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    The Arctic is warming even faster than scientists realized

    The Arctic is heating up at a breakneck speed compared with the rest of Earth. And new analyses show that the region is warming even faster than scientists thought. Over the last four decades, the average Arctic temperature increased nearly four times as fast as the global average, researchers report August 11 in Communications Earth & Environment.

    And that’s just on average. Some parts of the Arctic Ocean, such as the Barents Sea between Russia and Norway’s Svalbard archipelago, are warming as much as seven times as fast, meteorologist Mika Rantanen of the Finnish Meteorological Institute in Helsinki and colleagues found. Previous studies have tended to say that the Arctic’s average temperature is increasing two to three times as fast as elsewhere, as humans continue causing the climate to change.

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    To calculate the true pace of the accelerated warming, a phenomenon called Arctic amplification, the researchers averaged four sets of satellite data from 1979 to 2021 (SN: 7/1/20). Globally, the average temperature increase over that time was about 0.2 degrees Celsius per decade. But the Arctic was warming by about 0.75 degrees C per decade.

    Even the best climate models are not doing a great job of reproducing that warming, Rantanen and colleagues say. The inability of the models to realistically simulate past Arctic amplification calls into question how well the models can project future changes there.

    It’s not clear where the problem lies. One issue may be that the models are struggling with correctly simulating the sensitivity of Arctic temperatures to the loss of sea ice. Vanishing snow and ice, particularly sea ice, are one big reason why Arctic warming is on hyperspeed. The bright white snow and ice create a reflective shield that bounces incoming radiation from the sun back into space. But open ocean waters or bare rocks absorb that heat, raising the temperature. More

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    Sea sponges launch slow-motion snot rockets to clean their pores

    The next time you spot a sea sponge, say “gesundheit!” Some sponges regularly “sneeze” to clear debris from their porous bodies.

    As filter feeders, sponges draw in water through inlet pores — called ostia — and strain it through an internal canal system for nutrients. But there are also inedible bits in the water, like sediment. To prevent the undesirable junk from clogging up their outer pores, a Caribbean tube sponge (Aplysina archeri) uses mucus to trap and sneeze out unwanted particles, Niklas Kornder, a marine biologist at the University of Amsterdam, and colleagues report online August 10 in Current Biology. To the team’s surprise, it found that the sponge expels its snot from the same pores through which it absorbs water.

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    It’s “like someone with a runny nose,” says team member Sally Leys, an evolutionary biologist at the University of Alberta in Edmonton, Canada. “It’s constantly streaming, but it’s going counterflow to the in-current.”

    Researchers knew that sponges used contractions dubbed “sneezing” to move water through their bodies in a one-way flow. Typically, water comes in through numerous ostia and leaves through the osculum, a hole near the sponges’ top.

    But when the team captured time-lapse video of A. archeri, it saw tiny specks of mucus exiting from the ostia, moving against the flow of incoming water. Sneezelike contractions appeared to expel and move the specks along a “mucus highway” across the surface of the sponge to points where they collected in stringy, gooey clumps. Unlike an explosive human sneeze, the sponges slowly and continuously secreted debris-laden mucus from their ostia, with one contraction taking between 20 and 50 minutes, the study finds.

    [embedded content]
    The Caribbean tube sponge (Aplysina archeri) uses contractions — called “sneezes” — to help eject mucus from its pores, or ostia. As the time-lapse video zooms in closer, it’s possible to see tiny specks of debris floating out of these pores and traveling along a “mucus highway” where they collect into stringy clumps of goo floating above the surface of the sponge. In real time, this sponge takes between 20 and 50 minutes to complete a sneeze.

    Other sea critters feast on these ocean boogers, like brittle stars and small crustaceans. Scientists view sponges primarily as habitat builders, but the mucus buffet shows they also perform an important function as food providers, says Amanda Kahn, a marine biologist at Moss Landing Marine Labs in California who was not involved with this work.

    “There’s so much to be said for a study that really spends time and watches,” Kahn says. “They let the animals show for themselves what was happening.”

    Most sponges appear to sneeze, so it’s likely not just A. archeri that uses the counterflow technique, Leys says. The team also noted a similar behavior in an Indo-Pacific sponge (Chelonaplysilla sp). But biologists need to dig deeper to figure out how widespread the mechanism is. It’s also unclear exactly what the mucus is or how it’s moving backward through pores. More

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    Relocated beavers helped mitigate some effects of climate change

    In the upper reaches of the Skykomish River in Washington state, a pioneering team of civil engineers is keeping things cool. Relocated beavers boosted water storage and lowered stream temperatures, indicating such schemes could be an effective tool to mitigate some of the effects of climate change.

    In just one year after their arrival, the new recruits brought average water temperatures down by about 2 degrees Celsius and raised water tables as much as about 30 centimeters, researchers report in the July Ecosphere. While researchers have discussed beaver dams as a means to restore streams and bulk up groundwater, the effects following a large, targeted relocation had been relatively unknown (SN: 3/26/21).

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    “That water storage is so critical during the drier periods, because that’s what can keep the ecosystem resilient to droughts and fires,” says Emily Fairfax, an ecohydrologist at California State University Channel Islands in Camarillo who was not involved with the study.

    The Skykomish River flows down the west side of Washington’s Cascade Mountains. Climate change is already transforming the region’s hydrology: The snowpack is shrinking, and snowfall is turning to rain, which drains quickly. Waters are also warming, which is bad news for salmon populations that struggle to survive in hot water.

    Beavers are known to tinker with hydrology too (SN: 7/27/18). They build dams, ponds and wetlands, deepening streams for their burrows and lodges (complete with underwater entrances). The dams slow the water, storing it upstream for longer, and cool it as it flows through the ground underneath.

    From 2014 to 2016, aquatic ecologist Benjamin Dittbrenner and colleagues relocated 69 beavers (Castor canadensis) from lowland areas of the state to 13 upstream sites in the Skykomish River basin, some with relic beaver ponds and others untouched. As beavers are family-oriented, the team moved whole clans to increase the chances that they would stay put.

    The researchers also matched singletons up with potential mates, which seemed to work well: “They were not picky at all,” says Dittbrenner, of Northeastern University in Boston. Fresh logs and wood cuttings got the beavers started in their new neighborhoods.

    At the five sites that saw long-term construction, beavers built 14 dams. Thanks to those dams, the volume of surface water — streams, ponds, wetlands — increased to about 20 times that of streams with no new beaver activity. Meanwhile below ground, wells at three sites showed that after dam construction the amount of groundwater grew to more than twice that was stored on the surface in ponds. Stream temperatures downstream of the dams fell by 2.3 degrees C on average, while streams not subject to the beavers’ tinkering warmed by 0.8 degrees C. These changes all came within the first year after relocation.

    “We’re achieving restoration objectives almost instantly, which is really cool,” Dittbrenner says.

    Crucially, the dams lowered temperatures enough to almost completely take the streams out of the harmful range for salmon during a particularly hot summer. “These fish are also experiencing heat waves within the water system, and the beavers are protecting them from it,” Fairfax says. “That to me was huge.”

    The study also found that small, shallow abandoned beaver ponds were actually warming streams, perhaps because the cooling system had broken down over time. Targeting these ponds as potential relocation sites could be the most effective way to bring temperatures down, the researchers say.  When relocated populations establish and breed, young beavers leaving their homes could seek those abandoned spots out first, Dittbrenner says, as it uses less energy than starting from scratch. “If they find a relic pond, it’s game on.”      More

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    Electrical bacteria may help clean oil spills and curb methane emissions

    The small motorboat anchors in the middle of the Chesapeake Bay. Shrieks of wintering birds assault the vessel’s five crew members, all clad in bright orange flotation suits. One of the crew slowly pulls a rope out of the water to retrieve a plastic tube, about the length of a person’s arm and filled with mud from the bottom of the bay. As the tube is hauled on board, the stench of rotten eggs fills the air.

    “Chesapeake Bay mud is stinky,” says Sairah Malkin, a biogeochemist at the University of Maryland Center for Environmental Science in Cambridge who is aboard the boat. The smell comes from sulfuric chemicals called sulfides within the mud. They’re quite toxic, Malkin explains.

    Malkin and her team venture out onto the bay every couple of months to sample the foul muck and track the abundance of squiggling mud dwellers called cable bacteria. The microbes are living wires: Their threadlike bodies — thinner than a human hair — can channel electricity.

    Sairah Malkin, of the University of Maryland Center for Environmental Science, cuts holes in a large sediment coring tube to sample mud collected from the bottom of the Chesapeake Bay.Clara Fuchsman

    Cable bacteria use that power to chemically rewire their surroundings. While some microbes in the area produce sulfides, the cable bacteria remove those chemicals and help prevent them from moving up into the water column. By managing sulfides, cable bacteria may protect fish, crustaceans and other aquatic organisms from a “toxic nightmare,” says Filip Meysman, a biogeochemist at the University of Antwerp in Belgium. “They’re kind of like guardian angels in these coastal ecosystems.”

    Now, scientists are studying how these living electrical filaments might do good in other ways. Laboratory experiments show that cable bacteria can support other microbes that consume crude oil, so researchers are investigating how to encourage the bacteria’s growth to help clean up oil spills. What’s more, researchers have shown that cable bacteria could help slash emissions of a potent greenhouse gas — methane — into the atmosphere.

    There’s plenty of evidence that cable bacteria exert a strong influence over their microbial neighbors, Meysman says. The next step, he says, is to figure out how to channel that influence for the greater good.

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    Electric life

    Under the microscope, cable bacteria resemble long sausage links. Their multicellular bodies can grow up to 5 centimeters long. Embedded in the envelope of each cell are parallel “wires” of conductive proteins, which the bacteria use to channel electrons. According to Meysman, the wires are more conductive than the semi­conductors found in electronics.

    About a decade ago, a team of scientists first discovered cable bacteria, in sediment collected from the bottom of Denmark’s Aarhus Bay. Since then, cable bacteria have been found on at least four continents, in streams, lakes, estuaries and coastal environments. “Name me a country, and I’ll show you where the cable bacteria are,” Meysman says.

    Most often, cable bacteria nestle shallow in the sediment, with one end positioned near the surface where there is oxygen and the other end plugged into deeper, sulfide-rich zones. Using their filamentous bodies as electrical conduits, cable bacteria snatch electrons from sulfides on one end and off-load them to oxygen — an eager electron acceptor — at the other, says Nicole Geerlings, a biogeochemist at Utrecht University in the Netherlands. Similar to how batteries charge and release energy by transferring electrons between an anode and cathode, cable bacteria power themselves by channeling electrons, she says. “The electron transport gives [cable bacteria] energy.”

    This unique lifestyle allows cable bacteria to survive in an environment that many organisms could not endure.

    A cable bacterium (right) has a multicellular, segmented body that can grow up to 5 centimeters. Electrically conductive, parallel fibers (visible in the close-up at left) encase the body.From left: N. Geerlings/Utrecht Univ.; Silvia Hidalgo Martinez/Univ. of Antwerp

    Toxic fire wall

    In 2015, Malkin, Meysman and colleagues reported that cable bacteria may help to counteract the onset of euxinia — a fatal buildup of sulfides in oxygen-starved bodies of water. Euxinia can trigger mass die-offs of fish, crustaceans and other aquatic life.

    The lethal phenomenon can occur after fertilizers or sewage are washed into the sea or lakes. That flow of nutrients can trigger algal blooms. When those nutrients are depleted, the blooms die, and large quantities of organic matter sink and accumulate on the sediment. Microbes then decompose the dead material, devouring much of the oxygen in the surrounding water in the process. When oxygen levels become critically low, sulfides may begin to leak from the sediment into the water, giving rise to euxinia.

    Sediments near the bottom of this core sample, taken from the Chesapeake Bay, are probably dark due to the presence of sulfides, while sediments near the top are lighter because cable bacteria have removed the sulfides.S. Malkin

    While studying cable bacteria in a brackish body of water in the Netherlands, Malkin and colleagues discovered a thin layer of rust coating the lake’s bottom. As the cable bacteria pulled electrons from sulfides, converting the noxious chemicals into less-harmful sulfates, the water within the sediment became more acidic, which dissolved some minerals containing iron. The now-mobile iron percolated upward in the sediment, until it interacted with oxygen to form rust.

    This layer of rust could capture sulfides that would otherwise flow into the water, acting as a “fire wall” that could delay euxinia for over a month, or even prevent it altogether, the researchers reported. Even when the cable bacteria’s population dropped, the rust layer persisted, protecting other aquatic creatures from sulfide exposure. The rust may explain why even though instances of nutrient pollution, algal blooms and oxygen depletion are relatively common, reports of euxinia are rare.

    Oil cleanup

    Some researchers are trying to harness the bacteria’s electrical abilities to tackle another devastating threat to coastal ecosystems — oil spills.

    When an oil spill happens in a body of water, booms, skimmers or sorbents are often deployed to limit the spread of hydrocarbons on the surface. But oil may also wash onto beaches, mix with sediments in shallow waters and aggregate onto sinking particles of organic debris, hitching a ride to the seafloor.

    Cleaning up oil at the bottom of the sea is a difficult job, says Ugo Marzocchi, a biogeochemist at Aarhus University in Denmark. “I am not aware of a very effective way to remove hydrocarbons from the seafloor,” he says. “In inland freshwater systems, what is generally done is to dig out the sediments,” he says, an expensive strategy that would be even more costly at sea.

    [embedded content]
    Electrical cable bacteria (white filaments) emerge from the seafloor sediment (at bottom) stretching their bodies to reach a zone of oxygen in the water. The stringy organisms use the oxygen to offload electrons they’ve harvested from harmful sulfides found in the sediment. As sulfide concentrations go down, the water becomes more habitable to microbes that can clean up oil spills.

    Some soil-dwelling microorganisms can use hydrocarbons to fuel their metabolism, and researchers have been studying how some of these oil burners might assist in the cleanup of contaminated sediments. But as they break down hydrocarbons, the microbes generate those concerning sulfides, which are detrimental to the microbes’ own survival, Marzocchi says. In other words, the microbes can help clean up the oil for only so long before they’re overwhelmed by their own toxic waste.

    Cable bacteria might be just the solution, Marzocchi thought. In 2016, researchers reported finding evidence of the electrical microbes in a tar oil-contaminated groundwater aquifer in Germany. Knowing that cable bacteria could occupy sediments contaminated with hydrocarbons, Marzocchi and colleagues reasoned that these bacteria might be able to assist oil-burning microbes and accelerate oil cleanup.

    The researchers filled several containers with oil-contaminated sediment from Aarhus Bay — which contained naturally occurring oil-eating bacteria. The group then injected a few containers with cable bacteria and monitored the degree of hydrocarbon degradation in all of the containers over seven weeks. By the end of the test, the concentration of alkanes — a type of hydrocarbon — in the sediment with cable bacteria had dropped from 0.125 milligrams per gram of sediment to 0.086 milligrams per gram — a 31 percent drop. That’s 23 percentage points more than the 9 percent decrease in the control samples. Cable bacteria helped accelerate the metabolic activity of their oil-eating neighbors by converting the toxic sulfides into sulfates. The sulfates didn’t harm the oil-eating microbes — in fact, they used the chemicals as fuel.

    The researchers are now trying to develop methods to promote cable bacteria growth in the field and see if it’s possible to enhance their effect on oil degradation. One catch is that in oil-contaminated sediment, oxygen is quickly used up by the microbes that break down hydrocarbons. That’s a problem since cable bacteria need access to oxygen. Salts that slowly release oxygen or nitrate — which cable bacteria can use in place of oxygen — might help spur the electrical organisms’ growth at oil spills. But more work is needed to identify the right chemical components and dosage, Marzocchi says.

    Meanwhile, scientists are investigating how cable bacteria might help reduce emission of another hydrocarbon — one that accumulates in the sky.

    Methane at the root

    Colorless, odorless methane is the simplest hydrocarbon (SN: 8/15/20, p. 8). It consists of a single carbon atom attached to a quartet of hydrogen atoms. And it’s a potent greenhouse gas — more than 25 times as effective at trapping heat in the atmosphere as carbon dioxide.

    One major source of methane is rice paddies (SN: 9/25/21, p. 16). During the growing season, rice farmers typically flood their fields to help stave off weeds and pests. Methane-producing microbes — aptly named methanogens — thrive in these waterlogged soils. Paddy-dwelling methanogens are so prolific that rice fields are estimated to generate about 11 percent of all human-induced methane emissions.

    But cable bacteria like paddies too. In 2019, Vincent Scholz, a microbiologist at Aarhus University, and colleagues reported that cable bacteria could flourish among the roots of rice plants and several other aquatic plant species.

    In an experiment, pots of rice plants grown in soils with cable bacteria (right) developed orange layers of rust and emitted less methane than pots without cable bacteria (left).V.V. Scholz/Aarhus Univ.

    That discovery inspired the researchers to investigate how the bacteria interact with methanogens in soils that grow rice. The team grew its own rice plants — some potted in soils with cable bacteria, and some without — and monitored methane emissions.

    To the researchers’ surprise, adding cable bacteria reduced rice soil methane emissions by 93 percent. In the process of removing electrons from sulfides, the bacteria generate sulfates, which other microbes can use as fuel. These sulfate-consuming microbes outcompeted methanogens for nutrients such as hydrogen and acetate in the rice soils, the researchers found. The results were “quite amazing,” Scholz says, though the effectiveness of the electrical microbes in real rice fields has yet to be tested.

    There are signs that cable bacteria are already plugged into real rice paddy soils. After analyzing genetic data collected from rice paddies in the United States, India, Vietnam and China, Scholz and colleagues reported in 2021 the presence of cable bacteria at sites in all four countries. Scholz is in Northern California this summer studying how cable bacteria live in rice fields and whether they’re already impacting methane emissions. He is also exploring ways to introduce cable bacteria to rice fields where they don’t yet exist or enhance the microbes’ numbers in fields where they do.

    There is still much to discover about how the wispy electrical conductors influence our world, Malkin says. Back in the Chesapeake Bay, she and colleagues have found that cable bacteria tend to flourish in the spring, a surge that has also been observed in the Netherlands. The findings add to a growing body of work that suggests cable bacteria are opportunistic organisms that interact with their environments in similar ways all around the world.

    If cable bacteria are already hard at work across the planet, then a bit of coaxing from researchers may be all it takes to turn the mud-dwelling creatures into the most helpful neighbors that a living thing could ask for. More

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    Humans may not be able to handle as much heat as scientists thought

    More than 2,000 people dead from extreme heat and wildfires raging in Portugal and Spain. High temperature records shattered from England to Japan. Overnights that fail to cool.

    Brutal heat waves are quickly becoming the hallmark of the summer of 2022.

    And even as climate change continues to crank up the temperature, scientists are working fast to understand the limits of humans’ resilience to heat extremes. Recent research suggests that heat stress tolerance in people may be lower than previously thought. If true, millions more people could be at risk of succumbing to dangerous temperatures sooner than expected.

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    “Bodies are capable of acclimating over a period of time” to temperature changes, says Vivek Shandas, an environmental planning and climate adaptation researcher at Portland State University in Oregon. Over geologic time, there have been many climate shifts that humans have weathered, Shandas says. “[But] we’re in a time when these shifts are happening much more quickly.”

    Just halfway through 2022, heat waves have already ravaged many countries. The heat arrived early in southern Asia: In April, Wardha, India, saw a high of 45° Celsius (113° Fahrenheit); in Nawabshah, Pakistan, in May recorded temperatures rose to 49.5° C (121.1° F).

    Extreme heat alerts blared across Europe beginning in June and continuing through July, the rising temperatures exacerbating drought and sparking wildfires. The United Kingdom shattered its hottest-ever record July 19 when temperatures reached 40.3° C in the English village of Coningsby. The heat fueled fires in France, forcing thousands to evacuate from their homes. 

    And the litany goes on: Japan experienced its worst June heat wave since record-keeping began in 1875, leading to the country’s highest-ever recorded June temperature of 40.2° C.  China’s coastal megacities, from Shanghai to Chengdu, were hammered by heat waves in July as temperatures in the region also rose above 40° C. And in the United States, a series of heat waves gripped the Midwest, the South and the West in June and July. Temperatures soared to 42° C in North Platte, Neb., and to 45.6° C in Phoenix.

    The current global rate of warming on Earth is unprecedented (SN: 7/24/19). And scientists have long predicted that human-caused climate change will increase the occurrence of heat waves. Globally, humans’ exposure to extreme heat tripled from 1983 to 2016, particularly in South Asia.

    The heat already is taking an increasing toll on human health. It can cause heat cramps, heat exhaustion and heat stroke, which is often fatal. Dehydration can lead to kidney and heart disease. Extreme heat can even change how we behave, increasing aggression and decreasing our ability to focus (SN: 8/18/21).

    Staying cool

    The human body has various ways to shed excess heat and keep the core of the body at an optimal temperature of about 37° C (98.6° F). The heart pumps faster, speeding up blood flow that carries heat to the skin (SN: 4/3/18). Air passing over the skin can wick away some of that heat. Evaporative cooling — sweating — also helps.

    But there’s a limit to how much heat humans can endure. In 2010, scientists estimated that theoretical heat stress limit to be at a “wet bulb” temperature of 35° C. Wet bulb temperatures depend on a combination of humidity and “dry bulb” air temperature measured by a thermometer. Those variables mean a place could hit a wet bulb temperature of 35° C in different ways — for instance, if the air is that temperature and there’s 100 percent humidity, or if the air temperature is 45° C and there’s 50 percent humidity. The difference is due to evaporative cooling.

    When water evaporates from the skin or another surface, it steals away energy in the form of heat, briefly cooling that surface. That means that in drier regions, the wet bulb temperature — where that ephemeral cooling effect happens readily — will be lower than the actual air temperature. In humid regions, however, wet and dry bulb temperatures are similar, because the air is so moist it’s difficult for sweat to evaporate quickly.

    So when thinking about heat stress on the body, scientists use wet bulb temperatures because they are a measure of how much cooling through evaporation is possible in a given climate, says Daniel Vecellio, a climate scientist at Penn State.

    “Both hot/dry and warm/humid environments can be equally dangerous,” Vecellio says — and this is where the body’s different cooling strategies come into play. In hot, dry areas, where the outside temperature may be much hotter than skin temperature, human bodies rely entirely on sweating to cool down, he says. In warm, humid areas, where the air temperature may actually be cooler than skin temperatures (but the humidity makes it seem warmer than it is), the body can’t sweat as efficiently. Instead, the cooler air passing over the skin can draw away the heat.

    How hot is too hot?

    Given the complexity of the body’s cooling system, and the diversity of human bodies, there isn’t really a one-size-fits-all threshold temperature for heat stress for everybody. “No one’s body runs at 100 percent efficiency,” Vecellio says. Different body sizes, the ability to sweat, age and acclimation to a regional climate all have a role.

    Still, for the last decade, that theoretical wet bulb 35° C number has been considered to be the point beyond which humans can no longer regulate their bodies’ temperatures. But recent laboratory-based research by Vecellio and his colleagues suggests that a general, real-world threshold for human heat stress is much lower, even for young and healthy adults.

    The researchers tracked heat stress in two dozen subjects ranging in age from 18 to 34, under a variety of controlled climates. In the series of experiments, the team varied humidity and temperature conditions within an environmental chamber, sometimes holding temperature constant while varying the humidity, and sometimes vice versa.

    The subjects exerted themselves within the chamber just enough to simulate minimal outdoor activity, walking on a treadmill or pedaling slowly on a bike with no resistance. During these experiments, which lasted for 1.5 to two hours, the researchers measured the subjects’ skin temperatures using wireless probes and assessed their core temperatures using a small telemetry pill that the subjects swallowed.

    In warm and humid conditions, the subjects in the study were unable to tolerate heat stress at wet bulb temperatures closer to 30° or 31° C, the team estimates. In hot and dry conditions, that wet bulb temperature was even lower, ranging from 25° to 28° C, the researchers reported in the February Journal of Applied Physiology. For context, in a very dry environment at about 10 percent humidity, a wet bulb temperature of 25° C would correspond to an air temperature of about 50° C (122° F).

    These results suggest that there is much more work to be done to understand what humans can endure under real-world heat and humidity conditions, but that the threshold may be much lower than thought, Vecellio says. The 2010 study’s theoretical finding of 35° C may still be “the upper limit,” he adds. “We’re showing the floor.”

    And that’s for young, healthy adults doing minimal activity. Thresholds for heat stress are expected to be lower for outdoor workers required to exert themselves, or for the elderly or children. Assessing laboratory limits for more at-risk people is the subject of ongoing work for Vecellio and his colleagues.

    A worker wipes away sweat in Toulouse, France, on July 13. An intense heat wave swept across Europe in mid-July, engulfing Spain, Portugal, France, England and other countries.VALENTINE CHAPUIS/AFP via Getty Images

    If the human body’s tolerance for heat stress is generally lower than scientists have realized, that could mean millions more people will be at risk from the deadliest heat sooner than scientists have realized. As of 2020, there were few reports of wet bulb temperatures around the world reaching 35° C, but climate simulations project that limit could be regularly exceeded in parts of South Asia and the Middle East by the middle of the century.

    Some of the deadliest heat waves in the last two decades were at lower wet bulb temperatures: Neither the 2003 European heat wave, which caused an estimated 30,000 deaths, nor the 2010 Russian heat wave, which killed over 55,000 people, exceeded wet bulb temperatures of 28° C.

    Protecting people

    How best to inform the public about heat risk is “the part that I find to be tricky,” says Shandas, who wasn’t involved in Vecellio’s research. Shandas developed the scientific protocol for the National Integrated Heat Health Information System’s Urban Heat Island mapping campaign in the United States.

    It’s very useful to have this physiological data from a controlled, precise study, Shandas says, because it allows us to better understand the science behind humans’ heat stress tolerance. But physiological and environmental variability still make it difficult to know how best to apply these findings to public health messaging, such as extreme heat warnings, he says. “There are so many microconsiderations that show up when we’re talking about a body’s ability to manage [its] internal temperature.”

    One of those considerations is the ability of the body to quickly acclimate to a temperature extreme. Regions that aren’t used to extreme heat may experience greater mortality, even at lower temperatures, simply because people there aren’t used to the heat. The 2021 heat wave in the Pacific Northwest wasn’t just extremely hot — it was extremely hot for that part of the world at that time of year, which makes it more difficult for the body to adapt, Shandas says (SN: 6/29/21).

    Heat that arrives unusually early and right on the heels of a cool period can also be more deadly, says Larry Kalkstein, a climatologist at the University of Miami and the chief heat science advisor for the Washington, D.C.–based nonprofit Adrienne Arsht-Rockefeller Foundation Resilience Center. “Often early season heat waves in May and June are more dangerous than those in August and September.”

    One way to improve communities’ resilience to the heat may be to treat heat waves like other natural disasters — including give them names and severity rankings (SN: 8/14/20). As developed by an international coalition known as the Extreme Heat Resilience Alliance, those rankings form the basis for a new type of heat wave warning that explicitly considers the factors that impact heat stress, such as wet bulb temperature and acclimation, rather than just temperature extremes.

    The rankings also consider factors such as cloud cover, wind and how hot the temperatures are overnight. “If it’s relatively cool overnight, there’s not as much negative health outcome,” says Kalkstein, who created the system. But overnight temperatures aren’t getting as low as they used to in many places. In the United States, for example, the average minimum temperatures at nighttime are now about 0.8° C warmer than they were during the first half of the 20th century, according to the country’s Fourth National Climate Assessment, released in 2018 (SN: 11/28/18).

    By naming heat waves like hurricanes, officials hope to increase citizens’ awareness of the dangers of extreme heat. Heat wave rankings could also help cities tailor their interventions to the severity of the event. Six cities are currently testing the system’s effectiveness: four in the United States and in Athens, Greece, and Seville, Spain. On July 24, with temperatures heading toward 42° C, Seville became the first city in the world to officially name a heat wave, sounding the alarm for Heat Wave Zoe.

    As 2022 continues to smash temperature records around the globe, such warnings may come not a moment too soon. More

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    How to make jet fuel from sunlight, air and water vapor

    Jet fuel can now be siphoned from the air.

    Or at least that’s the case in Móstoles, Spain, where researchers demonstrated that an outdoor system could produce kerosene, used as jet fuel, with three simple ingredients: sunlight, carbon dioxide and water vapor. Solar kerosene could replace petroleum-derived jet fuel in aviation and help stabilize greenhouse gas emissions, the researchers report in the July 20 Joule.

    Burning solar-derived kerosene releases carbon dioxide, but only as much as is used to make it, says Aldo Steinfeld, an engineer at ETH Zurich. “That makes the fuel carbon neutral, especially if we use carbon dioxide captured directly from the air.”

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    Kerosene is the fuel of choice for aviation, a sector responsible for around 5 percent of human-caused greenhouse gas emissions. Finding sustainable alternatives has proven difficult, especially for long-distance aviation, because kerosene is packed with so much energy, says chemical physicist Ellen Stechel of Arizona State University in Tempe who was not involved in the study.

    In 2015, Steinfeld and his colleagues synthesized solar kerosene in the laboratory, but no one had produced the fuel entirely in a single system in the field. So Steinfeld and his team positioned 169 sun-tracking mirrors to reflect and focus radiation equivalent to about 2,500 suns into a solar reactor atop a 15-meter-tall tower. The reactor has a window to let the light in, ports that supply carbon dioxide and water vapor as well as a material used to catalyze chemical reactions called porous ceria.

    Within the solar reactor, porous ceria (shown) gets heated by sunlight and reacts with carbon dioxide and water vapor to produce syngas, a mixture of hydrogen gas and carbon monoxide.ETH Zurich

    When heated with solar radiation, the ceria reacts with carbon dioxide and water vapor in the reactor to produce syngas — a mixture of hydrogen gas and carbon monoxide. The syngas is then piped to the tower’s base where a machine converts it into kerosene and other hydrocarbons.

    Over nine days of operation, the researchers found that the tower converted about 4 percent of the used solar energy into roughly 5,191 liters of syngas, which was used to synthesize both kerosene and diesel. This proof-of-principle setup produced about a liter of kerosene a day, Steinfeld says.

    “It’s a major milestone,” Stechel says, though the efficiency needs to be improved for the technology to be useful to industry. For context, a Boeing 747 passenger jet burns around 19,000 liters of fuel during takeoff and the ascent to cruising altitude. Recovering heat unused by the system and improving the ceria’s heat absorption could boost the tower’s efficiency to more than 20 percent, making it economically practical, the researchers say. More

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    Underground heat pollution could be tapped to mitigate climate change

    The secret to efficiently heating some buildings might lurk beneath our feet, in the heat that humans have inadvertently stored underground. 

    Just as cities warm the surrounding air, giving rise to urban heat islands, so too does human infrastructure warm the underlying earth (SN: 3/27/09). Now, an analysis of groundwater well sites across Europe and parts of North America and Australia reveals that roughly a couple thousand of those locations possess excess underground heat that could be recycled to warm buildings for a year, researchers report July 8 in Nature Communications.

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    What’s more, even if humans managed to remove all this accumulated thermal pollution, existing infrastructure at about a quarter of the locations would continue to warm the ground enough that heat could be harvested for many years to come. That could reduce reliance on fossil fuels, and help mitigate climate change.

    This work showcases the impact that underground heat recycling could have if harnessed on a large scale, says hydrogeologist Grant Ferguson of the University of Saskatchewan in Saskatoon, Canada, who was not involved in the study. “There’s a lot of untapped potential out there.”

    Heat leaks into the subsurface from the warm roots of structures such as buildings, parking garages and tunnels, and from artificial surfaces such as asphalt, which absorb solar radiation. In Lyon, France, for example, researchers in 2016 found that human infrastructure warmed groundwater by more than 4 degrees Celsius.

    Scientists don’t fully understand how heat pollution alters underground environments. But warming of the subsurface can cause contaminants, such as arsenic, to move through groundwater more readily.

    Extracting the thermal pollution could be accomplished by piping groundwater to heat pumps at the surface. The water, warmed underground by all that trapped heat, could then warm buildings as it releases heat into their cooler interiors, says Susanne Benz, an environmental scientist at Dalhousie University in Halifax, Canada.

    Harnessing underground heat in this way could provide some communities with a reliable and low-energy means to warm their homes, Benz says. “And if we don’t use it, it will just continue to accumulate,” she says.

    Benz and her colleagues analyzed the population size, heating demand and groundwater temperature at more than 6,000 locations, most of which were in Europe. The researchers found that at about 43 percent of the locations — mostly those near highly populated areas — enough heat had accumulated in the top 20 meters of earth to satisfy a year’s worth of the local heating demand.

    Curious about sustainability, the researchers also identified places where the continuous flow of heat into the underground — and not just the stockpiled thermal pollution — was high. Their calculations show that if all of the accumulated heat was first extracted, the heat that continued leaking from existing infrastructure could be harvested at about 25 percent of the 6,000 locations. At 18 percent of locations, this recycled heat could satisfy at least a quarter of the heating demand of the local population.

    Constructing systems to take advantage of human heat pollution today could one day help residents harvest heat from climate change, the researchers say.

    Using climate projections for the end of the century, the team probed the feasibility of extracting underground heat in a warmer world. In the most optimistic warming scenario considered, which assumes greenhouse gas emissions peak about the year 2040, the researchers found that climate change would warm the ground enough by the end of the century that underground heat recycling at 81 percent of the studied locations could meet more than a quarter of locals’ heating demands. If there are no efforts to curb emissions, that number rises to 99 percent of locations.

    Though the researchers focused mostly on Europe, Benz says that other continents probably also possess abundant underground heat that could be harnessed. In Europe and elsewhere, heat recycling might be most feasible in suburban areas, she says, where there is sufficient accumulated underground heat to help meet local heating demands, and space to install heat recycling systems.

    Looking ahead, Benz plans to investigate whether cooling the subsurface can help reduce aboveground temperatures in urban environments. “This might actually be a little additional tool to control [aboveground] urban heat.” More

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    In the battle of human vs. water, ‘Water Always Wins’

    Water Always WinsErica Gies Univ. of Chicago, $26

    Humans have long tried to wrangle water. We’ve straightened once-meandering rivers for shipping purposes. We’ve constructed levees along rivers and lakes to protect people from flooding. We’ve erected entire cities on drained and filled-in wetlands. We’ve built dams on rivers to hoard water for later use.

    “Water seems malleable, cooperative, willing to flow where we direct it,” environmental journalist Erica Gies writes in Water Always Wins. But it’s not, she argues.

    Levees, which narrow channels causing water to flow higher and faster, nearly always break. Cities on former wetlands flood regularly — often catastrophically. Dams starve downstream environs of sediment needed to protect coastal areas against rising seas. Straightened streams flow faster than meandering ones, scouring away riverbed ecosystems and giving water less time to seep downward and replenish groundwater supplies.

    In addition to laying out this damage done by supposed water control, Gies takes readers on a hopeful global tour of solutions to these woes. Along the way, she introduces “water detectives”— scientists, engineers, urban planners and many others who, instead of trying to control water, ask: What does water want?

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    These water detectives have found ways to give the slippery substance the time and space it needs to trickle underground. Around Seattle’s Thornton Creek, for instance, reclaimed land now allows for regular flooding, which has rejuvenated depleted riverbed habitat and created an urban oasis. In California’s Central Valley, scientists want to find ways to shunt unpolluted stormwater into ancient, sediment-filled subsurface canyons that make ideal aquifers. Feeding groundwater supplies will in turn nourish rivers from below, helping to maintain water levels and ecosystems.

    While some people are exploring new ways to manage water, others are leaning on ancestral knowledge. Without the use of hydrologic mapping tools, Indigenous peoples of the Andes have a detailed understanding of the plumbing that links surface waters with underground storage. Researchers in Peru are now studying Indigenous methods of water storage, which don’t require dams, in hopes of ensuring a steady flow of water to Lima — Peru’s populous capital that’s periodically afflicted by water scarcity. These studies may help convince those steeped in concrete-centric solutions to try something new. “Decision makers come from a culture of concrete,” Gies writes, in which dams, pipes and desalination plants are standard.Understanding how to work with, not against, water will help humankind weather this age of drought and deluge that’s being exacerbated by climate change. Controlling water, Gies convincingly argues, is an illusion. Instead, we must learn to live within our water means because water will undoubtedly win.

    Buy Water Always Wins from Bookshop.org. Science News is a Bookshop.org affiliate and will earn a commission on purchases made from links in this article. More