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Source: GeoHealth

Small particulate matter (PM2.5) in air pollution raises the risks of respiratory problems, cardiovascular disease, and even cognitive decline. Heat waves, which are occurring more often with climate change, can cause heatstroke and exacerbate conditions such as asthma and diabetes. When heat and pollution coincide, they can create a deadly combination.

Existing studies on hot and polluted episodes (HPEs) have often focused on local, urban settings, so their findings are not necessarily representative of HPEs around the world. To better understand premature mortality associated with pollution exposure during HPEs at multiple scales and settings, Huang et al. looked at a global record of climate and PM2.5 levels from 1990 to 2019.

The team used data from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), which included hourly concentration measurements of PM2.5 in the form of dust, sea salt, black carbon, organic carbon, and sulfate particles. Daily maximum temperatures were obtained via satellite data from ERA5 (the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis).

The researchers also conducted a meta-analysis of health literature, identifying relevant research using the search terms “PM2.5,” “high temperature,” “heatwaves,” and “all-cause mortality” in the PubMed, Scopus, and Web of Science databases. Then, they conducted a statistical analysis to estimate PM2.5-associated premature mortality events during HPEs.

They found that both the frequency of HPEs and maximum PM2.5 levels during HPEs have increased significantly over the past 30 years. The team estimated that exposure to PM2.5 during HPEs caused 694,440 premature deaths globally between 1990 and 2019, 80% of which occurred in the Global South. With an estimated 142,765 deaths, India had the highest mortality burden by far, surpassing the combined total of China and Nigeria, which had the second- and third-highest burdens. The United States was the most vulnerable of the Global North countries, with an estimated 32,227 deaths.

The work also revealed that PM2.5 pollution during HPEs has steadily increased in the Global North, despite several years of emission control endeavors, and that the frequency of HPEs in the Global North surpassed that of the Global South in 2010. The researchers point out that the study shows the importance of global collaboration on climate change policies and pollution mitigation to address environmental inequalities. (GeoHealth, https://doi.org/10.1029/2024GH001290, 2025)

—Sarah Derouin (@sarahderouin.com), Science Writer

Citation: Derouin, S. (2025), Heat and pollution events are deadly, especially in the Global South, Eos, 106, https://doi.org/10.1029/2025EO250151. Published on 14 May 2025. Text © 2025. 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.

Knowing where to turn for help in the wake of a wildfire can feel overwhelming. With wildfires affecting an increasing number of communities throughout Arizona, residents need clear guidance and actionable steps to recover.

Emissions and atmospheric concentrations of methane continue to increase, making it the second most important human-influenced greenhouse gas in terms of climate forcing after carbon dioxide. In fact, methane concentrations have risen faster over the past five-year period than in any period since record-keeping began, and yet research suggests that reducing methane emissions may be cheaper than carbon dioxide mitigation for a comparable climate benefit.

Stifling heat and sticky air often make summertime in the city uncomfortable. Due to the heat island effect, urban areas are significantly warmer than nearby rural areas, even at night. This, combined with more frequent extreme weather events caused by climate change, often render the city an unpleasant environment in the summer.

The retreat of the planet's glaciers is one of the most visible and dramatic indicators of the far-reaching impact of climate change on the world's ecosystems.

The skunky smell of pot smoke. Burning stenches from a pet food factory. Smoke from construction sites. These are the smells that communities of color and lower income people in Denver are disproportionately exposed to at home and at work, according to a new study.

The study, published in the Journal of Exposure Science and Environmental Epidemiology, is one of the first to examine the environmental justice dimensions of bad odors in an urban setting.

“Odors are often ignored because they’re difficult to study and regulate.”

There’s been a wealth of research in recent years showing that people of color and those with lower incomes are exposed to more air pollution, including nitrogen oxides and particulate matter. Exposure to air pollution causes or exacerbates cardiovascular and respiratory illnesses, among other health problems, and increases the overall risk of death.

Odors are more challenging to measure than other kinds of air pollution because they are chemically complex mixtures that dissipate quickly. “Odors are often ignored because they’re difficult to study and regulate,” said Arbor Quist, an environmental epidemiologist at the Ohio State University who was not involved with the research.

Though other kinds of air pollution in the United States are limited by federal laws and regulated at the state level, smells are typically regulated under local nuisance laws. Though somewhat subjective—some folks don’t mind a neighbor toking up—odors can have a big impact on how people experience their environment, and whether they feel safe. Bad smells can limit people’s enjoyment of their homes and yards, and reduce property values.

“Odor is one of the ways municipalities can take action on air pollution.”

Odors are more than a nuisance—they pose real health risks. Exposure to foul smells is associated with headache, elevated blood pressure, irritated eyes and throat, nausea, and stress, among other ills.

University of Colorado Denver urban planning researcher Priyanka deSouza said local regulation of odors gives municipalities an opportunity to intervene in environmental health. “Odor is one of the ways municipalities can take action on air pollution,” she said.

Previous research on ambient odor air pollution has focused on point sources, including chemical spills and concentrated animal-feeding operations such as industrial hog farms. DeSouza said Denver’s unusually robust odor enforcement system made it possible to study the environmental justice dimensions of smelly air over a large geographical area.

Making a Stink

The city maintains a database of odor complaints that includes a description of the smell and the address of the complaint. DeSouza’s team used machine learning to identify themes in complaints made from 2014 to 2023. They found four major clusters: smells related to a Purina pet food factory, smells from a neighbor’s property, reports of smoke from construction and other work, and complaints about marijuana and other small industrial sources.

They used the text of the odor complaints and the locations of the complaints to deduce the likely source of the odor. For instance, complaints about the pet food factory often included the words night, dog, bad, and burn. Marijuana-related complaints frequently used the words strong and fume.

They also matched complaint locations against the addresses of 265 facilities that have been required by the city to come up with odor control plans for reasons including the nature of their business, or because five or more complaints have been filed about them within 30 days. (Growing, processing, or manufacturing marijuana occurs in 257 of these facilities.)

Less privileged people in Denver are more likely to live or work near businesses cited for creating bad smells, including marijuana facilities. Credit: Elsa Olofsson at cbdoracle.com/Flickr, CC BY 2.0

Less privileged census blocks—those with higher percentages of non-white workers and residents, residents with less formal education, lower median incomes, and lower property values—were more likely to contain a potentially smelly facility, according to the analysis. DeSouza said this is likely due to structural racism and historical redlining in Denver.

The facilities were concentrated in a part of the city that is isolated by two major freeways. Previous research has shown that people in these neighborhoods are exposed to more traffic-related air pollution, and that people of color, particularly Hispanic and Latino populations, are more likely to live there.

Yet people living and working in those areas weren’t more likely to register a complaint about bad smells than people in other parts of the city. In fact, most of the complaints came from parts of the city that are gentrifying. DeSouza said it’s not clear why people who live or work near a stinky facility aren’t more likely to complain than people who live farther away from one.

It may be that wind is carrying smells to more affluent neighborhoods, where more privileged people are more aware of Denver’s laws and feel empowered to complain. The research team, which includes researchers from the city’s public health department, is continuing to study odors in the city. Their next step is to integrate information about wind speed and direction with the odor complaints.

Quist said the study is unique in that it factors in potential workplace exposures, where people spend a large part of their day. Workplace exposures can also have health effects that aren’t captured in research that looks only at where people live. “A lot of research has focused on residential disparities,” she said, adding that the inclusion in the analysis of facilities that have had to submit odor-monitoring plans is also significant. “This is an important paper,” she said.

DeSouza said she suspects that people who live and work near smelly facilities may not be complaining because they feel disenfranchised. “People are resigned to odors, they have been living there a long time, and they don’t feel they have a voice.” If residents in less privileged neighborhoods were able to successfully lodge an odor complaint and get results, it may make them feel more connected in general to the city government, she added.

“I’m really interested in supporting policy action,” she said. “We’re trying to get residents to be aware that they can complain.”

—Katherine Bourzac, Science Writer

Citation: Bourzac, K. (2025), Denver’s stinkiest air is concentrated in less privileged neighborhoods, Eos, 106, https://doi.org/10.1029/2025EO250183. Published on 13 May 2025. Text © 2025. 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.

Source: Journal of Geophysical Research: Oceans

As freshwater from glacier melt, river runoff, and precipitation enters the Arctic Ocean, a circular current called the Beaufort Gyre traps it near the surface, slowly releasing the water into the Atlantic Ocean over decades. Warming global temperatures may weaken the wind patterns that keep the gyre turning, which could slow or even stop the current and release a flood of freshwater with a volume comparable to that of the Great Lakes. This deluge would cool and freshen the surrounding Arctic and North Atlantic oceans, affecting sea life and fisheries and possibly disrupting weather patterns in Europe.

Athanase et al. analyzed the Beaufort Gyre’s circulation patterns using 27 climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), which informed the most recent Intergovernmental Panel on Climate Change (IPCC) report.

Before trying to predict the future behavior of the gyre, the researchers turned to the past. To assess how well CMIP6 models capture the gyre’s behavior, they compared records of how the gyre actually behaved to CMIP6 simulations of how it behaved, given known conditions in the ocean and the atmosphere.

Most CMIP6 models do not capture the gyre’s behavior very well, it turns out. Some models did not predict any circulation, when circulation clearly occurred. Others overestimated the area or strength of the gyre, shifted it too far north, or inaccurately estimated sea ice thickness within the gyre. Eleven of the models produced sea ice thickness estimates the researchers called “unacceptable.”

Despite these problems, the researchers pushed ahead, using the 18 CMIP6 models that most closely reflected the gyre’s true behavior to predict how circulation could change under two future emissions scenarios: intermediate and high. Most of the tested models showed that the gyre’s circulation will decline significantly by the end of this century, but their predictions for exactly when varied from the 2030s to the 2070s. Three models predicted that the gyre will not stop turning at all.

The gyre is most likely to disappear if emissions remain high, but it may stabilize as a smaller gyre if emissions are only moderate, the researchers found. Despite substantial uncertainty, the results are a reminder that when it comes to preventing the most disruptive effects of climate change, “every fraction of a degree matters,” they write. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2024JC021873, 2025)

—Saima May Sidik (@saimamay.bsky.social), Science Writer

Citation: Sidik, S. M. (2025), The uncertain fate of the Beaufort Gyre, Eos, 106, https://doi.org/10.1029/2025EO250186. Published on 13 May 2025. Text © 2025. 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.

An international research team studying fossilized oyster shells has revealed substantial annual temperature variation in sea water during the Early Cretaceous. The finding overturns the assumption that Earth's greenhouse periods are marked by universally warmer and uniformly stable temperatures.

Carbon dioxide removal (CDR) strategies use a wide range of techniques to capture CO2 from the air and store it durably, offering a frontier solution for counteracting the increasing levels of the greenhouse gas in our environment. Increasing the alkalinity of wastewater by treating it with alkaline minerals can substantially boost the CO2 sequestration abilities, finds a study appearing in Science Advances.

A "blocking" weather system lingering high above the UK has produced one of the driest, warmest and brightest starts to spring on record.

Sphalerite is a very cool mineral. It is a beautiful, complex and diverse zinc sulfide (ZnS) mineral that also hosts a treasure trove of other critical elements. These include manganese, cadmium, mercury, indium, thallium, gallium, germanium, antimony, tin, lead, silver and cobalt.

Researchers at the University of Miami are providing improved insights into how extreme heat should be defined and addressed. The findings were published in an article titled "Where heat does not come in waves: A framework for understanding and managing chronic heat" in the journal Environmental Research: Climate.

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

Arctic ponds play a key role in permafrost thaw and greenhouse gas emissions; however, their physical mixing processes remain poorly characterized. Most conceptual models assume that vertical, one-dimensional mixing—driven by surface cooling due to which water becomes denser, and sinks vertically, mixing the water mass from the top down—is the primary mechanism for deep water renewal.

Henderson and MacIntyre [2025] challenges that model by showing that two-dimensional thermal overturning circulation dominates in a shallow permafrost pond. Specifically, nighttime surface cooling in shallow areas generates cold, dense water that flows downslope along the pond bed, displacing and renewing deeper waters. Using high-resolution velocity, temperature, and other related measurements, the authors demonstrate that these gravity currents ventilate the bottom despite persistent stable stratification during nighttime. These findings reveal that lateral thermal flows can drive vertical exchange in small water bodies. The results have important implications for biogeochemical modeling and upscaling greenhouse gas fluxes across Arctic landscapes.

This is a diagram of how cold water moves at night in a pond. At night, the shallow parts of the pond (near the right edge) cool down faster than the deeper parts. This creates thin layers of cold, dense water near the shore. Because this water is denser (heavier), it sinks and flows sideways along the sloped pond bottom toward the deepest part of the pond—like a slow, underwater landslide of cold water. As this cold water flows downhill, it pushes the existing bottom water upward, creating a gentle circulation loop: surface water cools and sinks at the edges, flows along the bottom, and pushes older deep water upward toward the middle. Credit: Henderson and MacIntyre, Figure 3a

Citation: Henderson, S. M., & MacIntyre, S. (2025). Thermal overturning circulation in an Arctic pond. Geophysical Research Letters, 52, e2024GL114541. https://doi.org/10.1029/2024GL114541

—Valeriy Ivanov, Editor, Geophysical Research Letters

Text © 2025. 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.

Author(s): Rima Mebrek, Rachid Fermous, Moufida Benzekka, and Rabia Amour

The current study examines, using a nonextensive statistical framework satisfying the H-theorem constraint 0≤q≤2, the dynamics of dust-acoustic shock waves in complex plasmas under the influence of both gravity and microgravity within adiabatic and nonadiabatic fluctuating charge. The results highli…

[Phys. Rev. E 111, 055203] Published Tue May 13, 2025

In the modern world, a reliable supply of hydrogen gas is vital for the function of society. Fertilizer produced from hydrogen contributes to the food supply of half the global population, and hydrogen is also a key energy component in many roadmaps to a carbon-neutral future, essential if we are to prevent the worst predictions of climate change.

SummaryTeleseismic P-wave coda autocorrelation has been increasingly applied to subsurface structure characterization, given its potential to infer velocities. However, the inversion of coda autocorrelation data has not been extensively investigated regarding data processing (stacking and move-out correction), inversion approaches (Monte Carlo or metaheuristic), model parameterization, and applicability. Here, we propose an inversion method for teleseismic P-wave coda autocorrelation based on particle swarm optimization and a treatment of uncertainty. This inversion method utilizes the arrival time information of reflected (or converted) waves contained in the binned stack waveforms, demonstrating promising model adaptability and robustness. Synthetic data tests show that this method accurately inverted various geological models without prior information, such as the number of crustal layers, surface sedimentary layers, and low-velocity zones within the crust. The method was successfully applied to the QSPA station near the South Pole, revealing an ice sheet thickness of approximately 2900 m, with a 340 m thick low shear-wave velocity ice layer at the base, likely containing up to 15% water. Beneath the ice sheet, we infer a 400 m thick subglacial sediment layer. The uncertainties of the thickness of the low shear wave velocity ice and the sedimentary layer are 150 m and 10 m, respectively. These findings and the potential of the proposed method open up new directions for glacier dynamics research in the region. Additionally, we apply the method to the BOSA station near Kimberley, South Africa, which confirms clear Moho and intracrustal interfaces, consistent with receiver functions and deep seismic reflection data results. This study improves the inversion algorithm for teleseismic P-wave coda autocorrelation and expands its application scenarios.

SummaryGeophysical simulations for complex subsurface structures and material distributions require the evaluation of partial differential equations by means of numerical methods. However, the mentioned high complexity often yields computationally very costly simulations, especially for electromagnetic (EM) and seismic methods. When used in the context of parameter estimation or inversion studies, this aspect severely limits the number of simulations that are affordable. However, especially for structured model analysis methods, such as global sensitivity analyses or inversions, often thousands to millions of forward simulation runs are required. To address this challenge, we propose utilizing a physics-based machine learning method, namely the non-intrusive reduced basis method, aiming at constructing low-dimensional surrogate models to significantly reduce the computational cost associated with the numerical forward model while preserving the physical principles. We demonstrate the effectiveness and benefits of the surrogate models using broadband Magnetotelluric (MT) responses of a 2-D model that mimics a conceptual volcano-hosted geothermal system. Next to being a first such application, we also show how ML reduced basis method can be adapted to consistently treat complex-valued variables – an aspect that has been overlooked in previous studies. Additionally, reducing computation time by several orders of magnitude through the surrogate enables us to perform a global sensitivity analysis for MT applications. Despite additional insights, such an analysis has been normally deemed infeasible given the high computational burden. The methods developed here are presented in a generalized form, making this approach feasible for other electromagnetic techniques with a low-dimensional parameter space.

SummaryThe triple junction between the North American, Caribbean, and Cocos plates at the Guatemala-Mexico border is not well understood. It forms a broad region from around the active Tacaná volcano up to the Guatemala City graben. Tacaná is the westernmost active volcano of the Central American volcanic arc and is located at the intersection of four major active faults: the Polochic, Motagua, Jalpatagua, and Tonalá faults. Using seismicity around the Tacaná volcano, we show that there is moderate to low tectonic seismic activity between the Guatemala City graben and the Tacaná volcano, possibly related to the ancient extremes of the Motagua and Jalpatagua faults. Therefore, we speculate that the triple junction would be located onshore, around the Tacaná volcano.We located earthquakes around the Tacaná volcano between January 2017 and October 2018, a period that includes the large Mw8.2 Tehuantepec (Chiapas) earthquake of 8 September 2017, located ∼190 km away. We identified four distinct types of seismicity, interpreted as having tectonic, hydrothermal, intermediate depth magmatic, and deep magmatic origins. The tectonic seismicity occurred at depths between ∼5 km and ∼30 km b.s.l., and may be associated with three faults around the Tacaná volcanic complex. These faults are oriented in NE-SW, aligned with the four Tacaná volcanic edifices; NW-SE, consistent with the Jalpatagua fault; and approximately EW, corresponding to the Motagua fault. The hydrothermal seismicity is observed at shallow depths, from the subsurface to about 2 km b.s.l., predominantly in the western sector of the Tacaná summit, and partially beneath the San Antonio volcano, an area known for intense hydrothermal activity. This seismicity is spatially related to the shallow portions of the same three faults described above. The intermediate depth magmatic seismicity is detected at depths between 5 and 12 km b.s.l. and is interpreted to be related to the presence of a shallow magma chamber beneath the Tacaná volcanic complex. Finally, the deep magmatic seismicity is located in the eastern part of the Tacaná, at depths ranging from 15 km to about 22 km b.s.l. This seismicity is interpreted to be due to a vertical dike intrusion that connects a deep magma reservoir located between 30 km and 40 km depth, to the hypothesized shallower magma chamber associated with the intermediate depth seismicity.