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Floating along Venus’s thick atmosphere are shadowy patches, morphing in shape and size, like huge algal blooms. Scientists first photographed these atmospheric features in 1927, and some researchers have suggested that these so-called unknown absorbers could be signs of life.

“Could there be life in the clouds?”“For all we know [they] could be bacteria,” said Sanjay Limaye, a planetary scientist at the University of Wisconsin–Madison. “Could there be life in the clouds?”

Although scientists have their hypotheses, no one has confirmed what is causing the dark areas in the atmosphere. NASA’s new mission to Venus, DAVINCI+ (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, and Imaging), may bring scientists closer to an answer.

DAVINCI+ Answers the Call

The mission, announced in June, will drop a probe into Venus’s clouds—a beach ball–sized titanium sphere that will dive through the atmosphere and, for more than an hour, collect data while falling about 70 kilometers (43.5 miles). This mission, scheduled to launch between 2028 and 2030, will be the first time a spacecraft will probe the planet’s atmosphere in situ since 1985 when the Soviet Union’s Vega 2 investigated the planet’s atmosphere.

“We’re still trying to get the right measurements to simply ask the right questions.”Set to launch around 2029, DAVINCI+ isn’t designed to detect life. “We’re still trying to get the right measurements to simply ask the right questions,” said Jim Garvin, DAVINCI+’s principal investigator. But among the mission’s other scientific goals, researchers hope it will help solve the mystery of these atmospheric patches and, more broadly, provide a deeper understanding of the atmosphere, which is crucial for determining Venus’s habitability.

An Old, Unanswered Question

Is there life on Venus? Because Venus has many similarities to Earth—such as its size and interior composition—many scientists once thought Venus could be an oasis for life. But when spacecraft began exploring Venus in the 1960s, they uncovered an inhospitable surface environment. The planet showcases a thick carbon dioxide atmosphere with crushing average pressures 92 times those at Earth’s sea level and surface temperatures hot enough to melt lead.

Then in 1967, Harold Morowitz and Carl Sagan proposed that although life can’t survive on the surface, some microbes may possibly survive in the clouds. Early Venus missions found evidence of water vapor in the atmosphere. In the cloud layers roughly 50 kilometers (30 miles) above the planet’s surface, atmospheric pressures are comparable to those at Earth’s sea level, and temperatures range between 100°C (212°F) and 60°C (140°F)—much cooler and more hospitable than the surface. On Earth, for instance, some organisms—such as microbes in hydrothermal vents—can survive in temperatures as high as 121°C (249.8°F).

In addition, the patches are created when something, perhaps microbes or some biological process, absorbs primarily ultraviolet light from the Sun amounting to about half the Sun’s energy that reaches Venus, according to Limaye. In 2018, Limaye and his colleagues found that the patches absorbed light at many of the same wavelengths as some terrestrial bacteria and biological molecules, such as proteins.

Using DAVINCI+ to Get One Step Closer

The unknown absorbers, of course, could be nonbiological. Scientists have already detected some sulfur-bearing compounds in Venus’s atmosphere that absorb at least some of the ultraviolet light, and other similar chemical species might be the main cause of the dark patches, Garvin said. DAVINCI+ will try to help determine the chemistry that’s producing the bulk of these dark patches and perhaps point scientists toward a biological or nonbiological origin.

During two flybys before it releases the probe, the DAVINCI+ carrier spacecraft will try to identify the absorbers using a high-resolution ultraviolet spectrometer. An ultraviolet camera will also take videos of the clouds at high resolution and study how the dark patches move.

If life does exist in the clouds, it likely would have originated the same way it did on Earth: in an ocean. Some computer models of Venus’s ancient climate suggest it did once have a shallow ocean, chemical traces of which might still exist in the planet’s atmosphere. An onboard mass spectrometer will measure hydrogen and its chemical sibling deuterium to reveal how much water the surface has lost throughout Venus’s history. The probe’s laser spectrometer will not only help identify what’s absorbing ultraviolet light but also measure chemicals important for determining habitability, such as sulfuric acid, water, and chemical nutrients.

“It is a great time to be interested in Venus….We’re going to learn spectacular stuff.”Vastly superior to the instruments that last visited Venus decades ago, the spectrometers “are an order of magnitude higher in resolution [and] precision,” Garvin said.

DAVINCI+ won’t be alone at Venus. In the next decade, NASA, the European Space Agency, and the Indian Space Research Organisation will send three more spacecraft—VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy), EnVision, and a to-be-named orbiter—to the planet, beginning a new era of Venus exploration. “It is a great time to be interested in Venus,” Garvin said. “We’re going to learn spectacular stuff.”

—Jaime Cordova (@jaimecor_94), Science Writer

Although referred to as DAVINCI+ in this article, the mission is in the process of changing its name, from DAVINCI+ to DAVINCI.

This piece was produced with support from the National Association of Science Writers’ David Perlman Virtual Mentoring Program.

Rock glaciers are enigmatic landforms composed of mixtures of rock and ice that behave in a manner distinct from debris-free glaciers. The insulating properties of the rock debris contained within a rock glacier make these features resistant to climatic warming, but their evolution is poorly understood.

Cusicanqui et al. [2021] present, in unprecedented detail, an elegant investigation of the geometry and dynamics of Laurichard rock glacier in France. It spans nearly seven decades and provides a benchmark for future studies of these features.

The results demonstrate that while the net annual mass turnover of Laurichard rock glacier is close to zero, it is experiencing significant change—losing mass from the upper and middle sections while the lower section has advanced by over ten meters. The flow of the rock glacier is so slow, at less than one meter per year, that these recent changes may represent a response to cooling during the Little Ice Age about 200 years ago. However, an acceleration in rock glacier flow after the 1990s observed here and elsewhere in the European Alps is likely driven by increasing basal temperatures arising from recent climatic heating.

Citation: Cusicanqui, D., Rabatel, A., Vincent, C., Bodin, X., Thibert, E., & Francou, B. [2021]. Interpretation of volume and flux changes of the Laurichard rock glacier between 1952 and 2019, French Alps. Journal of Geophysical Research: Earth Surface, 126, e2021JF006161. https://doi.org/10.1029/2021JF006161

—Ann Rowan, Associate Editor, JGR: Earth Surface

A little bit of global warming may go a long way. A recent mathematical analysis of the climate of the Cenozoic­—our current geologic era, starting at the demise of the dinosaurs 66 million years ago—says that natural processes may amplify small amounts of warming, turning them into “hyperthermal” events that can last for thousands of years or longer. This finding suggests that human-induced climate change could make our planet susceptible to more extreme warming events in the future.

“We considered all of the fluctuations involved rather than picking out the big ones.”Scientists have studied several major Cenozoic warming events in detail, including the Paleocene-Eocene Thermal Maximum, in which global temperatures jumped by more than 5°C and remained elevated for tens of thousands of years. Such events can help scientists understand how the planet responds to climate changes and predict how it might react to current human-caused changes.

Constantin Arnscheidt and Daniel Rothman of the Lorenz Center at the Massachusetts Institute of Technology, however, decided to examine the climate–carbon cycle history of the entire period. Their study was published in Science Advances.

“We wanted to understand the more general behavior of sub-million-year climate–carbon cycle fluctuations throughout the Cenozoic,” said Arnscheidt, a graduate student and the study’s lead author. “And so, for the first time, we considered all of the fluctuations involved rather than picking out the big ones.”

Warming Bias

The researchers used a database of benthic foraminifera found in deep-ocean sediments. The single-celled organisms are protected by shells of calcium carbonate. Changes in surface temperature, surface inorganic carbon, ocean chemistry, and other climate factors alter the carbon and oxygen isotope ratios in the shells, making it possible for scientists to use them as climate proxies.

Arnscheidt and Rothman used statistical methods to analyze the database. “Climate fluctuations on a wide range of timescales are the result of many complex processes that are impossible to model exactly,” said Arnscheidt. “Stochastic models, which have long been employed to understand shorter-term climate variability, capture essential aspects of this behavior by including random-noise terms.”

Their results showed an imbalance between global warming and global cooling, with a strong bias toward extreme warming events. There were more warming than cooling events, they produced a greater swing in temperatures, and they lasted longer. This trend continued until the start of the Pliocene, about 5.3 million years ago, when the global climate cooled considerably and ice sheets began covering North America.

Unidentified natural processes pump additional carbon and other warming compounds into the atmosphere and increase the temperature, leading to extreme and long-lasting warming events.The bias in the statistics was consistent with the principle of “multiplicative noise,” in which the extent of changes in a system depends on its state. In this case, if temperature variations over periods of thousands or tens of thousands of years increase as the climate gets warmer, “this would result in a warming bias precisely like the one observed,” Arnscheidt said.

A warming bias would suggest that a little bit of global warming may trigger natural biological or geochemical processes (which the researchers say still need to be identified) that operate more efficiently under warmer conditions. These processes pump additional carbon and other warming compounds into the atmosphere and increase the temperature even more, leading to extreme and long-lasting warming events.

The initial impulse for warming events could come from changes in the eccentricity of Earth’s orbit, which varies over a period of about 100,000 years. Scientists have observed that some warming events appear to align with this cycle but haven’t been able to explain how the changing eccentricity could cause large climate swings. The new model suggests that although the initial change in climate caused by the cycle might be small, the multiplier effects could turn it into a major event.

Exploring Climate’s Operational Boundaries

The new study suggests that if current warming continues, the climate could become more susceptible to extreme warming events like those seen in the geologic record.“The paper does push us to explore much more Earth’s response to orbital forcing in the different climate states,” said Thomas Westerhold, director of the Center for Marine Environmental Sciences at the University of Bremen, Germany, who led the development of the foraminifera database but was not involved in this project. “The climate system seems to have operational boundaries that once they are passed, the system moves into a different state….We need to know where those boundaries are that once crossed, we cannot simply make undone.”

The study doesn’t say that multiplicative effects will boost the effects of anthropogenic climate change anytime soon, Arnscheidt noted. It does, however, suggest that if current warming continues, the climate could become more susceptible to extreme warming events like those seen in the geologic record.

“Fundamentally, this study highlights that there is much yet to be learned about the mechanisms governing Earth’s long-term climate evolution and that human climate forcing today may have far-reaching effects on the long-term future,” Arnscheidt said.

—Damond Benningfield (damond5916@att.net), Science Writer

Robbie Mallett often thinks about the first time he stood on old sea ice in the Arctic.

“It’s like a landscape,” he said. “It’s got ridges and landforms almost. It’s just an amazing place. And I think it’s a really sad thing that we’re basically losing a whole place.”

Mallett is a Ph.D. student and sea ice researcher at University College London. His most recent research accentuates how the loss of this sea ice landscape could accelerate because of one unique characteristic: It can float away.

In a new paper published in Communications Earth and Environment, Mallett and other researchers describe how powerful winds during the winter of 2020–2021 blew a vast amount of sea ice south into warmer waters, putting it at risk of melting over the summer.

A Sprawling High-Pressure System

“It almost wasn’t appropriate to call it the ‘Beaufort Sea high’ at all. It was just this huge, sprawling, high-pressure system that dominated the whole Arctic Ocean.”The investigation started after Mallett received an interesting email from his graduate adviser, Julienne Stroeve. She told him that an area of high pressure over the Beaufort Sea near the north coast of Alaska (the Beaufort Sea high) was unusually strong.

“It almost wasn’t appropriate to call it the ‘Beaufort Sea high’ at all,” Mallett said. “It was just this huge, sprawling, high-pressure system that dominated the whole Arctic Ocean.”

The location and strength of the Beaufort Sea high, associated with a sudden warming in the stratosphere on 5 January 2020, generated record-breaking surface winds that persistently swirled around the center of the Arctic Ocean. Mallett wanted to investigate how much older sea ice was at the whim of these winds.

Robbie Mallett experienced the perennial sea ice in the Arctic during a 2019 research expedition. Credit: Robbie Mallett Old Sea Ice Blew into the Beaufort Sea

Scientists are particularly interested in older sea ice, called perennial sea ice, that has lasted through at least one melt season. Perennial ice is thicker, so it has a better chance of surviving the summer months when its cooling properties are most crucial. “It shows up when you need it,” Mallett said.

The researchers used a series of satellite images in the microwave spectrum to track the ice flow over months. They also used data from the European Space Agency’s satellite CryoSat radar altimeter, which bounces pulses off the ice’s surface to determine its age based on how thick it is. “When you combine that with how the ice is moving, you can see what the old ice is getting up to,” said Mallett.

The winds associated with the strong Beaufort Sea high blew ice westward from the north of Greenland toward Alaska. The winds flushed first-year ice out of the Beaufort Sea, replacing it with old ice from the Arctic. By the end of the winter, nearly a quarter of all the perennial sea ice in the Arctic Ocean was in the Beaufort Sea, which is not a hospitable place for sea ice to spend the summer.

“It’s in a dangerous place,” Mallett said. “It’s in a place that is just much warmer, both in the air and water temperature.”

“Thinner Ice Is More Mobile”

Thinner ice in the Arctic is associated with the warming climate, and although the researchers did not attribute the events of last winter to climate change, Kent Moore, a University of Toronto atmospheric physicist, expects that thinner ice is generally a factor in ice transport. “Thinner ice is more mobile,” said Moore, who was not involved in the new research.

Moore is curious whether the ice tracked in 2020 was as mobile in other years when the Beaufort Sea high was extreme or the outcome was the consequence of thinner ice. If thinner ice were to blame, we might expect more ice to be blown around in the future.

“The last ice area may not be as resilient to climate change as we think.”Thinning ice appears to be affecting a stretch of the Arctic Ocean known as the last ice area, which scientists predicted will retain ice even after other regions become ice free in the summer. Last summer, ice blew out of the last ice area, and Mallett and colleagues also found that ice left the region last winter, although Mallett said it’s hard to know exactly how much.

“The last ice area may not be as resilient to climate change as we think,” Moore said.

For now, though, it’s not all bad news in the Beaufort Sea. New satellite data came out in early August, and Mallett said a lot of the ice is still intact.

“It’s surprised me how tough that ice has been in the Beaufort Sea,” Mallett said. “All we can do is wait for the next data release.”

—Andrew Chapman (@andrew7chapman), Science Writer

Basaltic melts erupting on the Earth’s surface preserve information on the temperature and pressure of the Earth’s upper mantle in the region where they form at several tens of kilometers mantle depth. The retrieval of the mantle temperatures – a key parameter to understanding mantle flow – is complicated, however, because the basaltic melts cool en route to surface and modify through crystallization of several mineral phases, such as olivine ± plagioclase ± clinopyroxene in variable extent and proportions. The accuracy of upper mantle temperatures thus critically depends on how well the individual crystallization paths can be reversed.

Krein et al. [2021] present a sophisticated automated algorithm named ‘ReversePetrogen’ (RevPET) that return erupted basaltic melts to ‘primary’ melts (that is melts in equilibrium with mantle prior to crystallization) by back-adding the most plausible mineral assemblage lost. Application of RevPET to existing large data sets of basaltic melts (n=13,589) from the global mid-ocean ridge system retrieves viable primary melts and associated mantle temperatures and pressures, for 72 percent of the data. The robustness of RevPET is validated through general consistency with earlier studies that predict comparable ranges of apparent mantle melting temperatures (Tp* = 1322°C ± 56°C) beneath the mid-ocean ridges.

While this result is remarkable, the true asset of the RevPET algorithm is that it allows to explore the interplay between basalt composition and the inherent mantle heterogeneity, melting mode and temperature. Thus, the RevPET tool is valuable for designing future experimental and observational studies that explore the thermal state of an inaccessible region of Earth.

Citation: Krein, S. B., Molitor, Z. J., & Grove, T. L. [2021]. ReversePetrogen: A Multiphase dry reverse fractional crystallization-mantle melting thermobarometer applied to 13,589 mid-ocean ridge basalt glasses. Journal of Geophysical Research: Solid Earth, 126, e2020JB021292. https://doi.org/10.1029/2020JB021292

—Susanne Straub, Associate Editor, JGR: Solid Earth

It is now widely accepted that both climate and tectonics interact to play a role in shaping mountain landscapes, but beyond that, uncertainty remains as to the degree to which each plays a role, and how. Mandal et al. [2021] report erosion rates based on cosmogenic 10Be measurements made on Siwalik Group sediments shed from Himalaya. As pointed out in an accompanying Viewpoint by Codilean and Sadler [2021], determining accurate erosion rates in this way is difficult, but the dataset raises interesting questions about the roles of tectonics and climate in active settings. Mandal et al. go on to propose that the ~1-Myr cyclicity evident in their dataset results not from a climate driver, but from an emergent phenomenon related to tectonic accretion of material to the Himalaya. This proposal will generate debate and stimulate more study of how specific sets of processes impact the coupled tectonic/climate system.

Citation: Kumar, S., Scherier, D. & Wittmann, H. [2021]. Tectonic accretion controls erosional cyclicity in the Himalaya. AGU Advances, 2, e2021AV000487. https://doi.org/10.1029/2021AV000487

—Peter Zeitler, Editor, AGU Advances

Global methane emissions are increasing, but we are not sure why. Positive feedbacks of CH4 emissions from wetlands to climate change may be contributing to the increase. Ma et al. [2021] combine biogeochemical models and satellite-derived CH4 concentration observations to examine climatic feedbacks to emissions from wetlands, from the equator to the poles. Tropical wetlands emit the 72% of global wetland emissions of CH4, and those emissions are shown to be most sensitive to changes in precipitation. In contrast, higher latitude wetlands emit much less overall, but their emissions are highly sensitive to temperature. In a companion Viewpoint, Thompson [2021] describes the novel way that Ma et al. [2021]  compare bottom-up estimates based on land surface models to those derived from a top-down atmospheric inversion model. She also notes that positive feedbacks of wetland CH4 emissions to climate change will require still stronger mitigation efforts in other sectors to avoid exceeding 1.5°C or even 2.0°C global warming.

Citation: Ma, S., Worden, J., Zhang, Y., Poulter, B., Cusworth, D. et al. [2021]. Satellite constraints on the latitudinal distribution and temperature sensitivity of wetland methane emissions. AGU Advances, 2, e2021AV000408.  https://doi.org/10.1029/2021AV000408

—Eric Davidson, Editor, AGU Advances

On behalf of the Earth and space sciences community, we congratulate the 35 recipients who are receiving AGU’s highest honors for their excellence in scientific research, education, communication, and outreach.

These honorees—scientists, leaders, educators, journalists, and communicators—have made outstanding achievements and contributions by pushing forward the frontiers of our science. Each recipient embodies our shared vision of a thriving, sustainable, and equitable future powered by discovery, innovation, and action. These recipients have worked with integrity, respect, and collaboration while creating deep engagement in education, diversity, and outreach.

Discovery and solution science involves many individuals and teams within the community and around the world. We are grateful to our honorees’ families, friends, colleagues, and other supporters who have been and continue to be instrumental to their success.

AGU will formally recognize this year’s recipients during the #AGU21 Fall Meeting. This celebration is a chance for us to recognize the outstanding work of our colleagues and be inspired by their accomplishments and stories. We will share additional details on the event at agu.org/fall-meeting.

Finally, we are grateful to the Honors and Recognition Committee, the selection committees, nominators, nomination supporters, volunteers, and staff for their support and commitment to AGU’s Honors Program.

Please join us in congratulating our esteemed class of 2021 AGU honorees.

—Susan Lozier, President, AGU; and LaToya Myles (honors@agu.org), Chair, Honors and Recognition Committee, AGU

 

Medals

William Bowie Medal James L. Burch, Southwest Research Institute

John Adam Fleming Medal David Dunlop, University of Toronto

Walter H. Bucher Medal Mark Harrison, University of California, Los Angeles

Maurice Ewing Medal Eelco Johan Rohling, Australian National University

Robert E. Horton Medal Diane M. McKnight, University of Colorado Boulder

Harry H. Hess Medal Peter B. Kelemen, Columbia University

Roger Revelle Medal Clara Deser, National Center for Atmospheric Research

Inge Lehmann Medal Jean-Paul Montagner, Institut de Physique du Globe de Paris

Joanne Simpson Medal for Mid-Career Scientists Jennifer Biddle, University of Delaware Jacob Bortnik, University of California, Los Angeles Anna M. Michalak, Carnegie Institution for Science

James B. Macelwane Medal

Elizabeth A. Barnes, Colorado State University Christopher H. K. Chen, Queen Mary University of London Ciaran J. Harman, Johns Hopkins University Christopher T. Reinhard, Georgia Institute of Technology Anja Schmidt, University of Cambridge

Devendra Lal Memorial Medal Vimal Mishra, Indian Institute of Technology Gandhinagar

Awards

Ambassador Award Fatima F. G. Abrantes, Instituto Português do Mar e da Atmosfera Madhulika Guhathakurta, NASA Susan Joy Hassol, Climate Communication Ambrose Jearld Jr., NOAA (retired) and Woods Hole Partnership Education Program Aradhna Tripati, University of California, Los Angeles

Edward A. Flinn III Award Bart Nijssen, University of Washington

Athelstan Spilhaus Award Sarah Stewart Johnson, Georgetown University

Charles S. Falkenberg Award Ryan P. Abernathey, Columbia University

International Award Atalay Ayele, Addis Ababa University

Excellence in Earth and Space Science Education Award The GLOBE Program

Africa Award for Research Excellence in Ocean Sciences Marjolaine Krug, Department of Forestry, Fisheries and the Environment, South Africa

Africa Award for Research Excellence in Space Science Roelf Du Toit Strauss, North-West University

Science for Solutions Award Lorenzo Rosa, ETH Zurich

Robert C. Cowen Award for Sustained Achievement in Science Journalism Mark Fischetti, Scientific American

Walter Sullivan Award for Excellence in Science Journalism – Features Jonathan O’Callaghan, Freelance Space Journalist

David Perlman Award for Research Excellence in Science Journalism – News Sarah Scoles, Freelance Journalist

 

Prizes

Asahiko Taira International Scientific Ocean Drilling Research Prize Rosalind M. Coggon, University of Southampton

Climate Communication Prize Andrew E. Dessler, Texas A&M University

Out of all planets in the solar system, Venus has the most volcanoes. Much of the planet is covered in volcanic deposits that are less than 300 million years old, and volcanic activity has played a pivotal role in its history. Although the precise timeline of Venus’s volcanic past is still under debate and some data suggest that the planet may still have active volcanoes, the evidence remains inconclusive.

To date, researchers have had difficulty determining whether there are active volcanoes on Venus for multiple reasons. The planet’s atmosphere is corrosive and features high pressures and temperatures—above 450°C (842°F)—that make it inhospitable for the kinds of spacecraft that can last for years on Mars or the Moon. Meanwhile, thick clouds of sulfuric acid limit visible observation of the planet’s surface, so researchers have turned to other remote measurements, including radar collected by NASA’s Magellan spacecraft, to map it.

According to D’Incecco et al., a new methodology could finally help solve the mysteries of volcanic activity on Venus. As applied in a recent study, this approach combines geologic mapping of cooled lava flows from past eruptions with additional radar data from the Magellan mission. Specifically, it relies on measurements of the planet’s radar emissivity—a measure of how its surface interacts with and emits microwave radiation.

Different parts of Venus’s surface have different levels of emissivity that correspond to different properties of rocks, providing clues to their composition. In particular, recent research suggests that radar emissivity can be used to determine the degree of chemical weathering experienced by lava flows after they erupt and contact the harsh atmosphere. Such weathering happens over weeks or months, so emissivity could potentially help identify fresh lava flows.

The authors combined radar emissivity measurements with geologic mapping to compare three Venusian volcanoes: Maat Mons, Ozza Mons, and Sapas Mons. The findings suggest that some lava flows at Maat Mons might be relatively young.

Looking ahead, the same approach could be applied to additional Magellan data to further explore Venus’s volcanism. The methodology could also be important for future Venus missions that will provide higher-resolution radar emissivity measurements, including the European Space Agency’s EnVision mission and NASA’s Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy (VERITAS) mission.

Alongside information from additional upcoming missions, including NASA’s DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging) mission and the Venera-D mission, the new strategy could finally help reveal which, if any, of Venus’s volcanoes are still active, as well as provide new insights into the planet’s volcanic past. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2021JE006909, 2021)

—Sarah Stanley, Science Writer

This is an authorized translation of an Eos article. Esta es una traducción al español autorizada de un artículo de Eos.

La contaminación del aire está ligada a más de 4 millones de muertes alrededor del mundo cada año, según la Organización Mundial de la Salud.  Los contaminantes atmosféricos como los aerosoles o el ozono no sólo afectan a la salud humana, sino que también al clima global, aunque se quedan en la atmósfera por un tiempo significativamente menor que el dióxido de carbono. Su tiempo de vida atmosférico tan corto hace de los aerosoles, el ozono y del metano, también llamados forzadores climáticos de vida corta (SLCFs, por sus siglas en inglés), objetivos primarios para una mitigación rápida. Pero hasta ahora, había poco consenso en el impacto que la mitigación de los SLCF podría tener en el ambiente o en la salud humana.

En un nuevo estudio, Zheng y Unger usaron un modelo global del sistema Tierra para simular el impacto que una reducción de 50% de SLCFs tendría en muertes prematuras ligadas a la contaminación por PM2.5 (material particulado menor a 2.5 micrometros, que incluye sulfato, nitrato, carbono negro, carbono orgánico, arcilla y otras partículas) y a temperaturas globales medias de aire superficial. Los autores combinaron el modelo global químico-climático ModelE2 de la NASA con el modelo Interactivo de la Biosfera Terrestre de Yale, y analizaron los efectos atmosféricos de reducir los SLCF por sector, incluyendo el agrícola, el de residuos de quema agrícola, el doméstico, la industria, el de transporte, el de manejo de residuos y el de envíos.

El estudio muestra que los beneficios de la mitigación de SLCF varían por sector: por ejemplo, un 50% de reducción de emisiones en el sector energético tuvo el impacto más grande en la salud humana, evitando 4 millones de muertes en 20 años. Mientras tanto, desde la perspectiva climática, reducciones en los sectores doméstico, agrícola y de manejo de residuos fueron modestos (-0.085, -0.034 y -0.033 K, respectivamente). Por primera vez, el estudio muestra que la variabilidad controlada por el tiempo en los niveles de contaminación de aire tiene un rol importante en la evaluación de riesgos de la salud humana.

Aunque el estudio tiene incertidumbres sobre los impactos climáticos de los contaminantes de aerosol y la sensibilidad de las condiciones de la salud a exposición de contaminantes aéreos, este muestra perspectivas que podrían ayudar a los políticos a priorizar los esfuerzos de mitigación de SLFC. Reducir las emisiones en los sectores agrícola y doméstico, por ejemplo, podría tener los mayores beneficios tanto para la salud humana como para el clima. (GeoHealth, https://doi.org/10.1029/2021GH000422, 2021)

—Kate Wheeling, Escritora de ciencia

This translation by Anthony Ramírez-Salazar (@Anthnyy) and Edith Emilia Carriquiry Chequer (@eecarry) was made possible by a partnership with Planeteando. Esta traducción fue posible gracias a una asociación con Planeteando.

This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。

根据世界卫生组织的数据，每年全球有400多万人死于空气污染。像气溶胶和臭氧这样的大气污染物不仅影响人类健康，也影响全球气候——尽管它们在大气中停留的时间比二氧化碳短得多。它们在大气中的短暂寿命使得气溶胶、臭氧和甲烷这些所谓的短寿命气候强迫因子(Short Lived Climate Forcers, SLCFs)成为快速减缓气候变化的主要目标。到目前为止，对于缓解SLCF可能对环境或人类健康产生何种影响，人们几乎还没有达成共识。

在一项新的研究中，Zheng和Unger使用全球地球系统模型模拟了SLCF减少50%对PM2.5(小于2.5微米的颗粒物，包括硫酸盐、硝酸盐、黑碳、有机碳、粘土和其他颗粒)污染有关的过早死亡和全球平均地表空气温度的影响。作者将NASA的ModelE2全球化学气候模型与耶鲁大学的交互式陆地生物圈模型(Yale Interactive Terrestrial Biosphere model)相结合，并按行业分解了减少SLCF的大气效应，这些行业包括农业、农业废物燃烧、家庭、能源、工业、运输、废物管理和航运。

研究表明，减缓SLCF的好处因行业而异：例如，能源部门减少50%的排放对人类健康的影响最大，在20年内避免了大约400万人过早死亡。同时，从气候角度来看，家庭、农业和废物管理部门的减少影响最大，尽管温度下降幅度不是很大，分别为−0.085、−0.034和−0.033开氏度。这项研究首次表明，天气驱动的空气污染水平变化在人类健康风险评估中发挥着重要作用。

尽管该研究在气溶胶污染物对气候的影响以及健康状况对空气污染暴露的敏感性方面存在不确定性，但它提供了一些见解，可以帮助决策者优先考虑SLFC的缓解努力。例如，减少农业和家庭的排放可能对气候和人类健康的好处最大。(GeoHealth, https://doi.org/10.1029/2021GH000422, 2021)

-科学作家Kate Wheeling

This translation was made by Wiley. 本文翻译由Wiley提供。

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With a yearslong monitoring effort, scientists have tracked the buildup and release of gas pressure beneath Italy’s Mount Etna leading up to its Christmas Eve eruption in 2018. According to new research, some types of gas built up continuously within the volcanic system for a year prior to the eruption, whereas pressure from other gases ebbed and flowed.

“We are able to recognize a process occurring inside the volcano which causes eruptions and to state, ‘Ok, it is starting, it is growing, it is at critical levels!’ At Etna it lasts months to years.”“We are now able to quantify the pressure accumulation in the magmatic reservoir while [the buildup is] developing,” said Antonio Paonita, a geochemist at Istituto Nazionale di Geofisica e Vulcanologia Sezione di Palermo in Italy and lead author of the study. “We are able to recognize a process occurring inside the volcano which causes eruptions and to state, ‘Ok, it is starting, it is growing, it is at critical levels!’ At Etna it lasts months to years.”

When combined with advanced theories for how magma recharges within Etna’s magmatic system, one of the most active in the world, this new insight into how pressure builds up will help scientists better understand and predict its eruptions.

Gases Track Magma Movement

What goes on inside a volcano’s magma reservoirs controls the volcano’s behavior at the surface. Magma and volatile gases flow into a chamber from deep within Earth and sometimes find nonexplosive ways out through conduits, sills, and dikes (as for magma) or degassing vents. Volcanoes tend to erupt when a magma chamber becomes overpressurized, which can happen when more magma and gas enter the chamber than leave it.

Pressure buildup in some volcanic systems can stretch for tens of years leading up to an eruption. Other systems, however, such as Kīlauea and the Alaskan volcanoes in the United States, the Aleutians that stretch between Alaska and Russia, Nyamuragira in the Democratic Republic of the Congo, and Mount Etna, “normally exhibit quicker dynamics and frequent eruptive activity” spanning months or years, Paonita explained. As theories of magma recharge of a reservoir become more sophisticated, surface and remote monitoring of volcanic degassing can help researchers estimate the overall state of pressurization within a volcanic system and anticipate its eruption potential.

“Each gas is then indicative of a range of depth where degassing is occurring and magma dynamics is acting.”Mount Etna is an excellent testing ground for such theories for a number of reasons: It erupts regularly, scientists have modeled its magma recharge system, and an extensive network of instruments continuously monitors the volcano’s degassing. With a combination of remote sensing and on-site sampling, the researchers analyzed the degassing patterns of carbon dioxide (CO2), sulfur dioxide (SO2), hydrochloric acid, and helium isotopes starting roughly a year prior to the 24 December 2018 eruption until about a year after.

“Different gases are released from magma at different depths along the [magma] ascent path,” Paonita explained. “Roughly speaking, each gas is then indicative of a range of depth where degassing is occurring and magma dynamics is acting.”

The team found that the helium isotope ratio emitted by Etna steadily rose from the first half of 2017 all the way up to the eruption, after which it dropped significantly. CO2 flux, which had been low and steady, increased in June 2018 and then fell and rose again cyclically until the eruption. SO2 flux, however, rose only in the weeks immediately preceding the eruption (from about 5,000 metric tons per day to about 12,000 metric tons per day) and fell back to typical levels after the eruption.

“Our study highlighted an imbalance between the amount of gas normally rising with the magma from the mantle beneath a volcano and that emitted in pre- and inter-eruptive phases,” Paonita said in a statement. “Recognizing and quantifying this ‘imbalance’ and its evolution almost in real time provides a new interpretative key for evaluating the ‘state of activity’ of the volcano.” The team published these results in Science Advances on 1 September.

Bespoke Volcanic Systems

Mount Etna looms over Sicily’s second-largest city, Catania; has erupted 50 times so far in 2021; and has grown 31 meters taller in the past 6 months. Can these results help volcanologists predict eruptions? Perhaps for Mount Etna, but probably not for other volcanoes.

Degassing data’s predictive power ultimately depends on how well we understand a particular magmatic system.Long-term surveillance of volcano degassing could anticipate an eruption, but its predictive power ultimately depends on how well we understand a particular magmatic system, Paonita said. A rise in the concentrations of CO2 and noble gases, for example, generally points to magma movement many kilometers below the surface, whereas a sharp rise in SO2 implies magma moving closer to the surface. “In theory, we can interpret degassing data with no basic knowledge of [a] system,” he said.

In reality, however, volcano behavior depends on the internal structure of a magmatic system, and although Mount Etna is an archetype of open-conduit volcanoes, each one is unique. “Our experience on that volcanic system—for example, long records of signals to be compared to its eruptive behavior—and our geological knowledge are precious and irreplaceable information for interpreting monitored signals in the right context.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Forest recovery is an important tool to fight climate change. Recent research, however, shows that recovery in the Amazon has a long way to go to become truly effective.

Secondary forests—wooded areas intentionally replanted after a timber harvest has destroyed a primary or old-growth forest—are one way communities and businesses have responded to deforestation. The trees and shrubs in secondary forests do not entirely replace the trees lost in primary forests, but the plant biomass acts as a carbon sink that offsets carbon emissions associated with the initial deforestation.

According to a new study, however, secondary forests have offset less than 10% of deforestation-caused carbon emissions in the Amazon—even as they take up almost 30% of the total deforested area in the region. With territory accounting for about 60% of the biome, Brazil leads the trend: The country had the lowest carbon offset rate (9%) and the smallest forest area recovery (24.8%).

On the opposite end of the spectrum, Ecuador had the largest forest area recovery (56.9%), whereas Guyana had the highest carbon offset rate (23.8%). These countries, however, represent a small fraction of the Amazon, as they account for just 1.5% and 3% of the biome, respectively.

“Now that there’s data available to all individual countries in the Amazon, they don’t need to make estimates based [solely] on Brazilian findings.”The study, published in Environmental Research Letters, is the first to analyze forest loss and recovery at both national and subnational levels for the whole Amazon region. The researchers analyzed data from all nine Amazonian countries (Bolivia, Brazil, Colombia, Ecuador, France (through the department of French Guiana), Guyana, Peru, Suriname, and Venezuela) and the nine Brazilian states that make up the biome (Acre, Amapá, Amazonas, Maranhão, Mato Grosso, Pará, Rondônia, Roraima, and Tocantins).

The analysis builds on land cover data from the Brazilian Annual Land Use and Land Cover Mapping Project (MapBiomas) between 1985 and 2017, as well as estimates of aboveground biomass and carbon sequestration rates for the period.

The team used MapBiomas remote sensing maps for each year, looking pixel by pixel for the areas that were covered and not covered by vegetation to track changes in land use. “We overlapped the maps looking for where there was vegetation in a given year but not in the next (meaning the area was deforested) and where the opposite happened, meaning there was forest recovery,” explained coauthor Erika Berenguer, a researcher at the University of Oxford and Lancaster University in the United Kingdom.

“The resolution of each pixel is 30 square meters, so MapBiomas gave us quite fine-grained material to work on,” said lead author and Lancaster University researcher Charlotte Smith. Besides fine resolution, the study gives a good picture of what is happening in the whole biome, she said. “Now that there’s data available to all individual countries in the Amazon, they don’t need to make estimates based [solely] on Brazilian findings.”

International and Interstate Disparities

Brazilian states account for more landmass in the region and for a larger share of deforestation. Researchers found that by 2017, the deforested area in Pará alone—more than 260,000 square kilometers, an area larger than the U.S. state of Oregon—was more than twice the cleared area of all other Amazonian countries combined. Deforestation-related carbon emissions from Mato Grosso, Pará, and Rondônia surpass those of any other individual Amazonian country.

Contrasts are stark also among Brazilian states themselves. Whereas Tocantins lost more than 80% of its primary forest and less than 20% of this area was recovered with secondary forest, Amapá had only 4% of its total forest area razed and recovered almost 70% of it with secondary forest. Amapá also managed to offset more than a quarter of its deforestation emissions (26.9%), whereas Tocantins offset only a little more than a tenth (13%).

It is worth noting that Amapá has more than 4 times the forest area of Tocantins, and more than 70% of its area is protected as conservation units or Indigenous lands. The state has the lowest deforestation rates in the Brazilian Amazon according to the Amazon Deforestation Monitoring Project, part of Brazil’s National Institute for Space Research.

Older Forests Have Greater Carbon Sequestration

University of Connecticut professor Robin Chazdon, who did not take part in the study, said it confirms trends observed in previous research about carbon recovery in reforested regions. “It also shows the need for deeper analysis of the economic, social, and political factors that are part of these trends,” she said.

Chazdon explained that the amount of remaining forest in a place is a predictor for unassisted vegetation regrowth. “Sometimes there’s a time lag between forest clearance and land use,” she said, hinting that older secondary forests may yield higher carbon sequestration rates.

The numbers in the study back Chazdon’s observations: Almost 80% of all secondary forest vegetation analyzed was less than 20 years old, with an average age of 8 years. Guyana and Suriname had some of the oldest secondary forests studied, and these countries had the highest carbon recovery rates of the whole biome.

“We’re always told the story of how we are failing the Amazon forest. But places like Ecuador and Amapá show that the Amazon is not all about failure.”“This means that trees must be given time to grow, so their carbon absorption can make some difference,” Berenguer said. She stressed that secondary forests are not absorbing as much carbon as they could for two primary reasons: Deforestation emissions in the Amazon are still overwhelmingly high, and at the same time, secondary forests are razed at a young age across most of the biome. “It is counterproductive to plant a hectare and tear another 10 down,” she added.

Despite the scenario, the researchers see some space for hope. “We’re always told the story of how we are failing the Amazon forest. But places like Ecuador and Amapá show that the Amazon is not all about failure. They’re two cases that need to be looked at in detail so we can learn something that can be useful to the whole biome,” Berenguer said.

“Latin America has the highest forest recovery capacity in the world, with the Amazon forest having the highest potential across the region,” said Chazdon. “Brazil is the single country with the highest forest recovery capacity in the world—but social, economic, and political factors impede regrowth.”

—Meghie Rodrigues (@meghier), Science Writer

Lara Mani was tired of hearing about the Yellowstone supervolcano. Every so often, another news story would appear, proclaiming that the Yellowstone caldera system could erupt with such ferocity that the impacts could cascade into a global catastrophe. “Yes, there’s plausibility in that,” said Mani, a research associate at the University of Cambridge’s Centre for the Study of Existential Risk, “but that’s not the only mechanism. There’s another way that can happen.”

Smaller eruptions, depending on where they occur, could also have catastrophic impacts, Mani thought. Historically, researchers have focused largely on the physical risk—the magnitude of potential eruptions. That’s at least in part because the vulnerability side—the transport routes, communication networks, and other infrastructure that if disrupted would affect societies around the globe—has become a problem only more recently.

“Most of the vulnerability is a relatively new (late 20th–21st century) product of how we humans have changed our technologies, economies, and flow of services,” said Chris Newhall of the Earth Observatory of Singapore. But we’ve already seen how small eruptions can lead to major disruptions. Consider the 2010 eruption of Eyjafjallajökull in Iceland, which grounded more than 100,000 flights and cost the global economy upward of $5 billion.

“That should never have reached the global platform that it did; it was such a small eruption,” Mani said. “Why? What’s the mechanism behind that? What does this mean? That’s where it started.” In a new study in Nature Communications, Mani and her colleagues began brainstorming identifying areas where smaller eruptions could combine with human-made vulnerabilities with catastrophic results. The new knowledge could lead to risk assessments and changes to preparedness.

Pinch Points

Mani and her colleagues began by looking at choke points along shipping routes—a focus that was highlighted this year when a container ship ran aground in the Suez Canal, bringing a major global trade route to a halt. They also looked at air traffic routes and other critical infrastructure like underwater cables and manufacturing hubs. The team identified seven “pinch points,” where active volcanoes overlapped with these vulnerabilities. Four of these points were clustered together in a highly populated geographic corridor from Southeast Asia through the South China Sea. “It makes sense that where you have people, you have systems to sustain those societies,” Mani said.

Pinch points mark the clustering of critical systems and infrastructures with regions of lower-magnitude volcanic activity. These pinch points are presented with the likely associated volcanic hazard and the potentially affected systems. Credit: Mani et al., 2021, https://doi.org/10.1038/s41467-021-25021-8

A small eruption at Mount Paektu on the China–North Korea border, for example, could disrupt air routes between Seoul and Osaka or Tokyo—some of the busiest routes in the world. In the Luzon Strait, a landslide or tsunami caused by an eruption along the Luzon Volcanic Arc could sever critical submarine cables connecting countries from China and Taiwan to the Philippines. Some 40% of global trade passes through the Strait of Malacca (between Malaysia and Indonesia); an eruption of any number of volcanoes along the Indonesian archipelago could shut down air and maritime traffic. The cascading impacts of these events are unpredictable and difficult to calculate: The 6-day blockage of the Suez Canal, for example, cost the Egyptian government as much as $90 million in lost toll revenue. Global trade revenue sank by as much as $10 billion.

“We’ve prioritized efficiency over resilience. If something goes wrong, there isn’t an alternative.”“We’ve prioritized efficiency over resilience,” Mani said. “If something goes wrong, there isn’t an alternative.”

Taiwan is home to the Taiwan Semiconductor Manufacturing Company (TSMC), responsible for manufacturing 90% of the world’s advanced microchips and nodes. An eruption in the Tatun Volcano Group could close the port of Taipei, isolating TSMC from the rest of the world. “Anything that happens to TSMC…sends a shock wave [through society],” said Mani. “Everybody knows that it’s a critical vulnerability, but no one has ever thought about what it’s vulnerable to.”

The team also identified pinch points in the Mediterranean, the North Atlantic, and the Pacific Northwest, where the eruption of one of the Cascades volcanoes could melt glaciers or ice caps, triggering a debris flow that could potentially reach all the way to Seattle.

Mani hopes that pointing out these vulnerabilities in global systems will ultimately help to build resilience. “My hope is that it will raise some questions to the volcanology community, the volcanic risk community, to start having these discussions about what this risk really looks like,” she said, “so that disaster managers, international organizations, and governments can start thinking about mitigation and prevention.”

—Kate Wheeling (@KateWheeling), Science Writer

Utkin and Afanasyev [2021] present a semi-empirical coupled model of compaction-driven fluid flow and numerically solve it to simulate non-reactive transport of magmatic fluid across both the ductile and brittle zones. Their approach accounts for the thermal softening of the rocks and the plastic deformation of their solid matrix through decompaction weakening while guaranteeing material balance for the fluid and solid phases everywhere in the model.

A single numerical simulation concurrently models the following physical mechanisms: Porosity waves form vertical high-porosity channels which transport magmatic fluid across the ductile zone, culminating in high-porosity lenses right beneath the brittle to ductile transition. In this transition zone, magmatic fluid transport occurs through the roof of those high-porosity lenses, resulting in a plume of hydrothermal convection in the brittle zone sitting atop each lens and following a narrowing path toward the surface. The pattern of hydrothermal convection in the brittle zone is completed by meteoric water forming other plumes between the lenses as well as mixing with the magmatic fluid in a process that transfers heat to the surface.

Studying the physical mechanisms of fluid transport in the upper crust is particularly relevant to understand the formations of exploitable geothermal resources and of ore deposits.

Citation: Utkin, I., & Afanasyev, A. [2021]. Decompaction weakening as a mechanism of fluid focusing in hydrothermal systems. Journal of Geophysical Research: Solid Earth, 126, e2021JB022397. https://doi.org/10.1029/2021JB022397

—Beatriz Quintal, Associate Editor, JGR: Solid Earth

The onset of geodesy and seismic monitoring has produced a richer picture of slip in subduction zones that includes not only megathrust earthquakes, but also variations of slow slip events of different sizes and durations. Slow slip events can rival large earthquakes in terms of cumulative moment. Many of these slow slip events occur in the transition zone between the shallow brittle and deeper ductile regimes. Behr et al. [2021] model this transition as a narrow zone of strong clasts embedded within a ductile matrix, as has been observed in outcrops of exhumed subduction zones (as shown in the figure above). The authors simulate slip while systematically varying strength contrasts and relative proportions of weak and strong material. They find three slip modes that result from these variations: aseismic slip with no earthquakes, slow-slip, and regular earthquakes, which mirror observations from subduction zones as well as what is observed geologically in exhumed subduction zones.

Citation: Behr, W., Gerya, T., Cannizzari, C. & Blass, R. [2021]. Transient Slow Slip Characteristics of Frictional-Viscous Subduction Megathrust Shear Zones. AGU Advances, 2, e2021AV000416. https://doi.org/10.1029/2021AV000416

—Tom Parsons, Editor, AGU Advances

When solar wind slams into Earth’s magnetic field, the impacts ripple down through the planet’s ionosphere, the outer shell of the atmosphere full of charged particles. A global array of high-frequency radars known as the Super Dual Auroral Radar Network (SuperDARN) tracks ionospheric plasma circulation from the ground, giving researchers insights into the interactions between solar wind, the magnetosphere, and the ionosphere. Though widely used in space physics research, the network is not comprehensive—each ground-based radar can measure plasma velocity only in its line-of-sight direction, for example. As a result, there are major spatial and temporal gaps in the SuperDARN archive.

Historically, researchers have filled in these gaps with models that make assumptions based either on climatological averages of the SuperDARN data or on solar wind measurements. In a new study, Shore et al. present a new method using a data-interpolating empirical orthogonal function technique, which allows researchers to detect patterns within existing SuperDARN plasma velocity data and then use this information to fill in gaps. The team used observations collected by the network’s Northern Hemisphere stations in February 2001 and filled in missing information at any given time using the velocity patterns deduced from data collected at a given location throughout the month and from other network locations at the same time.

The SuperDARN data set is critical for understanding space weather and its potential impacts on the technologies underlying things like radio communications and satellite services, and this new technique can provide researchers with the most accurate estimates yet of ionospheric electrodynamic variability. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2021JA029272, 2021)

—Kate Wheeling, Science Writer

The northern Indian Ocean consists of two seas: the Bay of Bengal to the east and the Arabian Sea to the west. Historically, tropical cyclone activity in the Bay of Bengal is generally higher than that in the Arabian Sea. But new research showed a shift in this trend.

Researchers found that between 1982 and 2019, there was a significant increase in the frequency, duration, and intensity of cyclonic storms over the Arabian Sea. Specifically, they noted a 52% increase in the frequency of cyclonic storms, an 80% increase in their duration, and an increase in intensity of about 20% in the premonsoon period and 40% postmonsoon. In addition, researchers documented a tripling of the accumulated cyclone energy in the Arabian Sea. The study was published in Climate Dynamics.

“We studied data covering about 38 years by dividing [the period] into two epochs of 19 years each. In the Arabian Sea, we found that the intensity, frequency, and duration [are] increasing, but in the Bay of Bengal there has been no significant change,” said Medha Deshpande, lead author of the study and a scientist at the Indian Institute of Tropical Meteorology (IITM).

Reasons for the increase in cyclonic activity in the Arabian Sea include increases in sea surface temperature and tropical cyclone heat potential. Both measures are reliable indicators of climate change.

Warming Seas and Cyclonic Activity

The recent Sixth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) showed that the Indian Ocean is experiencing the world’s fastest rate of ocean surface warming.

Roxy Mathew Koll is a climate scientist at IITM, a coauthor of the new study, and a reviewer of recent IPCC reports. He explained that in the Indian Ocean, the Arabian Sea showed temperature changes reaching up to 1.2°C–1.4℃ over the past 20 years. “Compared to global ocean surface warming of 0.8°C–0.9℃, this is quite large,” he said.

A warmer Arabian Sea means more heat for cyclones to draw energy from. It also means more moisture for cyclones to feed on. So warming seas allow for the genesis and maintenance of severe cyclonic storms.

Disaster Preparedness, Mangroves, and Free-Flowing Rivers

On the basis of past cyclone tracks, Koll listed the Indian states and territories that may be most affected by increased activity: Lakshadweep, Gujarat, Maharashtra, Karnataka, and Kerala. Lakshadweep, composed entirely of tiny islands hundreds of kilometers off the coast of Kerala, is particularly vulnerable. The archipelago’s very survival has come under serious questioning given the threats posed by cyclonic activity, sea level rise, and coastal erosion.

Experts said one manner in which states could prepare for the onslaught by cyclone is by conserving mangrove ecosystems. Such techniques also have benefits for climate adaptation and disaster risk reduction. Detailing the benefits mangroves offer, Koll said they reduce the impact of winds and flooding during cyclones and can regrow following cyclonic damage.

In addition to mangrove conservation, “we need to allow rivers to bring fresh water, sediments, and nutrients to estuaries and deltas,” said Jagdish Krishnaswamy, a senior fellow at the Suri Sehgal Centre for Biodiversity and Conservation, Ashoka Trust for Research in Ecology and the Environment. Krishnaswamy, also a coordinating lead author of the IPCC report, was not involved in the new study.

Low-lying coastal areas depend on such sediment flow from rivers to offset soil erosion into the sea. India’s west coast is a very narrow strip of land abutted by the mountains of the Western Ghats, leaving its population “highly vulnerable to disasters because of sea level rise, reduced sediment flow because of dams upstream, and increasing cyclonic activities,” Krishnaswamy noted.

Overall, Krishnaswamy said, the increased vulnerability of the west coast to cyclonic activity demands that developmental plans (including the country’s Coastal Regulation Zone notification system) take the effects of climate change into consideration. In particular, he stressed that natural climate infrastructure like mangroves be given more attention to enhance resilience to flooding and storms.

—Rishika Pardikar (@rishpardikar), Science Writer

Problems from coastal erosion to climate dynamics require a better handle on ocean wave phenomena. Satellites image the surface expression of ocean waves. However, there are coverage limits, and solid earth recordings can provide complementary constraints for ocean and surface dynamics. Here, Shaddox et al. [2021] expand prior environmental seismology analysis and focus on solitary ocean waves passing by a near-ideal test setting, an atoll in the South China Sea which is known to experience large amplitude wave activity. By combing data from a permanent borehole seismometer, temporary stations, satellites and ocean sensors, the authors find tantalizing evidence for the detection of the subtle tilting that might be expected from the ocean-land interactions around the island. Similar signals had been seen on ocean bottom seismometers, but if the land-based detection were to become routine, perhaps with improved seismic sensors, more complete records of ocean dynamics would become available.

Citation: Shaddox, H., Brodsky, E., Davis, K. & Ramp, S. [2021]. Seismic Detection of Oceanic Internal Gravity Waves from Subaerial Seismometers. AGU Advances, 2, e2021AV000475. https://doi.org/10.1029/2021AV000475

—Thorsten W. Becker, Editor, AGU Advances

There’s a stubborn, heat-absorbing particle that floats along in Earth’s atmosphere: It initially doesn’t like water, it absorbs light, and it takes its time moving on. Black carbon in the atmosphere tends to linger until it finally absorbs enough water to fall from the sky. In the meantime, black carbon absorbs the Sun’s energy and heats up surrounding air, creating a radiative effect.

Fresh, young black carbon tends to be resistant to water. Over time, the particles age and become more hygroscopic, or able to absorb water from the air. But when does black carbon start absorbing water, act as cloud nuclei, and remove itself from the atmosphere?

Researchers previously investigated the hygroscopic conditions of black carbon in the lab, with limited conditions on chemical sources and water vapor conditions. In all of these studies, the cloud nucleation values of black carbon were indirect measurements.

In a new study by Hu et al., researchers concurrently measured the concentration of cloud condensation nuclei and black carbon particles. The sampling site was near heavily trafficked roads and industrial centers in Wuhan, China, an urban megacity in the central part of the country.

They first corrected for the size of particles, then measured cloud condensation nuclei and individual black carbon particles in certain levels of water supersaturation in the atmosphere. The team found that the activation diameter, or the size of the black carbon particle where half of the particles will nucleate and precipitate out, was 144 ± 21 nanometers at 0.2% supersaturation. How these black carbon–containing particles could act as cloud nuclei is determined by their size combined with their coatings, the authors say, and in general, the less saturated the air was, the bigger the particles had to be to nucleate.

In addition, the team found that a particle itself may influence the size of nucleation. For instance, the amount of organic content in a particle or any coating on the black carbon can change the hygroscopicity and therefore the activation.

The research team noted that their work can help improve estimates of the longevity of suspended black carbon particles in the atmosphere and therefore the radiative impacts those particles can have.

(Journal of Geophysical Research: Atmospheres, https://doi.org/10.1029/2021JD034649, 2021)

—Sarah Derouin, Science Writer