want to have large settlements, you need a nutritional base. But the soil in the Amazon is extensively leached of nutrients, and naturally poor for growing most crops,” says Taylor Perron, the Cecil and Ida Green Professor of Earth, Atmospheric and Planetary Sciences at MIT. “We argue here that people played a role in creating dark earth, and intentionally modified the ancient environment to make it a better place for human populations.”

    And as it turns out, dark earth contains huge amounts of stored carbon. As generations worked the soil, for instance by enriching it with scraps of food, charcoal, and waste, the earth accumulated the carbon-rich detritus and kept it locked up for hundreds to thousands of years. By purposely producing dark earth, then, early Amazonians may have also unintentionally created a powerful, carbon-sequestering soil.

    “The ancient Amazonians put a lot of carbon in the soil, and a lot of that is still there today,” says co-author Samuel Goldberg, who performed the data analysis as a graduate student at MIT and is now an assistant professor at the University of Miami. “That’s exactly what we want for climate change mitigation efforts. Maybe we could adapt some of their indigenous strategies on a larger scale, to lock up carbon in soil, in ways that we now know would stay there for a long time.”

    The team’s study appears today in Science Advances. Other authors include former MIT postdoc and lead author Morgan Schmidt, anthropologist Michael Heckenberger of the University of Florida, and collaborators from multiple institutions across Brazil.

    Modern intent

    In their current study, the team synthesized observations and data that Schmidt, Heckenberger, and others had previously gathered, while working with Indigenous communities in the Amazon since the early 2000s,  with new data collected in 2018-19. The scientists focused their fieldwork in the Kuikuro Indigenous Territory in the Upper Xingu River basin in the southeastern Amazon. This region is home to modern Kuikuro villages as well as archaeological sites where the ancestors of the Kuikuro are thought to have lived. Over multiple visits to the region, Schmidt, then a graduate student at the University of Florida, was struck by the darker soil around some archaeological sites.

    “When I saw this dark earth and how fertile it was, and started digging into what was known about it, I found it was a mysterious thing — no one really knew where it came from,” he says.

    Schmidt and his colleagues began making observations of the modern Kuikuro’s practices of managing the soil. These practices include generating “middens” — piles of waste and food scraps, similar to compost heaps, that are maintained in certain locations around the center of a village. After some time, these waste piles decompose and mix with the soil to form a dark and fertile earth, that residents then use to plant crops. The researchers also observed that Kuikuro farmers spread organic waste and ash on farther fields, which also generates dark earth, where they can then grow more crops.

    “We saw activities they did to modify the soil and increase the elements, like spreading ash on the ground, or spreading charcoal around the base of the tree, which were obviously intentional actions,” Schmidt says.

    In addition to these observations, they also conducted interviews with villagers to document the Kuikuro’s beliefs and practices relating to dark earth. In some of these interviews, villagers referred to dark earth as “eegepe,” and described their daily practices in creating and cultivating the rich soil to improve its agricultural potential.

    Based on these observations and interviews with the Kuikuro, it was clear that Indigenous communities today intentionally produce dark earth, through their practices to improve the soil. But could the dark earth found in nearby archaeological sites have been made through similar intentional practices?

    A bridge in soil

    In search of a connection, Schmidt joined Perron’s group as a postdoc at MIT. Together, he, Perron, and Goldberg carried out a meticulous analysis of soils in both archaeological and modern sites in the Upper Xingu region. They discovered similarities in dark earth’s spatial structure: Deposits of dark earth were found in a radial pattern, concentrating mostly in the center of both modern and ancient settlements, and stretching, like spokes of a wheel, out to the edges. Modern and ancient dark earth was also similar in composition, and was enriched in the same elements, such as carbon, phosphorus, and other nutrients.

    “These are all the elements that are in humans, animals, and plants, and they’re the ones that reduce the aluminum toxicity in soil, which is a notorious problem in the Amazon,” Schmidt says. “All these elements make the soil better for plant growth.”

    “The key bridge between the modern and ancient times is the soil,” Goldberg adds. “Because we see this correspondence between the two time periods, we can infer that these practices that we can observe and ask people about today, were also happening in the past.”

    In other words, the team was able to show for the first time that ancient Amazonians intentionally worked the soil, likely through practices similar to today’s, in order to grow enough crops to sustain large communities.

    Going a step further, the team calculated the amount of carbon in ancient dark earth. They combined their measurements of soil samples, with maps of where dark earth has been found through several ancient settlements. Their estimates revealed that each ancient village contains several thousand tons of carbon that has been sequestered in the soil for hundreds of years as a result of Indigenous, human activities.

    As the team concludes in their paper, “modern sustainable agriculture and climate change mitigation efforts, inspired by the persistent fertility of ancient dark earth, can draw on traditional methods practiced to this day by Indigenous Amazonians.”

    This research at MIT was supported, in part, by the Abdul Latif Jameel Water and Food Systems Lab and the Department of the Air Force Artificial Intelligence Accelerator. Field research was supported by grants to the University of Florida from the National Science Foundation, the Wenner-Gren Foundation and the William Talbott Hillman Foundation, and was sponsored in Brazil by the Museu Goeldi and Museu Nacional. More

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    Fast-tracking fusion energy’s arrival with AI and accessibility

    As the impacts of climate change continue to grow, so does interest in fusion’s potential as a clean energy source. While fusion reactions have been studied in laboratories since the 1930s, there are still many critical questions scientists must answer to make fusion power a reality, and time is of the essence. As part of their strategy to accelerate fusion energy’s arrival and reach carbon neutrality by 2050, the U.S. Department of Energy (DoE) has announced new funding for a project led by researchers at MIT’s Plasma Science and Fusion Center (PSFC) and four collaborating institutions.

    Cristina Rea, a research scientist and group leader at the PSFC, will serve as the primary investigator for the newly funded three-year collaboration to pilot the integration of fusion data into a system that can be read by AI-powered tools. The PSFC, together with scientists from the College of William and Mary, the University of Wisconsin at Madison, Auburn University, and the nonprofit HDF Group, plan to create a holistic fusion data platform, the elements of which could offer unprecedented access for researchers, especially underrepresented students. The project aims to encourage diverse participation in fusion and data science, both in academia and the workforce, through outreach programs led by the group’s co-investigators, of whom four out of five are women. 

    The DoE’s award, part of a $29 million funding package for seven projects across 19 institutions, will support the group’s efforts to distribute data produced by fusion devices like the PSFC’s Alcator C-Mod, a donut-shaped “tokamak” that utilized powerful magnets to control and confine fusion reactions. Alcator C-Mod operated from 1991 to 2016 and its data are still being studied, thanks in part to the PSFC’s commitment to the free exchange of knowledge.

    Currently, there are nearly 50 public experimental magnetic confinement-type fusion devices; however, both historical and current data from these devices can be difficult to access. Some fusion databases require signing user agreements, and not all data are catalogued and organized the same way. Moreover, it can be difficult to leverage machine learning, a class of AI tools, for data analysis and to enable scientific discovery without time-consuming data reorganization. The result is fewer scientists working on fusion, greater barriers to discovery, and a bottleneck in harnessing AI to accelerate progress.

    The project’s proposed data platform addresses technical barriers by being FAIR — Findable, Interoperable, Accessible, Reusable — and by adhering to UNESCO’s Open Science (OS) recommendations to improve the transparency and inclusivity of science; all of the researchers’ deliverables will adhere to FAIR and OS principles, as required by the DoE. The platform’s databases will be built using MDSplusML, an upgraded version of the MDSplus open-source software developed by PSFC researchers in the 1980s to catalogue the results of Alcator C-Mod’s experiments. Today, nearly 40 fusion research institutes use MDSplus to store and provide external access to their fusion data. The release of MDSplusML aims to continue that legacy of open collaboration.

    The researchers intend to address barriers to participation for women and disadvantaged groups not only by improving general access to fusion data, but also through a subsidized summer school that will focus on topics at the intersection of fusion and machine learning, which will be held at William and Mary for the next three years.

    Of the importance of their research, Rea says, “This project is about responding to the fusion community’s needs and setting ourselves up for success. Scientific advancements in fusion are enabled via multidisciplinary collaboration and cross-pollination, so accessibility is absolutely essential. I think we all understand now that diverse communities have more diverse ideas, and they allow faster problem-solving.”

    The collaboration’s work also aligns with vital areas of research identified in the International Atomic Energy Agency’s “AI for Fusion” Coordinated Research Project (CRP). Rea was selected as the technical coordinator for the IAEA’s CRP emphasizing community engagement and knowledge access to accelerate fusion research and development. In a letter of support written for the group’s proposed project, the IAEA stated that, “the work [the researchers] will carry out […] will be beneficial not only to our CRP but also to the international fusion community in large.”

    PSFC Director and Hitachi America Professor of Engineering Dennis Whyte adds, “I am thrilled to see PSFC and our collaborators be at the forefront of applying new AI tools while simultaneously encouraging and enabling extraction of critical data from our experiments.”

    “Having the opportunity to lead such an important project is extremely meaningful, and I feel a responsibility to show that women are leaders in STEM,” says Rea. “We have an incredible team, strongly motivated to improve our fusion ecosystem and to contribute to making fusion energy a reality.” More

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    Putting public service into practice

    Salomé Otero ’23 doesn’t mince words about the social impact internship she had in 2022. “It was transformational for me,” she says.

    Otero, who majored in management with a concentration in education, always felt that education would play some role in her career path after MIT, but she wasn’t sure how. That all changed her junior year, when she got an email from the Priscilla King Gray Public Service Center (PKG Center) about an internship at The Last Mile, a San Francisco-based nonprofit that provides education and technology training for justice-impacted individuals.

    Otero applied and was selected as a web curriculum and re-entry intern at The Last Mile the summer between her junior and senior year — an eye-opening experience that cemented her post-graduation plans. “You hear some amazing stories, like this person was incarcerated before the iPhone had come out. Now he’s a software developer,” she explains. “And for me, the idea of using computer science education for good appealed to me on many fronts. But even if I hadn’t gotten the opportunity to work at The Last Mile, the fact that I saw a job description for this role and learned that companies have the resources to make a difference … I didn’t know that there were people and organizations dedicating their time and energy into this.”

    She was so inspired that, when she returned for her senior year, Otero found work at two education labs at MIT, completed another social impact internship over Independent Activities Period (IAP) at G{Code}, an education nonprofit that provides computer science education to women and nonbinary people of color, and decided to apply to graduate school. “I can tell you with 100 percent certainty that I would not be pursuing a PhD in education policy right now if it weren’t for the PKG Center,” she says. She will begin her doctorate this fall.

    Otero’s experience doesn’t surprise Jill Bassett, associate dean and director of the PKG Center. “MIT students are deeply concerned about the world’s most challenging problems,” she says. “And social impact internships are an incredible way for them to leverage their unique talents and skills to help create meaningful change while broadening their perspectives and discovering potential career paths.”

    “There’s a lot more out there”

    Founded 35 years ago, the PKG Center offers a robust portfolio of experiential learning programs broadly focused on four themes: climate change, health equity, racial justice, and tech for social good. The Center’s Social Impact Internship Program provides funded internships to students interested in working with government agencies, nonprofits, and social ventures. Students reap rich rewards from these experiences, including learning ways to make social change, informing their academic journey and career path, and gaining valuable professional skills.

    “It was a really good learning opportunity,” says Juliet Liao ’23, a graduate of MIT’s Naval ROTC program who commissioned as a submarine officer in June. She completed a social impact internship with the World Wildlife Fund, where she researched greenhouse gas emissions related to the salmon industry. “I haven’t had much exposure to what work outside of the Navy looks like and what I’m interested in working on. And I really liked the science-based approach to mitigating greenhouse gas emissions.”

    Amina Abdalla, a rising junior in biological engineering, arrived at MIT with a strong interest in health care and determined to go to medical school. But her internship at MassHealth, the Medicaid and Children’s Health Insurance Program provider for the state of Massachusetts, broadened her understanding of the complexity of the health care system and introduced her to many career options that she didn’t know existed.

    “They did coffee chats between interns and various people who work in MassHealth, such as doctors, lawyers, policy advocates, and consultants. There’s a lot more out there that one can do with the degree that they get and the knowledge they gain. It just depends on your interests, and I came away from that really excited,” she says. The experience inspired her to take a class in health policy before she graduates. “I know I want to be a doctor and I have a lot of interest in science in general, but if I could do some kind of public sector impact with that knowledge, I would definitely be interested in doing that.”

    Social impact internships also provide an opportunity for students to hone their analytical, technical, and people skills. Selma Sharaf ’22 worked on developing a first-ever climate action plan for Bennett College in Greensboro, North Carolina, one of two all-women’s historically Black colleges and universities in the United States. She conducted research and stakeholder interviews with nonprofits; sustainability directors at similar colleges; local utility companies; and faculty, staff, and students at Bennett.

    “Our external outreach efforts with certain organizations allowed me to practice having conversations about energy justice and climate issues with people who aren’t already in this space. I learned how useful it can be to not only discuss the overall issues of climate change and carbon emissions, but to also zoom in on more relatable personal-level impacts,” she says. Sharaf is currently working in clean energy consulting and plans to pursue a master’s degree at Stanford University’s Atmosphere/Energy Program this fall.

    Working with “all stars”

    Organizations that partner with the PKG Center are often constrained by limited technical and financial resources. Since the program is funded by the PKG Center, these internships help expand their organizational capacity and broaden their impact; MIT students can take on projects that might not otherwise get done, and they also bring fresh skills and ideas to the organization — and the zeal to pursue those ideas.

    Emily Moberg ’11, PhD ’16 got involved with the social impact internship programs in 2020. Moberg, who is the director of Scope 3 Carbon Measurement and Mitigation at the World Wildlife Fund, has worked with 20 MIT students since then, including Liao. The body of work that Liao and several other interns completed has been published in the form of 10 briefs onmitigating greenhouse gas emissions from key commodities, such as soy, beef, coffee, and palm oil.

    “Social impact interns bring technical skills, deep curiosity, and tenacity,” Moberg says. “I’ve worked with students across many majors, including computer and materials science; all of them bring a new, fresh perspective to our problems and often sophisticated quantitative ability. Their presence often helps us to investigate new ideas or expand a project. In some cases, interns have proposed new projects and ideas themselves. The support from the PKG Center for us to host these interns has been critical, especially for these new explorations.”

    Anne Carrington Hayes, associate professor and executive director of the Global Leadership and Interdisciplinary Studies program at Bennett College, calls the MIT interns she’s worked with since 2021 “all stars.” The work Sharaf and three other students performed has culminated in a draft climate action plan that will inform campus renovations and other measures that will be implemented at the college in the coming years.

    “They have been foundational in helping me to research, frame, collect data, and engage with our students and the community around issues of environmental justice and sustainability, particularly from the lens of what would be impactful and meaningful for women of color at Bennett College,” she says.

    Balancing supply and demand

    Bassett says that the social impact internship program has grown exponentially in the past few years. Before the pandemic, the program served five students from summer 2019 to spring 2020; it now serves about 125 students per year. Over that time, funding has become a significant limiting factor; demand for internships was three times the number of available internships in summer 2022, and five times the supply during IAP 2023.

    “MIT students have no shortage of opportunities available to them in the private sector, yet students are seeking social impact internships because they want to apply their skills to issues that they care about,” says Julie Uva, the PKG Center’s program administrator for social impact internships and employment. “We want to ensure every student who wants a social impact internship can access that experience.”

    MIT has taken note of this financial shortfall: the Task Force 2021 report recommended fundraising to alleviate the under-supply of social impact experiential learning opportunities (ELOs), and MIT’s Fast Forward Climate Action Plan called on the Institute to make a climate or clean-energy ELOs available to every undergraduate who wants one. As a result, the Office of Experiential Learning is working with Resource Development to raise new funding to support many more opportunities, which would be available to students not only through the PKG Center but also other offices and programs, such as MIT D-Lab, Undergraduate Research Opportunity Programs, MISTI, and the Environmental Solutions Initiative, among others.

    That’s welcome news to Salomé Otero. She’s familiar with the Institute’s fundraising efforts, having worked as one of the Alumni Association’s Tech Callers. Now, as an alumna herself and a former social impact intern, she has an appreciation for the power of philanthropy.

    “MIT is ahead of the game compared to so many universities, in so many ways,” she says. “But if they want to continue to do that in the most impactful way possible, I think investing in ideas and missions like the PKG Center is the way to go. So when that call comes, I’ll tell whoever is working that night shift, ‘Yeah, I’ll donate to the PKG Center.’” More

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    Explained: The 1.5 C climate benchmark

    The summer of 2023 has been a season of weather extremes.

    In June, uncontrolled wildfires ripped through parts of Canada, sending smoke into the U.S. and setting off air quality alerts in dozens of downwind states. In July, the world set the hottest global temperature on record, which it held for three days in a row, then broke again on day four.

    From July into August, unrelenting heat blanketed large parts of Europe, Asia, and the U.S., while India faced a torrential monsoon season, and heavy rains flooded regions in the northeastern U.S. And most recently, whipped up by high winds and dry vegetation, a historic wildfire tore through Maui, devastating an entire town.

    These extreme weather events are mainly a consequence of climate change driven by humans’ continued burning of coal, oil, and natural gas. Climate scientists agree that extreme weather such as what people experienced this summer will likely grow more frequent and intense in the coming years unless something is done, on a persistent and planet-wide scale, to rein in global temperatures.

    Just how much reining-in are they talking about? The number that is internationally agreed upon is 1.5 degrees Celsius. To prevent worsening and potentially irreversible effects of climate change, the world’s average temperature should not exceed that of preindustrial times by more than 1.5 degrees Celsius (2.7 degrees Fahrenheit).

    As more regions around the world face extreme weather, it’s worth taking stock of the 1.5-degree bar, where the planet stands in relation to this threshold, and what can be done at the global, regional, and personal level, to “keep 1.5 alive.”

    Why 1.5 C?

    In 2015, in response to the growing urgency of climate impacts, nearly every country in the world signed onto the Paris Agreement, a landmark international treaty under which 195 nations pledged to hold the Earth’s temperature to “well below 2 degrees Celsius above pre-industrial levels,” and going further, aim to “limit the temperature increase to 1.5 degrees Celsius above pre-industrial levels.”

    The treaty did not define a particular preindustrial period, though scientists generally consider the years from 1850 to 1900 to be a reliable reference; this time predates humans’ use of fossil fuels and is also the earliest period when global observations of land and sea temperatures are available. During this period, the average global temperature, while swinging up and down in certain years, generally hovered around 13.5 degrees Celsius, or 56.3 degrees Fahrenheit.

    The treaty was informed by a fact-finding report which concluded that, even global warming of 1.5 degrees Celsius above the preindustrial average, over an extended, decades-long period, would lead to high risks for “some regions and vulnerable ecosystems.” The recommendation then, was to set the 1.5 degrees Celsius limit as a “defense line” — if the world can keep below this line, it potentially could avoid the more extreme and irreversible climate effects that would occur with a 2 degrees Celsius increase, and for some places, an even smaller increase than that.

    But, as many regions are experiencing today, keeping below the 1.5 line is no guarantee of avoiding extreme, global warming effects.

    “There is nothing magical about the 1.5 number, other than that is an agreed aspirational target. Keeping at 1.4 is better than 1.5, and 1.3 is better than 1.4, and so on,” says Sergey Paltsev, deputy director of MIT’s Joint Program on the Science and Policy of Global Change. “The science does not tell us that if, for example, the temperature increase is 1.51 degrees Celsius, then it would definitely be the end of the world. Similarly, if the temperature would stay at 1.49 degrees increase, it does not mean that we will eliminate all impacts of climate change. What is known: The lower the target for an increase in temperature, the lower the risks of climate impacts.”

    How close are we to 1.5 C?

    In 2022, the average global temperature was about 1.15 degrees Celsius above preindustrial levels. According to the World Meteorological Organization (WMO), the cyclical weather phenomenon La Niña recently contributed to temporarily cooling and dampening the effects of human-induced climate change. La Niña lasted for three years and ended around March of 2023.

    In May, the WMO issued a report that projected a significant likelihood (66 percent) that the world would exceed the 1.5 degrees Celsius threshold in the next four years. This breach would likely be driven by human-induced climate change, combined with a warming El Niño — a cyclical weather phenomenon that temporarily heats up ocean regions and pushes global temperatures higher.

    This summer, an El Niño is currently underway, and the event typically raises global temperatures in the year after it sets in, which in this case would be in 2024. The WMO predicts that, for each of the next four years, the global average temperature is likely to swing between 1.1 and 1.8 degrees Celsius above preindustrial levels.

    Though there is a good chance the world will get hotter than the 1.5-degree limit as the result of El Niño, the breach would be temporary, and for now, would not have failed the Paris Agreement, which aims to keep global temperatures below the 1.5-degree limit over the long term (averaged over several decades rather than a single year).

    “But we should not forget that this is a global average, and there are variations regionally and seasonally,” says Elfatih Eltahir, the H.M. King Bhumibol Professor and Professor of Civil and Environmental Engineering at MIT. “This year, we had extreme conditions around the world, even though we haven’t reached the 1.5 C threshold. So, even if we control the average at a global magnitude, we are going to see events that are extreme, because of climate change.”

    More than a number

    To hold the planet’s long-term average temperature to below the 1.5-degree threshold, the world will have to reach net zero emissions by the year 2050, according to the Intergovernmental Panel on Climate Change (IPCC). This means that, in terms of the emissions released by the burning of coal, oil, and natural gas, the entire world will have to remove as much as it puts into the atmosphere.

    “In terms of innovations, we need all of them — even those that may seem quite exotic at this point: fusion, direct air capture, and others,” Paltsev says.

    The task of curbing emissions in time is particularly daunting for the United States, which generates the most carbon dioxide emissions of any other country in the world.

    “The U.S.’s burning of fossil fuels and consumption of energy is just way above the rest of the world. That’s a persistent problem,” Eltahir says. “And the national statistics are an aggregate of what a lot of individuals are doing.”

    At an individual level, there are things that can be done to help bring down one’s personal emissions, and potentially chip away at rising global temperatures.

    “We are consumers of products that either embody greenhouse gases, such as meat, clothes, computers, and homes, or we are directly responsible for emitting greenhouse gases, such as when we use cars, airplanes, electricity, and air conditioners,” Paltsev says. “Our everyday choices affect the amount of emissions that are added to the atmosphere.”

    But to compel people to change their emissions, it may be less about a number, and more about a feeling.

    “To get people to act, my hypothesis is, you need to reach them not just by convincing them to be good citizens and saying it’s good for the world to keep below 1.5 degrees, but showing how they individually will be impacted,” says Eltahir, who specializes on the study of regional climates, focusing on how climate change impacts the water cycle and frequency of extreme weather such as heat waves.

    “True climate progress requires a dramatic change in how the human system gets its energy,” Paltsev says. “It is a huge undertaking. Are you ready personally to make sacrifices and to change the way of your life? If one gets an honest answer to that question, it would help to understand why true climate progress is so difficult to achieve.” More

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    Simple superconducting device could dramatically cut energy use in computing, other applications

    MIT scientists and their colleagues have created a simple superconducting device that could transfer current through electronic devices much more efficiently than is possible today. As a result, the new diode, a kind of switch, could dramatically cut the amount of energy used in high-power computing systems, a major problem that is estimated to become much worse. Even though it is in the early stages of development, the diode is more than twice as efficient as similar ones reported by others. It could even be integral to emerging quantum computing technologies.

    The work, which is reported in the July 13 online issue of Physical Review Letters, is also the subject of a news story in Physics Magazine.

    “This paper showcases that the superconducting diode is an entirely solved problem from an engineering perspective,” says Philip Moll, director of the Max Planck Institute for the Structure and Dynamics of Matter in Germany. Moll was not involved in the work. “The beauty of [this] work is that [Moodera and colleagues] obtained record efficiencies without even trying [and] their structures are far from optimized yet.”

    “Our engineering of a superconducting diode effect that is robust and can operate over a wide temperature range in simple systems can potentially open the door for novel technologies,” says Jagadeesh Moodera, leader of the current work and a senior research scientist in MIT’s Department of Physics. Moodera is also affiliated with the Materials Research Laboratory, the Francis Bitter Magnet Laboratory, and the Plasma Science and Fusion Center (PSFC).

    The nanoscopic rectangular diode — about 1,000 times thinner than the diameter of a human hair — is easily scalable. Millions could be produced on a single silicon wafer.

    Toward a superconducting switch

    Diodes, devices that allow current to travel easily in one direction but not in the reverse, are ubiquitous in computing systems. Modern semiconductor computer chips contain billions of diode-like devices known as transistors. However, these devices can get very hot due to electrical resistance, requiring vast amounts of energy to cool the high-power systems in the data centers behind myriad modern technologies, including cloud computing. According to a 2018 news feature in Nature, these systems could use nearly 20 percent of the world’s power in 10 years.

    As a result, work toward creating diodes made of superconductors has been a hot topic in condensed matter physics. That’s because superconductors transmit current with no resistance at all below a certain low temperature (the critical temperature), and are therefore much more efficient than their semiconducting cousins, which have noticeable energy loss in the form of heat.

    Until now, however, other approaches to the problem have involved much more complicated physics. “The effect we found is due [in part] to a ubiquitous property of superconductors that can be realized in a very simple, straightforward manner. It just stares you in the face,” says Moodera.

    Says Moll of the Max Planck Institute, “The work is an important counterpoint to the current fashion to associate superconducting diodes [with] exotic physics, such as finite-momentum pairing states. While in reality, a superconducting diode is a common and widespread phenomenon present in classical materials, as a result of certain broken symmetries.”

    A somewhat serendipitous discovery

    In 2020 Moodera and colleagues observed evidence of an exotic particle pair known as Majorana fermions. These particle pairs could lead to a new family of topological qubits, the building blocks of quantum computers. While pondering approaches to creating superconducting diodes, the team realized that the material platform they developed for the Majorana work might also be applied to the diode problem.

    They were right. Using that general platform, they developed different iterations of superconducting diodes, each more efficient than the last. The first, for example, consisted of a nanoscopically thin layer of vanadium, a superconductor, which was patterned into a structure common to electronics (the Hall bar). When they applied a tiny magnetic field comparable to the Earth’s magnetic field, they saw the diode effect — a giant polarity dependence for current flow.

    They then created another diode, this time layering a superconductor with a ferromagnet (a ferromagnetic insulator in their case), a material that produces its own tiny magnetic field. After applying a tiny magnetic field to magnetize the ferromagnet so that it produces its own field, they found an even bigger diode effect that was stable even after the original magnetic field was turned off.

    Ubiquitous properties

    The team went on to figure out what was happening.

    In addition to transmitting current with no resistance, superconductors also have other, less well-known but just as ubiquitous properties. For example, they don’t like magnetic fields getting inside. When exposed to a tiny magnetic field, superconductors produce an internal supercurrent that induces its own magnetic flux that cancels the external field, thereby maintaining their superconducting state. This phenomenon, known as the Meissner screening effect, can be thought of as akin to our bodies’ immune system releasing antibodies to fight the infection of bacteria and other pathogens. This works, however, only up to some limit. Similarly, superconductors cannot entirely keep out large magnetic fields.

    The diodes the team created make use of this universal Meissner screening effect. The tiny magnetic field they applied — either directly, or through the adjacent ferromagnetic layer — activates the material’s screening current mechanism for expelling the external magnetic field and maintaining superconductivity.

    The team also found that another key factor in optimizing these superconductor diodes is tiny differences between the two sides, or edges, of the diode devices. These differences “create some sort of asymmetry in the way the magnetic field enters the superconductor,” Moodera says.

    By engineering their own form of edges on diodes to optimize these differences — for example, one edge with sawtooth features, while the other edge not intentionally altered — the team found that they could increase the efficiency from 20 percent to more than 50 percent. This discovery opens the door for devices whose edges could be “tuned” for even higher efficiencies, Moodera says.

    In sum, the team discovered that the edge asymmetries within superconducting diodes, the ubiquitous Meissner screening effect found in all superconductors, and a third property of superconductors known as vortex pinning all came together to produce the diode effect.

    “It is fascinating to see how inconspicuous yet ubiquitous factors can create a significant effect in observing the diode effect,” says Yasen Hou, first author of the paper and a postdoc at the Francis Bitter Magnet Laboratory and the PSFC. “What’s more exciting is that [this work] provides a straightforward approach with huge potential to further improve the efficiency.”

    Christoph Strunk is a professor at the University of Regensburg in Germany. Says Strunk, who was not involved in the research, “the present work demonstrates that the supercurrent in simple superconducting strips can become nonreciprocal. Moreover, when combined with a ferromagnetic insulator, the diode effect can even be maintained in the absence of an external magnetic field. The rectification direction can be programmed by the remnant magnetization of the magnetic layer, which may have high potential for future applications. The work is important and appealing both from the basic research and from the applications point of view.”

    Teenage contributors

    Moodera noted that the two researchers who created the engineered edges did so while still in high school during a summer at Moodera’s lab. They are Ourania Glezakou-Elbert of Richland, Washington, who will be going to Princeton University this fall, and Amith Varambally of Vestavia Hills, Alabama, who will be entering Caltech.

    Says Varambally, “I didn’t know what to expect when I set foot in Boston last summer, and certainly never expected to [be] a coauthor in a Physical Review Letters paper.

    “Every day was exciting, whether I was reading dozens of papers to better understand the diode phenomena, or operating machinery to fabricate new diodes for study, or engaging in conversations with Ourania, Dr. Hou, and Dr. Moodera about our research.

    “I am profoundly grateful to Dr. Moodera and Dr. Hou for providing me with the opportunity to work on such a fascinating project, and to Ourania for being a great research partner and friend.”

    In addition to Moodera and Hou, corresponding authors of the paper are professors Patrick A. Lee of the MIT Department of Physics and Akashdeep Kamra of Autonomous University of Madrid. Other authors from MIT are Liang Fu and Margarita Davydova of the Department of Physics, and Hang Chi, Alessandro Lodesani, and Yingying Wu, all of the Francis Bitter Magnet Laboratory and the Plasma Science and Fusion Center. Chi is also affiliated with the U.S. Army CCDC Research Laboratory.

    Authors also include Fabrizio Nichele, Markus F. Ritter, and Daniel Z. Haxwell of IBM Research Europe; Stefan Ilićof Materials Physics Center (CFM-MPC); and F. Sebastian Bergeret of CFM-MPC and Donostia International Physics Center.

    This work was supported by the Air Force Office of Sponsored Research, the Office of Naval Research, the National Science Foundation, and the Army Research Office. Additional funders are the European Research Council, the European Union’s Horizon 2020 Research and Innovation Framework Programme, the Spanish Ministry of Science and Innovation, the A. v. Humboldt Foundation, and the Department of Energy’s Office of Basic Sciences. More

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    How forests can cut carbon, restore ecosystems, and create jobs

    To limit the frequency and severity of droughts, wildfires, flooding, and other adverse consequences of climate change, nearly 200 countries committed to the Paris Agreement’s long-term goal of keeping global warming well below 2 degrees Celsius. According to the latest United Nations Intergovernmental Panel on Climate Change (IPCC) Report, achieving that goal will require both large-scale greenhouse gas (GHG) emissions reduction and removal of GHGs from the atmosphere.

    At present, the most efficient and scalable GHG-removal strategy is the massive planting of trees through reforestation or afforestation — a “natural climate solution” (NCS) that extracts atmospheric carbon dioxide through photosynthesis and soil carbon sequestration.

    Despite the potential of forestry-based NCS projects to address climate change, biodiversity loss, unemployment, and other societal needs — and their appeal to policymakers, funders, and citizens — they have yet to achieve critical mass, and often underperform due to a mix of interacting ecological, social, and financial constraints. To better understand these challenges and identify opportunities to overcome them, a team of researchers at Imperial College London and the MIT Joint Program on the Science and Policy of Global Change recently studied how environmental scientists, local stakeholders, and project funders perceive the risks and benefits of NCS projects, and how these perceptions impact project goals and performance. To that end, they surveyed and consulted with dozens of recognized experts and organizations spanning the fields of ecology, finance, climate policy, and social science.

    The team’s analysis, which appears in the journal Frontiers in Climate, found two main factors that have hindered the success of forestry-based NCS projects.

    First, the ambition — levels of carbon removal, ecosystem restoration, job creation, and other environmental and social targets — of selected NCS projects is limited by funders’ perceptions of their overall risk. Among other things, funders aim to minimize operational risk (e.g., Will newly planted trees survive and grow?), political risk (e.g., Just how secure is their access to the land where trees will be planted?); and reputational risk (e.g., Will the project be perceived as an exercise in “greenwashing,” or fall way short of its promised environmental and social benefits?). Funders seeking a financial return on their initial investment are also concerned about the dependability of complex monitoring, reporting, and verification methods used to quantify atmospheric carbon removal, biodiversity gains, and other metrics of project performance.

    Second, the environmental and social benefits of NCS projects are unlikely to be realized unless the local communities impacted by these projects are granted ownership over their implementation and outcomes. But while engaging with local communities is critical to project performance, it can be challenging both legally and financially to set up incentives (e.g., payment and other forms of compensation) to mobilize such engagement.

    “Many carbon offset projects raise legitimate concerns about their effectiveness,” says study lead author Bonnie Waring, a senior lecturer at the Grantham Institute on Climate Change and the Environment, Imperial College London. “However, if nature climate solution projects are done properly, they can help with sustainable development and empower local communities.”

    Drawing on surveys and consultations with NCS experts, stakeholders, and funders, the research team highlighted several recommendations on how to overcome key challenges faced by forestry-based NCS projects and boost their environmental and social performance.

    These recommendations include encouraging funders to evaluate projects based on robust internal governance, support from regional and national governments, secure land tenure, material benefits for local communities, and full participation of community members from across a spectrum of socioeconomic groups; improving the credibility and verifiability of project emissions reductions and related co-benefits; and maintaining an open dialogue and shared costs and benefits among those who fund, implement, and benefit from these projects.

    “Addressing climate change requires approaches that include emissions mitigation from economic activities paired with greenhouse gas reductions by natural ecosystems,” says Sergey Paltsev, a co-author of the study and deputy director of the MIT Joint Program. “Guided by these recommendations, we advocate for a proper scaling-up of NCS activities from project levels to help assure integrity of emissions reductions across entire countries.” More

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    Study: The ocean’s color is changing as a consequence of climate change

    The ocean’s color has changed significantly over the last 20 years, and the global trend is likely a consequence of human-induced climate change, report scientists at MIT, the National Oceanography Center in the U.K., and elsewhere.  

    In a study appearing today in Nature, the team writes that they have detected changes in ocean color over the past two decades that cannot be explained by natural, year-to-year variability alone. These color shifts, though subtle to the human eye, have occurred over 56 percent of the world’s oceans — an expanse that is larger than the total land area on Earth.

    In particular, the researchers found that tropical ocean regions near the equator have become steadily greener over time. The shift in ocean color indicates that ecosystems within the surface ocean must also be changing, as the color of the ocean is a literal reflection of the organisms and materials in its waters.

    At this point, the researchers cannot say how exactly marine ecosystems are changing to reflect the shifting color. But they are pretty sure of one thing: Human-induced climate change is likely the driver.

    “I’ve been running simulations that have been telling me for years that these changes in ocean color are going to happen,” says study co-author Stephanie Dutkiewicz, senior research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences and the Center for Global Change Science. “To actually see it happening for real is not surprising, but frightening. And these changes are consistent with man-induced changes to our climate.”

    “This gives additional evidence of how human activities are affecting life on Earth over a huge spatial extent,” adds lead author B. B. Cael PhD ’19 of the National Oceanography Center in Southampton, U.K. “It’s another way that humans are affecting the biosphere.”

    The study’s co-authors also include Stephanie Henson of the National Oceanography Center, Kelsey Bisson at Oregon State University, and Emmanuel Boss of the University of Maine.

    Above the noise

    The ocean’s color is a visual product of whatever lies within its upper layers. Generally, waters that are deep blue reflect very little life, whereas greener waters indicate the presence of ecosystems, and mainly phytoplankton — plant-like microbes that are abundant in upper ocean and that contain the green pigment chlorophyll. The pigment helps plankton harvest sunlight, which they use to capture carbon dioxide from the atmosphere and convert it into sugars.

    Phytoplankton are the foundation of the marine food web that sustains progressively more complex organisms, on up to krill, fish, and seabirds and marine mammals. Phytoplankton are also a powerful muscle in the ocean’s ability to capture and store carbon dioxide. Scientists are therefore keen to monitor phytoplankton across the surface oceans and to see how these essential communities might respond to climate change. To do so, scientists have tracked changes in chlorophyll, based on the ratio of how much blue versus green light is reflected from the ocean surface, which can be monitored from space

    But around a decade ago, Henson, who is a co-author of the current study, published a paper with others, which showed that, if scientists were tracking chlorophyll alone, it would take at least 30 years of continuous monitoring to detect any trend that was driven specifically by climate change. The reason, the team argued, was that the large, natural variations in chlorophyll from year to year would overwhelm any anthropogenic influence on chlorophyll concentrations. It would therefore take several decades to pick out a meaningful, climate-change-driven signal amid the normal noise.

    In 2019, Dutkiewicz and her colleagues published a separate paper, showing through a new model that the natural variation in other ocean colors is much smaller compared to that of chlorophyll. Therefore, any signal of climate-change-driven changes should be easier to detect over the smaller, normal variations of other ocean colors. They predicted that such changes should be apparent within 20, rather than 30 years of monitoring.

    “So I thought, doesn’t it make sense to look for a trend in all these other colors, rather than in chlorophyll alone?” Cael says. “It’s worth looking at the whole spectrum, rather than just trying to estimate one number from bits of the spectrum.”

     The power of seven

    In the current study, Cael and the team analyzed measurements of ocean color taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite, which has been monitoring ocean color for 21 years. MODIS takes measurements in seven visible wavelengths, including the two colors researchers traditionally use to estimate chlorophyll.

    The differences in color that the satellite picks up are too subtle for human eyes to differentiate. Much of the ocean appears blue to our eye, whereas the true color may contain a mix of subtler wavelengths, from blue to green and even red.

    Cael carried out a statistical analysis using all seven ocean colors measured by the satellite from 2002 to 2022 together. He first looked at how much the seven colors changed from region to region during a given year, which gave him an idea of their natural variations. He then zoomed out to see how these annual variations in ocean color changed over a longer stretch of two decades. This analysis turned up a clear trend, above the normal year-to-year variability.

    To see whether this trend is related to climate change, he then looked to Dutkiewicz’s model from 2019. This model simulated the Earth’s oceans under two scenarios: one with the addition of greenhouse gases, and the other without it. The greenhouse-gas model predicted that a significant trend should show up within 20 years and that this trend should cause changes to ocean color in about 50 percent of the world’s surface oceans — almost exactly what Cael found in his analysis of real-world satellite data.

    “This suggests that the trends we observe are not a random variation in the Earth system,” Cael says. “This is consistent with anthropogenic climate change.”

    The team’s results show that monitoring ocean colors beyond chlorophyll could give scientists a clearer, faster way to detect climate-change-driven changes to marine ecosystems.

    “The color of the oceans has changed,” Dutkiewicz says. “And we can’t say how. But we can say that changes in color reflect changes in plankton communities, that will impact everything that feeds on plankton. It will also change how much the ocean will take up carbon, because different types of plankton have different abilities to do that. So, we hope people take this seriously. It’s not only models that are predicting these changes will happen. We can now see it happening, and the ocean is changing.”

    This research was supported, in part, by NASA. More

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    Studying rivers from worlds away

    Rivers have flowed on two other worlds in the solar system besides Earth: Mars, where dry tracks and craters are all that’s left of ancient rivers and lakes, and Titan, Saturn’s largest moon, where rivers of liquid methane still flow today.

    A new technique developed by MIT geologists allows scientists to see how intensely rivers used to flow on Mars, and how they currently flow on Titan. The method uses satellite observations to estimate the rate at which rivers move fluid and sediment downstream.

    Applying their new technique, the MIT team calculated how fast and deep rivers were in certain regions on Mars more than 1 billion years ago. They also made similar estimates for currently active rivers on Titan, even though the moon’s thick atmosphere and distance from Earth make it harder to explore, with far fewer available images of its surface than those of Mars.

    “What’s exciting about Titan is that it’s active. With this technique, we have a method to make real predictions for a place where we won’t get more data for a long time,” says Taylor Perron, the Cecil and Ida Green Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “And on Mars, it gives us a time machine, to take the rivers that are dead now and get a sense of what they were like when they were actively flowing.”

    Perron and his colleagues have published their results today in the Proceedings of the National Academy of Sciences. Perron’s MIT co-authors are first author Samuel Birch, Paul Corlies, and Jason Soderblom, with Rose Palermo and Andrew Ashton of the Woods Hole Oceanographic Institution (WHOI), Gary Parker of the University of Illinois at Urbana-Champaign, and collaborators from the University of California at Los Angeles, Yale University, and Cornell University.

    River math

    The team’s study grew out of Perron and Birch’s puzzlement over Titan’s rivers. The images taken by NASA’s Cassini spacecraft have shown a curious lack of fan-shaped deltas at the mouths of most of the moon’s rivers, contrary to many rivers on Earth. Could it be that Titan’s rivers don’t carry enough flow or sediment to build deltas?

    The group built on the work of co-author Gary Parker, who in the 2000s developed a series of mathematical equations to describe river flow on Earth. Parker had studied measurements of rivers taken directly in the field by others. From these data, he found there were certain universal relationships between a river’s physical dimensions — its width, depth, and slope — and the rate at which it flowed. He drew up equations to describe these relationships mathematically, accounting for other variables such as the gravitational field acting on the river, and the size and density of the sediment being pushed along a river’s bed.

    “This means that rivers with different gravity and materials should follow similar relationships,” Perron says. “That opened up a possibility to apply this to other planets too.”

    Getting a glimpse

    On Earth, geologists can make field measurements of a river’s width, slope, and average sediment size, all of which can be fed into Parker’s equations to accurately predict a river’s flow rate, or how much water and sediment it can move downstream. But for rivers on other planets, measurements are more limited, and largely based on images and elevation measurements collected by remote satellites. For Mars, multiple orbiters have taken high-resolution images of the planet. For Titan, views are few and far between.

    Birch realized that any estimate of river flow on Mars or Titan would have to be based on the few characteristics that can be measured from remote images and topography — namely, a river’s width and slope. With some algebraic tinkering, he adapted Parker’s equations to work only with width and slope inputs. He then assembled data from 491 rivers on Earth, tested the modified equations on these rivers, and found that the predictions based solely on each river’s width and slope were accurate.

    Then, he applied the equations to Mars, and specifically, to the ancient rivers leading into Gale and Jezero Craters, both of which are thought to have been water-filled lakes billions of years ago. To predict the flow rate of each river, he plugged into the equations Mars’ gravity, and estimates of each river’s width and slope, based on images and elevation measurements taken by orbiting satellites.

    From their predictions of flow rate, the team found that rivers likely flowed for at least 100,000 years at Gale Crater and at least 1 million years at Jezero Crater — long enough to have possibly supported life. They were also able to compare their predictions of the average size of sediment on each river’s bed with actual field measurements of Martian grains near each river, taken by NASA’s Curiosity and Perseverance rovers. These few field measurements allowed the team to check that their equations, applied on Mars, were accurate.

    The team then took their approach to Titan. They zeroed in on two locations where river slopes can be measured, including a river that flows into a lake the size of Lake Ontario. This river appears to form a delta as it feeds into the lake. However, the delta is one of only a few thought to exist on the moon — nearly every viewable river flowing into a lake mysteriously lacks a delta. The team also applied their method to one of these other delta-less rivers.

    They calculated both rivers’ flow and found that they may be comparable to some of the biggest rivers on Earth, with deltas estimated to have a flow rate as large as the Mississippi. Both rivers should move enough sediment to build up deltas. Yet, most rivers on Titan lack the fan-shaped deposits. Something else must be at work to explain this lack of river deposits.

    In another finding, the team calculated that rivers on Titan should be wider and have a gentler slope than rivers carrying the same flow on Earth or Mars. “Titan is the most Earth-like place,” Birch says. ”We’ve only gotten a glimpse of it. There’s so much more that we know is down there, and this remote technique is pushing us a little closer.”

    This research was supported, in part, by NASA and the Heising-Simons Foundation. More