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    MIT-derived algorithm helps forecast the frequency of extreme weather

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    To assess a community’s risk of extreme weather, policymakers rely first on global climate models that can be run decades, and even centuries, forward in time, but only at a coarse resolution. These models might be used to gauge, for instance, future climate conditions for the northeastern U.S., but not specifically for Boston.

    To estimate Boston’s future risk of extreme weather such as flooding, policymakers can combine a coarse model’s large-scale predictions with a finer-resolution model, tuned to estimate how often Boston is likely to experience damaging floods as the climate warms. But this risk analysis is only as accurate as the predictions from that first, coarser climate model.

    “If you get those wrong for large-scale environments, then you miss everything in terms of what extreme events will look like at smaller scales, such as over individual cities,” says Themistoklis Sapsis, the William I. Koch Professor and director of the Center for Ocean Engineering in MIT’s Department of Mechanical Engineering.

    Sapsis and his colleagues have now developed a method to “correct” the predictions from coarse climate models. By combining machine learning with dynamical systems theory, the team’s approach “nudges” a climate model’s simulations into more realistic patterns over large scales. When paired with smaller-scale models to predict specific weather events such as tropical cyclones or floods, the team’s approach produced more accurate predictions for how often specific locations will experience those events over the next few decades, compared to predictions made without the correction scheme.

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    This animation shows the evolution of storms around the northern hemisphere, as a result of a high-resolution storm model, combined with the MIT team’s corrected global climate model. The simulation improves the modeling of extreme values for wind, temperature, and humidity, which typically have significant errors in coarse scale models. Credit: Courtesy of Ruby Leung and Shixuan Zhang, PNNL

    Sapsis says the new correction scheme is general in form and can be applied to any global climate model. Once corrected, the models can help to determine where and how often extreme weather will strike as global temperatures rise over the coming years. 

    “Climate change will have an effect on every aspect of human life, and every type of life on the planet, from biodiversity to food security to the economy,” Sapsis says. “If we have capabilities to know accurately how extreme weather will change, especially over specific locations, it can make a lot of difference in terms of preparation and doing the right engineering to come up with solutions. This is the method that can open the way to do that.”

    The team’s results appear today in the Journal of Advances in Modeling Earth Systems. The study’s MIT co-authors include postdoc Benedikt Barthel Sorensen and Alexis-Tzianni Charalampopoulos SM ’19, PhD ’23, with Shixuan Zhang, Bryce Harrop, and Ruby Leung of the Pacific Northwest National Laboratory in Washington state.

    Over the hood

    Today’s large-scale climate models simulate weather features such as the average temperature, humidity, and precipitation around the world, on a grid-by-grid basis. Running simulations of these models takes enormous computing power, and in order to simulate how weather features will interact and evolve over periods of decades or longer, models average out features every 100 kilometers or so.

    “It’s a very heavy computation requiring supercomputers,” Sapsis notes. “But these models still do not resolve very important processes like clouds or storms, which occur over smaller scales of a kilometer or less.”

    To improve the resolution of these coarse climate models, scientists typically have gone under the hood to try and fix a model’s underlying dynamical equations, which describe how phenomena in the atmosphere and oceans should physically interact.

    “People have tried to dissect into climate model codes that have been developed over the last 20 to 30 years, which is a nightmare, because you can lose a lot of stability in your simulation,” Sapsis explains. “What we’re doing is a completely different approach, in that we’re not trying to correct the equations but instead correct the model’s output.”

    The team’s new approach takes a model’s output, or simulation, and overlays an algorithm that nudges the simulation toward something that more closely represents real-world conditions. The algorithm is based on a machine-learning scheme that takes in data, such as past information for temperature and humidity around the world, and learns associations within the data that represent fundamental dynamics among weather features. The algorithm then uses these learned associations to correct a model’s predictions.

    “What we’re doing is trying to correct dynamics, as in how an extreme weather feature, such as the windspeeds during a Hurricane Sandy event, will look like in the coarse model, versus in reality,” Sapsis says. “The method learns dynamics, and dynamics are universal. Having the correct dynamics eventually leads to correct statistics, for example, frequency of rare extreme events.”

    Climate correction

    As a first test of their new approach, the team used the machine-learning scheme to correct simulations produced by the Energy Exascale Earth System Model (E3SM), a climate model run by the U.S. Department of Energy, that simulates climate patterns around the world at a resolution of 110 kilometers. The researchers used eight years of past data for temperature, humidity, and wind speed to train their new algorithm, which learned dynamical associations between the measured weather features and the E3SM model. They then ran the climate model forward in time for about 36 years and applied the trained algorithm to the model’s simulations. They found that the corrected version produced climate patterns that more closely matched real-world observations from the last 36 years, not used for training.

    “We’re not talking about huge differences in absolute terms,” Sapsis says. “An extreme event in the uncorrected simulation might be 105 degrees Fahrenheit, versus 115 degrees with our corrections. But for humans experiencing this, that is a big difference.”

    When the team then paired the corrected coarse model with a specific, finer-resolution model of tropical cyclones, they found the approach accurately reproduced the frequency of extreme storms in specific locations around the world.

    “We now have a coarse model that can get you the right frequency of events, for the present climate. It’s much more improved,” Sapsis says. “Once we correct the dynamics, this is a relevant correction, even when you have a different average global temperature, and it can be used for understanding how forest fires, flooding events, and heat waves will look in a future climate. Our ongoing work is focusing on analyzing future climate scenarios.”

    “The results are particularly impressive as the method shows promising results on E3SM, a state-of-the-art climate model,” says Pedram Hassanzadeh, an associate professor who leads the Climate Extremes Theory and Data group at the University of Chicago and was not involved with the study. “It would be interesting to see what climate change projections this framework yields once future greenhouse-gas emission scenarios are incorporated.”

    This work was supported, in part, by the U.S. Defense Advanced Research Projects Agency. More

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      in Environment

      New tool predicts flood risk from hurricanes in a warming climate

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      Coastal cities and communities will face more frequent major hurricanes with climate change in the coming years. To help prepare coastal cities against future storms, MIT scientists have developed a method to predict how much flooding a coastal community is likely to experience as hurricanes evolve over the next decades.

      When hurricanes make landfall, strong winds whip up salty ocean waters that generate storm surge in coastal regions. As the storms move over land, torrential rainfall can induce further flooding inland. When multiple flood sources such as storm surge and rainfall interact, they can compound a hurricane’s hazards, leading to significantly more flooding than would result from any one source alone. The new study introduces a physics-based method for predicting how the risk of such complex, compound flooding may evolve under a warming climate in coastal cities.

      One example of compound flooding’s impact is the aftermath from Hurricane Sandy in 2012. The storm made landfall on the East Coast of the United States as heavy winds whipped up a towering storm surge that combined with rainfall-driven flooding in some areas to cause historic and devastating floods across New York and New Jersey.

      In their study, the MIT team applied the new compound flood-modeling method to New York City to predict how climate change may influence the risk of compound flooding from Sandy-like hurricanes over the next decades.  

      They found that, in today’s climate, a Sandy-level compound flooding event will likely hit New York City every 150 years. By midcentury, a warmer climate will drive up the frequency of such flooding, to every 60 years. At the end of the century, destructive Sandy-like floods will deluge the city every 30 years — a fivefold increase compared to the present climate.

      “Long-term average damages from weather hazards are usually dominated by the rare, intense events like Hurricane Sandy,” says study co-author Kerry Emanuel, professor emeritus of atmospheric science at MIT. “It is important to get these right.”

      While these are sobering projections, the researchers hope the flood forecasts can help city planners prepare and protect against future disasters. “Our methodology equips coastal city authorities and policymakers with essential tools to conduct compound flooding risk assessments from hurricanes in coastal cities at a detailed, granular level, extending to each street or building, in both current and future decades,” says study author Ali Sarhadi, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences.

      The team’s open-access study appears online today in the Bulletin of the American Meteorological Society. Co-authors include Raphaël Rousseau-Rizzi at MIT’s Lorenz Center, Kyle Mandli at Columbia University, Jeffrey Neal at the University of Bristol, Michael Wiper at the Charles III University of Madrid, and Monika Feldmann at the Swiss Federal Institute of Technology Lausanne.

      The seeds of floods

      To forecast a region’s flood risk, weather modelers typically look to the past. Historical records contain measurements of previous hurricanes’ wind speeds, rainfall, and spatial extent, which scientists use to predict where and how much flooding may occur with coming storms. But Sarhadi believes that the limitations and brevity of these historical records are insufficient for predicting future hurricanes’ risks.

      “Even if we had lengthy historical records, they wouldn’t be a good guide for future risks because of climate change,” he says. “Climate change is changing the structural characteristics, frequency, intensity, and movement of hurricanes, and we cannot rely on the past.”

      Sarhadi and his colleagues instead looked to predict a region’s risk of hurricane flooding in a changing climate using a physics-based risk assessment methodology. They first paired simulations of hurricane activity with coupled ocean and atmospheric models over time. With the hurricane simulations, developed originally by Emanuel, the researchers virtually scatter tens of thousands of “seeds” of hurricanes into a simulated climate. Most seeds dissipate, while a few grow into category-level storms, depending on the conditions of the ocean and atmosphere.

      When the team drives these hurricane simulations with climate models of ocean and atmospheric conditions under certain global temperature projections, they can see how hurricanes change, for instance in terms of intensity, frequency, and size, under past, current, and future climate conditions.

      The team then sought to precisely predict the level and degree of compound flooding from future hurricanes in coastal cities. The researchers first used rainfall models to simulate rain intensity for a large number of simulated hurricanes, then applied numerical models to hydraulically translate that rainfall intensity into flooding on the ground during landfalling of hurricanes, given information about a region such as its surface and topography characteristics. They also simulated the same hurricanes’ storm surges, using hydrodynamic models to translate hurricanes’ maximum wind speed and sea level pressure into surge height in coastal areas. The simulation further assessed the propagation of ocean waters into coastal areas, causing coastal flooding.

      Then, the team developed a numerical hydrodynamic model to predict how two sources of hurricane-induced flooding, such as storm surge and rain-driven flooding, would simultaneously interact through time and space, as simulated hurricanes make landfall in coastal regions such as New York City, in both current and future climates.  

      “There’s a complex, nonlinear hydrodynamic interaction between saltwater surge-driven flooding and freshwater rainfall-driven flooding, that forms compound flooding that a lot of existing methods ignore,” Sarhadi says. “As a result, they underestimate the risk of compound flooding.”

      Amplified risk

      With their flood-forecasting method in place, the team applied it to a specific test case: New York City. They used the multipronged method to predict the city’s risk of compound flooding from hurricanes, and more specifically from Sandy-like hurricanes, in present and future climates. Their simulations showed that the city’s odds of experiencing Sandy-like flooding will increase significantly over the next decades as the climate warms, from once every 150 years in the current climate, to every 60 years by 2050, and every 30 years by 2099.

      Interestingly, they found that much of this increase in risk has less to do with how hurricanes themselves will change with warming climates, but with how sea levels will increase around the world.

      “In future decades, we will experience sea level rise in coastal areas, and we also incorporated that effect into our models to see how much that would increase the risk of compound flooding,” Sarhadi explains. “And in fact, we see sea level rise is playing a major role in amplifying the risk of compound flooding from hurricanes in New York City.”

      The team’s methodology can be applied to any coastal city to assess the risk of compound flooding from hurricanes and extratropical storms. With this approach, Sarhadi hopes decision-makers can make informed decisions regarding the implementation of adaptive measures, such as reinforcing coastal defenses to enhance infrastructure and community resilience.

      “Another aspect highlighting the urgency of our research is the projected 25 percent increase in coastal populations by midcentury, leading to heightened exposure to damaging storms,” Sarhadi says. “Additionally, we have trillions of dollars in assets situated in coastal flood-prone areas, necessitating proactive strategies to reduce damages from compound flooding from hurricanes under a warming climate.”

      This research was supported, in part, by Homesite Insurance. More

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      in Environment

      3 Questions: How are cities managing record-setting temperatures?

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      July 2023 was the hottest month globally since humans began keeping records. People all over the U.S. experienced punishingly high temperatures this summer. In Phoenix, there were a record-setting 31 consecutive days with a high temperature of 110 degrees Fahrenheit or more. July was the hottest month on record in Miami. A scan of high temperatures around the country often yielded some startlingly high numbers: Dallas, 110 F; Reno, 108 F; Salt Lake City, 106 F; Portland, 105 F.

      Climate change is a global and national crisis that cannot be solved by city governments alone, but cities suffering from it can try to enact new policies reducing emissions and adapting its effects. MIT’s David Hsu, an associate professor of urban and environmental planning, is an expert on metropolitan and regional climate policy. In one 2017 paper, Hsu and some colleagues estimated how 11 major U.S. cities could best reduce their carbon dioxide emissions, through energy-efficient home construction and retrofitting, improvements in vehicle gas mileage, more housing density, robust transit systems, and more. As we near the end of this historically hot summer, MIT News talked to Hsu about what cities are now doing in response to record heat, and the possibilities for new policy measures.

      Q: We’ve had record-setting temperatures in many cities across the U.S. this summer. Dealing with climate change certainly isn’t just the responsibility of those cities, but what have they been doing to make a difference, to the extent they can?

      A: I think this is a very top-of-mind question because even 10 or 15 years ago, we talked about adapting to a changed climate future, which seemed further off. But literally every week this summer we can refer to [dramatic] things that are already happening, clearly linked to climate change, and are going to get worse. We had wildfire smoke in the Northeast and throughout the Eastern Seaboard in June, this tragic wildfire in Hawaii that led to more deaths than any other wildfire in the U.S., [plus record high temperatures]. A lot of city leaders face climate challenges they thought were maybe 20 or 30 years in the future, and didn’t expect to see happen with this severity and intensity.

      One thing you’re seeing is changes in governance. A lot of cities have recently appointed a chief heat officer. Miami and Phoenix have them now, and this is someone responsible for coordinating response to heat waves, which turn out to be one of the biggest killers among climatological effects. There is an increasing realization not only among local governments, but insurance companies and the building industry, that flooding is going to affect many places. We have already seen flooding in the seaport area in Boston, the most recently built part of our city. In some sense just the realization among local governments, insurers, building owners, and residents, that some risks are here and now, already is changing how people think about those risks.

      Q: To what extent does a city being active about climate change at least signal to everyone, at the state or national level, that we have to do more? At the same time, some states are reacting against cities that are trying to institute climate initiatives and trying to prevent clean energy advances. What is possible at this point?

      A: We have this very large, heterogeneous and polarized country, and we have differences between states and within states in how they’re approaching climate change. You’ve got some cities trying to enact things like natural gas bans, or trying to limit greenhouse gas emissions, with some state governments trying to preempt them entirely. I think cities have a role in showing leadership. But one thing I harp on, having worked in city government myself, is that sometimes in cities we can be complacent. While we pride ourselves on being centers of innovation and less per-capita emissions — we’re using less than rural areas, and you’ll see people celebrating New York City as the greenest in the world — cities are responsible for consumption that produces a majority of emissions in most countries. If we’re going to decarbonize society, we have to get to zero altogether, and that requires cities to act much more aggressively.

      There is not only a pessimistic narrative. With the Inflation Reduction Act, which is rapidly accelerating the production of renewable energy, you see many of those subsidies going to build new manufacturing in red states. There’s a possibility people will see there are plenty of better paying, less dangerous jobs in [clean energy]. People don’t like monopolies wherever they live, so even places people consider fairly conservative would like local control [of energy], and that might mean greener jobs and lower prices. Yes, there is a doomscrolling loop of thinking polarization is insurmountable, but I feel surprisingly optimistic sometimes.

      Large parts of the Midwest, even in places people think of as being more conservative, have chosen to build a lot of wind energy, partly because it’s profitable. Historically, some farmers were self-reliant and had wind power before the electrical grid came. Even now in some places where people don’t want to address climate change, they’re more than happy to have wind power.

      Q: You’ve published work on which cities can pursue which policies to reduce emissions the most: better housing construction, more transit, more fuel-efficient vehicles, possibly higher housing density, and more. The exact recipe varies from place to place. But what are the common threads people can think about?

      A: It’s important to think about what the status quo is, and what we should be preparing for. The status quo simply doesn’t serve large parts of the population right now. Heat risk, flooding, and wildfires all disproportionately affect populations that are already vulnerable. If you’re elderly, or lack access to mobility, information, or warnings, you probably have a lower risk of surviving a wildfire. Many people do not have high-quality housing, and may be more exposed to heat or smoke. We know the climate has already changed, and is going to change more, but we have failed to prepare for foreseeable changes that already here. Lots of things that are climate-related but not only about climate change, like affordable housing, transportation, energy access for everyone so they can have services like cooking and the internet — those are things that we can change going forward. The hopeful message is: Cities are always changing and being built, so we should make them better. The urgent message is: We shouldn’t accept the status quo. More

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      in Environment

      Explained: The 1.5 C climate benchmark

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      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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      in Environment

      Preparing Colombia’s cities for life amid changing forests

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      It was an uncharacteristically sunny morning as Marcela Angel MCP ’18, flanked by a drone pilot from the Boston engineering firm AirWorks and a data collection team from the Colombian regional environmental agency Corpoamazonia, climbed a hill in the Andes Mountains of southwest Colombia. The area’s usual mountain cloud cover — one of the major challenges to working with satellite imagery or flying UAVs (unpiloted aerial vehicles, or drones) in the Pacific highlands of the Amazon — would roll through in the hours to come. But for now, her team had chosen a good day to hike out for their first flight. Angel is used to long travel for her research. Raised in Bogotá, she maintained strong ties to Colombia throughout her master’s program in the MIT Department of Urban Studies and Planning (DUSP). Her graduate thesis, examining Bogotá’s management of its public green space, took her regularly back to her hometown, exploring how the city could offer residents more equal access to the clean air, flood protection and day-to-day health and social benefits provided by parks and trees. But the hill she was hiking this morning, outside the remote city of Mocoa, had taken an especially long time to climb: five years building relationships with the community of Mocoa and the Colombian government, recruiting project partners, and navigating the bureaucracy of bringing UAVs into the country. Now, her team finally unwrapped their first, knee-high drone from its tarp and set it carefully in the grass. Under the gathering gray clouds, the buzz of its rotors joined the hum of insects in the trees, and the machine at last took to the skies.

      From Colombia to Cambridge

      “I actually grew up on the last street before the eastern mountains reserve,” Angel says of her childhood in Bogotá. “I’ve always been at that border between city and nature.” This idea, that urban areas are married to the ecosystems around them, would inform Angel’s whole education and career. Before coming to MIT, she studied architecture at Bogotá’s Los Andes University; for her graduation project she proposed a plan to resettle an informal neighborhood on Bogotá’s outskirts to minimize environmental risks to its residents. Among her projects at MIT was an initiative to spatially analyze Bogotá’s tree canopy, providing data for the city to plan a tree-planting program as a strategy to give vulnerable populations in the city more access to nature. And she was naturally intrigued when Colombia’s former minister of environment and sustainable development came to MIT in 2017 to give a guest presentation to the DUSP master’s program. The minister, Luis Gilberto Murillo (now the Colombian ambassador to the United States), introduced the students to the challenges triggered by a recent disaster in the city of Mocoa, on the border between the lowland Amazon and the Andes Mountains. Unprecedented rainstorms had destabilized the surrounding forests, and that April a devastating flood and landslide had killed hundreds of people and destroyed entire neighborhoods. And as climate change contributed to growing rainfall in the region, the risks of more landslide events were rising. Murillo provided useful insights into how city planning decisions had contributed to the crisis. But he also asked for MIT’s support addressing future landslide risks in the area. Angel and Juan Camilo Osorio, a PhD candidate at DUSP, decided to take up the challenge, and in January 2018 and 2019, a research delegation from MIT traveled to Colombia for a newly-created graduate course. Returning once again to Bogotá, Angel interviewed government agencies and nonprofits to understand the state of landslide monitoring and public policy. In Mocoa, further interviews and a series of workshops helped clarify what locals needed most and what MIT could provide: better information on where and when landslides might strike, and a process to increase risk awareness and involve traditionally marginalized groups in decision-making processes around that risk. Over the coming year, a core team formed to put the insights from this trip into action, including Angel, Osorio, postdoc Norhan Bayomi of the MIT Environmental Solutions Initiative (ESI) and MIT Professor John Fernández, director of the ESI and one of Angel’s mentors at DUSP. After a second visit to Mocoa that brought into the fold Indigenous groups, environmental agencies, and the national army, a plan was formed: MIT would partner with Corpoamazonia and build a network of community researchers to deploy and test drone technology and machine learning models to monitor the mountain forests for both landslide risks and signs of forest health, while implementing a participatory planning process with residents. “What our projects aim to do is give the communities new tools to continue protecting and restoring the forest,” says Angel, “and support new and inclusive development models, even in the face of new challenges.”

      Lifelines for the climate

      The goal of tropical forest conservation is an urgent one. As forests are cut down, their trees and soils release carbon they have stored over millennia, adding huge amounts of heat-trapping carbon dioxide to the atmosphere. Deforestation, mainly in the tropics, is now estimated to contribute more to climate change than any country besides the United States and China — and once lost, tropical forests are exceptionally hard to restore. “Tropical forests should be a natural way to slow and reverse climate change,” says Angel. “And they can be. But today, we are reaching critical tipping points where it is just the opposite.” This became the motivating force for Angel’s career after her graduation. In 2019, Fernández invited her to join the ESI and lead a new Natural Climate Solutions Program, with the Mocoa project as its first centerpiece. She quickly mobilized the partners to raise funding for the project from the Global Environmental Facility and the CAF Development Bank of Latin America and the Caribbean, and recruited additional partners including MIT Lincoln Laboratories, AirWorks, and the Pratt Institute, where Osorio had become an assistant professor. She hired machine learning specialists from MIT to begin design on UAVs’ data processing, and helped assemble a local research network in Mocoa to increase risk awareness, promote community participation, and better understand what information city officials and community groups needed for city planning and conservation. “This is the amazing thing about MIT,” she says. “When you study a problem here, you’re not just playing in a sandbox. Everyone I’ve worked with is motivated by the complexity of the technical challenge and the opportunity for meaningful engagement in Mocoa, and hopefully in many more places besides.” At the same time, Angel created opportunities for the next generation of MIT graduate students to follow in her footsteps. With Fernández and Bayomi, she created a new course, 4.S23 (Biodiversity and Cities), in which students traveled to Colombia to develop urban planning strategies for the cities of Quidbó and Leticia, located in carbon-rich and biodiverse areas. The course has been taught twice, with Professor Gabriella Carolini joining the teaching team for spring 2023, and has already led to a student report to city officials in Quidbó recommending ways to enhance biodiversity and adapt to climate change as the city grows, a multi-stakeholder partnership to train local youth and implement a citizen-led biodiversity survey, and a seed grant from the MIT Climate and Sustainability Consortium to begin providing both cities detailed data on their tree cover derived from satellite images. “These regions face serious threats, especially on a warming planet, but many of the solutions for climate change, biodiversity conservation, and environmental equity in the region go hand-in-hand,” Angel says. “When you design a city to use fewer resources, to contribute less to climate change, it also causes less pressure on the environment around it. When you design a city for equity and quality of life, you’re giving attention to its green spaces and what they can provide for people and as habitat for other species. When you protect and restore forests, you’re protecting local bioeconomies.”

      Bringing the data home

      Meanwhile, in Mocoa, Angel’s original vision is taking flight. With the team’s test flights behind them, they can now begin creating digital models of the surrounding area. Regular drone flights and soil samples will fill in changing information about trees, water, and local geology, allowing the project’s machine learning specialists to identify warning signs for future landslides and extreme weather events. More importantly, there is now an established network of local community researchers and leaders ready to make use of this information. With feedback from their Mocoan partners, Angel’s team has built a prototype of the online platform they will use to share their UAV data; they’re now letting Mocoa residents take it for a test drive and suggest how it can be made more user-friendly. Her visit this January also paved the way for new projects that will tie the Environmental Solutions Initiative more tightly to Mocoa. With her project partners, Angel is exploring developing a course to teach local students how to use UAVs like the ones her team is flying. She is also considering expanded efforts to collect the kind of informal knowledge of Mocoa, on the local ecology and culture, that people everywhere use in making their city planning and emergency response decisions, but that is rarely codified and included in scientific risk analyses. It’s a great deal of work to offer this one community the tools to adapt successfully to climate change. But even with all the robotics and machine learning models in the world, this close, slow-unfolding engagement, grounded in trust and community inclusion, is what it takes to truly prepare people to confront profound changes in their city and environment. “Protecting natural carbon sinks is a global socio-environmental challenge, and one where it is not enough for MIT to just contribute to the knowledge base or develop a new technology,” says Angel. “But we can help mobilize decision-makers and nontraditional actors, and design more inclusive and technology-enhanced processes, to make this easier for the people who have lifelong stakes in these ecosystems. That is the vision.” More

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      in Environment

      Q&A: Are far-reaching fires the new normal?

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      Where there’s smoke, there is fire. But with climate change, larger and longer-burning wildfires are sending smoke farther from their source, often to places that are unaccustomed to the exposure. That’s been the case this week, as smoke continues to drift south from massive wildfires in Canada, prompting warnings of hazardous air quality, and poor visibility in states across New England, the mid-Atlantic, and the Midwest.

      As wildfire season is just getting going, many may be wondering: Are the air-polluting effects of wildfires a new normal?

      MIT News spoke with Professor Colette Heald of the Department of Civil and Environmental Engineering and the Department of Earth, Atmospheric and Planetary Sciences, and Professor Noelle Selin of the Institute for Data, Systems and Society and the Department of Earth, Atmospheric and Planetary Sciences. Heald specializes in atmospheric chemistry and has studied the climate and health effects associated with recent wildfires, while Selin works with atmospheric models to track air pollutants around the world, which she uses to inform policy decisions on mitigating  pollution and climate change. The researchers shared some of their insights on the immediate impacts of Canada’s current wildfires and what downwind regions may expect in the coming months, as the wildfire season stretches into summer.  

      Q: What role has climate change and human activity played in the wildfires we’ve seen so far this year?

      Heald: Unusually warm and dry conditions have dramatically increased fire susceptibility in Canada this year. Human-induced climate change makes such dry and warm conditions more likely. Smoke from fires in Alberta and Nova Scotia in May, and Quebec in early June, has led to some of the worst air quality conditions measured locally in Canada. This same smoke has been transported into the United States and degraded air quality here as well. Local officials have determined that ignitions have been associated with lightning strikes, but human activity has also played a role igniting some of the fires in Alberta.

      Q: What can we expect for the coming months in terms of the pattern of wildfires and their associated air pollution across the United States?

      Heald: The Government of Canada is projecting higher-than-normal fire activity throughout the 2023 fire season. Fire susceptibility will continue to respond to changing weather conditions, and whether the U.S. is impacted will depend on the winds and how air is transported across those regions. So far, the fire season in the United States has been below average, but fire risk is expected to increase modestly through the summer, so we may see local smoke influences as well.

      Q: How has air pollution from wildfires affected human health in the U.S. this year so far?

      Selin: The pollutant of most concern in wildfire smoke is fine particulate matter (PM2.5) – fine particles in the atmosphere that can be inhaled deep into the lungs, causing health damages. Exposure to PM2.5 causes respiratory and cardiovascular damage, including heart attacks and premature deaths. It can also cause symptoms like coughing and difficulty breathing. In New England this week, people have been breathing much higher concentrations of PM2.5 than usual. People who are particularly vulnerable to the effects are likely experiencing more severe impacts, such as older people and people with underlying conditions. But PM2.5 affects everyone. While the number and impact of wildfires varies from year to year, the associated air pollution from them generally lead to tens of thousands of premature deaths in the U.S. overall annually. There is also some evidence that PM2.5 from fires could be particularly damaging to health.

      While we in New England usually have relatively lower levels of pollution, it’s important also to note that some cities around the globe experience very high PM2.5 on a regular basis, not only from wildfires, but other sources such as power plants and industry. So, while we’re feeling the effects over the past few days, we should remember the broader importance of reducing PM2.5 levels overall for human health everywhere.

      Q: While firefighters battle fires directly this wildfire season, what can we do to reduce the effects of associated air pollution? And what can we do in the long-term, to prevent or reduce wildfire impacts?

      Selin: In the short term, protecting yourself from the impacts of PM2.5 is important. Limiting time outdoors, avoiding outdoor exercise, and wearing a high-quality mask are some strategies that can minimize exposure. Air filters can help reduce the concentrations of particles in indoor air. Taking measures to avoid exposure is particularly important for vulnerable groups. It’s also important to note that these strategies aren’t equally possible for everyone (for example, people who work outside) — stressing the importance of developing new strategies to address the underlying causes of increasing wildfires.

      Over the long term, mitigating climate change is important — because warm and dry conditions lead to wildfires, warming increases fire risk. Preventing the fires that are ignited by people or human activities can help.  Another way that damages can be mitigated in the longer term is by exploring land management strategies that could help manage fire intensity. More

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      in Environment

      3 Questions: New MIT major and its role in fighting climate change

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      Launched this month, MIT’s new Bachelor of Science in climate system science and engineering is jointly offered by the departments of Civil and Environmental Engineering (CEE) and Earth, Atmospheric and Planetary Sciences (EAPS). As part of MIT’s commitment to aid the global response to climate change, the new degree program is designed to train the next generation of leaders, providing a foundational understanding of both the Earth system and engineering principles — as well as an understanding of human and institutional behavior as it relates to the climate challenge. Jadbabaie and Van der Hilst discuss the new Course 1-12 multidisciplinary major and why it’s needed now at MIT. 

      Q: What was the idea behind launching this new major at MIT?

      Jadbabaie: Climate change is an incredibly important issue that we must address, and time is of the essence. MIT is in a unique position to play a leadership role in this effort. We not only have the ability to advance the science of climate change and deepen our understanding of the climate system, but also to develop innovative engineering solutions for sustainability that can help us meet the climate goals set forth in the Paris Agreement. It is important that our educational approach also incorporates other aspects of this cross-cutting issue, ranging from climate justice, policy, to economics, and MIT is the perfect place to make this happen. With Course 1’s focus on sustainability across scales, from the nano to the global scale, and with Course 12 studying Earth system science in general, it was a natural fit for CEE and EAPS to tackle this challenge together. It is my belief that we can leverage our collective expertise and resources to make meaningful progress. There has never been a more crucial time for us to advance students’ understanding of both climate science and engineering, as well as their understanding of the societal implications of climate risk.

      Van der Hilst: Climate change is a global issue, and the solutions we urgently need for building a net-zero future must consider how everything is connected. The Earth’s climate is a complex web of cause and effect between the oceans, atmosphere, ecosystems, and processes that shape the surface and environmental systems of the planet. To truly understand climate risks, we need to understand the fundamental science that governs these interconnected systems — and we need to consider the ways that human activity influences their behavior. The types of large-scale engineering projects that we need to secure a sustainable future must take into consideration the Earth system itself. A systems approach to modeling is crucial if we are to succeed at inventing, designing, and implementing solutions that can reduce greenhouse gas emissions, build climate resilience, and mitigate the inevitable climate-related natural disasters that we’ll face. That’s why our two departments are collaborating on a degree program that equips students with foundational climate science knowledge alongside fundamental engineering principles in order to catalyze the innovation we’ll need to meet the world’s 2050 goals.

      Q: How is MIT uniquely positioned to lead undergraduate education in climate system science and engineering? 

      Jadbabaie: It’s a great example of how MIT is taking a leadership role and multidisciplinary approach to tackling climate change by combining engineering and climate system science in one undergraduate major. The program leverages MIT’s academic strengths, focusing on teaching hard analytical and computational skills while also providing a curriculum that includes courses in a wide range of topics, from climate economics and policy to ethics, climate justice, and even climate literature, to help students develop an understanding of the political and social issues that are tied to climate change. Given the strong ties between courses 1 and 12, we want the students in the program to be full members of both departments, as well as both the School of Engineering and the School of Science. And, being MIT, there is no shortage of opportunities for undergraduate research and entrepreneurship — in fact, we specifically encourage students to participate in the active research of the departments. The knowledge and skills our students gain will enable them to serve the nation and the world in a meaningful way as they tackle complex global-scale environmental problems. The students at MIT are among the most passionate and driven people out there. I’m really excited to see what kind of innovations and solutions will come out of this program in the years to come. I think this undergraduate major is a fantastic step in the right direction.

      Q: What opportunities will the major provide to students for addressing climate change?

      Van der Hilst: Both industry and government are actively seeking new talent to respond to the challenges — and opportunities — posed by climate change and our need to build a sustainable future. What’s exciting is that many of the best jobs in this field call for leaders who can combine the analytical skill of a scientist with the problem-solving mindset of an engineer. That’s exactly what this new degree program at MIT aims to prepare students for — in an expanding set of careers in areas like renewable energy, civil infrastructure, risk analysis, corporate sustainability, environmental advocacy, and policymaking. But it’s not just about career opportunities. It’s also about making a real difference and safeguarding our future. It’s not too late to prevent much more damaging changes to Earth’s climate. Indeed, whether in government, industry, or academia, MIT students are future leaders — as such it is critically important that all MIT students understand the basics of climate system science and engineering along with math, physics, chemistry, and biology. The new Course 1-12 degree was designed to forge students who are passionate about protecting our planet into the next generation of leaders who can fast-track high-impact, science-based solutions to aid the global response, with an eye toward addressing some of the uneven social impacts inherent in the climate crisis. More

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      in Environment

      Preparing to be prepared

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      The Kobe earthquake of 1995 devastated one of Japan’s major cities, leaving over 6,000 people dead while destroying or making unusable hundreds of thousands of structures. It toppled elevated freeway segments, wrecked mass transit systems, and damaged the city’s port capacity.

      “It was a shock to a highly engineered, urban city to have undergone that much destruction,” says Miho Mazereeuw, an associate professor at MIT who specializes in disaster resilience.

      Even in a country like Japan, with advanced engineering, and policies in place to update safety codes, natural forces can overwhelm the built environment.

      “There’s nothing that’s ever guaranteed safe,” says Mazereeuw, an associate professor of architecture and urbanism in MIT’s Department of Architecture and director of the Urban Risk Lab. “We [think that] through technology and engineering we can solve things and fight nature. Whereas it’s really that we’re living with nature. We’re part of this natural ecosystem.”

      That’s why Mazereeuw’s work on disaster resilience focuses on plans, people, and policies, well as technology and design to prepare for the future. In the Urban Risk Lab, which Mazereeuw founded, several projects are based on the design of physical objects, spaces, and software platforms, but many others involve community-level efforts, so that local governments have workable procedures in case of emergency.

      “What we can do for ourselves and each other is have plans in place so that if something does happen, the level of chaos and fear can be reduced and we can all be there to help each other through,” Mazereeuw says. When it comes to disaster preparedness, she adds, “Definitely a lot of it is on the built environment side of things, but a lot of it is also social, making sure that in our communities, we know who would need help, and we have those kinds of relationships beforehand.”

      The Kobe earthquake was a highly influential event for Mazereeuw. She has researched the response to it and has a book coming out about natural disasters, policies, and design in Japan. Beyond that, the Kobe event helped reinforce her sense that when it comes to disaster preparedness, progress can be made many ways. For her research, teaching, and innovative work at the Urban Risk Lab, Mazereeuw was granted tenure at MIT last year.

      Two cultures grappling with nature

      Mazereeuw has one Dutch parent and one Japanese parent, and both cultures helped produce her interest in managing natural forces. On her Dutch side, many family friends were involved with local government and water management — practically an existential issue in a country that sits largely below sea level.

      Mazereeuw’s parents, however, were living in Japan in 1995. And while they happened to be away while the Kobe earthquake hit, her Japanese links helped spur her interest in studying the event and its aftermath.

      “I think that was a wake-up call for me, too, about how we need to plan and design cities to reduce the impact of chaos at the time of disasters,” Mazereeuw says.

      Mazereeuw earned her undergraduate degree from Wesleyan University, majoring in earth and environmental sciences and in studio art. After working in an architectural office in Tokyo, she decided to attend graduate school, receiving her dual masters from Harvard University’s Graduate School of Design, with a thesis about Kobe and disaster readiness. She then worked in architecture offices, including the Office of Metropolitan Architecture in Rotterdam, but returned to academia to work on climate change and disaster resilience.   

      Mazereeuw’s book, “Design Before Disaster,” explores this subject in depth, from urban planning to coastal-safety strategies to community-based design frameworks, and is forthcoming from the University of Virginia Press.

      Since joining the MIT faculty, Mazereeuw has also devoted significant time to the launch and growth of the Urban Risk Lab, an interdisciplinary group working on an array of disaster-preparedness efforts. One such project has seen lab members work with local officials from many places — including Massachusetts, California, Georgia, and Puerto Rico — to add to their own disaster-preparedness planning.

      A plan developed by local officials with community input, Mazereeuw suggests, will likely function better than one produced by, say, consultants from outside a community, as she has seen happen many times: “A report on a dusty shelf isn’t actionable,” she says. “This way it’s a decision-making process by the people involved.”

      In a project based on physical design, the Urban Risk Lab has also been working with the U.S. Federal Emergency Management Agency on an effort to produce temporary postdisaster housing for the OCONUS region (Alaska, Hawaii, and other U.S. overseas territories). The lab’s design, called SEED (Shelter for Emergency Expansion Design), features a house that is compact enough to be shipped anywhere and unfolds on-site, while being sturdy enough to withstand follow-up events such as hurricanes, and durable enough to be incorporated into longer-term housing designs.

      “We felt it had to be really, really good quality, so it would be a resource, rather than something temporary that disintegrates after five years,” Mazereeuw says. “It’s built to be a small safety shelter but also could be part of a permanent house.”

      A grand challenge, and a plethora of projects

      Mazereeuw is also a co-lead of one of the five multiyear projects selected in 2022 to move forward as part of MIT’s Climate Grand Challenges competition. Along with Kerry Emanuel and Paul O’Gorman, of MIT’s Department of Earth, Atmospheric and Planetary Sciences, Mazereeuw will help direct a project advancing climate modeling by quantifying the risk of extreme weather events for specific locations. The idea is to help vulnerable urban centers and other communities prepare for such events.

      The Urban Risk Lab has many other kinds of projects in its portfolio, following Mazereeuw’s own interest in conceptualizing disaster preparedness broadly. In collaboration with officials in Japan, and with support from Google, lab members worked on interactive, real-time flood-mapping software, in which residents can help officials know where local flooding has reached emergency levels. The researchers also created an AI module to prioritize the information.

      “Residents really have the most localized information, which you can’t get from a satellite,” Mazereeuw says. “They’re also the ones who learn about it first, so they have a lot of information that emergency managers can use for their response. The program is really meant to be a conduit between the efforts of emergency managers and residents, so that information flow can go in both directions.”

      Lab members in the past have also mapped the porosity of the MIT campus, another effort that used firsthand knowledge. Additionally, lab members are currently engaging with a university in Chile to design tsunami response strategies; developing a community mapping toolkit for resilience planning in Thailand and Vietnam; and working with Mass Audubon to design interactive furniture for children to learn about ecology.  

      “Everything is tied together with this interest in raising awareness and engaging people,” Mazereeuw says.

      That also describes Mazereeuw’s attitude about participation in the Urban Risk Lab, a highly cross-disciplinary place with members who have gravitated to it from around MIT.

      “Our lab is extremely interdisciplinary,” Mazereeuw says. “We have students coming in from all over, from different parts of campus. We have computer science and engineering students coming into the lab and staying to get their graduate degrees alongside many architecture and planning students.” The lab also has five full-time researchers — Aditya Barve, Larisa Ovalles, Mayank Ojha, Eakapob Huangthananpan, and Saeko Baird — who lead their own projects and research groups.

      What those lab members have in common is a willingness to think proactively about reducing disaster impacts. Being prepared for those events itself requires preparation.

      Even in the design world, Mazereeuw says, “People are reactive. Because something has happened, that’s when they go in to help. But I think we can have a larger impact by anticipating and designing for these issues beforehand.” 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