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      in Environment

      Detailed images from space offer clearer picture of drought effects on plants

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      “MIT is a place where dreams come true,” says César Terrer, an assistant professor in the Department of Civil and Environmental Engineering. Here at MIT, Terrer says he’s given the resources needed to explore ideas he finds most exciting, and at the top of his list is climate science. In particular, he is interested in plant-soil interactions, and how the two can mitigate impacts of climate change. In 2022, Terrer received seed grant funding from the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) to produce drought monitoring systems for farmers. The project is leveraging a new generation of remote sensing devices to provide high-resolution plant water stress at regional to global scales.

      Growing up in Granada, Spain, Terrer always had an aptitude and passion for science. He studied environmental science at the University of Murcia, where he interned in the Department of Ecology. Using computational analysis tools, he worked on modeling species distribution in response to human development. Early on in his undergraduate experience, Terrer says he regarded his professors as “superheroes” with a kind of scholarly prowess. He knew he wanted to follow in their footsteps by one day working as a faculty member in academia. Of course, there would be many steps along the way before achieving that dream. 

      Upon completing his undergraduate studies, Terrer set his sights on exciting and adventurous research roles. He thought perhaps he would conduct field work in the Amazon, engaging with native communities. But when the opportunity arose to work in Australia on a state-of-the-art climate change experiment that simulates future levels of carbon dioxide, he headed south to study how plants react to CO2 in a biome of native Australian eucalyptus trees. It was during this experience that Terrer started to take a keen interest in the carbon cycle and the capacity of ecosystems to buffer rising levels of CO2 caused by human activity.

      Around 2014, he began to delve deeper into the carbon cycle as he began his doctoral studies at Imperial College London. The primary question Terrer sought to answer during his PhD was “will plants be able to absorb predicted future levels of CO2 in the atmosphere?” To answer the question, Terrer became an early adopter of artificial intelligence, machine learning, and remote sensing to analyze data from real-life, global climate change experiments. His findings from these “ground truth” values and observations resulted in a paper in the journal Science. In it, he claimed that climate models most likely overestimated how much carbon plants will be able to absorb by the end of the century, by a factor of three. 

      After postdoctoral positions at Stanford University and the Universitat Autonoma de Barcelona, followed by a prestigious Lawrence Fellowship, Terrer says he had “too many ideas and not enough time to accomplish all those ideas.” He knew it was time to lead his own group. Not long after applying for faculty positions, he landed at MIT. 

      New ways to monitor drought

      Terrer is employing similar methods to those he used during his PhD to analyze data from all over the world for his J-WAFS project. He and postdoc Wenzhe Jiao collect data from remote sensing satellites and field experiments and use machine learning to come up with new ways to monitor drought. Terrer says Jiao is a “remote sensing wizard,” who fuses data from different satellite products to understand the water cycle. With Jiao’s hydrology expertise and Terrer’s knowledge of plants, soil, and the carbon cycle, the duo is a formidable team to tackle this project.

      According to the U.N. World Meteorological Organization, the number and duration of droughts has increased by 29 percent since 2000, as compared to the two previous decades. From the Horn of Africa to the Western United States, drought is devastating vegetation and severely stressing water supplies, compromising food production and spiking food insecurity. Drought monitoring can offer fundamental information on drought location, frequency, and severity, but assessing the impact of drought on vegetation is extremely challenging. This is because plants’ sensitivity to water deficits varies across species and ecosystems. 

      Terrer and Jiao are able to obtain a clearer picture of how drought is affecting plants by employing the latest generation of remote sensing observations, which offer images of the planet with incredible spatial and temporal resolution. Satellite products such as Sentinel, Landsat, and Planet can provide daily images from space with such high resolution that individual trees can be discerned. Along with the images and datasets from satellites, the team is using ground-based observations from meteorological data. They are also using the MIT SuperCloud at MIT Lincoln Laboratory to process and analyze all of the data sets. The J-WAFS project is among one of the first to leverage high-resolution data to quantitatively measure plant drought impacts in the United States with the hopes of expanding to a global assessment in the future.

      Assisting farmers and resource managers 

      Every week, the U.S. Drought Monitor provides a map of drought conditions in the United States. The map has zero resolution and is more of a drought recap or summary, unable to predict future drought scenarios. The lack of a comprehensive spatiotemporal evaluation of historic and future drought impacts on global vegetation productivity is detrimental to farmers both in the United States and worldwide.  

      Terrer and Jiao plan to generate metrics for plant water stress at an unprecedented resolution of 10-30 meters. This means that they will be able to provide drought monitoring maps at the scale of a typical U.S. farm, giving farmers more precise, useful data every one to two days. The team will use the information from the satellites to monitor plant growth and soil moisture, as well as the time lag of plant growth response to soil moisture. In this way, Terrer and Jiao say they will eventually be able to create a kind of “plant water stress forecast” that may be able to predict adverse impacts of drought four weeks in advance. “According to the current soil moisture and lagged response time, we hope to predict plant water stress in the future,” says Jiao. 

      The expected outcomes of this project will give farmers, land and water resource managers, and decision-makers more accurate data at the farm-specific level, allowing for better drought preparation, mitigation, and adaptation. “We expect to make our data open-access online, after we finish the project, so that farmers and other stakeholders can use the maps as tools,” says Jiao. 

      Terrer adds that the project “has the potential to help us better understand the future states of climate systems, and also identify the regional hot spots more likely to experience water crises at the national, state, local, and tribal government scales.” He also expects the project will enhance our understanding of global carbon-water-energy cycle responses to drought, with applications in determining climate change impacts on natural ecosystems as a whole. More

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      in Environment

      Low-cost device can measure air pollution anywhere

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      Air pollution is a major public health problem: The World Health Organization has estimated that it leads to over 4 million premature deaths worldwide annually. Still, it is not always extensively measured. But now an MIT research team is rolling out an open-source version of a low-cost, mobile pollution detector that could enable people to track air quality more widely.

      The detector, called Flatburn, can be made by 3D printing or by ordering inexpensive parts. The researchers have now tested and calibrated it in relation to existing state-of-the-art machines, and are publicly releasing all the information about it — how to build it, use it, and interpret the data.

      “The goal is for community groups or individual citizens anywhere to be able to measure local air pollution, identify its sources, and, ideally, create feedback loops with officials and stakeholders to create cleaner conditions,” says Carlo Ratti, director of MIT’s Senseable City Lab. 

      “We’ve been doing several pilots around the world, and we have refined a set of prototypes, with hardware, software, and protocols, to make sure the data we collect are robust from an environmental science point of view,” says Simone Mora, a research scientist at Senseable City Lab and co-author of a newly published paper detailing the scanner’s testing process. The Flatburn device is part of a larger project, known as City Scanner, using mobile devices to better understand urban life.

      “Hopefully with the release of the open-source Flatburn we can get grassroots groups, as well as communities in less developed countries, to follow our approach and build and share knowledge,” says An Wang, a researcher at Senseable City Lab and another of the paper’s co-authors.

      The paper, “Leveraging Machine Learning Algorithms to Advance Low-Cost Air Sensor Calibration in Stationary and Mobile Settings,” appears in the journal Atmospheric Environment.

      In addition to Wang, Mora, and Ratti the study’s authors are: Yuki Machida, a former research fellow at Senseable City Lab; Priyanka deSouza, an assistant professor of urban and regional planning at the University of Colorado at Denver; Tiffany Duhl, a researcher with the Massachusetts Department of Environmental Protection and a Tufts University research associate at the time of the project; Neelakshi Hudda, a research assistant professor at Tufts University; John L. Durant, a professor of civil and environmental engineering at Tufts University; and Fabio Duarte, principal research scientist at Senseable City Lab.

      The Flatburn concept at Senseable City Lab dates back to about 2017, when MIT researchers began prototyping a mobile pollution detector, originally to be deployed on garbage trucks in Cambridge, Massachusetts. The detectors are battery-powered and rechargable, either from power sources or a solar panel, with data stored on a card in the device that can be accessed remotely.

      The current extension of that project involved testing the devices in New York City and the Boston area, by seeing how they performed in comparison to already-working pollution detection systems. In New York, the researchers used 5 detectors to collect 1.6 million data points over four weeks in 2021, working with state officials to compare the results. In Boston, the team used mobile sensors, evaluating the Flatburn devices against a state-of-the-art system deployed by Tufts University along with a state agency.

      In both cases, the detectors were set up to measure concentrations of fine particulate matter as well as nitrogen dioxide, over an area of about 10 meters. Fine particular matter refers to tiny particles often associated with burning matter, from power plants, internal combustion engines in autos and fires, and more.

      The research team found that the mobile detectors estimated somewhat lower concentrations of fine particulate matter than the devices already in use, but with a strong enough correlation so that, with adjustments for weather conditions and other factors, the Flatburn devices can produce reliable results.

      “After following their deployment for a few months we can confidently say our low-cost monitors should behave the same way [as standard detectors],” Wang says. “We have a big vision, but we still have to make sure the data we collect is valid and can be used for regulatory and policy purposes,”

      Duarte adds: “If you follow these procedures with low-cost sensors you can still acquire good enough data to go back to [environmental] agencies with it, and say, ‘Let’s talk.’”

      The researchers did find that using the units in a mobile setting — on top of automobiles — means they will currently have an operating life of six months. They also identified a series of potential issues that people will have to deal with when using the Flatburn detectors generally. These include what the research team calls “drift,” the gradual changing of the detector’s readings over time, as well as “aging,” the more fundamental deterioration in a unit’s physical condition.

      Still, the researchers believe the units will function well, and they are providing complete instructions in their release of Flatburn as an open-source tool. That even includes guidance for working with officials, communities, and stakeholders to process the results and attempt to shape action.

      “It’s very important to engage with communities, to allow them to reflect on sources of pollution,” says Mora. 

      “The original idea of the project was to democratize environmental data, and that’s still the goal,” Duarte adds. “We want people to have the skills to analyze the data and engage with communities and officials.” More

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      in Energy

      How to pull carbon dioxide out of seawater

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      As carbon dioxide continues to build up in the Earth’s atmosphere, research teams around the world have spent years seeking ways to remove the gas efficiently from the air. Meanwhile, the world’s number one “sink” for carbon dioxide from the atmosphere is the ocean, which soaks up some 30 to 40 percent of all of the gas produced by human activities.

      Recently, the possibility of removing carbon dioxide directly from ocean water has emerged as another promising possibility for mitigating CO2 emissions, one that could potentially someday even lead to overall net negative emissions. But, like air capture systems, the idea has not yet led to any widespread use, though there are a few companies attempting to enter this area.

      Now, a team of researchers at MIT says they may have found the key to a truly efficient and inexpensive removal mechanism. The findings were reported this week in the journal Energy and Environmental Science, in a paper by MIT professors T. Alan Hatton and Kripa Varanasi, postdoc Seoni Kim, and graduate students Michael Nitzsche, Simon Rufer, and Jack Lake.

      The existing methods for removing carbon dioxide from seawater apply a voltage across a stack of membranes to acidify a feed stream by water splitting. This converts bicarbonates in the water to molecules of CO2, which can then be removed under vacuum. Hatton, who is the Ralph Landau Professor of Chemical Engineering, notes that the membranes are expensive, and chemicals are required to drive the overall electrode reactions at either end of the stack, adding further to the expense and complexity of the processes. “We wanted to avoid the need for introducing chemicals to the anode and cathode half cells and to avoid the use of membranes if at all possible” he says.

      The team came up with a reversible process consisting of membrane-free electrochemical cells. Reactive electrodes are used to release protons to the seawater fed to the cells, driving the release of the dissolved carbon dioxide from the water. The process is cyclic: It first acidifies the water to convert dissolved inorganic bicarbonates to molecular carbon dioxide, which is collected as a gas under vacuum. Then, the water is fed to a second set of cells with a reversed voltage, to recover the protons and turn the acidic water back to alkaline before releasing it back to the sea. Periodically, the roles of the two cells are reversed once one set of electrodes is depleted of protons (during acidification) and the other has been regenerated during alkalization.

      This removal of carbon dioxide and reinjection of alkaline water could slowly start to reverse, at least locally, the acidification of the oceans that has been caused by carbon dioxide buildup, which in turn has threatened coral reefs and shellfish, says Varanasi, a professor of mechanical engineering. The reinjection of alkaline water could be done through dispersed outlets or far offshore to avoid a local spike of alkalinity that could disrupt ecosystems, they say.

      “We’re not going to be able to treat the entire planet’s emissions,” Varanasi says. But the reinjection might be done in some cases in places such as fish farms, which tend to acidify the water, so this could be a way of helping to counter that effect.

      Once the carbon dioxide is removed from the water, it still needs to be disposed of, as with other carbon removal processes. For example, it can be buried in deep geologic formations under the sea floor, or it can be chemically converted into a compound like ethanol, which can be used as a transportation fuel, or into other specialty chemicals. “You can certainly consider using the captured CO2 as a feedstock for chemicals or materials production, but you’re not going to be able to use all of it as a feedstock,” says Hatton. “You’ll run out of markets for all the products you produce, so no matter what, a significant amount of the captured CO2 will need to be buried underground.”

      Initially at least, the idea would be to couple such systems with existing or planned infrastructure that already processes seawater, such as desalination plants. “This system is scalable so that we could integrate it potentially into existing processes that are already processing ocean water or in contact with ocean water,” Varanasi says. There, the carbon dioxide removal could be a simple add-on to existing processes, which already return vast amounts of water to the sea, and it would not require consumables like chemical additives or membranes.

      “With desalination plants, you’re already pumping all the water, so why not co-locate there?” Varanasi says. “A bunch of capital costs associated with the way you move the water, and the permitting, all that could already be taken care of.”

      The system could also be implemented by ships that would process water as they travel, in order to help mitigate the significant contribution of ship traffic to overall emissions. There are already international mandates to lower shipping’s emissions, and “this could help shipping companies offset some of their emissions, and turn ships into ocean scrubbers,” Varanasi says.

      The system could also be implemented at locations such as offshore drilling platforms, or at aquaculture farms. Eventually, it could lead to a deployment of free-standing carbon removal plants distributed globally.

      The process could be more efficient than air-capture systems, Hatton says, because the concentration of carbon dioxide in seawater is more than 100 times greater than it is in air. In direct air-capture systems it is first necessary to capture and concentrate the gas before recovering it. “The oceans are large carbon sinks, however, so the capture step has already kind of been done for you,” he says. “There’s no capture step, only release.” That means the volumes of material that need to be handled are much smaller, potentially simplifying the whole process and reducing the footprint requirements.

      The research is continuing, with one goal being to find an alternative to the present step that requires a vacuum to remove the separated carbon dioxide from the water. Another need is to identify operating strategies to prevent precipitation of minerals that can foul the electrodes in the alkalinization cell, an inherent issue that reduces the overall efficiency in all reported approaches. Hatton notes that significant progress has been made on these issues, but that it is still too early to report on them. The team expects that the system could be ready for a practical demonstration project within about two years.

      “The carbon dioxide problem is the defining problem of our life, of our existence,” Varanasi says. “So clearly, we need all the help we can get.”

      The work was supported by ARPA-E. More

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      in Environment

      Featured video: Investigating our blue ocean planet

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      A five-year doctoral degree program, the MIT – Woods Hole Oceanographic Institution (WHOI) Joint Program in Oceanography/Applied Ocean Science and Engineering combines the strengths of MIT and WHOI to create one of the largest oceanographic facilities in the world. Graduate study in oceanography encompasses virtually all the basic sciences as they apply to the marine environment: physics, chemistry, geochemistry, geology, geophysics, and biology.

      “As a species and as a society we really want to understand the planet that we live on and our place in it,” says Professor Michael Follows, who serves as director of the MIT-WHOI Joint Program.

      “The reason I joined the program was because we cannot afford to wait to be able to address the climate crisis,” explains graduate student Paris Smalls. “The freedom to be able to execute on and have your interests come to life has been incredibly rewarding.”

      “If you have a research problem, you can think of the top five people in that particular niche of a topic and they’re either down the hallway or have some association with WHOI,” adds graduate student Samantha Clevenger. “It’s a really incredible place in terms of connections and just having access to really anything you need.”

      Video by: Melanie Gonick/MIT | 5 min, 12 sec More

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      in Environment

      Looking to the past to prepare for an uncertain future

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      Aviva Intveld, an MIT senior majoring in Earth, atmospheric, and planetary sciences, is accustomed to city life. But despite hailing from metropolitan Los Angeles, she has always maintained a love for the outdoors.

      “Growing up in L.A., you just have a wealth of resources when it comes to beautiful environments,” she says, “but you’re also constantly living connected to the environment.” She developed a profound respect for the natural world and its effects on people, from the earthquakes that shook the ground to the wildfires that displaced inhabitants.

      “I liked the lifestyle that environmental science afforded,” Intveld recalls. “I liked the idea that you can make a career out of spending a huge amount of time in the field and exploring different parts of the world.”

      From the moment she arrived at MIT, Intveld threw herself into research on and off campus. During her first semester, she joined Terrascope, a program that encourages first-year students to tackle complex, real-world problems. Intveld and her cohort developed proposals to make recovery from major storms in Puerto Rico faster, more sustainable, and more equitable.

      Intveld also spent a semester studying drought stress in the lab of Assistant Professor David Des Marais, worked as a research assistant at a mineral sciences research lab back in L.A., and interned at the World Wildlife Fund. Most of her work focused on contemporary issues like food insecurity and climate change. “I was really interested in questions about today,” Intveld says.

      Her focus began to shift to the past when she interned as a research assistant at the Marine Geoarchaeology and Micropaleontology Lab at the University of Haifa. For weeks, she would spend eight hours a day hunched over a microscope, using a paintbrush to sort through grains of sand from the coastal town of Caesarea. She was looking for tiny spiral-shaped fossils of foraminifera, an organism that resides in seafloor sediments.

      These microfossils can reveal a lot about the environment in which they originated, including extreme weather events. By cataloging diverse species of foraminifera, Intveld was helping to settle a rather niche debate in the field of geoarchaeology: Did tsunamis destroy the harbor of Caesarea during the time of the ancient Romans?

      But in addition to figuring out if and when these natural disasters occurred, Intveld was interested in understanding how ancient communities prepared for and recovered from them. What methods did they use? Could those same methods be used today?

      Intveld’s research at the University of Haifa was part of the Onward Israel program, which offers young Jewish people the chance to participate in internships, academic study, and fellowships in Israel. Intveld describes the experience as a great opportunity to learn about the culture, history, and diversity of the Israeli community. The trip was also an excellent lesson in dealing with challenging situations.

      Intveld suffers from claustrophobia, but she overcame her fears to climb through the Bar Kokhba caves, and despite a cat allergy, she grew to adore the many stray cats that roam the streets of Haifa. “Sometimes you can’t let your physical limitations stop you from doing what you love,” she quips.

      Over the course of her research, Intveld has often found herself in difficult and even downright dangerous situations, all of which she looks back on with good humor. As part of an internship with the National Oceanic and Atmospheric Administration, she spent three months investigating groundwater in Homer, Alaska. While she was there, she learned to avoid poisonous plants out in the field, got lost bushwhacking, and was twice charged by a moose.

      These days, Intveld spends less time in the field and more time thinking about the ancient past. She works in the lab of Associate Professor David McGee, where her undergraduate thesis research focuses on reconstructing the paleoclimate and paleoecology of northeastern Mexico during the Early Holocene. To get an idea of what the Mexican climate looked like thousands of years ago, Intveld analyzes stable isotopes and trace elements in stalagmites taken from Mexican caves. By analyzing the isotopes of carbon and oxygen present in these stalagmites, which were formed over thousands of years from countless droplets of mineral-rich rainwater, Intveld can estimate the amount of rainfall and average temperature in a given time period.

      Intveld is primarily interested in how the area’s climate may have influenced human migration. “It’s very interesting to learn about the history of human motivation, what drives us to do what we do,” she explains. “What causes humans to move, and what causes us to stay?” So far, it seems the Mexican climate during the Early Holocene was quite inconsistent, with oscillating periods of wet and dry, but Intveld needs to conduct more research before drawing any definitive conclusions.

      Recent research has linked periods of drought in the geological record to periods of violence in the archaeological one, suggesting ancient humans often fought over access to water. “I think you can easily see the connections to stuff that we deal with today,” Intveld says, pointing out the parallels between paleolithic migration and today’s climate refugees. “We have to answer a lot of difficult questions, and one way that we can do so is by looking to see what earlier human communities did and what we can learn from them.”

      Intveld recognizes the impact of the past on our present and future in many other areas. She works as a tour guide for the List Visual Arts Center, where she educates people about public art on the MIT campus. “[Art] interested me as a way to experience history and learn about the story of different communities and people over time,” she says.

      Intveld is also unafraid to acknowledge the history of discrimination and exclusion in science. “Earth science has a big problem when it comes to inclusion and diversity,” she says. As a member of the EAPS Diversity, Equity and Inclusion Committee, she aims to make earth science more accessible.

      “Aviva has a clear drive to be at the front lines of geoscience research, connecting her work to the urgent environmental issues we’re all facing,” says McGee. “She also understands the critical need for our field to include more voices, more perspectives — ultimately making for better science.”

      After MIT, Intveld hopes to pursue an advanced degree in the field of sustainable mining. This past spring, she studied abroad at Imperial College London, where she took courses within the Royal School of Mines. As Intveld explains, mining is becoming crucial to sustainable energy. The rise of electric vehicles in places like California has increased the need for energy-critical elements like lithium and cobalt, but mining for these elements often does more harm than good. “The current mining complex is very environmentally destructive,” Intveld says.

      But Intveld hopes to take the same approach to mining she does with her other endeavors — acknowledging the destructive past to make way for a better future. More

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      in Environment

      Earth can regulate its own temperature over millennia, new study finds

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      The Earth’s climate has undergone some big changes, from global volcanism to planet-cooling ice ages and dramatic shifts in solar radiation. And yet life, for the last 3.7 billion years, has kept on beating.

      Now, a study by MIT researchers in Science Advances confirms that the planet harbors a “stabilizing feedback” mechanism that acts over hundreds of thousands of years to pull the climate back from the brink, keeping global temperatures within a steady, habitable range.

      Just how does it accomplish this? A likely mechanism is “silicate weathering” — a geological process by which the slow and steady weathering of silicate rocks involves chemical reactions that ultimately draw carbon dioxide out of the atmosphere and into ocean sediments, trapping the gas in rocks.

      Scientists have long suspected that silicate weathering plays a major role in regulating the Earth’s carbon cycle. The mechanism of silicate weathering could provide a geologically constant force in keeping carbon dioxide — and global temperatures — in check. But there’s never been direct evidence for the continual operation of such a feedback, until now.

      The new findings are based on a study of paleoclimate data that record changes in average global temperatures over the last 66 million years. The MIT team applied a mathematical analysis to see whether the data revealed any patterns characteristic of stabilizing phenomena that reined in global temperatures on a  geologic timescale.

      They found that indeed there appears to be a consistent pattern in which the Earth’s temperature swings are dampened over timescales of hundreds of thousands of years. The duration of this effect is similar to the timescales over which silicate weathering is predicted to act.

      The results are the first to use actual data to confirm the existence of a stabilizing feedback, the mechanism of which is likely silicate weathering. This stabilizing feedback would explain how the Earth has remained habitable through dramatic climate events in the geologic past.

      “On the one hand, it’s good because we know that today’s global warming will eventually be canceled out through this stabilizing feedback,” says Constantin Arnscheidt, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “But on the other hand, it will take hundreds of thousands of years to happen, so not fast enough to solve our present-day issues.”

      The study is co-authored by Arnscheidt and Daniel Rothman, professor of geophysics at MIT.

      Stability in data

      Scientists have previously seen hints of a climate-stabilizing effect in the Earth’s carbon cycle: Chemical analyses of ancient rocks have shown that the flux of carbon in and out of Earth’s surface environment has remained relatively balanced, even through dramatic swings in global temperature. Furthermore, models of silicate weathering predict that the process should have some stabilizing effect on the global climate. And finally, the fact of the Earth’s enduring habitability points to some inherent, geologic check on extreme temperature swings.

      “You have a planet whose climate was subjected to so many dramatic external changes. Why did life survive all this time? One argument is that we need some sort of stabilizing mechanism to keep temperatures suitable for life,” Arnscheidt says. “But it’s never been demonstrated from data that such a mechanism has consistently controlled Earth’s climate.”

      Arnscheidt and Rothman sought to confirm whether a stabilizing feedback has indeed been at work, by looking at data of global temperature fluctuations through geologic history. They worked with a range of global temperature records compiled by other scientists, from the chemical composition of ancient marine fossils and shells, as well as preserved Antarctic ice cores.

      “This whole study is only possible because there have been great advances in improving the resolution of these deep-sea temperature records,” Arnscheidt notes. “Now we have data going back 66 million years, with data points at most thousands of years apart.”

      Speeding to a stop

      To the data, the team applied the mathematical theory of stochastic differential equations, which is commonly used to reveal patterns in widely fluctuating datasets.

      “We realized this theory makes predictions for what you would expect Earth’s temperature history to look like if there had been feedbacks acting on certain timescales,” Arnscheidt explains.

      Using this approach, the team analyzed the history of average global temperatures over the last 66 million years, considering the entire period over different timescales, such as tens of thousands of years versus hundreds of thousands, to see whether any patterns of stabilizing feedback emerged within each timescale.

      “To some extent, it’s like your car is speeding down the street, and when you put on the brakes, you slide for a long time before you stop,” Rothman says. “There’s a timescale over which frictional resistance, or a stabilizing feedback, kicks in, when the system returns to a steady state.”

      Without stabilizing feedbacks, fluctuations of global temperature should grow with timescale. But the team’s analysis revealed a regime in which fluctuations did not grow, implying that a stabilizing mechanism reigned in the climate before fluctuations grew too extreme. The timescale for this stabilizing effect — hundreds of thousands of years — coincides with what scientists predict for silicate weathering.

      Interestingly, Arnscheidt and Rothman found that on longer timescales, the data did not reveal any stabilizing feedbacks. That is, there doesn’t appear to be any recurring pull-back of global temperatures on timescales longer than a million years. Over these longer timescales, then, what has kept global temperatures in check?

      “There’s an idea that chance may have played a major role in determining why, after more than 3 billion years, life still exists,” Rothman offers.

      In other words, as the Earth’s temperatures fluctuate over longer stretches, these fluctuations may just happen to be small enough in the geologic sense, to be within a range that a stabilizing feedback, such as silicate weathering, could periodically keep the climate in check, and more to the point, within a habitable zone.

      “There are two camps: Some say random chance is a good enough explanation, and others say there must be a stabilizing feedback,” Arnscheidt says. “We’re able to show, directly from data, that the answer is probably somewhere in between. In other words, there was some stabilization, but pure luck likely also played a role in keeping Earth continuously habitable.”

      This research was supported, in part, by a MathWorks fellowship and the National Science Foundation. More

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      in Environment

      Ocean microbes get their diet through a surprising mix of sources, study finds

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      One of the smallest and mightiest organisms on the planet is a plant-like bacterium known to marine biologists as Prochlorococcus. The green-tinted microbe measures less than a micron across, and its populations suffuse through the upper layers of the ocean, where a single teaspoon of seawater can hold millions of the tiny organisms.

      Prochlorococcus grows through photosynthesis, using sunlight to convert the atmosphere’s carbon dioxide into organic carbon molecules. The microbe is responsible for 5 percent of the world’s photosynthesizing activity, and scientists have assumed that photosynthesis is the microbe’s go-to strategy for acquiring the carbon it needs to grow.

      But a new MIT study in Nature Microbiology today has found that Prochlorococcus relies on another carbon-feeding strategy, more than previously thought.

      Organisms that use a mix of strategies to provide carbon are known as mixotrophs. Most marine plankton are mixotrophs. And while Prochlorococcus is known to occasionally dabble in mixotrophy, scientists have assumed the microbe primarily lives a phototrophic lifestyle.

      The new MIT study shows that in fact, Prochlorococcus may be more of a mixotroph than it lets on. The microbe may get as much as one-third of its carbon through a second strategy: consuming the dissolved remains of other dead microbes.

      The new estimate may have implications for climate models, as the microbe is a significant force in capturing and “fixing” carbon in the Earth’s atmosphere and ocean.

      “If we wish to predict what will happen to carbon fixation in a different climate, or predict where Prochlorococcus will or will not live in the future, we probably won’t get it right if we’re missing a process that accounts for one-third of the population’s carbon supply,” says Mick Follows, a professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), and its Department of Civil and Environmental Engineering.

      The study’s co-authors include first author and MIT postdoc Zhen Wu, along with collaborators from the University of Haifa, the Leibniz-Institute for Baltic Sea Research, the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, and Potsdam University.

      Persistent plankton

      Since Prochlorococcus was first discovered in the Sargasso Sea in 1986, by MIT Institute Professor Sallie “Penny” Chisholm and others, the microbe has been observed throughout the world’s oceans, inhabiting the upper sunlit layers ranging from the surface down to about 160 meters. Within this range, light levels vary, and the microbe has evolved a number of ways to photosynthesize carbon in even low-lit regions.

      The organism has also evolved ways to consume organic compounds including glucose and certain amino acids, which could help the microbe survive for limited periods of time in dark ocean regions. But surviving on organic compounds alone is a bit like only eating junk food, and there is evidence that Prochlorococcus will die after a week in regions where photosynthesis is not an option.

      And yet, researchers including Daniel Sher of the University of Haifa, who is a co-author of the new study, have observed healthy populations of Prochlorococcus that persist deep in the sunlit zone, where the light intensity should be too low to maintain a population. This suggests that the microbes must be switching to a non-photosynthesizing, mixotrophic lifestyle in order to consume other organic sources of carbon.

      “It seems that at least some Prochlorococcus are using existing organic carbon in a mixotrophic way,” Follows says. “That stimulated the question: How much?”

      What light cannot explain

      In their new paper, Follows, Wu, Sher, and their colleagues looked to quantify the amount of carbon that Prochlorococcus is consuming through processes other than photosynthesis.

      The team looked first to measurements taken by Sher’s team, which previously took ocean samples at various depths in the Mediterranean Sea and measured the concentration of phytoplankton, including Prochlorococcus, along with the associated intensity of light and the concentration of nitrogen — an essential nutrient that is richly available in deeper layers of the ocean and that plankton can assimilate to make proteins.

      Wu and Follows used this data, and similar information from the Pacific Ocean, along with previous work from Chisholm’s lab, which established the rate of photosynthesis that Prochlorococcus could carry out in a given intensity of light.

      “We converted that light intensity profile into a potential growth rate — how fast the population of Prochlorococcus could grow if it was acquiring all it’s carbon by photosynthesis, and light is the limiting factor,” Follows explains.

      The team then compared this calculated rate to growth rates that were previously observed in the Pacific Ocean by several other research teams.

      “This data showed that, below a certain depth, there’s a lot of growth happening that photosynthesis simply cannot explain,” Follows says. “Some other process must be at work to make up the difference in carbon supply.”

      The researchers inferred that, in deeper, darker regions of the ocean, Prochlorococcus populations are able to survive and thrive by resorting to mixotrophy, including consuming organic carbon from detritus. Specifically, the microbe may be carrying out osmotrophy — a process by which an organism passively absorbs organic carbon molecules via osmosis.

      Judging by how fast the microbe is estimated to be growing below the sunlit zone, the team calculates that Prochlorococcus obtains up to one-third of its carbon diet through mixotrophic strategies.

      “It’s kind of like going from a specialist to a generalist lifestyle,” Follows says. “If I only eat pizza, then if I’m 20 miles from a pizza place, I’m in trouble, whereas if I eat burgers as well, I could go to the nearby McDonald’s. People had thought of Prochlorococcus as a specialist, where they do this one thing (photosynthesis) really well. But it turns out they may have more of a generalist lifestyle than we previously thought.”

      Chisholm, who has both literally and figuratively written the book on Prochlorococcus, says the group’s findings “expand the range of conditions under which their populations can not only survive, but also thrive. This study changes the way we think about the role of Prochlorococcus in the microbial food web.”

      This research was supported, in part, by the Israel Science Foundation, the U.S. National Science Foundation, and the Simons Foundation. More

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      in Environment

      Studying floods to better predict their dangers

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      “My job is basically flooding Cambridge,” says Katerina “Katya” Boukin, a graduate student in civil and environmental engineering at MIT and the MIT Concrete Sustainability Hub’s resident expert on flood simulations. 

      You can often find her fine-tuning high-resolution flood risk models for the City of Cambridge, Massachusetts, or talking about hurricanes with fellow researcher Ipek Bensu Manav.

      Flooding represents one of the world’s gravest natural hazards. Extreme climate events inducing flooding, like severe storms, winter storms, and tropical cyclones, caused an estimated $128.1 billion of damages in 2021 alone. 

      Climate simulation models suggest that severe storms will become more frequent in the coming years, necessitating a better understanding of which parts of cities are most vulnerable — an understanding that can be improved through modeling.

      A problem with current flood models is that they struggle to account for an oft-misunderstood type of flooding known as pluvial flooding. 

      “You might think of flooding as the overflowing of a body of water, like a river. This is fluvial flooding. This can be somewhat predictable, as you can think of proximity to water as a risk factor,” Boukin explains.

      However, the “flash flooding” that causes many deaths each year can happen even in places nowhere near a body of water. This is an example of pluvial flooding, which is affected by terrain, urban infrastructure, and the dynamic nature of storm loads.

      “If we don’t know how a flood is propagating, we don’t know the risk it poses to the urban environment. And if we don’t understand the risk, we can’t really discuss mitigation strategies,” says Boukin, “That’s why I pursue improving flood propagation models.”

      Boukin is leading development of a new flood prediction method that seeks to address these shortcomings. By better representing the complex morphology of cities, Boukin’s approach may provide a clearer forecast of future urban flooding.

      Katya Boukin developed this model of the City of Cambridge, Massachusetts. The base model was provided through a collaboration between MIT, the City of Cambridge, and Dewberry Engineering.

      Image: Katya Boukin

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      “In contrast to the more typical traditional catchment model, our method has rainwater spread around the urban environment based on the city’s topography, below-the-surface features like sewer pipes, and the characteristics of local soils,” notes Boukin.

      “We can simulate the flooding of regions with local rain forecasts. Our results can show how flooding propagates by the foot and by the second,” she adds.

      While Boukin’s current focus is flood simulation, her unconventional academic career has taken her research in many directions, like examining structural bottlenecks in dense urban rail systems and forecasting ground displacement due to tunneling. 

      “I’ve always been interested in the messy side of problem-solving. I think that difficult problems present a real chance to gain a deeper understanding,” says Boukin.

      Boukin credits her upbringing for giving her this perspective. A native of Israel, Boukin says that civil engineering is the family business. “My parents are civil engineers, my mom’s parents are, too, her grandfather was a professor in civil engineering, and so on. Civil engineering is my bloodline.”

      However, the decision to follow the family tradition did not come so easily. “After I took the Israeli equivalent of the SAT, I was at a decision point: Should I go to engineering school or medical school?” she recalls.

      “I decided to go on a backpacking trip to help make up my mind. It’s sort of an Israeli rite to explore internationally, so I spent six months in South America. I think backpacking is something everyone should do.”

      After this soul searching, Boukin landed on engineering school, where she fell in love with structural engineering. “It was the option that felt most familiar and interesting. I grew up playing with AutoCAD on the family computer, and now I use AutoCAD professionally!” she notes.

      “For my master’s degree, I was looking to study in a department that would help me integrate knowledge from fields like climatology and civil engineering. I found the MIT Department of Civil and Environmental Engineering to be an excellent fit,” she says.

      “I am lucky that MIT has so many people that work together as well as they do. I ended up at the Concrete Sustainability Hub, where I’m working on projects which are the perfect fit between what I wanted to do and what the department wanted to do.” 

      Boukin’s move to Cambridge has given her a new perspective on her family and childhood. 

      “My parents brought me to Israel when I was just 1 year old. In moving here as a second-time immigrant, I have a new perspective on what my parents went through during the move to Israel. I moved when I was 27 years old, the same age as they were. They didn’t have a support network and worked any job they could find,” she explains.

      “I am incredibly grateful to them for the morals they instilled in my sister, who recently graduated medical school, and I. I know I can call my parents if I ever need something, and they will do whatever they can to help.”

      Boukin hopes to honor her parents’ efforts through her research.

      “Not only do I want to help stakeholders understand flood risks, I want to make awareness of flooding more accessible. Each community needs different things to be resilient, and different cultures have different ways of delivering and receiving information,” she says.

      “Everyone should understand that they, in addition to the buildings and infrastructure around them, are part of a complex ecosystem. Any change to a city can affect the rest of it. If designers and residents are aware of this when considering flood mitigation strategies, we can better design cities and understand the consequences of damage.” More