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Pots with fancifully molded eyes, noses and mouths were one of the tip-offs.

Adrian Chase already had a growing sense that Maya society wasn’t quite what it’s been traditionally portrayed as: powerful rulers reigning while powerless commoners obeyed — or perhaps lived far enough from seats of power to operate largely on their own. Work by Chase and others had started to create a picture of a more politically complex society.

An archaeologist at the University of Chicago, Chase leads excavations of residential sites in and near the ancient Maya city center of Caracol in what’s now Belize. This city once sprawled across valleys, hillsides and hilltops. At its height, Caracol stretched 240 square kilometers, about the size of Milwaukee, before it was abandoned and swallowed by the forest.

Accumulating archaeological evidence had convinced Chase that shared social practices, such as placing pottery and other ritual items in special shrines, bonded groups of farm families into dozens of distinct neighborhoods within Caracol’s urban sprawl.

Consider those face-decorated pots. Varying shapes and spacings of molded eyes and other facial features added up to signature ceramic looks at different neighborhood-linked shrines. And those pots were just one element of a range of shrine offerings — including three-legged plates, curved jars with thin necks, and small medicine bottles and paint pots — that neighborhoods appeared to combine in distinctive ways.

And then there were the teeth. Individuals buried at some neighborhood shrines had either carved jade nuggets implanted in their teeth or their teeth filed in one of two styles. No such dental decorations appeared among the dead interred at other shrines. Various tooth alterations further defined neighborhood- specific shrine practices.

Pottery styles and tooth alterations together formed patterns specific to neighborhoods, Chase says. “There is a community aspect to these finds that reflects tight-knit neighborhoods.”

Caracol citizens, including those who lived well beyond downtown temples and pyramids, were not simple farmers growing crops in the service of a king, Chase suspects. Groups of as many as several hundred people had formed farming neighborhoods that built local ritual structures and followed distinctive ceremonial practices, apparently through their own collective efforts.

Neighborhoods, in turn, belonged to administrative districts with ties to royalty and other downtown political big shots. Stone compounds scattered throughout the city — each with their own ceremonial centers and plazas that probably hosted marketplaces and ritual events attended by crowds from nearby neighborhoods — represented districts’ bureaucratic service centers.

Neighborhoods and districts formed rungs of a political system in which central rulers sometimes gained power and laid down the law. At other times, royal dynasties crumbled and lower rungs in the political hierarchy assumed primary control.

Chase’s findings at Caracol have contributed to a shift in thinking about ancient Maya societies that has intensified over the last decade.

These societies, which originated as early as around 3,000 years ago, came to be known for giant stone pyramids, vast plazas and elite ballcourts discovered at jungle sites across Mesoamerica, a cultural region that extended from central Mexico to much of Central America before Spanish contact in the 1500s. These edifices had long suggested to researchers that Maya rulers wielded absolute power. So did hieroglyphics carved on stone slabs, which described kings’ exploits.

But expanded archaeological research, ongoing translations of Maya writings and the rise of airborne laser technology that sees through jungles are revealing a vast urban sprawl around major Maya ceremonial sites. Similarly extensive, low-density settlements have recently been discovered in other tropical areas around the world previously known only for giant ritual structures, such as Cambodia’s Angkor Wat temple (SN: 5/14/16, p. 22).

Among the Maya, shifting circumstances would have tilted the balance of power. For instance, rural population booms might strengthen the hand of neighborhood-level elites. Military defeats of a royal dynasty could shift power to midlevel, district officials.

“A lot of Mesoamerican settlements probably had nested units of power,” Chase says. “There was no simple division between Maya elites and commoners.”

Vaulted stone structures give insight into Maya political structures

Laura Gilabert-Sansalvador did not have Mesoamerican politics on her mind in 2013 when she began studying stone palaces at La Blanca, an ancient Maya site in Guatemala. But her project ended up providing insights into not just physical structures, but also power structures.

Working toward a doctorate in architecture, Gilabert-Sansalvador wanted to decipher ancient techniques for erecting roofs on structures ranging from huts to temples.

Large rooms inside La Blanca palaces featured vaulted roofs, a tricky technical feat that Maya stonemasons worked to improve for more than 1,000 years. Inspired by La Blanca’s artfully angled room toppers, Gilabert-Sansalvador launched a project to draw, digitize and analyze vaulted buildings throughout the Maya lowlands of southern Mexico and Guatemala.

Vaulted structures featured two horizontal stone walls topped by rows of stones arranged to angle inward and meet at a central row of stones, creating an inverted V- or U-shaped roof.

Because Maya vaults required thick, load-bearing walls, they rarely exceeded 3 meters in width. Long, narrow vaulted structures in urban centers were often connected to form rectangular, oval or L shapes around courtyards. Some sites from the Classic Maya period — which ran from about A.D. 250 to 900 and is considered by many to be the zenith of the Maya civilization — include small numbers of vaulted stone buildings. These structures were much fancier and sturdier than farmers’ huts and thus researchers suspect high-ranking officials lived there. Other Classic Maya sites contain a high percentage of vaulted structures that may have served a variety of purposes, including storing important objects, hosting feasts and housing elites.

With her doctorate and a database of measurements for the remains of 200 vaulted stone buildings in hand, Gilabert-Sansalvador arrived at Tulane University’s Middle American Research Institute in New Orleans in 2021 as a visiting researcher. There she met Tulane archaeologist Francisco Estrada-Belli, who viewed her architectural expertise as essential for solving a Maya mystery.

Estrada-Belli had spent two decades excavating small structures that had been covered in dirt over time on forest floors at several ancient Maya sites. Some structures retained only plaster floors, consistent with having been farmers’ huts made of thatch and wooden poles that had long since decayed. But others were bordered by remains of thick stone and mortar walls, raising questions about who had lived there.

In reviewing aerial images of ancient Maya buildings across southern Mexico and Guatemala, Estrada-Belli had surmised that earth-covered mounds at least 1 meter tall corresponded to the rubble of collapsed stone structures, including those with vaulted roofs, like the ones he had excavated. But he could not be sure.

Gilabert-Sansalvador’s database offered an opportunity to evaluate that suspicion with lidar, short for light detection and ranging. In archaeology, airborne lidar technology uses laser pulses to detect remains of ancient structures and objects otherwise hidden by forests and ground cover. Lidar has revealed general features of interconnected Maya cities and extensive rural drainage channels and terraces dating to at least 2,300 years ago (SN: 10/27/18, p. 11).

The challenge was to develop a geometric measure of collapsed vaulted structures that lidar could detect.

Lidar illuminates Maya neighborhoods

In 2021 and 2022, Gilabert-Sansalvador, now at the Polytechnic University of València in Spain, joined Estrada-Belli and three other researchers to review measurements in her database plus measurements of another 251 vaulted structures collected by other excavation teams. Those buildings come from throughout Maya territory, from southern Mexico and Central America to as far north as the Yucatán Peninsula.

Inspecting the entire sample of 451 structures, the researchers found that collapsed vaulted buildings had a much higher volume of rubble, formed taller mounds and had steeper sides than same-sized buildings made of perishable materials, such as thatched-roof huts.

To verify that these mound dimensions spotlight only crumpled stone structures with vaulted roofs, the team examined stone buildings previously identified in excavations and ground surveys at the Classic Maya site of Tikal in Guatemala. Overall, the researchers’ method correctly distinguished between remnants of vaulted and nonvaulted structures, such as ballcourts lined by stone walls, ceremonial buildings and inscribed stone monuments, up to 97 percent of the time.

Confident in the method, the team then analyzed 11 lidar data­sets that covered Tikal and seven other Classic Maya urban centers, along with several rural territories. Lidar analyses encompassed a total of around 60,000 square kilometers, nearly the area of West Virginia. About 111,000 previously identified structures were analyzed for signs of having been built with vaulted roofs.

A picture emerged of clusters of vaulted stone buildings, typical of ruling elites’ houses in major centers. But they were in farming communities as far as five kilometers from the nearest urban core. As lidar images of rural stone compounds accumulated, Estrada-Belli felt increasingly surprised: “We checked our tests many times and concluded that this result was in fact correct.”

Small groups of huts, possibly occupied by extended families of farmers and other settlers, encircled shared plazas. Neighborhoods were made up of sets of huts clustered around stone buildings, which may have housed low-level nobles or other elites, the researchers reported in the September Journal of Archaeological Science. Sets of neighborhoods, in turn, clustered around large stone structures that may have housed higher-ranking officials, to form administrative districts.

“We now have quantitative measures of ancient Maya neighborhoods, which have been hard to define or identify,” Estrada-Belli says.

Urban sprawl managed by low- and midlevel officials flourished despite a lack of horses and wheeled vehicles, Estrada-Belli says. Transportation consisted of walking and river travel.

Raised roads, or causeways, ran from farmsteads, neighborhoods and districts to urban centers, making foot travel easier and pit stops convenient. Public plazas dotting the country­side hosted ritual gatherings and served as marketplaces. Rural elites’ duties included mediating local disputes and organizing community projects such as reservoir and causeway construction, Estrada-Belli suspects. In exchange, local officials probably collected taxes on market transactions.

Toward the end of the Classic Maya period, from around A.D. 600 to 900, local political authorities lived among many farming communities, Estrada-Belli says.

Any lingering suspicions that Maya farmers played no part in political decisions that affected their daily lives do not hold up, he contends. “We can now talk about one common model of urban organization among the Classic Maya that included the less populated countryside,” Estrada-Belli says. Maya political elites directed the construction of stone compounds at prominent locations in interconnected neighborhoods and administrative districts. This highlights the importance of central rulers in forming and running these complex political systems, he suspects.

Even among researchers impressed by the new lidar findings, though, some doubt that multilayered political systems always revolved around a king or elite political power brokers, as proposed by Estrada-Belli.

Some ancient Maya cities featured collective actions by local communities while others emphasized royal edicts, these investigators contend. And the same community could dramatically alter its political system as times and conditions changed.

Political variation across sites fits with archaeological and lidar discoveries over the last two decades that challenge a popular idea that Classic Maya cities collapsed rapidly around A.D. 900, over a span of 50 to 100 years. A group of 15 Maya researchers summarized these recent findings July 24 in the Proceedings of the National Academy of Sciences.

Residents of Maya urban centers often found ways, whether through local or centralized decision making, to survive droughts and military defeats previously thought to have been society killers, research now suggests. Major sites suffered population losses over as many as 100 to 200 years before emptying out.

At that point, Maya people who had developed a taste for social and political flexibility established towns and smaller cities elsewhere. Maya culture soldiered on after Classic period cities lost their appeal.

Why urban centers turned into ghost cities over a couple of hundred years, some more quickly than others, is poorly understood. That raises questions about precisely who lived in Estrada-Belli’s newly identified Maya stone structures and what they were up to.

Who lived in vaulted buildings?

Excavations of those stone structures, guided by the lidar findings, will help to clarify who lived there.

Some occupants of rural vaulted structures may have belonged to noble lineages that served the royal interests, says anthropological archaeologist Andrew Scherer of Brown University in Providence, R.I. Ancient DNA evidence indicates that rulers of a 2,000-year-old nomadic empire in Asia followed a similar strategy, sending members of royal lineages to oversee distant territories (SN Online: 7/2/23).

But Maya rural elites may have acquired wealth and power in local communities without being appointed by a paramount ruler, Scherer cautions. If so, it’s not clear who, if anyone, pulled the strings of neighborhood and district officials.

Advances in deciphering Maya writing and ongoing excavations indicate that midlevel authorities wielded considerable power at rural settlements aligned with urban centers such as Tikal, says anthropological archaeologist John Walden of Harvard University. Midlevel elites ran public rituals and feasts, hosted marketplaces and maintained diplomatic ties with their counterparts in nearby communities, Walden concluded in the Spring 2023 issue of The Mayanist.

It’s an open question whether some vaulted structures served as homes for heads of local kin groups or clans that prioritized their own interests over those of kings and urban big shots, Walden says.

But the new lidar findings underscore a central point, Scherer says. “Authority in some fashion was dispersed on the landscape and not clustered in Maya civic ceremonial centers.”

Reconstructing Caracol politics

At Caracol, one of the largest Classic Maya cities, authority took chameleon-like turns, Chase says. “Caracol shifted between more collective and more autocratic systems of governance over its 1,500-year life span,” he says. “The city experienced great transformations and changes as it grew.”

Chase has reconstructed Caracol’s wild historical ride using an array of evidence accumulated over the last four decades, including deciphered Maya written records carved on stone slabs, archaeological finds and lidar imagery. His conclusions appear in the 2023 Research Reports in Belizean Archaeology and in a chapter of an upcoming book that he coedited, Ancient Mesoamerican Population History. For instance, carved hieroglyphics include dates when specific rulers assumed power and won or lost battles with kings of rival cities. And lidar maps have guided ongoing excavations of farming sites outside Caracol’s city core.

Chase’s own connection to Caracol began before he could talk. His parents, anthropological archaeologists Diane Chase and Arlen Chase, both at the University of Houston, brought him there every year, starting as an infant, after launching a Caracol fieldwork project in 1985.

As a high school junior steeped in archaeology, Chase helped run a Caracol excavation. Now he oversees multiple excavations and on-site lab investigations of unearthed artifacts.

Caracol started out small too. Around 600 B.C., three villages collectively built reservoirs, causeways and ceremonial sites. Residents of the villages formed a single site that was governed without central rulers for about 700 years. A royal dynasty assumed power in A.D. 331. Successful wars against the nearby cities of Tikal and Naranjo between 553 and 680 sparked a population boom. A minimum of 100,000 people inhabited Caracol at its peak.

Urban and rural areas coalesced into a “garden city,” Chase says. He has mapped 373 neighborhoods, each linked to a nearby public space that hosted market and ritual events. In each neighborhood, residents carved agricultural terraces out of adjacent hillsides and constructed small reservoirs. Groups of neighborhoods formed 25 districts, each containing a monumental center with reservoirs, ballcourts or other large structures that provided public services, he reported in the June Journal of Anthropological Archaeology.

Chase ended up defining neighborhoods not just by combinations of pottery offerings and dental practices, but also by distances of farmers’ huts to the nearest district plaza. Farmers who would have walked similar routes over Caracol’s rugged hills to district sites presumably forged ties on those trips, which cultivated feelings of belonging to neighborhoods with common practices, such as leaving certain types of offerings at local shrines, Chase suspects.

Naranjo’s military defeat of Caracol in 680 ushered in roughly a century of decentralized government, Chase says. “Faceless administrators” who went unnamed in Maya writings oversaw taxation and the provision of services to urban communities. Policies at that time led to widespread wealth, community-wide ritual ceremonies and relatively equal access to market products and agricultural land.

New rulers who aligned themselves with powerful Maya gods assumed power in 798. These kings instituted autocratic policies and oversaw a sharp rise in wealth disparities. Those developments may have instigated a population exodus from Caracol. By 900, the garden city had been abandoned.

Estrada-Belli suspects a system of Caracol neighborhood and district officials operated out of regularly spaced, elite residences, much like the compounds of vaulted structures his team has identified elsewhere. Plans are in the works to probe lidar data at Caracol for signs of collapsed vaulted structures in or near previously identified neighborhoods, Chase says.

Classic-era sites in the northern Maya lowlands of the Yucatán Peninsula, which generally have drawn less scientific attention than Classic Maya sites to the south, also deserve closer lidar scrutiny. Vaulted structures still stand at some of those centers, including large sites such as Chichén Itzá, Estrada-Belli says.

New excavations guided by lidar discoveries, and lidar analyses informed by the dimensions of excavated buildings, may clarify Classic Maya power structures at sites on the Yucatán Peninsula.

The layering of authority and its reach across ancient Maya urban areas is just beginning to emerge from a forested shroud.

Nesting chinstrap penguins take nodding off to the extreme. The birds briefly dip into a slumber many thousands of times per day, sleeping for only seconds at a time. 

The penguins’ breeding colonies are noisy and stressful places, and threats from predatory birds and aggressive neighbor penguins are unrelenting. The extremely disjointed sleep schedule may help the penguins to protect their young while still getting enough shut-eye, researchers report in the Dec. 1 Science. 

The findings add to evidence “that avian sleep can be very different from the sleep of land mammals,” says UCLA neuroscientist Jerome Siegel. 

Nearly a decade ago, behavioral ecologist Won Young Lee of the Korea Polar Research Institute in Incheon noticed something peculiar about how chinstrap penguins (Pygoscelis antarcticus) nesting on Antarctica’s King George Island were sleeping. They would seemingly doze off for very short periods of time in their cacophonous colonies. Then in 2018, Lee learned about frigate birds’ ability to steal sleep while airborne on days-long flights. 

Lee teamed up with sleep ecophysiologist Paul-Antoine Libourel of the Lyon Neuroscience Research Center in France and other researchers to investigate the penguins’ sleep. In 2019, the team studied the daily sleep patterns of 14 nesting chinstrap penguins using data loggers mounted on the birds’ backs. The devices had electrodes surgically implanted into the penguins’ brains for measuring brain activity. Other instruments on the data loggers recorded the animals’ movements and location.

Nesting penguins had incredibly fragmented sleep patterns, taking over 600 “microsleeps” an hour, each averaging only four seconds, the researchers found. At times, the penguins slept with only half of their brain; the other half stayed awake. All together, the oodles of snoozes added up, providing over 11 hours of sleep for each brain hemisphere across more than 10,000 brief sleeps each day. 

Some marine mammals and other types of birds have strange or restricted sleep patterns too, often when staying alert is important. Dolphins can sleep with half their brain at a time, letting them remain vigilant for over two weeks straight. To stay wary of predators, mallard ducks can sleep with one half of their brain at a time too (SN: 2/6/99). And elephant seals dramatically reduce their sleeping hours while out at sea (SN: 4/20/23). But the sheer number of microsleeps seen in chinstrap penguins is unprecedented among animals, Lee says.

“It seems that the penguins do not have any time where they decrease their vigilance,” Libourel says. “Just a slight increase of microsleep-bout length around noon.”

The sleep pattern may help the penguins balance the brain’s need for rest with the demands of nesting. Predatory birds like brown skuas (Stercorarius antarcticus) patrol penguin colonies looking to plunder undefended eggs and chicks. “Penguin parents should be vigilant all the time during breeding to keep their offspring safe,” Lee says. There’s also constant commotion and noise in the colony disrupting sleep. Such extremely interrupted sleep may reflect the penguins’ flexibility in handling the stressors of raising chicks.

The many micronaps did appear to be at least partially restorative to their brains, since the studied penguins were able to function well enough to both survive and successfully raise their chicks. It’s unclear if the penguins’ sleep pattern changes after the breeding season.

“Sleep seems to be very diverse and flexible among species,” Lee says. “I believe that there are still many things unrevealed about animal sleep. By studying their sleep behavior, we can understand how animals have evolved to achieve brain restoration.”

How do you look for an animal you don’t even know exists anymore?

The last sighting of the purple-winged ground dove (Paraclaravis geoffroyi) — a small, bamboo-loving dove native to the South American Atlantic Forest in Brazil, Argentina and Paraguay — was in 1985. But, researchers wondered, was it possible to capture the elusive bird’s sound in the wild to find out if any individuals are left?

It’s not an unheard-of idea. Scientists have used bioacoustics — a subfield of ecology that relies on sound to make environmental analyses — for everything from recording dolphins’ communication patterns to studying bats from afar to avoid virus spillover from humans (SN: 12/7/17; SN: 10/23/22). With artificial intelligence, it is now possible to use large audio datasets to train algorithms to spot different animal sounds within the cacophony of a natural background.

But the problem is that recordings of the purple-winged ground dove singing are as rare as the bird itself.

“I came across [the bird’s song] watching a 1985 interview with Carlos Keller, a former bird breeder in São Paulo state, who had a few individuals of the dove,” says Carlos Araújo, an ecologist at the Instituto de Biología Subtropical at the Universidad Nacional de Misiones in Argentina. “And they sang while he spoke.”

With Keller’s help, Araujo and colleagues accessed the decades-old recording and isolated the bird’s song.

The next challenge was to see if it was even possible to identify individual bird songs amidst the sounds of other birds chirping, leaves rustling, rain falling, insects whirring and gnawing and larger animals moving through the forest.

“We took a step back and did some analyses with other birds that are critically endangered but there are known individuals,” Araújo says. The team focused on three species found in Foz do Iguaçu, a national park that straddles the border of Brazil and Argentina: the cherry-throated tanager (Nemosia rourei), the Alagoas antwren (Myrmotherula snowi) and the blue-eyed ground-dove (Columbina cyanopis). These birds live in the same environments as the purple-winged ground dove. And the blue-eyed ground dove’s story inspires hope: The species went missing in 1941 and was rediscovered in 2016.

The researchers installed 30 recorders in strategic spots along green areas in the Brazilian part of Foz do Iguaçu and recorded from July 2021 to April 2022. They also used data from another 100 recorders on the Argentinian side of Foz.

“We went looking for the Guadua trinii bamboo to place the recorders,” says Benjamin Phalan, Head of Conservation at Parque das Aves, a private institution in Foz do Iguaçu focused on the conservation of Atlantic Forest birds. Like the purple-winged ground dove, the three bird species follow the flowering season of the G. trinii bamboo, which happens about once every 30 years.

The team pushed through thickets of bamboo, braved ticks and biting flies, and watched out for venomous snakes such as jacaracas pit vipers. Bumping into these snakes is “rare but can happen. So we use galoshes or gaiters to protect us in case anyone steps on a snake or near it,” Phalan says.

The recorders captured one minute of landscape sound every 10 minutes and generated about 3,000 days’ worth of recordings. “A lot of data to sift through,” says Araújo.

Readily available analysis software wouldn’t work. These software, Araújo says, “need a lot of data input. With such rare species, we just don’t have that much data to train the identification algorithm.”

So the team started from scratch, working with the little data they had for the three endangered birds. First, Araújo created a signal template — exactly like the birds’ singing — based on just a few recordings. The algorithm then compares that template with the soundscape recordings, separating signal from noise. If it spots a sound that is similar to the template, chances are that it is the bird that the researchers are looking for.

The method relies on a statistical model “that is not new, but was used in a very clever and unusual way,” says David Donoso, an ecosystem ecology researcher at the Technische Universität Darmstadt in Germany. Donoso and colleagues recently used bioacoustics to investigate the recovery of Choco, a biodiversity hot spot in Ecuador that had been transformed in an agricultural area.

There are different approaches to bioacoustics depending on what you’re looking for, Donoso says. “You can either use fewer recordings to map a whole animal soundscape to tell what species are there, like we did, or you can use lots of recordings to look for a single sound pattern,” he says. The study at Foz do Iguaçu “shows that you can use a relatively simple model to answer a complex question — and it works.”

The tool worked reasonably well to identify the cherry-throated tanager and blue-eyed ground-dove singing, but not so much for the Alagoas antwren, Araújo’s team reports October 23 in Bioacoustics. “We’re trying to understand what happened, but we know that the algorithm works,” he says.

The next step, Araújo says, is to refine the algorithm’s precision to find the Alagoas antwren and train it to look for the purple-winged ground dove. And they will do so at the same time. “We’re aiming at both goals at once because we’re running against the clock to find these birds,” Araújo says. “In the end, we are looking for a ghost.” But not a silent one, he hopes. 

This summer was the hottest ever recorded on Earth, and 2023 is on track to be the hottest year. Heat waves threatened people’s health across North America, Europe and Asia. Canada had its worst wildfire season ever, and flames devastated the city of Lahaina in Maui. Los Angeles was pounded by an unheard-of summer tropical storm while rains in Libya caused devastating floods that left thousands dead and missing. This extreme weather is a warning sign that we are living in a climate crisis, and a call to action.

Carbon dioxide emissions from burning fossil fuels are the main culprit behind climate change, and scientists say they must be reined in. But there’s another greenhouse gas to deal with: methane. Tackling methane may be the best bet for putting the brakes on rising temperatures in the short term, says Rob Jackson, an Earth systems scientist at Stanford University and chair of the Global Carbon Project, which tracks greenhouse gas emissions. “Methane is the strongest lever we have to slow global warming over the next few decades.”

That’s because it’s relatively short-lived in the atmosphere — methane lasts about 12 years, while CO₂ can stick around for hundreds of years. And on a molecule-per-molecule basis, methane is more potent. Over the 20-year period after it’s emitted, methane can warm the atmosphere more than 80 times as much as an equivalent amount of CO₂.

We already have strategies for cutting methane emissions — fixing natural gas leaks (methane is the main component of natural gas), phasing out coal (mining operations release methane), eating less meat and dairy (cows burp up lots of methane) and electrifying transportation and appliances. Implementing all existing methane-mitigation strategies could slow global warming by 30 percent over the next decade, research has shown.

But some climate scientists, including Jackson, say we need to go further. Several methane sources will be difficult, if not impossible, to eliminate. That includes some human-caused emissions, such as those produced by rice paddies and cattle farming — though practices do exist to reduce these emissions (SN: 11/28/15, p. 22). Some natural sources are poised to release more methane as the world warms. There are signs that tropical wetlands are already releasing more of the gas into the atmosphere, and rapid warming in the Arctic could turn permafrost into a hot spot for methane-making microbes and release a bomb of methane stored in the currently frozen soil.

So scientists want to develop ways to remove methane directly from the air.

Three billion metric tons more methane exist in the atmosphere today than in preindustrial times. Removing that excess methane would cool the planet by 0.5 degrees Celsius, Jackson says.

Similar “negative emissions” strategies are already in limited use for CO₂. That gas is captured where it’s emitted, or directly from the air, and then stored somewhere. Methane, however, is a tricky molecule to capture, meaning scientists need different approaches.

Most ideas are still in early research stages. The National Academies of Sciences, Engineering and Medicine is currently studying these potential technologies, their state of readiness and possible risks, and what further research and funding are needed. Some of the approaches include re-engineering bacteria that are already pros at eating methane and developing catalytic reactors to place in coal-mine vents and other methane-rich places to chemically transform the gas.

“Methane is a sprint and CO₂ is a marathon,” says Desirée Plata, a civil and environmental engineer at MIT. For scientists focused on removing greenhouse gases, it’s off to the races.

Microbes already remove methane from the air

Methane, CH₄, is readily broken down in the atmosphere, where sunshine and highly reactive hydroxyl radicals are abundant. But it’s a different story when chemists try to work with the molecule. Methane’s four carbon-hydrogen bonds are strong and stable. Currently, chemists must expose the gas to extremely high temperatures and pressures to break it down.

Even getting hold of the gas is difficult. Despite its potent warming power, it’s present in low concentrations in the atmosphere. Only 2 out of every 1 million air molecules are methane (by comparison, about 400 of every 1 million air molecules are CO₂). So it’s challenging to grab enough methane to store it or efficiently convert it into something else.

Nature’s chemists, however, can take up and transform methane even in these challenging conditions. These microbes, called methanotrophs, use enzymes to eat methane. The natural global uptake of methane by methanotrophs living in soil is about 30 million metric tons per year. Compare that with the roughly 350 million tons of methane that human activities pumped into the atmosphere in 2022, according to the International Energy Agency.

Microbiologists want to know whether it’s possible to get these bacteria to take up more methane more quickly.

Lisa Stein, a microbiologist at the University of Alberta in Edmonton, Canada, studies the genetics and physiology of these microbes. “We do basic research to understand how they thrive in different environments,” she says.

Methanotrophs work especially slowly in low-oxygen environments, Stein says, like wetland muck and landfills, the kinds of places where methane is plentiful. In these environments, microbes that make methane, called methanogens, generate the gas faster than methanotrophs can gobble it up.

But it might be possible to develop soil amendments and other ecosystem modifications to speed microbial methane uptake, Stein says. She’s also talking with materials scientists about engineering a surface to encourage methanotrophs to grow faster and thus speed up their methane consumption.

Scientists hope to get around this speed bump with a more detailed understanding of the enzyme that helps many methanotrophs feast on methane. Methane monooxygenase, or MMO, grabs the molecule and, with the help of copper embedded in the enzyme, uses oxygen to break methane’s carbon-hydrogen bonds. The enzyme ultimately produces methanol that the microbes then metabolize.

Boosting MMO’s speed could not only help with methane removal but also allow engineers to put methanotrophs to work in industrial systems. Turning methane into methanol would be the first step, followed by several faster reactions, to make an end product like plastic or fuel.

“Methane monooxygenases are not superfast enzymes,” says Amy Rosenzweig, a chemist at Northwestern University in Evanston, Ill. Any reaction involving MMO will impose a speed limit on the proceedings. “That is the key step, and unless you understand it, it’s going to be very difficult to make an engineered organism do what you want,” Rosenzweig says.

Enzymes are often shaped to fit their reactants — in this case, methane — like a glove. So having a clear view of MMO’s physical structure could help researchers tweak the enzyme’s actions. MMO is embedded in a lipid membrane in the cell. To image it, structural biologists have typically started by using detergents to remove the lipids, which inactivates the enzyme and results in an incomplete picture of it and its activity. But Rosenzweig and colleagues recently managed to image the enzyme in this lipid context. This unprecedented view of MMO in its native state, published in 2022 in Science, revealed a previously unseen site where copper binds.

But that’s still not the entire picture. Rosenzweig says she hopes her structural studies, along with other work, will lead to a breakthrough soon enough to help forestall further consequences of global warming. “Maybe people get lucky and engineer a strain quickly,” Rosenzweig says. “You don’t know until you try.”

Chemists make progress on catalysts

Other scientists seek to put methane-destroying chemical reactors close to methane sources. These reactors typically use a catalyst to speed up the chemical reactions that convert methane into a less planet-warming molecule. These catalysts often require high temperatures or other stringent conditions to operate, contain expensive metals like platinum, and don’t work well at the concentrations of methane found in ambient air.

One promising place to start, though, is coal mines. Coal mining is associated with tens of millions of tons of methane emissions worldwide every year. Although coal-fired power plants are being phased out in many countries, coal will be difficult to eliminate entirely due to its key role in steel production, says Plata, of MIT.

To develop a catalyst that might work in a coal mine, Plata found inspiration in MMO. Her team developed a catalyst material based on a silicate material embedded with copper — the same metal found in MMO and much less expensive than those usually required to oxidize methane. The material is also porous, which improves the catalyst’s efficiency because it has a larger surface area, and thus more places for reactions to occur, than a nonporous material would. The catalyst turns methane into CO₂, a reaction that releases heat, which is needed to further fuel the reaction. If methane concentrations are high enough, the reaction will be self-sustaining, Plata says.

Turning methane into CO₂ may sound counterproductive, but it reduces warming overall because methane traps much more heat than CO₂ and is far less abundant in the atmosphere. If all the excess methane in the atmosphere were turned into CO₂, according to a 2019 study led by Jackson, it would result in only 8.2 billion additional tons of CO₂ — equivalent to just a few months of CO₂ emissions at today’s rates. And the net effect would be to lessen the heating of the atmosphere by a sixth.

Cattle feedlots are another place where Plata’s catalytic reactor might work. Barns outfitted with fans to keep cattle comfortable move air around, so reactors could be fitted to these ventilation systems. The next step is determining whether methane concentrations at industrial dairy farms are high enough for the catalyst to work.

Another researcher making progress is energy scientist and engineer Arun Majumdar, one of Jackson’s collaborators at Stanford. In January, Majumdar published initial results describing a catalyst that converts methane into methanol, with an added boost from high-energy ultraviolet light. This UV blast adds the energy needed to overcome CH₄’s stubborn bonds — and the carefully designed catalyst stays on target. Previous catalyst designs tended to produce a mix of CO₂ and methanol, but this catalyst mostly sticks to making methanol.

Is geoengineering a path to methane removal?

A more extreme approach to speed up methane’s natural breakdown is to change the chemistry of the atmosphere itself. A few companies, such as the U.S.-based Blue Dot Change, have proposed releasing chemicals into the sky to enhance methane oxidation.

Natalie Mahowald, an atmospheric chemist at Cornell University, decided to evaluate this type of geoengineering.

“I’m not super excited about throwing more things into the atmosphere,” Mahowald says. To meet the goals of the Paris Agreement, limiting global warming to 1.5 to 2 degrees Celsius above the preindustrial average, though, it’s worth exploring all possibilities, she says. “If we’re going to meet these targets,” she says “we’re going to need some of these crazy ideas to work. So I’m willing to look at it. But I’m looking with a scientist’s critical eye.”

The main strategy proposed by advocates would inject iron aerosols into the air over the ocean on a sunny day. These aerosols would react with salty sea spray aerosols to form chlorine, which would then attack methane in the atmosphere and initiate further chemical reactions that turn it into CO₂. Mahowald wondered how much chlorine would be needed — and if there might be any unintended consequences.

Detailed modeling revealed something alarming. The iron injections could have the opposite of the intended effect, Mahowald and colleagues reported in July in Nature Communications. Chlorine won’t attack methane if ozone is around. Instead, chlorine will first break down all the ozone it can find. But ozone plays a key role in generating the hydroxyl radicals that naturally break down atmospheric methane. So when ozone levels fall, Mahowald says, the concentration and lifetime of methane molecules in the atmosphere actually increases. To use this strategy to break down methane, geo­engineers would need to add a tremendous amount of chlorine to the atmosphere — enough to first break down the ozone, then attack methane.

Removing 20 percent of the atmosphere’s methane, thus reducing the planet’s surface temperature by 0.2 degrees Celsius by 2050, for example, would require creating about 630 million tons of atmospheric chlorine every year. That would in turn require injecting perhaps tens of millions of tons of iron. A form of particulate matter, these iron aerosols could worsen air quality; inhaling particulate matter is associated with a range of health problems, particularly cardiovascular and lung disease. This atmospheric tinkering could also create hydrochloric acid that could reach the ocean and acidify it.

And there’s no guarantee that some of the chlorine wouldn’t make it all the way up to the ozone layer, depleting the planetary shield that protects us from the sun’s harmful UV rays. Mahowald is still studying this possibility.

Methane is a sprint and CO₂ is a marathon.

Desirée Plata

Mahowald is ambivalent about doing research on geoengineering. “We’re just throwing out ideas here because we’re in a terrible, terrible position,” she says. She’s worried about what could happen if all the methane locked up in the world’s permafrost escapes. If scientists can figure out how to use iron aerosols effectively, without adverse effects — and if such geoengineering is accepted by society — we might need it.

“We’re just trying to see, is there any hope this could work and would we ever want to do it? Would it have enough benefits to outweigh the disadvantages?”

The committee organized by the National Academies to investigate methane removal is taking these kinds of ethical questions into account, as well as considering the potential cost and scale of technologies. Stein, a committee member, says a framework proposed by Spark Climate Solutions provides some guidance. The organization, a nonprofit based in San Francisco that evaluates methane-removal technologies, proposes investing in tech that can remove tens of millions of tons of methane per year in the coming decades, at a cost of less than $2,000 per ton. Spark cofounder David Mann says the numbers are designed to focus attention and investment on technologies that can make a real difference in curbing climate change in the near term.

The National Academies group aims to make recommendations about research priorities on methane-removal technologies by next summer. It’s likely that a portfolio of different technologies will be necessary. What works in a cattle feedlot may not work at a wastewater treatment plant, for instance.

Scientists focused on methane removal are eager for more researchers, research funding and companies to enter the fray — and quickly. “It’s been a crazy year,” Jackson says of 2023’s extreme weather. We’re already feeling the effects of global warming, but we can seize the moment, he says. “This problem is not something for our grandchildren. It’s here.”

An Australian mosquito species knows the best spot to drink its bloody meals: a frog’s nostril.

The bloodsuckers are surprisingly selective when dining on frogs, seemingly picking no other place on the body to feast, researchers report November 21 in Ethology. Frogs’ sniffers may be an easy and productive place for the mosquitoes to pierce the thin skin and drink up. The new finding could one day help scientists better understand the transmission of some frog diseases.

Behavioral biologist John Gould discovered the nostril-nibbling insects while studying frogs in ponds on Australia’s Kooragang Island. From 2020 through 2022, Gould occasionally noticed mosquitoes on the faces of the frogs he was surveying and would take photos.

“It was only once I laid out all the photos together that I realized something very particular and surprising was happening,” says Gould, of the University of Newcastle in Callaghan, Australia.  In the 12 photos that Gould took of mosquitoes on frogs, every single bloodsucker was feeding on the skin of the frog’s nostril. 

Some mosquitoes feed only on frogs and toads but bite various parts of the body. The mosquito that caught Gould’s eye, Mimomyia elegans, has a generalized diet of amphibians, mammals and birds. “Yet its feeding strategy when using frogs appears to be highly specialized,” Gould says.

The nostril skin may be especially soft and thin, making it easier for the mosquito’s biting mouthparts to pierce, Gould says. Alternatively, he notes, there could be a high density of blood vessels near the surface of the nostril skin. 

Dining at this venue on a renowned insect eater is risky, considering the nostrils rest just above a powerful, sticky tongue (SN:10/5/22). But the mosquitoes might have a stealthy work-around. Gould observed some of the mosquitoes landing on the frogs’ backs first before carefully walking up toward the head. This, he says, might keep them from being detected and eaten. 

Gould and colleagues have shown in previous work that mosquitoes may be vectors for amphibian chytrid fungus, a grave threat to amphibians globally. “Determining where exactly mosquitoes land and subsequently feed on frogs may allow scientists to better understand the spread of the infection across the skin surfaces of frogs,” he says.

Some of the photographed mosquitoes were feeding on green and golden bell frogs (Litoria aurea). Those frogs are considered vulnerable to extinction, in part due to habitat loss, by the International Union for Conservation of Nature.

A laboratory experiment to carefully watch frogs and mosquitoes to confirm the insects’ nasal predilections would be helpful, says Manuela Carnaghi, an insect behavioral ecologist at the University of Greenwich in Chatham, England, who was not involved with the study.

Determining precisely how mosquitoes target and bite multiple kinds of hosts is key for understanding disease transmission in animals, Carnaghi says. It’s particularly important, she says, when considering the ability of a mosquito-borne pathogen or parasite to jump between different species.