EOS

Source: AGU Advances

The origins of the earliest life on Earth, prior to the rise of oxygen and photosynthesis, remain a mystery. Graveyards in brine pools at the bottom of the Red Sea may hold some answers.

Brine pools are underwater ponds or lakes that sit at the bottom of the sea. They’re dark, full of salt, and devoid of oxygen. For years, they were presumed to be lifeless. But research revealed that for certain extremophiles, these brine pools aren’t inhospitable: They’re oases. And the bacteria and archaea that thrive there leave geochemical signatures long after they’re gone, Chakraborty et al. show in a new study.

The researchers analyzed the geochemical composition of sediments and organic matter in an active brine pool, three nonbrine seafloor spots, and a spot they suspected was an “extinct” brine pool based on mineral rings around a depression filled with dead marine organisms. They used metagenomics and metatranscriptomics to characterize the microbial communities at the sites.

The active pool, 1,770 meters below the surface of the Red Sea, was teeming with bacteria and archaea. And the sediments under the microbial mat were extremely enriched in metals like manganese, iron, molybdenum, and copper, with some areas hosting concentrations upward of 100 times higher than their non–brine pool counterparts. The extinct pool, nearly 1,400 meters below the sea surface, had similar enrichment patterns.

The presence of oxidized manganese and molybdenum-enriched organic matter in the sediments of both the active and extinct brine pools will improve interpretations of similar patterns in the rock record. Metagenomic analyses of the active pool revealed manganese oxidizers such as Nitrospira.

That finding, together with oxidized iron-manganese phases in the sediment, offers some evidence that microbial oxidation of Mn(II) to manganese oxides could have served as a mechanism for energy production prior to the rise of atmospheric oxygen during the Great Oxidation Event around 2.4–2.2 billion years ago.

Overall, though the authors note that more research is needed, the findings support hypotheses that metal enrichment in the early oceans could have occurred independently of oxygenic photosynthesis or photoautotrophy. Chemotrophic oxidation of manganese and iron could well have been the engine of the earliest life in the oceans. (AGU Advances, https://doi.org/10.1029/2026AV002570, 2026)

—Rebecca Dzombak, Science Writer

Citation: Dzombak, R. (2026), Briny “death pools” hold clues to early life, Eos, 107, https://doi.org/10.1029/2026EO260301. Published on 22 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Geophysical Research Letters

The Van Allen radiation belts are huge, doughnut-shaped regions of highly energetic charged particles trapped by Earth’s magnetosphere. These charged particles play a major role in space weather, so studying them is important for predicting and managing risks to satellites, astronauts, power grids, and other infrastructure.

Geomagnetic storms and other events can rapidly and dramatically increase or reduce the number of highly energetic electrons trapped in the radiation belts. During a key type of event known as a relativistic microburst, trapped electrons escape from the outer belt into Earth’s atmosphere in an intense surge lasting less than 1 second. Microbursts could influence radiation belt hazards and may even alter atmospheric chemical composition.

However, new research by Romero-Minaya et al. challenges the prevailing understanding of what triggers highly energetic electron microbursts.

The study focuses on chorus waves—naturally occurring electromagnetic waves that ripple through the vast mass of charged particles, or plasma, surrounding Earth. Chorus waves are named for the sounds made by a radio receiver when it detects them. They are known to be able to accelerate trapped electrons to high speeds, and they are thought to be the primary drivers of microbursts.

The researchers analyzed statistical associations between chorus waves and relativistic microbursts using data from NASA’s Time History of Events and Macroscale Interactions During Substorms (THEMIS) and Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) missions. The dataset included chorus waves and microbursts detected by the satellites between June 2010 and November 2012.

They discovered that only a very small percentage of the chorus waves happened in conjunction with relativistic microbursts—far fewer than expected, given the strong links seen in prior studies.

The small number of chorus waves that were associated with relativistic microbursts tended to have larger amplitudes and other distinctive characteristics, suggesting that only a small subset of chorus waves drive microbursts at these high energies. Future research could explore this possibility and further clarify these surprising results, the researchers say. (Geophysical Research Letters, https://doi.org/10.1029/2026GL124627, 2026)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2026), Presumed role of chorus waves out of tune with new data, Eos, 107, https://doi.org/10.1029/2026EO260302. Published on 22 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

In Japan, record breaking rainfall associated with Typhoon Dujuan has triggered at least six fatal landslides in the Kanto region.

Over the last 24 hours or so, rainfall associated Typhoon Dujuan has swept across the Kanto Region in Japan, bringing exceptional (and in some cases record breaking) rainfall. There are multiple reports of landslides, some of which have been fatal.

The rainfall associated with typhoons can be hard to visualise. In Oshima, on the Izu islands, 832 mm were recorded in 48 hours – that is more than the entire annual rainfall of the city (Nottingham) in which I work. Totals exceeding 400 mm in 48 hours have been recorded widely across parts of Kanto.

The Japan Times has a report that describes a series of fatal landslide events. These include:

• Yokosuka, Kanagawa Prefecture: one fatality
• Yokosuka, Kanagawa Prefecture: two people missing
• Miura, Kanagawa Prefecture: one person missing
• Miura, Kanagawa Prefecture: one person missing
• Sodegaura, Chiba Prefecture: “a 51-year-old worker died after he and the heavy machinery he was operating fell into a bamboo grove while he was removing mud and debris from a road…A landslide had occurred around the site.”
• Kamogawa, Chiba Prefecture: one fatality
• Sanmu, Chiba Prefecture: one fatality

A cluster of six or more fatal landslides is quite unusual for Japan, which works extremely hard to manage landslide risk.

James Reynolds has been recording Typhoon Dujuan – he has tweeted this image of a landslide on Highway 34 near Kyonan Hota IC:-

A debris flow on Highway 34 near Kyonan Hota IC in Chiba triggered by Typhoon Dujuan. Image tweeted by James Reynolds.

Typhoon Dujuan is now moving away from Japan, so more information will emerge over the next 24 hours about the impact of the storm. I expect that we will see a large number of landslides in those upland areas most affected by the intense rainfall.

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On Wednesday 7 October 2026 at 6 pm I will deliver my NTU inaugural lecture entitled “Landslides in a changing climate”. This is a public lecture, so all are welcome.

In UK universities, there is a long tradition of inaugural lectures for newly appointed professors. Wikipedia describes an inaugural lecture as follows:-

“An inaugural lecture is a formal public lecture given at a university by a newly appointed full professor, the holder of a chair. It marks the professor’s official introduction to the academic community. These lectures are often attended by colleagues, students, and sometimes the general public. They are a way to showcase the professor’s expertise and to contribute to the intellectual life of the institution.“

Whilst I have been a professor in a variety of institutions since some time in the early Cretaceous, I am of course a newly appointed professor at NTU. As such I get the privilege of an inaugural lecture.

This is scheduled for Wednesday 7 October 2026, 6 pm (UK time) at the City Campus of NTU. It is a public event, so anyone can attend. I have chosen to title this: “Landslides in a changing climate”. This is the synopsis:-

Landslides are one of the most deadly but poorly appreciated natural hazards. Occurring on every continent on the planet, and indeed on other planets as well, they are responsible for thousands of deaths and billions of pounds worth of losses annually.

Over the 40 year career of Professor Petley, there has been growing evidence that the pattern of landslides is being heavily modified by the effects of human-induced climate change, which is altering both large-scale weather systems, such as the Asian monsoon, and localised rainfall events, such as cloudbursts.

This lecture will draw upon examples from New Zealand, the Himalayas and the UK to examine how both our understanding of the impacts of climate change on landslides, and the patterns of loss from landslides have changed. Reviewing initially the devastating August 2026 landslide and debris flow in Nepal and Tibet, in which over 5,000 people were killed, it will explore the ways in which new technologies have allowed huge improvements in our understanding of landslides. It will review global patterns of landslide losses, and investigate the ways in which these have are being changed by the rapid shifts occurring in our climate. Finally, it will review future prospects for landslide triggered losses, emphasising that both climate driven changes in the hazard and human driven changes in vulnerability mean that losses are likely to accelerate in the coming years.

You are welcome to attend – the event details are here:-

https://www.ntu.ac.uk/about-us/events/events/2026/10/professor-dave-petleys-inaugural-lecture

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On board the EPA research vessel Lake Guardian, every scientist works a 12-hour shift. From 4:00 p.m. to 4:00 a.m. or vice versa, researchers survey and sample the Great Lakes to better assess water quality and food web conditions.

This grab sampler takes sediment samples from the bottom of Lake Michigan—sometimes with views of the Chicago skyline. Credit: EPA

“We sample day or night, 24/7,” said Anne Scofield, a physical scientist at the EPA’s Great Lakes National Program Office, technical lead for the office’s Biology Monitoring Program, and one of the researchers on board the Lake Guardian during the office’s 43rd annual summer survey, conducted this August.

The annual summer surveys take about a month to traverse all five Great Lakes. Another annual survey in the springtime monitors lakes when their water temperatures are at their coldest. Since April, the Lake Guardian has traveled more than 12,500 nautical miles (23,150 kilometers) and sampled 282 locations. The vessel will travel for one more survey in Lake Superior and one more survey in Lake Erie before the end of the year.

“It really does remind me of being in the ocean, because the lakes are just so huge,” Scofield said.

Data from Lake Guardian surveys help scientists and natural resource managers track how stressors like nutrient pollution, chemical contaminants, and invasive species affect the ecology of the Great Lakes over time.

“It’s one of the foundational datasets that all the scientists in the region use.”

The Lake Guardian also offers non-EPA scientists a chance to join the survey, collect data, and use those data in their own research. Each annual survey is funded by the Great Lakes Restoration Initiative, a multiagency fund meant to understand and mitigate the largest threats to Great Lakes ecosystems.

“We’re the only group out there that is measuring the same things in the same places in the same way year after year after year for all five of the Great Lakes,” Scofield said. “It’s one of the foundational datasets that all the scientists in the region use.”

Freshwater Finds At night, tiny crustaceans called mysids migrate upward in the water column, giving scientists on board the chance to sample them. Credit: EPA

During their shifts on the Lake Guardian, scientists and crewmembers deploy sampling equipment and prepare samples for storage or analysis. At night, they deploy nets to collect mysids, the Great Lakes’ largest zooplankton and an important food source for fish.

The team uses water samples to monitor nutrient concentrations, algae, phytoplankton, zooplankton, and invertebrates living on the lake bed. They measure a suite of physical characteristics, too, such as turbidity, pH, and water clarity. And they drill sediment cores, which provide insight into how the chemistry and contaminants in the lakes have changed over time.

Every year, the Lake Guardian’s overall monitoring is supplemented by an in-depth study of one of the Great Lakes’ lake bed invertebrate communities. During those studies, an underwater video camera helps the team map the spatial distribution of invertebrates on the lake bed, and a giant claw collects chunks of sediment from the bottom of the lake for analysis.

This in-depth approach allows the agency to track changes in lake bed ecology, particularly changes to populations of invasive mussels. “We’re trying to understand their trajectories and what that might mean for the lakes going forward,” Scofield said.

Invasive quagga mussels threaten fisheries across the Great Lakes. Credit: EPA

The in-depth survey for 2026 is ongoing in Lake Superior. Scientists on board are monitoring and mapping the distribution of lake bed organisms such as Diporeia, a tiny freshwater crustacean that serves as an important food source for fish.

Though scientists have not yet analyzed data from the 2026 summer survey, Scofield said she has already noticed interesting features of lake health. In Lake Michigan, for example, the team noticed few mysids, especially in the southern basin of the lake. This observation contributes to a consistent trend documenting decreasing populations of mysids since the early 2000s, she said, possibly because of a reduction in phytoplankton in the lake as well as increasing water clarity over time, which limits habitat for these light-sensitive organisms.

Managing the Great Lakes

Many of the data collected by the Lake Guardian team are used to update the EPA’s State of the Great Lakes reports, which are published every 3 years and provide a summary of the health of the Great Lakes, from water quality to fish population metrics. These reports are part of a collaboration between the EPA and the Canada Water Agency to support the Great Lakes Water Quality Agreement, a binational commitment signed in 1972 to protect the waters of the Great Lakes.

Water sampling equipment deploys in Lake Superior. Credit: EPA

Scientists reference these reports in their research, and resource managers use the data to help make decisions. “Fishery managers, especially, are always wanting to connect with us to understand what’s going on with the lower food web,” Scofield said.

Vic Santucci, the Lake Michigan program manager in the Division of Fisheries at the Illinois Department of Natural Resources, is not involved in the Lake Guardian’s annual surveys but uses the data collected by the Lake Guardian team to make decisions about where, when, and how to manage Lake Michigan’s fisheries.

This video of Lake Michigan’s lake bed, taken in August 2025, shows the extent of invasive mussels. Credit: EPA

For example, in 2013 and 2016, Santucci used State of the Great Lakes report data on declines in lake productivity and the spread of invasive mussels to inform decisions to stock the lake with fewer salmon and trout.

“Long-term datasets are crucial for managing lakes the size of the Great Lakes,” Santucci wrote in an email.

—Grace van Deelen (@gvd.bsky.social), Staff Writer

Citation: van Deelen, G. (2026), Aboard the Lake Guardian, scientists search for clues about the Great Lakes’ health, Eos, 107, https://doi.org/10.1029/2026EO260299. Published on 21 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Space Weather

Solar storms can have major effects on terrestrial technology, dating back to the earliest days of railroads and telegraph communications—most infamously the Carrington Event of September 1859. For that reason, space weather researchers use recorded disturbances from the past to characterize the strength of these storms and fill in the history of the solar cycle.

Determining the dates of the first disruptive solar storm turned out to be complicated by an error in a 19th century article, Wild et al. explain. An 1871 Nature article claimed the first communications disruption from a solar storm occurred on 18 October 1841, when magnetic interference in railway signaling telegraph lines led to a delay in the 10:05 p.m. passenger train departure out of Exeter, England.

The problem, as these scientific detectives discovered? That railway line wasn’t yet running in 1841.

The 1871 Nature article indicated that the train was delayed by a few minutes on the evening of 18 October 1841 because the telegraph lines that allowed operators to check whether the tracks were clear had been disrupted by the solar storm. However, England’s South Devon Railway Company began operating passenger trains between Exeter and Newton Abbot only in 1846. The researchers dug into records of aurorae and railway timetables, cross-referencing these events to pin down what actually happened.

Railway schedules reveal the 10:05 p.m. train out of Exeter was only time-tabled for a period of just over a year, starting in 1848. Contemporary observers recorded strong sunspot and aurora activity around 18 October 1848, precisely 7 years after the date mentioned in the Nature article.

In other words, the 1871 Nature story got the date right but the year wrong. This mistake means the Exeter delay was not the first known solar storm to affect human technology. Instead, accounts of geomagnetic disturbances affecting the telegraph system of the Midland Railway near Derby, England, on 19 March 1847 stand as the earliest credible report on record.

Knowing the correct date fills in an important detail of the recorded history of geomagnetic weather and helps researchers understand the links between solar cycles and communications disruptions. (Space Weather, https://doi.org/10.1029/2026SW005239, 2026)

—Matthew R. Francis (@BowlerHatScience.org), Science Writer

Citation: Francis, M. R. (2026), Of cosmic rains and delayed trains, Eos, 107, https://doi.org/10.1029/2026EO260287. Published on 21 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Do forests cool the planet or warm it? It’s a deceptively simple question with no clear answer. The catch is that the same forest can push climate in opposite directions at once.

Forests are widely viewed as climate change mitigators—and planting trees as a partial climate solution—because they absorb carbon dioxide. Yet that framing is incomplete. Trees also release reactive gases called biogenic volatile organic compounds (BVOCs) that can influence cloud formation, contribute to air pollution, and extend the atmospheric lifetime of methane, a greenhouse gas that can trap about 80 times as much heat as carbon dioxide.

Although largely invisible to the public, BVOC emissions are significant. They account for roughly 90% of the global mass of nonmethane volatile organic compounds entering the atmosphere [Khan et al., 2025]. In natural habitats, forest trees are the dominant sources of BVOCs. They’re responsible for the familiar scent of pine stands and the bluish haze often seen above dense tropical canopies. Agricultural crops and wetlands are major sources in rural regions. In cities, BVOC emissions come primarily from parks, street trees, and remnant woodlands.

Accounting for the competing effects of BVOCs has become increasingly important for climate scientists, especially as forest habitats and footprints shift and land use patterns continue to change worldwide [Wang et al., 2024]. Better understanding whether, where, and to what extent these plant emissions affect the atmosphere will allow researchers to improve forecasts of air quality, cloud formation, and future warming.

From Leaves to Clouds

Whether forests cool or warm the planet depends on how BVOCs behave once they leave the foliage.

Cloud-shaping plant chemistry begins with photosynthesis in sunlit leaves.

Cloud-shaping plant chemistry begins with photosynthesis in sunlit leaves. From there, the normal steps of plant metabolism synthesize and release BVOCs. Globally, isoprene makes up the largest share of BVOC emissions and is especially emitted from many broad-leaved trees. Additional volatiles, such as monoterpenes and sesquiterpenes, are released in smaller amounts, often by conifers and stressed vegetation.

Once airborne, these invisible vapors oxidize rapidly and condense into microscopic specks known as secondary organic aerosols (SOAs). As SOAs drift and collide, they can grow into cloud condensation nuclei, the tiny seeds around which water droplets form. Particles larger than about 1 micrometer, about 1/100 the diameter of human hair, can influence cloud brightness and longevity, as well as Earth’s energy balance. The result is a chain of interactions that begins at the level of individual leaves and extends to regional and global climate systems.

These interactions are dynamic, not fixed. Rising temperatures generally amplify BVOC emissions. A 2°C–3°C rise in mean global temperature is expected to increase total BVOC emissions by 30%–45% worldwide. High-latitude, nutrient-limited ecosystems are especially sensitive. Researchers have found, for example, that isoprene emissions from Arctic sedges are exceptionally temperature sensitive, suggesting that warming could produce disproportionately large increases in emissions from these ecosystems.

But if temperatures rise beyond the range that plants can tolerate or warming is paired with prolonged drought, then photosynthesis can falter, and BVOC emissions can be suppressed. The system thus comprises a powerful and delicate feedback, in which plants respond to climate while simultaneously helping to regulate it through their effects on the clouds above.

A Climate Paradox

The paradox is that identical molecules released by living plants can either cool or warm Earth, depending entirely on the conditions in the atmosphere when and where they enter it (Figure 1).

Fig. 1. The same compounds emitted by forests can either cool or warm the atmosphere depending on background pollution levels and atmospheric chemistry. BVOCs, biogenic volatile organic compounds; NOx, nitrogen oxides. Credit: Mary Heinrichs/AGU

In cleaner air, the balance tilts toward a cooling effect of BVOCs. As SOAs seed clouds, droplet numbers increase, and clouds grow brighter. They reflect more of the Sun’s energy back into space. The longer those droplets persist, the more they extend a thin planetary shade over the landscape below.

Recent model estimates suggest that BVOC-driven aerosol effects may have a radiative cooling effect between −2.0 and −0.4 watts per square meter [Bellouin et al., 2020]. This value is smaller than the roughly 2–3 watts per square meter of warming from carbon dioxide currently. Nevertheless, the effect is large enough to shape regional weather and cloud feedbacks.

Under polluted skies, however, the same emissions can have the opposite effect. In the presence of nitrogen oxides from tailpipe exhaust, power plant emissions, and other combustion sources, for example, BVOCs help generate ozone, a greenhouse gas found in urban smog. They can also disrupt the chemistry that normally removes methane from the atmosphere, allowing it to remain aloft longer and trap more heat.

These warming pathways partially offset the cooling produced by biogenic aerosols, although current evidence indicates that the global cooling effect remains larger overall, with substantial regional variation and uncertainty among warming effects.

Temperature, sunlight, drought, and pollution thus determine whether forests act as air conditioners or furnaces with respect to warming.

The Air People Breathe

The consequences of plant vapors are not confined to clouds and climate. Biogenic volatile organic compounds (BVOCs) can also contribute to pollution.

The consequences of plant vapors are not confined to clouds and climate. BVOCs themselves can also contribute to pollution that exacerbates respiratory health conditions and leads to increased hospital emergency room visits and premature deaths.

Photochemical reactions in the air can intensify quickly above traffic corridors and rooftops, especially under summer sunlight. The ground-level ozone and SOAs (an important component of fine particulate matter) formed through reactions of BVOCs with nitrogen oxides are both harmful forms of air pollution. Ozone inflames airways in our lungs, worsens asthma, and is linked to higher mortality. Fine particles small enough to penetrate deep into the lungs are associated with heart disease, stroke, and premature death.

Haze hangs over Los Angeles, as seen from the Hollywood Hills. Credit: David Iliff/Wikimedia Commons, CC BY-SA 3.0

The risk is greatest where dense populations and human-caused emissions overlap with strong biogenic emissions, a scenario that characterizes places like Los Angeles, Atlanta, and Beijing. Even with stricter vehicle tailpipe standards and other emissions controls, ozone pollution persists in many cities around the world as heat, sunlight, and mixed emissions from anthropogenic and natural sources continue to interact.

A Gray Area of Greening Cities

Urban vegetation is one of the most visible tools that cities have for confronting another public health threat: extreme heat. Trees reduce heat exposure by shade- and evapotranspiration-driven cooling. They can also help filter pollutants from the air and are associated with benefits for mental health and well-being.

But not all trees are chemically equivalent. A recent meta-analysis covering 357 plant species found that broad-leaved trees such as oaks produce markedly different blends of BVOCs than pines and other conifers [Bao et al., 2023]. For example, 78% of broad-leaved trees emit isoprene, compared with only 48% of conifers, whereas 93% of conifers emit monoterpenes.

These emissions are also highly sensitive to climate. Another meta-analysis found that warming increased isoprene emissions globally by an average of 107% and monoterpene emissions by 60%, whereas drought reduced them by 27% and 33%, respectively [Chen et al., 2026]. Thus, the trees planted to cool tomorrow’s cities may behave differently under tomorrow’s climate conditions than they do today.

Reducing nitrogen oxide pollution decreases ground-level ozone formation, yet expanding urban tree cover may increase emissions of reactive BVOCs that offset these decreases.

This uncertainty creates a challenge for policymakers. Reducing nitrogen oxide pollution decreases ground-level ozone formation, yet expanding urban tree cover may increase emissions of reactive BVOCs that offset these decreases depending on species choice and local conditions.

A pioneering 2024 survey by the California Department of Transportation evaluated more than 260 commonly used roadside plants for their potential to contribute to ozone and fine particulate formation. The report identified willows (Salix spp.), American sweet gum (Liquidambar styraciflua), sycamores (Platanus spp.), gum trees (Eucalyptus spp.), and several oak species (Quercus spp.) among the highest BVOC emitters. In contrast, all pines (Pinus spp.) and other conifers were categorized as comparatively low emitters.

The survey’s findings underscore that urban greening strategies are not chemically neutral. Species selection can shape local atmospheric composition and influence whether vegetation improves or inadvertently worsens air quality. Questions of urban forestry, once framed mainly around shade and aesthetics, are increasingly considering how trees affect atmospheric chemistry.

Challenges for Atmospheric Modeling

Climate modelers must address three main challenges to translate the chemistry and behavior of BVOCs into realistic simulations of the atmosphere.

The first is accurately estimating the magnitudes of BVOC emissions themselves. Some analyses report uncertainties in modeled emissions estimates approaching or exceeding 100% [Wang et al., 2021]. Even for a single compound, such as isoprene, emissions can vary substantially depending on ecosystem composition. In some regions, updated land cover data reduced estimated emissions modestly, whereas in others they more than doubled them relative to estimates based on conventional land cover maps [Opacka et al., 2021].

BVOCs and their oxidation products can travel far beyond forested regions, influencing atmospheric processes well downwind of their sources.

The second challenge is that BVOC oxidation in the atmosphere remains incompletely understood. A major limitation for models has been the difficulty of representing the thousands of intermediate reactions involved in this chemistry. Recent work shows that incorporating more detailed oxidation mechanisms into current models can significantly alter predictions of SOA formation and its climatic effects, narrowing some of the models’ largest uncertainties [Zha et al., 2023].

The third challenge is one of scaling. Observations from high-altitude monitoring stations have shown that air masses containing BVOCs and their oxidation products can travel far beyond forested regions, influencing atmospheric processes well downwind of their sources [Okamoto and Tanimoto, 2016]. To capture these effects, models must account for processes occurring in individual leaves and then accurately simulate the transport and chemical evolution of BVOCs throughout the atmosphere [Guenther et al., 2012].

Although these difficulties limit our ability to resolve BVOC-driven climate feedbacks, available models have clearly revised the standard view of forests as passive carbon sinks.

Tracking the Chemical Pulse of Forests

New tools are narrowing gaps between living ecosystems and the climate models built to represent them. For decades, scientists estimated BVOC emissions by combining vegetation maps with average emission rates for different plant types and equations describing how emissions change with temperature and sunlight. In these models, forests were represented largely as static patches on a grid, with broad vegetation categories standing in for the diversity and responsiveness of real ecosystems. That simplified picture is now giving way to a far more observational, data-rich view of Earth’s vegetation.

The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is one example of how that transition is occurring. MEGAN estimates BVOC emissions by combining information about terrestrial vegetation with data on environmental conditions that influence emissions. Its latest generation, MEGANv3.2, improves upon earlier versions by estimating emission factors from measurements of individual plant species rather than relying on fixed categories of plant functional types.

Using MEGANv3.2 together with time-varying satellite observations of vegetation and meteorological reanalysis data, Wang et al. [2024] estimated that average annual global BVOC emissions from 2001 through 2020 amounted to about 835 million metric tons, including 348 million tons of isoprene and 185 million tons of monoterpenes.

The atmosphere responds not simply to how much vegetation is present but to what grows where and how vegetation is influenced by its changing environment.

The new model also illustrates why representing vegetation accurately matters. Although global isoprene emissions declined slightly during the study period, regional patterns differed sharply under varying influences from changes in vegetation, temperature, soil moisture, and atmospheric carbon dioxide [Wang et al., 2024]. In Europe, for example, higher temperatures helped increase emissions, whereas higher soil moisture was more important for increasing emissions in East and South Asia.

Earlier generations of MEGAN had shown the importance of vegetation type on BVOC emissions. Guenther et al. [2012] found that tropical forests, which cover less than a fifth of Earth’s land surface, account for roughly 80% of the isoprene and terpenes emitted by vegetation and about half of other plant-emitted volatiles, whereas other forested ecosystems covering a similar area contribute only about 10% of total emissions.

Such early estimates helped establish a fundamental principle that newer models are now able to examine in greater detail: The atmosphere responds not simply to how much vegetation is present but to what grows where and how vegetation is influenced by its changing environment.

Sensing Biogenic Volatiles from Orbit

Satellites are also driving much of the shift toward better data and improved understanding. Instruments such as the Tropospheric Monitoring Instrument (TROPOMI) aboard the European Space Agency’s Sentinel-5P satellite can detect atmospheric formaldehyde, a compound formed when isoprene oxidizes in air. Because isoprene is the dominant BVOC emitted by many forests, formaldehyde serves as a large-scale chemical fingerprint of plant emissions.

From hundreds of kilometers overhead, satellite instruments like TROPOMI and the Cross-track Infrared Sounder now allow a comparison of modeled emissions with real atmospheric chemistry across continents rather than at only a scattering of field sites.

Measurements of atmospheric formaldehyde reveal regions where vegetation releases large quantities of reactive gases. Because formaldehyde forms during the oxidation of plant-emitted compounds such as isoprene, these observations provide a global view of the chemical exchanges linking forests, clouds, air quality, and climate. These data, collected by the Sentinel-5P satellite, reflect averaged formaldehyde concentrations across the globe from 1 March to 31 May 2026. Credit: Sentinel-5P Product Algorithm Laboratory; contains modified Copernicus Sentinel-5P/TROPOMI data

Satellite observations have already revealed that even widely used emission inventories can contain substantial regional biases. For example, a prior version of MEGAN was found to overestimate total African isoprene emissions by 22%—and emissions in the central African rainforest by 43%—while underestimating emissions from southern deciduous forests by 21% [Marais et al., 2012]. Satellite observations have also shown that some mismatches between observations and models arise not from incorrect emissions estimates, but from incomplete understanding of atmospheric oxidation chemistry, particularly that of isoprene [Wells et al., 2020].

Other satellites observe plants more directly. Missions such as NASA’s Orbiting Carbon Observatories (OCO-2 and OCO-3) measure solar-induced fluorescence emitted by chlorophyll during photosynthesis. Because the amount and composition of BVOC emissions can change with plant productivity and metabolic activity, these data help to determine when ecosystems are active and how emissions respond to drought, heat waves, and seasonal change.

Continuing to Reveal Ecosystem Influences

The behaviors of clouds, aerosols, and tropical ecosystems still pose major challenges for atmospheric modeling, as does resolving the detailed chemistry of BVOCs. Thousands of reactions happen in air and aerosol droplets, and no satellite or global model can track them all in full.

Yet the atmosphere above forests is no longer being inferred and approximated from temperature curves or simplified assumptions. Innovative models and observing technologies are linking forest emissions to the beat of photosynthesis itself and revealing how ecosystems continuously influence climate, clouds, and air quality through dynamic chemical exchanges once treated as background noise.

References

Bao, X., et al. (2023), A meta-analysis on plant volatile organic compound emissions of different plant species and responses to environmental stress, Environ. Pollut., 318, 120886, https://doi.org/10.1016/j.envpol.2022.120886.

Bellouin, N., et al. (2020), Bounding global aerosol radiative forcing of climate change, Rev. Geophys., 58(1), e2019RG000660, https://doi.org/10.1029/2019RG000660.

Chen, J., et al. (2026), Global variability in isoprenoid emissions: Divergent responses to warming and drought driven by physiochemical controls, Plant Cell Environ., 49(8), 5,294–5,312, https://doi.org/10.1111/pce.70536.

Guenther, A. B., et al. (2012), The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): An extended and updated framework for modeling biogenic emissions, Geosci. Model Dev., 5(6), 1,471–1,492, https://doi.org/10.5194/gmd-5-1471-2012.

Khan, M. A. H., et al. (2025), Isoprene emissions, oxidation chemistry and environmental impacts, Atmosphere, 16(3), 259, https://doi.org/10.3390/atmos16030259.

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Author Information

Dennis Clark (drdennisclark@gmail.com), Arizona State University (retired), Tempe

Citation: Clark, D. (2026), Chemical conversations between forests and the sky affect air quality, clouds, and more, Eos, 107, https://doi.org/10.1029/2026EO260295. Published on 18 September 2026. Text © 2026. The authors. CC BY-NC-ND 3.0
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Venus’s pale face enshrouds a hostile reality unfolding beneath its clouds, one that’s inhospitable for life-forms as we know them. Acidic downpours and a crushing carbon dioxide–rich atmosphere lead to blistering surface temperatures of about 467°C (872°F) and atmospheric pressure about 93 times that of sea level on Earth.

Yet the clouds themselves, made almost entirely of sulfuric acid, have held astrobiologists’ curiosity for decades, especially in the upper reaches where the ambient conditions can host liquids and organic molecules brought by meteorite showers. Some see the clouds as an opportunity to test whether life-forms not only can survive concentrated sulfuric acid but also rely on it instead of on water.

In recent years, Massachusetts Institute of Technology planetary scientist Sara Seager and her team have demonstrated how the chemical bonds in amino acids and nucleic acid bases—the building blocks of proteins and DNA and RNA, respectively—can survive in concentrated sulfuric acid. The more concentrated sulfuric acid gets, the fewer water molecules are present to trigger the hydrolysis that breaks the molecule’s chemical bonds.

“This shouldn’t even be happening, and yet it does.”

In a study published in the Proceedings of the National Academy of Sciences of the United States of America, the team shows that some peptides—or chains of amino acids—can also remain intact in concentrated sulfuric acid. And they can go a step further, folding into a distinctive knot shape called an omega loop that could give these chains biological functions.

“This shouldn’t even be happening, and yet it does,” said coauthor Janusz Petkowski, an astrobiologist at Wrocław University of Science and Technology in Poland. He’s a longtime collaborator of Seager’s, who will assume an appointment at the University of Toronto in October.

In finding these shapes, the team has done away with the assumption that concentrated sulfuric acid destroys every peptide it comes in contact with. The finding could mean expanding the search for signs of life beyond Earth to new environments previously considered too hostile to support biological functions.

On Omega Loops

Omega loops are one of many shapes peptides can fold into in nature and are typically known to occur in water-based chemistry. Scientists didn’t think such bonds could exist in concentrated sulfuric acid; it was thought that the presence of excess protons and hydrogen bonds would inhibit folding or unfurl any 3D structure.

In the new work, researchers tested three synthesized peptides. While in water, the peptides arranged themselves as flat sheets without folding. In concentrated sulfuric acid, they folded into omega loops.

Not every peptide can remain stable in the acid, let alone fold. A few years ago, Seager’s team reported dipeptides degrading in the acid. But the latest study has astrobiologists reconsidering commonly held assumptions about organic compounds’ behavior in the medium.

“The cool part is they find some peptides are stable, some are not,” said Martin Rahm, a quantum chemist and astrobiologist at Chalmers University of Technology who was not involved in the study. Commenting on the omega loop, he said, “Seemingly, this is not like a random coil.”

However, Rahm was “less sure” about interpreting these peptides as bearing omega loops. Researchers used a spectroscopic technique called nuclear magnetic resonance to identify the structures, applying a magnetic field to the peptides and observing their atoms realign. But the researchers’ modeling software wasn’t designed to interpret structures in sulfuric acid–based media.

Though concentrated sulfuric acid is a “severely understudied” solvent, according to Petkowski, he said the team took care to adopt controls to avoid bias in their structural models, finding the three peptides tested bore omega loops of “slightly” different curvatures. The loops reemerged under every assumption they varied and tested for.

Life in an Acid Environment

It may be too early to speculate whether these omega loops have biochemical functions, in part because the study itself doesn’t necessarily point to this. “If they all fold into the same thing (omega loops), that might actually be bad for life,” Rahm said. The reason is that none of the peptides would fold into the other structures necessary for life as we know it, such as sheets and helices.

“From an astrobiological point of view, there could be sulfuric acid in many places and likely on Venus. So then, understanding what could survive in it, what kind of chemistry that can happen, would be important regardless [of] if it’s related to life or not.”

“There is a lot of work ahead of us,” Petkowski said. While he agreed with Rahm about the ubiquity of omega loops not necessarily pointing to life, he noted the team has only just begun experimenting with various peptides, exploring the many possible shapes peptides can fold into and amino acid sequences beyond the ones found in life on Earth. “One of the avenues of research is essentially looking at sulfuric acid as a solvent for life.”

“From an astrobiological point of view, there could be sulfuric acid in many places and likely on Venus,” Rahm said. “So then, understanding what could survive in it, what kind of chemistry that can happen, would be important regardless [of] if it’s related to life or not.”

That way, he added, “we can understand what we find when we go there.”

—Karthik Vinod (@karthikvin2000), Science Writer

Citation: Vinod, K. (2026), Venusian sulfur clouds might not be so inhospitable after all, Eos, 107, https://doi.org/10.1029/2026EO260298. Published on 18 September 2026. Text © 2026. The authors. CC BY-NC-ND 3.0
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Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances

Extreme heat events are an increasing threat to human health and ecosystem sustainability. While their rising frequency under global warming is well documented, much less is known about how their seasonality is changing, including whether extreme heat is occurring earlier or later in the year, potentially catching societies and ecosystems unprepared.

Ivanovich et al. [2026] characterize global changes in the seasonality of extremely dry and humid heat events using data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) over the period 1980-2024. Changes in seasonality are assessed by comparing the distribution of extreme heat events during 1980-1989 with that of the most recent decade in the historical record.

The results reveal substantial shifts in extreme heat seasonality over the past 45 years, with both dry and humid extreme heat seasons expanding across much of the globe. Importantly, these changes are often asymmetric. In regions such as western Europe and northeastern Russia, changes are dominated by an increase in pre-season extremes-analogous to springtime events in the midlatitudes. In contrast, much of the United States, eastern Europe, and eastern China have experienced stronger changes in late-season extremes.

The study also highlights important regional departures from the broader global trend. Although previous research has shown that the average warm season is lengthening substantially across the midlatitudes, some regions, including eastern Russia, have experienced a contraction of the extreme heat season. These regional asymmetries suggest that local and regional climate processes can modify, and in some areas, even outweigh the broader influence of global warming.

By revealing not only where extreme heat seasons are expanding, but also when within the year the greatest changes are occurring, these findings provide a new perspective on evolving heat risks and can help inform climate adaptation and risk-mitigation strategies.

Citation: Ivanovich, C. C., Cook, B., & McDermid, S. (2026). Extreme dry and humid heat seasons are changing asymmetrically. AGU Advances, 7, e2026AV002516. https://doi.org/10.1029/2026AV002516

—Alberto Montanari, Editor-in-Chief, AGU Advances

Text © 2026. The authors. CC BY-NC-ND 3.0
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Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances

Both tropospheric ozone and mineral dust are air pollutants capable of being transported over long distances from their original sources. Despite coming from different sources, both pose significant threats to human health, interact with the Earth’s climate system, and can negatively impact agricultural productivity. While scientists know that mineral dust acts as a natural sink for the ozone, the mechanisms represented in current global models are insufficient to explain the observed ozone reductions in dust-influenced regions.

Meidan et al. [2026] apply a global chemistry-climate model with explicit representation of dust-induced release of halogens, specifically chlorine and iodine, in the marine atmosphere. The authors demonstrate that this dust-catalyzed chemistry leads to substantial ozone reductions over marine regions, successfully matching real-world observations of dust-induced ozone loss. The authors also find that this natural ozone reduction yields surprisingly positive impacts far from dust sources, boosting crop production in major agricultural belts and lowering ozone-related mortality in densely populated areas like South Asia.

As climate change is expected to expand desert regions and increase global dust emissions in the future, this natural ozone-destroying mechanism has the potential to significantly modulate future tropospheric ozone levels.

Citation: Meidan, D., Bossolasco, A., Cuevas, C. A., Villamayor, J., Fernandez, R. P., Li, Q., et al. (2026). Global ozone reduction driven by dust-catalyzed halogen chemistry. AGU Advances, 7, e2026AV002453. https://doi.org/10.1029/2026AV002453

—Vaishali Naik, Editor, AGU Advances

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Most of the tens of thousands of hikers that trek up Utah’s Mount Timpanogos each year have no idea that the rockfall below them conceals an enormous glacier. And beyond the people who study them, knowledge that glaciers like these, called rock glaciers, even exist in Utah is not widespread, said Michael Thorne, a seismologist at the University of Utah.

But that’s what Timpanogos Glacier is: a glacier concealed by layers of fallen rock that contains rock debris. Its ice is internal, which is why so many Utah recreationists barely know it’s there.

Though it’s hidden, the glacier contains an enormous amount of ice: 1,550,000 cubic meters, or enough to fill Egypt’s largest pyramid, according to a new study published in the Journal of Geophysical Research: Earth Surface. The study provides a detailed 3D map of the rock glacier using a new approach and is an important step toward a better understanding of rock glaciers in Utah and beyond, said Doug Clark, a geologist at Western Washington University who was not involved in the study but researches rock glaciers in the western United States and New Zealand.

The study takes “an elegant approach to address one of the more vexing problems regarding rock glaciers: What is the internal ice content of these things?” Clark said.

Defining Gravity

“Can we come up with techniques for imaging the interior of these rock glaciers that don’t only rely on ground-penetrating radar?”

To measure regular glaciers and to know how much water they contain, scientists usually use ground-penetrating radar (GPR), which travels easily through ice. But the method doesn’t work as well with rock glaciers. GPR can’t always detect the bedrock beneath the glacier because it can’t penetrate the rock layer above it, so the method can’t always tell how thick a rock glacier really is.

“Part of our motivation has been, well, ‘Can we come up with techniques for imaging the interior of these rock glaciers that don’t only rely on ground-penetrating radar?’” said Thorne, who is also a coauthor of the new study. While teaching an undergraduate geology lab class, he had an idea: Could the research team use a gravimeter instead?

Because Earth’s surface and interior (and therefore mass) change very slightly depending on where on the planet you are, its gravity changes slightly, too. Over very dense bedrock, for example, you weigh slightly more than you would standing above a vast underground cave. A gravimeter measures these tiny changes in gravity and can therefore tell scientists the differences in density of underground material—such as the difference between rock and ice.

Some hikers might assume Timpanogos Rock Glacier is visible from the trail, but that’s just last winter’s snow. The glacier itself is hidden beneath a layer of loose rock. Credit: Robben Migacz, Michael Thorne

“As we get to areas where the ice is thicker and thicker, the gravitational acceleration is just lower and lower,” Thorne said.

Gravimeters were used previously to measure glaciers, but the method fell out of favor when GPR was developed. In addition, the gravimeters of today are more sensitive and accurate than ever before, allowing scientists to measure “really small deviations in the gravitational field,” said Leif Andersson, a glaciologist at the University of Utah and a coauthor of the new study. “The reason why the study was possible was the technology.”

University of Utah master’s student and ultrarunner Bronson Cvijanovich carried the gravimeter up a 5-mile, high-elevation trail, taking 232 gravimeter measurements over the course of six multiday trips to Timpanogos Glacier. Then, the team analyzed the data using a statistical method called Bayesian inversion, which compares thousands of predictions from simulations of the distribution of ice beneath the surface to real measurements of the glacier, giving researchers a measure of how well their data fit reality.

Cvijanovich and the gravimeter, which made imaging the rock glacier possible. Credit: Bronson Cvijanovich

According to Clark, the modeling in the study and the use of the gravimeter marked a “significant improvement over past efforts of estimating ice volume” in rock glaciers.

Using this method, along with some measurements of other rock glaciers, the researchers determined a relationship between the surface area of a rock glacier and the typical volume of ice beneath it. They estimated that Timpanogos Glacier contains enough ice to fill about 600 Olympic swimming pools with an equivalent amount of water.

“It’s a huge volume of ice—I’m surprised there is that much,” Anderson said.

Expanding their analysis, the researchers estimated that rock glaciers in the state of Utah hold about 1.08 cubic kilometers of ice, rock glaciers across the western United States hold up to about 13 cubic kilometers of ice, and all the known rock glaciers on Earth store about 52.38 cubic kilometers of ice. (For reference, the Antarctic Ice Sheet contains about 30 million cubic kilometers of ice.)

The Role of Rock Glaciers

Rock glaciers are a unique source of water, Thorne said, because they release water year-round, including at the end of summer when other water stores have been depleted. The layer of rock above them also insulates them from heat, making them more resilient in warming weather. Plus, they can act as environmental refuges for plants and wildlife (such as the American pika) because they provide a relatively cooler habitat. Understanding how much ice rock glaciers store is the first step in understanding how they might melt in the future, too.

The new study also opens an opportunity to start investigating the extent to which Utah’s rock glaciers contribute to the state’s water systems—they’re unaccounted for in the state’s hydrological models, meaning scientists don’t have the full picture of how their meltwater affects the rest of the state. “They represent these unrecognized ice reservoirs and water reservoirs,” Clark said. “They’re a unique and particularly resilient resource compared to other glaciers that are melting quite rapidly.”

Timpanogos Rock Glacier and Emerald Lake below it are visible from the summit of South Timpanogos. Credit: Michael Thorne

“If all that ice is stored, is it still growing? How much of it is melting and adding to the downstream hydrology? We don’t know that yet,” Anderson said. He added that it’s difficult to measure how much of the water coming off a rock glacier is from the glacier melt versus groundwater, but doing so would help to answer some of the outstanding questions about rock glaciers in Utah.

“I think this can open a new direction in the study of buried ice globally.”

He hopes other researchers apply the gravimeter and Bayesian analysis method elsewhere to see just how much ice is locked away in the world’s rock glaciers. “I think this can open a new direction in the study of buried ice globally,” he said.

Clark agreed. “It would be great for some other folks to replicate this with a few other rock glaciers, and for a wider variety of rock glaciers,” he said. “That would be an important test of [the data] they’ve got here.”

—Grace van Deelen (@gvd.bsky.social), Staff Writer

Citation: van Deelen, G. (2026), Scientists mapped a hidden glacier using gravity, Eos, 107, https://doi.org/10.1029/2026EO260297. Published on 17 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: AGU Advances

Understanding how wind changes in response to global warming is necessary for accurately modeling climate and weather, identifying risks to infrastructure, and assessing global wind power capacity.

Sunlight delivers energy to Earth. A small part of that energy is converted into atmospheric kinetic energy (i.e., winds), which eventually dissipates into heat and radiates back out to space.

This heat exchange process is called the “atmospheric heat engine.” But traditional models of this engine depend on complex processes such as cloud microphysics that remain poorly constrained, limiting the models’ predictive power.

One of the main questions about wind and climate change is why models and observationally constrained reanalysis exhibit only relatively weak and inconsistent changes in the atmospheric heat engine in response to warming. Researchers also debate whether a wetter atmosphere is decreasing the efficiency of the heat engine, weakening global wind energy dissipation.

Jansen et al. present a new approach to estimating the work that drives the winds, using just two quantities. The first is the height-weighted radiative energy loss of the atmosphere. The second is a bulk Bowen ratio—the ratio of the column-integrated upward sensible heat flux to latent heat flux, which reflects how much energy travels upward as warm air versus latent heat in the form of water vapor.

The study authors worked from first principles to show how those two factors (the height-weighted radiative energy loss and the bulk Bowen ration) can explain changes in the heat engine and wind dissipation in various climate scenarios, including today’s.

They found that increases in radiative cooling in the upper troposphere and a decrease in bulk Bowen ratio with warming are in competition with each other. More radiative cooling increases the atmospheric heat engine’s work output, whereas a decrease in the bulk Bowen ratio reduces that output.

The balance between the two determines changes in the atmosphere’s kinetic energy dissipation and shapes how wind responds to a warming world.

Under current climate conditions, these opposing mechanisms largely cancel each other out, the study found. That could explain the relatively weak and inconsistent changes in global wind energy dissipation during the 21st century predicted in comprehensive climate models and atmospheric reanalysis.

However, the authors note that near-constant global wind energy dissipation does not imply that the winds don’t change at all. Climate change can still lead to significant shifts in atmospheric circulation and in regional wind behavior. The authors’ own simulations show the storm tracks shifting poleward, with substantial regional wind changes.

The authors also applied their theory across a much wider range of climates and found that this near cancellation breaks down at the extremes. In very cold climates, the energy driving the winds drops sharply—consistent with the far less energetic circulation seen in simulations of the Neoproterozoic snowball Earth. In addition, they suggest that given its simplicity, the model could be useful for estimating atmospheric kinetic energy and circulation on exoplanets. (AGU Advances, https://doi.org/10.1029/2026AV002593, 2026)

—Rebecca Dzombak, Science Writer

Citation: Dzombak, R. (2026), Wind works: The atmosphere’s invisible energetic tug-of-war, Eos, 107, https://doi.org/10.1029/2026EO260294. Published on 17 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Journal of Geophysical Research: Biogeosciences

Rainwater connects the biogeochemical cycles of the land and the atmosphere. It’s effectively a chemical conveyor belt that delivers compounds to the ground during a process called wet deposition.

For decades, research on airborne chemicals and wet deposition focused on inorganic compounds in rainwater, particularly nitrate and sulfate, which are key drivers of acid rain. Lacking the means to detect volatile organic compounds (VOCs) in rainwater, scientists long assumed that rainwater-based cycling of these compounds, which can be found in some petroleum fuels, paint thinners, and pharmaceuticals, was negligible.

But recent improvements in analytical techniques revealed that VOCs are present in rainwater in higher concentrations than scientists thought. In a new review, Yañez-Serrano et al. estimate that of the roughly 460 teragrams of carbon delivered via wet deposition every year, about 100 teragrams come from wet deposition of VOCs. And climate change and human activities are exacerbating VOC emissions.

The authors argue that dissolved atmospheric volatile organic compounds have been “largely invisible” to the biogeosciences and are a missing link in carbon cycle modeling. VOCs are highly reactive and biologically labile, so even small concentrations can affect water chemistry, plants, and microorganisms at local to regional scales. Particularly in carbon-limited ecosystems, even a small amount of VOC deposition can trigger a rapid biological response.

The authors present key knowledge gaps and suggest next steps for the research community. VOCs pose unique analytical challenges because they are highly reactive and chemically diverse. But both detection and modeling will need to further improve to better assess the role of VOCs in the biogeochemical cycle and in fields like air pollution monitoring, the authors say.

As scientists collect more VOC monitoring data, modeling will need to incorporate it. Most atmospheric carbon budgets currently omit or underestimate water-soluble VOCs and their subsequent oxidized products, leaving this highly reactive form of carbon out of the picture. Modelers will need to explore VOC mechanics and transport and incorporate them into Earth system models.

Finally, observations of and experiments on the effects of VOC wet deposition on terrestrial ecosystems and biogeochemical cycles will be needed to understand the potential damage or disruptions VOCs could be causing and how those may change as climate change continues.

As climate change and human activities exacerbate VOC emissions and change rainwater patterns, understanding VOCs as an overlooked part of Earth’s biogeochemistry has, perhaps, never been more crucial. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2026JG009767, 2026)

—Rebecca Dzombak, Science Writer

Citation: Dzombak, R. (2026), Volatile organic compounds have been underestimated in the carbon cycle, Eos, 107, https://doi.org/10.1029/2026EO260296. Published on 16 September 2026. Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

In late April 2026, a weakened polar vortex drove the outbreak of a cold Arctic air mass that threatened European crops with frost just as the growing season was starting. Temperatures in some places dropped 10°C–15°C relative to the seasonal average, posing particular hazards for vineyards and orchards.

Severe cold air outbreaks (CAOs) like this aren’t uncommon: Another event, in February 2021, sent an Arctic blast that dropped temperatures precipitously through the central United States, causing prolonged, widespread, and costly power outages in Texas especially.

Outbreaks of cold, dry air from the Arctic, as well as influxes of warm and moist air masses to the region, influence and are being influenced by rapid changes occurring in the Arctic climate system.

Increasingly, outbreaks of cold, dry air from the Arctic, as well as influxes of warm and moist air masses to the region, influence and are being influenced by rapid changes occurring in the Arctic climate system, including enhanced warming and dramatic sea ice loss. These air mass transport events, which link the Arctic atmosphere with midlatitudes, are also often accompanied by extreme weather.

Air masses transform significantly as they travel over open ocean and sea ice. For example, their temperature and moisture contents, as well as cloud and precipitation patterns, evolve. These transforming characteristics determine both local and large-scale effects of weather events along the air mass transport paths. Seasonal variability, especially related to the influx of solar radiation (absent during polar night), can have dramatic influences on these air mass transformations. However, the processes driving these influences are not well understood.

Specifically, representations of the development of clouds and the atmospheric boundary layer (the layer closest to Earth’s surface) during air mass transport events to and from the Arctic, particularly during the polar night of winter, are a significant weakness of numerical weather and climate models.

Overcoming these deficiencies, which would help us understand and forecast the potential impacts of these events, can be achieved through coordinated observations intended to contrast seasonally varying influences. Such measurements are exceedingly rare, especially in winter, but forthcoming efforts can capitalize on newly developed techniques for observing air masses firsthand and for modeling their movement and transformation.

An Arctic-Midlatitude Link

The Arctic is a crucial regulator of the global climate system and is linked to processes that occur far beyond its boundaries. Atmospheric interactions between the Arctic and midlatitudes take place primarily through meridional (north to south or south to north) air mass transports, including CAOs and warm air intrusions (WAIs; Figure 1).

Fig. 1. Typical patterns of (a) cold air outbreaks (CAO) and (b) warm air intrusions (WAI) over the Fram Strait between Greenland (top left corner) and Svalbard, Norway (island in the top right), are shown. The color scale in (a) indicates the marine CAO (MCAO) index, in which higher values denote larger temperature differences between the surface and the lower atmospheric layer typical for stronger CAOs; in (b), the color scale indicates vertically integrated water vapor (IWV) contents in the atmosphere. Higher IWVs are typical of strong WAIs. Arrows indicate wind directions and velocities. The data come from the ERA5 (the fifth-generation global climate and weather reanalysis dataset produced by the European Centre for Medium-Range Weather Forecasts) reanalysis by Hersbach et al. [2020].

These dynamic exchanges influence near-surface air temperatures, sea ice extent and thickness, cloud formation, and the balance between incoming solar and outgoing terrestrial radiative energy. They also control the movement of energy (heat), moisture, and pollutants into and out of the Arctic, stimulating feedbacks that operate on local, regional, and global scales [Pithan et al., 2018]. For example, WAIs inject humidity (i.e., water vapor, a major greenhouse gas) into the Arctic, significantly increasing near-surface air temperatures, especially in winter. This humidity also promotes cloud development that further heats the Arctic surface and thus can limit sea ice growth.

Collectively, these exchanges and feedbacks determine how the Arctic shapes large-scale atmospheric circulation and weather patterns—both within and outside the Arctic—that often contribute to extreme, societally impactful events like severe winter storms, cold snaps, heat waves, and significant melting events [Zhang et al., 2025]. Given the wide-ranging implications of meridional air mass transports, observing, understanding, and modeling their fundamental drivers and behaviors, many of which vary seasonally and spatially, are essential steps for scientists.

Seasonal Contrasts Shape Dynamic Processes

The most striking seasonal difference in the Arctic arises from the extreme contrast between polar night and polar day.

The most striking seasonal difference in the Arctic arises from the extreme contrast between polar night and polar day that is driven by the profound effects of solar radiation “switching off and on.” This annual back-and-forth fundamentally alters the region’s radiative energy budget: During the polar night of winter, the surface predominantly loses energy, whereas in summer it gains energy. The radiative energy budget, in turn, modulates energy exchanges at the surface and the vertical distribution of heating and cooling throughout the atmosphere.

Radiative changes strongly influence the properties and structure of the atmospheric boundary layer through effects on vertical stratification and mixing processes. For instance, temperature inversions, which inhibit vertical mixing, tend to be stronger and more frequent in winter, whereas summer conditions can promote more vertical mixing. The radiative budget also affects turbulent and conductive heat fluxes at the surface, near-surface temperature variations, sea ice melting, and other surface processes and properties.

Seasonality affects north–south temperature gradients, further shaping atmospheric transport dynamics and influencing the frequency, properties, and intensity of key events like CAOs and WAIs. Cloud characteristics, including their coverage, thermodynamic phase (liquid versus ice), and precipitation type and frequency, also differ markedly between seasons. For example, the transition into the summer melt season supports a shift from mostly icy to more liquid-containing clouds [e.g., Lac et al., 2026], a change with significant influences on atmospheric boundary layer structure, radiative balance, and more.

Little is known about how seasonal variability affects air mass transformations.

Atmospheric composition also evolves over the year. Alongside variations in mixing and transport pathways, aerosol sources and properties shift because of changes in sunlight-driven photochemical activity, precipitation-driven removal of aerosol particles, surface conditions (e.g., melt pond formation), and biological production of particles and aerosol precursor gases [Schmale et al., 2021]. These aerosol transitions, in turn, affect cloud properties, precipitation efficiency, and possibly cloud lifetimes.

At the surface too, conditions are far from static. The frozen winter surface environment transitions into one with increasing meltwater, open ocean, and moisture availability, before eventually transitioning back after summer passes. These changes influence surface albedo, snow depth, surface roughness, and ice thickness, all of which modulate the exchange of heat, moisture, momentum, and matter between the atmosphere and surface.

Indeed, many drivers of, and constraints on, air mass transports vary seasonally. However, little is known about how seasonal variability affects air mass transformations, including rates of spatiotemporal changes in temperature and moisture that affect cloud formation and longevity, precipitation patterns, radiative properties, and surface interactions. In short, these transformation rates ultimately control the spatial extent of air masses and their impacts on people, yet they remain poorly understood.

Establishing Foundations for Accurate Models

The reliability and credibility of models for weather forecasting and for understanding long-term climate trends and feedbacks depend on strong foundations of observational ground truthing. These observations help models accurately represent fundamental physical processes such as Arctic amplification, meridional transport, and Arctic climate dynamics. However, building these foundations for the Arctic remains a major challenge.

A central issue is the particular scarcity of ground truth data collected over sea ice and during winter [Jung et al., 2016]. The lack of data makes it difficult to evaluate and improve models because key processes are insufficiently constrained.

Sea ice near Svalbard is seen through the clouds in spring 2026. Credit: Marcus Klingebiel

Characterizing the Arctic accurately across all seasons is essential because the effects of seasonal changes in the radiative energy budget extend beyond any single season. For example, although sea ice melting is limited during winter, the amount of ice growth during the dark season strongly influences how the ice evolves later in the year. The importance of interseasonal linkages like this one suggests that weaknesses in model representations of any single season can propagate through simulations over time, significantly affecting the longer-term trajectory of the Arctic that they portray.

With the limitations of available satellite data, in situ and remote sensing observations from ground-based and aerial platforms are indispensable.

Many current modeling tools, including global and regional climate models, reanalyses, and numerical weather prediction systems, exhibit substantial biases, particularly in representing clouds, humidity, and lower atmospheric structure. For example, models do not represent the height of the atmospheric boundary layer over sea ice well, and they often overemphasize cloud glaciation. These deficiencies are most pronounced in winter and in processes tied to net surface energy exchange, such as cloud phase partitioning, which are also among the processes least constrained by satellite observations.

With the limitations of available satellite data, in situ and remote sensing observations from ground-based and aerial platforms are indispensable. They provide high-resolution measurements that not only help calibrate and validate satellite data and support reanalyses but also enable a deeper understanding of the underlying mechanisms at work. Such observations are also crucial for improving model parameterizations and, ultimately, for building more reliable modeling tools.

Coordinated Campaigns Can Close Critical Gaps

Closing critical observational and modeling gaps and advancing predictive representations of Arctic weather and climate dynamics, including meridional air mass transport events, require coordinated research efforts. Field campaigns involving a variety of data-collecting platforms are needed to quantify seasonally and spatially varying processes and feed model development. Targeting the drastically underobserved winter season, for example, would help to isolate effects of solar radiation and other varying conditions.

Moreover, work is needed to implement and improve upon quasi-Lagrangian observational strategies [Wendisch et al., 2025]. These techniques focus on following a moving air mass and sampling it repeatedly as it travels and evolves, combining aircraft, ship-based, and ground-based measurements together with modeling to help constrain air mass transformation processes and rates [Karalis et al., 2025]. Initial quasi-Lagrangian aircraft-based measurements showed promise for estimating air mass temperature and moisture change rates, though they did not always agree well enough with model simulation results [Wendisch et al., 2025]. Further, cloud and precipitation change rates have not yet been derived from these observations.

A central objective of future campaigns should be directly observing and quantifying seasonal differences in the heating or cooling and the drying or moistening of air masses to guide model improvements. Upcoming initiatives offer valuable opportunities to expand the observational footprint and address this objective.

This fall, the Tara Polar station is scheduled to embark on an 18-month expedition—the first of 10 intended missions—to track atmospheric (and oceanic) conditions while drifting with Arctic sea ice. And in coming years, the Contrasting Polar Night & Day (CONIDA) airborne campaigns will follow CAOs and WAIs in the European Arctic, first during winter (CONIDA-Night, November–December 2028) and then during summer (CONIDA-Day, June–July 2029), to study transformations of clouds, precipitation, and radiative processes.

The multifaceted strategies of these efforts—more of which are needed—should provide the comprehensive, multiscale observational constraints we need to robustly characterize and model the processes governing and responding to Arctic seasonal variability, particularly meridional air mass transformations and their broader climate connections. These improvements will, in turn, allow us to sharpen forecasts of the effects of warm air arriving in the Arctic and of the cold air blasts that occasionally send midlatitude temperatures plummeting.

Acknowledgments

We thank Felix Pithan for his valuable discussion regarding this article and Marcus Klingebiel for providing Figure 1. This work was funded by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project ID 268020496–TRR 172 and project ID 316646266 SPP 1294.

References

Hersbach, H., et al. (2020), The ERA5 global reanalysis, Q. J. R. Meteorol. Soc., 146, 1,999–2,049, https://doi.org/10.1002/qj.3803.

Jung, T., et al. (2016), Advancing polar prediction capabilities on daily to seasonal time scales, Bull. Am. Meteorol. Soc., 97(9), 1,631–1,647, https://doi.org/10.1175/BAMS-D-14-00246.1.

Karalis, M., et al. (2025), Lagrangian single-column modeling of Arctic air mass transformation during HALO–(AC)³, Atmos. Chem. Phys., 25, 13,177–13,198, https://doi.org/10.5194/acp-25-13177-2025.

Lac, J., et al. (2026), Understanding the spring cloud onset over the Arctic sea ice, Atmos. Chem. Phys., 26, 4,189–4,213, https://doi.org/10.5194/acp-26-4189-2026.

Pithan, F., et al. (2018), Role of air-mass transformations in exchange between the Arctic and mid-latitudes, Nat. Geosci., 11, 8050812, https://doi.org/10.1038/s41561-018-0234-1.

Schmale, J., P. Zieger, and A. M. L. Ekman (2021), Aerosols in current and future Arctic climate, Nat. Clim. Change, 11, 95–105, https://doi.org/10.1038/s41558-020-00969-5.

Wendisch, M., et al. (2025), Observed and modeled Arctic airmass transformations during warm air intrusions and cold air outbreaks, Atmos. Chem. Phys., 25, 15,047–15,076, https://doi.org/10.5194/acp-25-15047-2025.

Zhang, X., et al. (2025), Weather and climate extremes in a changing Arctic, Nat. Rev. Earth Environ., 6, 691–711, https://doi.org/10.1038/s43017-025-00724-4.

Author Information

Manfred Wendisch (m.wendisch@uni-leipzig.de), Leipziger Institut für Meteorologie, Universität Leipzig, Germany; Matthew D. Shupe, Cooperative Institute for Research in Environmental Sciences and the National Snow and Ice Data Center, University of Colorado Boulder; also at Physical Sciences Laboratory, NOAA, Boulder, Colo.; Susanne Crewell, Institut für Geophysik und Meteorologie, Universität zu Köln, Cologne, Germany; Felix Ament, Meteorologie, Universität Hamburg, Germany; and Gunilla Svensson, Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Sweden

Citation: Wendisch, M., M. D. Shupe, S. Crewell, F. Ament, and G. Svensson (2026), The effects of polar night and day on Arctic air masses, Eos, 107, https://doi.org/10.1029/2026EO260293. Published on 16 September 2026. Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Solid Earth

Changes in how often earthquakes occur can reveal the evolution of stress on faults, providing a window into processes that are otherwise difficult to observe. Jiang et al. [2026] introduce T-rate, a Bayesian method that evaluates many possible stress histories to reconstruct stress changes from earthquake records and quantify the associated uncertainty. The method represents each episode of stress loading as a flexible rise, steady phase, and decline. Tests with simulated earthquake sequences show that T-rate can recover complex stress histories under a range of conditions.

Applied to the 2008 Reno–Mogul swarm, the preferred model identifies four loading phases, including a sharp increase beginning about three days before the magnitude 5.1 earthquake. The timing of this late increase remains relatively stable across the tested data-processing choices. Combined with independent GPS measurements of ground deformation and observations of rapid earthquake migration, the result points to slow fault motion without detectable earthquakes as a plausible source of the final loading phase. By turning widely available earthquake records into uncertainty-aware estimates of stress evolution, the openly available T-rate tool complements ground-deformation measurements, especially where they are sparse, and supports studies of earthquake swarms and other transient fault processes.

Citation: Jiang, Y., Trugman, D. T., & González, P. J. (2026). Bayesian inference of complex stress evolution in rate-and-state governed faults constrained by seismicity rate observations. Journal of Geophysical Research: Solid Earth, 131, e2026JB033922. https://doi.org/10.1029/2026JB033922

—Bogdan Enescu, Associate Editor, JGR: Solid Earth

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Researchers have calculated that Greenland and Antarctica have lost 11 trillion metric tons of ice since the 1970s, which has led to a global rise in sea level of more than 3 centimeters.

“Just over three centimetres of sea-level rise may sound small, but that puts another six to nine million people at risk of coastal flooding and erosion,” said Andrew Shepherd, head of the School of Geography and Natural Sciences at Northumbria University and founder of the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE), in a press release. 

 Related

•  Read the paper: “Mass balance of the Greenland and Antarctic ice sheets from the 1970s to 2023”
•  Ice Sheet Mass Balance Intercomparison Exercise
•  Antarctic Ice Sheet Has Lost a Connecticut-Sized Amount of Ice Over the Past 30 Years
 

IMBIE was founded to bring together data from various satellite missions in order to build a clearer picture of how the Greenland and Antarctic ice sheets have changed over the last few decades. Prior to today’s report, published today in Scientific Data, IMBIE’s most recent assessment calculated a rise of about 21 millimeters to global mean sea level between 1992 and 2020.

In the new assessment, researchers drew on data from 27 satellite missions spanning more than 50 years. The vast majority—about 84%—of the calculated ice loss came from glaciers and ice sheets discharging directly into the ocean, with only 16% of the loss caused by melting at the surface.

This “tells us the long-term trend is being driven by the dynamic response of the ice sheets to a warming ocean,” said Inès Otosaka lead researcher and professor of geography and natural sciences Northumbria University, in a press release.

Though global ice loss slowed between 2020 and 2023, overall ice loss has risen steeply since the 1980s: In Greenland, annual ice loss went from 60 billion metric tons in the 1980s to 264 billion metric tons in the 2010s. In Antarctica, annual loss went from about 48 billion metric tons in the 1980s to 202 billion metric tons in the 2010s.

Through most of the twentieth century, sea level rose by about 1.4 millimeters per year. Between 2006 and 2015, the rate was more than twice as high, at 3.6 millimeters per year.

—Emily Gardner (@emfurd.bsky.social), Deputy Editor

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A new paper (Wang et al. 2026) suggests that the bedrock failure that initiated the Nepal landslide disaster may have displayed measurable precursory deformation.

Inevitably, one of the key discussion points in the aftermath of the 26 August 2026 Nepal landslide disaster is whether the failure could have been anticipated. Opinions differ, but a key starting point is the identification of precursory signals in the days, weeks or months leading up to the failure.

The focus is inevitably on INSAR, but the terrain in the source area of the landslide (on the north face of Langtang Lirung) is unforgiving to this technique. An alternative lies in pixel offset tracking from optical imagery, which can extract movement in more challenging terrain.

In the journal Landslides, a paper published with impressive rapidity (Wang et al. 2026 – the article is paywalled but this link should provide access) uses the pixel offset tracking technique on Sentinel-2 satellite data to examine deformation of the glaciers in the area of the initial failure. They have compared movement of the main glacier, which was not involved in the landslide, and of the hanging glacier under which the landslide occurred. In the Google Earth image below, this is the portion of the glacier under the location marker (the hanging glacier) and main glacial area upslope:-

Google Earth image from 2017 showing the site of the 26 August 2026 landslide in Nepal.

Wang et al. (2026) have measured movement of these two parts of the glacier from 2018 to now. Until the early part of 2026, the two glaciers moved at a linear rate, although the main glacier moved at a much higher rate than the hanging glacier. But, from late 2025 or early 2026, the hanging glacier started to move faster, and from that point onwards showed a dramatically accelerating trend to failure.

Presumably, this is the development of failure in the underlying bedrock being transmitted through to the ice. By the end, the movement rate had increased from about 7.4 m per year to about 55 m per year.

Wang et al. (2026) have a slightly strange interpretation of the mechanical processes that led to this behaviour that I must admit I don’t really understand. To me, this is likely to have been a progressive failure of the bedrock, which is known to show this style of deformation. I would be very interested in seeing a plot of 1/velocity against time for the period of acceleration, which will give an indication as to whether there was a brittle failure mechanism in play.

But nonetheless, this is a fascinating result that might suggest that the initiating bedrock failure that started the disastrous cascade in Nepal demonstrated precursory signals. Please note though that this does not mean that the event itself could have been reliably predicted nor that a warning system can be easily developed.

Reference

Wang, T., Sassa, S., Yang, W. et al. 2026. Precursor of a powerful large glacier landslide causing tsunami floods in the 26 August 2026 Nepal disaster. Landslides. https://doi.org/10.1007/s10346-026-02842-6.

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Yellowstone is among the United States’ most popular national parks, with more than 4.5 million visitors every year. So it’s probably no surprise that park staff does some picking up after visitors. What may be surprising is that the staff has already recovered a record-setting 20,000+ pieces of trash, 5,600 rocks and sticks, and nearly 300 hats from the park’s hydrothermal areas so far this year, according to a USGS press release.

It’s no small feat to dislodge all of this trash from the park’s iconic hydrothermal features, and members of the park’s Geology Program are behind the effort. Much of it is done with shovels or short-handled grabber tools, but some efforts are more complicated, requiring fishing rods, strainers, slotted spoons, and grabber poles up to 30 feet long.

 Related

•  Caps, trash, and other funky hydrothermal finds: 2026 edition
•  Hot Spring Cleaning!
•  Hydrothermal hats and visitor safety: Walking in the boots of the Yellowstone National Park Geology Team
 

Most of this litter was left unintentionally; regardless, the USGS’s accounting of its cleanup serves as a good reminder for visitors to never throw anything into a hot spring or geyser, to hold on (or remove) their hats, and to stash their trash safely until they can get to a trash can.

Below is a list of some of the most notable finds of 2026.

The 280 hats recovered from Yellowstone’s hydrothermal areas this summer included several hats that appear to be from the park’s gift shops. Credit: Credit: National Park Service photo by Margery Price, September 2026 The Yellowstone Geology team collected more than $18.00 in coins from the park’s hydrothermal areas during summer 2026. Credit: National Park Service photo by Margery Price, September 2026

1. 36 pairs of sunglasses. All the better to see those geysers with, we suppose.
2. More than 280 hats. Hats galore! Some had place names, like San Diego, Bears Ears National Monument, Miami, or Yellowstone itself. Sun hats and tie dye hats, patriotic hats and pawprint hats. A baseball cap with the words “COWBOY HAT” written on it. These accessories were likely blown off by wind, and park visitors did the right thing by leaving them behind and not venturing into the geothermal areas to rescue them.
3. 54 camera lens caps. At least it wasn’t the cameras themselves? There did appear to be one children’s camera among the objects, though.
4. A single jingle bell.
5. Six Invisalign retainers! Oof, this one might have been more painful to lose than the 5 AirPods also found in the hydrothermal areas.
6. $18 in coins, including Canadian dollars, euros, pesos, and yen. There were a few dollar bills as well. Most of these appear to have been thrown into hot springs or geysers on purpose, which is not allowed and will not make your wishes come true. If you want to throw your coins somewhere, throw them in a real wishing well, or to us here at Eos.
7. Lots of Yellowstone paraphernalia. In addition to the hats, staff found six Yellowstone pressed pennies, 7 Polaroid photos (several of which were of the hydrothermal feature in which the photos were found), six Junior Ranger badges, and at least one Yellowstone pin. There’s something tragically poetic about this.
8. A single Uno card (yellow 4).
9. A tube of gouache paint (also yellow).
10. Three fortune cookie fortunes: “You are the center of every group attention,” “Trust in the journey, for it is leading you to blessings,” and one that isn’t quite readable.
11. 3 golf tees (there is not a golf course within the park).

—Emily Gardner (@emfurd.bsky.social), Deputy Editor

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2026. AGU. CC BY-NC-ND 3.0
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The most productive scientific programs are not those in which researchers know the answers to their questions in advance. Instead, they are those organized around questions that are genuinely open, consequential, and resolvable by investigation.

The discourse surrounding underground hydrogen storage (UHS) and natural geological hydrogen—increasingly discussed in recent years as a potentially important part of a lower-carbon energy system—offers such questions: How much of the hydrogen injected underground can be recovered later? Will Earth’s own hydrogen ever accumulate in commercially useful quantities?

The barriers should be the focus of research. They define what needs to be known, why it is not yet known, and what the consequences of knowing it would be.

Potential applications of UHS and natural hydrogen are rooted in real physical possibility. Yet deep uncertainties also exist that no honest assessment can resolve with currently available data. Addressing these uncertainties requires investigation through a rigorous scientific program justified on its own terms, regardless of preexisting ideas of whether commercial applications will eventually succeed.

The barriers facing applications of UHS and natural hydrogen are not evidence that researching them is futile, as some observers have suggested (e.g., in recent work questioning self-replenishing production and commentary urging scientific rigor over hype).

In fact, the opposite is true. The barriers should be the focus of research. They define what needs to be known, why it is not yet known, and what the consequences of knowing it would be.

Fixed Constraints for Subsurface Hydrogen

Though they may seem unrelated, UHS and natural hydrogen exploration share identical scientific foundations in the subsurface behavior of molecular hydrogen (H2). H2 is the smallest and lightest molecule in nature. It leaks through rock and cement far faster than methane (natural gas) and rises buoyantly along fractures and faults. Furthermore, many underground microbial communities consume H2 wherever water and suitable chemical partners are present.

Whether one is considering injecting and storing hydrogen underground or whether Earth has already done that on its own, the underlying science is the same. Research efforts looking into those questions are not parallel; they are studying the same geological process from opposite ends.

Hydrogen contains roughly 3.5 times less energy per unit volume than methane at any given pressure and temperature, a consequence of their respective molecular weights and bond chemistries. This physical fact sets an inescapable constraint for applications of either UHS or natural hydrogen exploration—no engineering advance can close that gap.

The Bulqizë mine in Albania hosts one of the few documented cases of intense natural hydrogen degassing from an underground mine, illustrating the tantalizing promise of natural hydrogen as a resource. Credit: Frédéric-Victor Donzé

It might seem reasonable to expect that this disadvantage would narrow at the high pressures found in deep reservoirs, where gases compress and pack more efficiently. Under reservoir conditions, however, methane actually compresses more efficiently than hydrogen, meaning the energy gap is, if anything, slightly greater at depth.

To be economically viable, hydrogen-generating or storage systems must compensate through high generation volumes, efficient trapping, and minimal microbial losses.

This gap is not a verdict against hydrogen as an alternative to methane. But it is a calibration that every economic model and every research design must incorporate. To be economically viable, hydrogen-generating or storage systems must compensate through high generation volumes, efficient trapping, and minimal microbial losses. The understanding of all these factors, apart from the volumetric comparison to methane, is far from complete—and is where vital science lives.

Underground Storage: Open Questions, Not Dead Ends

Whether geological formations can serve as reliable, large-scale hydrogen traps is a genuine open question. Some challenges involve engineering problems likely to be solved: For example, hydrogen embrittlement of steel, which is used throughout hydrogen infrastructure, from injection wells to pipelines and storage tanks, is a real, but tractable, problem.

The deeper unknowns are geoscientific and fall into three classes.

The first is geological specificity: The formations best suited to hydrogen storage—salt deposits and depleted gas fields with intact caprocks, for example—are not necessarily distributed where they are most needed operationally (Figure 1). Whereas some facilities could have a direct demand for hydrogen, others that generate surplus energy from renewable sources could use this energy to hydrolyze water, and the resulting hydrogen could be stored for use when energy demand exceeds supply. Quantifying the mismatch between storage locations and operational needs has barely begun.

Possible storage options for underground hydrogen include salt deposits, saline aquifers, and depleted hydrocarbon reservoirs with intact caprocks. Credit: Miocic et al., 2023, https://doi.org/10.1144/SP528-2022-88, CC BY 4.0

Second is the biological sink: Subsurface microbial communities can consume hydrogen at significant rates over operational timescales. Pilot experiments injecting hydrogen underground have documented substantial losses due to microbial activity—field pilots report losses from a few percent up to more than 50%. But how much consumption occurs varies across geological settings, and whether it can be predicted or suppressed remains unknown. Current estimates of full-system, round-trip efficiency (the percentage of energy retrieved from a storage system compared to the total energy initially used to charge it) span from 25% to 40%, reflecting genuine uncertainty.

The third unknown is caprock integrity: Hydrogen’s much higher diffusivity means that seals adequate for methane—shales, evaporites, and tight carbonates, for example—may not work for H2. However, experimentally based knowledge about hydrogen diffusion through these rocks under reservoir conditions is thin.

These unknowns aren’t dead ends; they outline valuable research directions.

Natural Hydrogen: Generation Is Certain, Accumulation Is Not

Earth’s crust generates hydrogen continuously. Serpentinization of iron-rich rocks, decomposition of water by natural radioactivity (radiolysis), and fluid circulation along active faults all contribute to H2 production within the lithosphere.

How much of this hydrogen reaches the atmosphere remains poorly constrained, though. Documented point sources account for far less than 1 megaton per year globally. Diffuse degassing across the ~2.5 million square kilometers of serpentinized terrains worldwide, potentially the dominant pathway, is essentially unmeasured, with estimates ranging from roughly 0.02 to a few megatons per year.

Whether any of this geologic hydrogen accumulates underground in commercially useful concentrations is also unclear. The one producing hydrogen well, located in Mali, yields the energy equivalent of roughly 30 kilowatts of continuous power: scientifically significant, but not a template for commercial production.

The geological conditions required for large, long-lived hydrogen accumulations are demanding.

Indeed, the geological conditions required for large, long-lived accumulations are demanding.

In many environments, dissolved hydrogen in groundwater never reaches the saturation needed to exsolve into a separate gas phase at all. Where it does, microbial communities that consume hydrogen may be active. Furthermore, gas accumulation requires a porous reservoir sealed by a caprock that can withstand hydrogen’s powerful tendency to escape. No such accumulation has been confirmed anywhere in the world; the Mali borehole, for example, taps a shallow (~120 meter) aquifer that continuously degasses hydrogen, not a sealed pressurized reservoir.

Also, unlike thermogenic methane, abiotic hydrogen generation can be continuous, making the sources of surface seeps fundamentally ambiguous. The same signal measured at the surface could indicate a large column of trapped hydrogen or a flow-through system with no accumulation at all. Distinguishing between these scenarios requires subsurface data—gathered from wells, seismic surveys, and pressure and geochemical measurements—that do not exist yet for most prospective terrains.

This catalog of uncertainties could be read as an argument against research. If commercial-scale UHS appears unlikely within a realistic timeline and if commercial production of natural hydrogen faces structural barriers, why treat the underlying science as indispensable?

The question is fair. We suggest, however, that scientific research into UHS and natural hydrogen production is justified on grounds that do not depend on confident commercial outlooks.

The Need for Research Now

The knowledge gaps described above cannot be closed within the compressed timelines that commercial deployment demands or by market forecasting.

The Cedars ophiolite north of San Francisco is a site of active, low-temperature serpentinization where hyperalkaline springs have been studied for decades as a natural analogue for subsurface hydrogen generation. Credit: Frédéric-Victor Donzé

They require systematic, hypothesis-driven scientific investigation. This research will require subsurface data, pilot injections, reactive transport experiments, and mechanistic characterization of microbial consumption and caprock/unconventional reservoir behavior. Ultimately, it will reveal the specific geological, biological, and thermodynamic conditions under which UHS and exploration for natural hydrogen could succeed.

A useful precedent comes from the development of enhanced geothermal systems (EGS): For more than 4 decades, systematic characterization of fracture networks, rock mechanics, and fluid-rock interactions in hot, dry rock proceeded despite deep uncertainty about commercial viability. That patient, systematic science—not optimistic projections—is what eventually let a handful of projects demonstrate technical feasibility only in the past few years.

The lesson is not that EGS were destined to succeed, but that sustained research was what allowed the question to be answered at all.

A research program that maps the subsurface, showing where storage is feasible and where natural accumulations can persist, will provide actionable knowledge about specific formations, specific depths, and specific trapping configurations. The economic value of such knowledge is asymmetric: Credible answers about viability in specific places and conditions could prevent costly commitments in the wrong places and, conversely, could direct exploration to potentially productive formations.

Billions of euros, dollars, yuan, and dinars invested in infrastructure will be guided, or misguided, by the quality of the science available when decisions are made. Indeed, major funding programs in Europe, North America, and China are already channeling substantial resources toward developing UHS and natural hydrogen projects. Those commitments will not wait for full scientific resolution of uncertainties.

Uncertain science, pursued systematically and transparently, is a far better foundation for public decisionmaking than perhaps overly optimistic commercial narratives that mask the unknowns.

In that context, the responsibility of the research community is not to endorse or reject individual programs, but to ensure that the knowledge base on which they rest is as rigorous as possible. Uncertain science, pursued systematically and transparently, is a far better foundation for public decisionmaking than perhaps overly optimistic commercial narratives that mask the unknowns.

Beyond these pragmatic considerations, understanding the subsurface behavior of molecular hydrogen—among the least characterized topics in applied geochemistry—has intrinsic scientific value. Hydrogen’s generation by serpentinization and radiolysis, its migration along faults, its interaction with minerals and fluids, its microbial consumption, and its occasional trapping are fundamental concerns of planetary chemistry. These concerns are directly relevant to illuminating the formation and early differentiation of Earth and other rocky planets, how life on Earth originated, and the functioning of today’s deep biosphere.

The tools required for this science, such as trace gas sensors, reactive transport models, and equations of state for high-pressure gas mixtures, already serve applications in geothermal monitoring, carbon storage, and astrobiology. The current mobilization of funding around hydrogen creates an unprecedented window of opportunity to accelerate investigations into these questions. But that window will not stay open indefinitely.

The Choice Ahead for Hydrogen Scientists

The deepest argument for pursuing research into UHS and natural hydrogen accumulation within a unified framework is not administrative, but scientific. Both are governed by the same set of physical constraints on generation, trapping, sealing, and microbial loss.

The uncertainties of each track are precisely what make dialogue between them productive. A subsurface environment inhospitable to developing storage today is also one where natural accumulations are unlikely to have survived. Conversely, identifying where natural hydrogen has persisted provides an empirical blueprint for where engineered storage might succeed. What limits one therefore informs the other.

Scientists studying underground hydrogen face a choice. They can court favor with hydrogen technology advocates and funders—a path that can bring faster funding and greater visibility—by framing their work as steps toward commercial deployment while risking future damage to their credibility if promises outpace evidence. Or they can frame their work as the rigorous investigation of a geochemical system whose commercial potential is uncertain but whose scientific significance is not.

The second framing is harder to sell. It is also more honest, more durable, and, ultimately, more powerful because it produces knowledge that retains its value regardless of which way commercial verdicts fall.

The open questions cataloged should not be obstacles to research. They are the research. The science required to find out whether UHS and natural hydrogen exploration are likely to succeed or fail has independent value that holds across every possible outcome.

Author Information

Laurent Truche (laurent.truche@univ-grenoble-alpes.fr) and Frédéric-Victor Donzé, Institut des Sciences de la Terre, Université Grenoble Alpes, Grenoble, France; and Chris Ballentine, Department of Earth Sciences, University of Oxford, U.K.

Citation: Truche, L., F.-V. Donzé, and C. Ballentine (2026), Underground hydrogen: Two high-reward bets, one indispensable science, Eos, 107, https://doi.org/10.1029/2026EO260292. Published on 15 September 2026. This article does not represent the opinion of AGU, Eos, or any of its affiliates. It is solely the opinion of the author(s). Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances

Gaining a better understanding of how extreme rainfall is evolving in the tropics under global warming is essential, as this region plays a central role in the Earth’s climate system and hosts some of the world’s most intense precipitation. Yet, despite its global significance, the tropics remain among the most poorly monitored regions, making improved observations and analyses critical for advancing climate science and informing adaptation.

Observed hourly extreme rainfall in tropical Singapore (1980–2024). Temporal trends in the annual number of events and accumulated amount of extreme rainfall (rainfall above a certain intensity threshold). The shaded area denotes the interquartile range (25th–75th percentile) of the 100-meter gridded rainfall reanalysis. “n.s” in the upper right indicates a non-significant trend. Credit: Zhuang et al. [2026], Figure 1a

By combining a unique dataset of weather radar observations and 122 rain gauges covering a 730 km² area in Singapore, Zhuang et al. [2026] reconstruct gridded rainfall fields at 100-meter spatial resolution over a 45-year period. They show that tropical extreme rainfall responds to warming in a fundamentally different way than commonly assumed—extremes intensify through greater spatial extent and longer persistence, while peak rainfall intensities remain largely unchanged. These findings provide new insight into how rainfall extremes evolve under global warming and offer essential information for improving climate risk assessment and adaptation strategies.

Citation: Zhuang, Q., Peleg, N., Prein, A. F., Babovic, V., & Fatichi, S. (2026). Equatorial extreme convective storms are expanding and becoming more persistent. AGU Advances, 7, e2026AV002370. https://doi.org/10.1029/2026AV002370

—Alberto Montanari, Editor-in-Chief, AGU Advances

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