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      By 2100, Greenland will be losing ice at its fastest rate in 12,000 years

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      By 2100, Greenland will be shedding ice faster than at any time in the past 12,000 years, scientists report October 1 in Nature.
      Since the 1990s, Greenland has shed its ice at an increasing rate (SN: 8/2/19). Meltwater from the island’s ice sheet now contributes about 0.7 millimeters per year to global sea level rise (SN: 9/25/19). But how does this rapid loss stack up against the ice sheet’s recent history, including during a 3,000-year-long warm period?
      Glacial geologist Jason Briner of the University at Buffalo in New York and colleagues created a master timeline of ice sheet changes spanning nearly 12,000 years, from the dawn of the Holocene Epoch 11,700 years ago and projected out to 2100.
      The researchers combined climate and ice physics simulations with observations of the extent of past ice sheets, marked by moraines. Those rocky deposits denote the edges of ancient, bulldozing glaciers. New fine-tuned climate simulations that include spatial variations in temperature and precipitation across the island also improved on past temperature reconstructions.
      During the past warm episode from about 10,000 to 7,000 years ago, Greenland lost ice at a rate of about 6,000 billion metric tons each century, the team estimates. That rate remained unmatched until the past two decades: From 2000 to 2018, the average rate of ice loss was similar, at about 6,100 billion tons per century.
      Over the next century, that pace will accelerate, the team says. How much depends on future greenhouse gas emissions: Under a lower-emissions scenario, ice loss is projected to average around 8,800 billion tons per century by 2100. With higher emissions, the rate of loss could ramp up to 35,900 billion tons per century.
      Lower emissions could slow the loss, but “no matter what humanity does, the ice will melt this century at a faster clip than it did during that warm period,” Briner says. More

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      Invasive jumping worms damage U.S. soil and threaten forests

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      What could be more 2020 than an ongoing invasion of jumping worms?
      These earthworms are wriggling their way across the United States, voraciously devouring protective forest leaf litter and leaving behind bare, denuded soil. They displace other earthworms, centipedes, salamanders and ground-nesting birds, and disrupt forest food chains. They can invade more than five hectares in a single year, changing soil chemistry and microbial communities as they go, new research shows. And they don’t even need mates to reproduce.
      Endemic to Japan and the Korean Peninsula, three invasive species of these worms — Amynthas agrestis, A. tokioensis and Metaphire hilgendorfi — have been in the United States for over a century. But just in the past 15 years, they’ve begun to spread widely (SNS: 10/7/16). Collectively known as Asian jumping worms, crazy worms, snake worms or Alabama jumpers, they’ve become well established across the South and Mid-Atlantic and have reached parts of the Northeast, Upper Midwest and West.
      Jumping worms are often sold as compost worms or fishing bait. And that, says soil ecologist Nick Henshue of the University at Buffalo in New York, is partially how they’re spreading (SN: 11/5/17). Fishers like them because the worms wriggle and thrash like angry snakes, which lures fish, says Henshue. They’re also marketed as compost worms because they gobble up food scraps far faster than other earthworms, such as nightcrawlers and other Lumbricus species.

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      But when it comes to ecology, the worms have more worrisome traits. Their egg cases, or cocoons, are so small that they can easily hitch a ride on a hiker’s or gardener’s shoe, or can be transported in mulch, compost or shared plants. Hundreds can exist within a square meter of ground.  
      Compared with Lumbricus worms, jumping worms grow faster and reproduce faster — and without a mate, so one worm can create a whole invasion. Jumping worms also consume more nutrients than other earthworms, turning soil into dry granular pellets that resemble coffee grounds or ground beef — Henshue calls it “taco meat.” This can make the soil inhospitable to native plants and tree seedlings and far more likely to erode.
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      Asian jumping worm species thrash furiously, unlike the more placid movements of other earthworm species. The jumping worms can also slime and shed their tails as defense mechanisms.
      To date, scientists have worried most about the worms’ effects on ground cover. Prior to a jumping worm invasion, the soft layer of decomposing leaves, bark and sticks covering the forest floor might be more than a dozen centimeters thick. What’s left afterward is bare soil with a different structure and mineral content, says Sam Chan, an invasive species specialist with Oregon Sea Grant at Oregon State University in Corvallis. Worms can reduce leaf litter by 95 percent in a single season, he says.
      That in turn can reduce or remove the forest understory, providing less nutrients or protection for the creatures that live there or for seedlings to grow. Eventually, different plants come in, usually invasive, nonnative species, says Bradley Herrick, an ecologist and research program manager at the University of Wisconsin–Madison Arboretum. And now, new research shows the worms are also changing the soil chemistry and the fungi, bacteria and microbes that live in the soils.
      Invasive jumping worms can clear a forest of leaf litter in just a couple of months, as these pictures taken in Jacobsburg State Park near Nazareth, Pa., in June 2016 (left) and August 2016 (right) show.Nick Henshue
      In a study in the October Soil Biology and Biochemistry, Herrick, soil scientist Gabriel Price-Christenson and colleagues tested samples from soils impacted by jumping worms. They were looking for changes in carbon and nitrogen levels and in soils’ release of carbon dioxide, which is produced by the metabolism of microbes and animals living in the soil. Results showed that the longer the worms had lived in the soils, the more the soils’ basal metabolic rate increased — meaning soils invaded by jumping worms could release more carbon dioxide into the atmosphere, says Price-Christenson, who is at the University of Illinois at Urbana-Champaign.
      Relative amounts of carbon and nitrogen in soils with jumping worms also shifted, the team found. That can affect plant communities, Herrick says. For example, although nitrogen is a necessary nutrient, if there’s too much, or it’s available at the wrong time of year, plants or other soil organisms won’t be able to use it. 
      The team also extracted DNA from worm poop and guts to examine differences in microbes among the jumping worm species, and tested the soils for bacterial and fungal changes. Each jumping worm species harbors a different collection of microbes in its gut, the results showed. That’s “a really important find,” Herrick says, “because for a long time, we were talking about jumping worms as a large group … but now we’re learning that [these different species] have different impacts on the soil, which will likely cascade down to having different effects on other worms, soil biota, pH and chemistry.”  
      The finding suggests each species might have a unique niche in the environment, with gut microbes breaking down particular food sources. This allows multiple species to invade and thrive together, Herrick says. This makes sense, given findings of multiple species together, but it’s still a surprise that such similar worms would have different niches, he says.    
      Scientists have been working hard to get a good handle on the biology of these worms, Henshue says. So the newly discovered soil chemistry and microbiology changes are “thoughtful” and important lines of research. But there’s still a lot that’s unknown, making it hard to predict how much farther the worms might spread and into what kinds of environments. One important question is how weather conditions affect the worms. For example, a prolonged drought this year in Wisconsin seems to have killed off many of the worms, Herrick says. Soils teeming with wriggling worms just a few weeks ago now hold far fewer.
      Perhaps that’s a hopeful sign that even these hardy worms have their limits, but in the meantime, the onslaught of worms continues its march — with help from the humans who spread them. More

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      Global warming may lead to practically irreversible Antarctic melting

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      How is melting a continent-sized ice sheet like stirring milk into coffee? Both are, for all practical purposes, irreversible.
      In a new study published in the Sept. 24 Nature, researchers outline a series of temperature-related tipping points for the Antarctic Ice Sheet. Once each tipping point is reached, changes to the ice sheet and subsequent melting can’t be truly reversed, even if temperatures drop back down to current levels, the scientists say.
      The full mass of ice sitting on top of Antarctica holds enough water to create about 58 meters of sea level rise. Although the ice sheet won’t fully collapse tomorrow or even in the next century, Antarctic ice loss is accelerating (SN: 6/13/18). So scientists are keen to understand the processes by which such a collapse might occur.
      “What we’re really interested in is the long-term stability” of the ice, says Ricarda Winkelmann, a climate scientist at Potsdam Institute for Climate Impact Research in Germany. In the new study, Winkelmann and her colleagues simulated how future temperature increases can lead to changes across Antarctica in the interplay between ice, oceans, atmosphere and land.

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      In addition to direct melting due to warming, numerous processes linked to climate change can speed up overall melting, called positive feedbacks, or slow it down, known as negative feedbacks.
      For example, as the tops of the ice sheets slowly melt down to lower elevations, the air around them becomes progressively warmer, speeding up melting. Warming temperatures also soften the ice itself, so that it slides more quickly toward the sea. And ocean waters that have absorbed heat from the atmosphere can transfer that heat to the vulnerable underbellies of Antarctic glaciers jutting into the sea, eating away at the buttresses of ice that keep the glaciers from sliding into the sea (SN: 9/11/20). The West Antarctic Ice Sheet is particularly vulnerable to such ocean interactions — but warm waters are also threatening sections of the East Antarctic Ice Sheet, such as Totten Glacier (SN: 11/1/17).
      In addition to these positive feedbacks, climate change can produce some negative feedbacks that delay the loss of ice. For example, warmer atmospheric temperatures also evaporate more ocean water, adding moisture to the air and producing increased snowfall (SN: 4/30/20).
      The new study suggests that below 1 degree Celsius of warming relative to preindustrial times, increased snowfall slightly increases the mass of ice on the continent, briefly outpacing overall losses. But that’s where the good news ends. Simulations suggest that after about 2 degrees Celsius of warming, the West Antarctic Ice Sheet will become unstable and collapse, primarily due to its interactions with warm ocean waters, increasing sea levels by more than 2 meters. That’s a warming target that the signatories to the 2015 Paris Agreement pledged not to exceed, but which the world is on track to surpass by 2100 (SN: 11/26/2019).
      As the planet continues to warm, some East Antarctic glaciers will follow suit. At 6 degrees Celsius of warming, “we reach a point where surface processes become dominant,” Winkelmann says. In other words, the ice surface is now at low enough elevation to accelerate melting. Between 6 and 9 degrees of warming, more than 70 percent of the total ice mass in Antarctica is loss, corresponding to an eventual sea level rise of more than 40 meters, the team found.
      Those losses in ice can’t be regained, even if temperatures return to preindustrial levels, the study suggests. The simulations indicate that for the West Antarctic Ice Sheet to regrow to its modern extent, temperatures would need to drop to at least 1 degree Celsius below preindustrial times.
      “What we lose might be lost forever,” Winkelmann says.
      There are other possible feedback mechanisms, both positive and negative, that weren’t included in these simulations, Winklemann adds — either because the mechanisms are negligible or because their impacts aren’t yet well understood. These include interactions with ocean-climate patterns such as the El Niño Southern Oscillation and with ocean circulation patterns, including the Atlantic Meridional Overturning Circulation.
      Previous research suggested that meltwater from the Greenland and Antarctic ice sheets might also play complicated feedback roles. Nicholas Golledge, a climate scientist with Victoria University of Wellington in New Zealand, reported in Nature in 2019 that flows of Greenland meltwater can slow ocean circulation in the Atlantic, while cold, fresh Antarctic meltwater can act like a seal on the surface ocean around the continent, trapping warmer, saltier waters below, where they can continue to eat away at the underbelly of glaciers.
      In a separate study published Sept. 23 in Science Advances, Shaina Sadai, a climate scientist at the University of Massachusetts Amherst, and her colleagues also examined the impact of Antarctic meltwater. In simulations that look out to the year 2250, the researchers found that in addition to a cool meltwater layer trapping warm water below it, that surface layer of freshwater would exert a strong cooling effect that could boost the volume of sea ice around Antarctica, which would in turn also keep the air there colder.
      A large plug of such meltwater, such as due to the West Antarctic Ice Sheet’s sudden collapse, could even briefly slow global warming, the researchers found. But that boon would come at a terrible price: rapid sea level rise, Sadai says. “This is not good news,” she adds. “We do not want a delayed surface temperature rise at the cost of coastal communities.”
      Because the volume and impact of meltwater is still uncertain, Winkelmann’s team didn’t include this factor. Robert DeConto, an atmospheric scientist also at the University of Massachusetts Amherst and a coauthor on the Science Advances study, notes that the effect depends on how scientists choose to simulate how the ice breaks apart. The study’s large meltwater volumes are the result of a controversial idea known as the marine ice-cliff hypothesis, which suggests that in a few centuries, tall ice cliffs in Antarctica might become brittle enough to suddenly crumble into the ocean like dominoes, raising sea levels catastrophically (SN: 2/6/19).
      Despite lingering uncertainties over the magnitude of feedbacks, one emerging theme — highlighted by the Nature paper — is consistent, DeConto says: Once the ice is lost, we can’t go back.
      “Even if we get our act together and reduce emissions dramatically, we will have already put a lot of heat into the ocean,” he adds. For ice to begin to grow back, “we’ll have to go back to a climate that’s colder than at the beginning of the Industrial Revolution, sort of like the next ice age. And that’s sobering.” More

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      What we know and don’t know about wildfire smoke’s health risks

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      Acrid smoke continues to pollute skies in the western United States. On some recent days, the air quality in Portland, Seattle, San Francisco and Los Angeles has been so hazardous, it’s ranked among the worst in the world. 
      It’s hard to predict when the smoke will fully clear. And with some parts of the West  having faced a week or more of extremely polluted air, the unusual, sustained nature of the assault is increasing worries about people’s health.
      There’s plenty of evidence that air pollution — a broad category that includes soot, smog, and other pollutants from sources such as traffic, industry and fires — can harm health. The list of medical ailments associated with exposure to dirty air includes respiratory diseases, cardiovascular disease and diabetes (SN: 9/19/17).
      Most of what’s known about the hazards of wildfire smoke has to do with particulate matter, the tiny bits of solids and liquids in polluted air. Wildfires are especially good at producing particles in a size range that can be dangerous to health. It isn’t clear yet if what fuels wildfire smoke — be it vegetation, a mix of trees and structures, or other human-made sources — affects the toxicity of particulate matter.
      A growing body of evidence points to a range of risks to health during or soon after wildfires, such as increased trips to the emergency room for chronic lung conditions. But there are many more questions than answers about the long-term risks for people struggling to cope with day upon day of polluted air, and facing longer and fiercer fire seasons each year due to climate change (SN: 8/27/20).
      Science News spoke with scientists about what’s in the air, the health risks and what more we need to learn.
      What’s in wildfire smoke?
      Wildfire smoke is a complex mixture of gases and particles that is similar to cigarette smoke but without the nicotine, says physician John Balmes of the University of California, San Francisco, who studies the effects of air pollution on health. “It has the same kind of mixture of nasty small particles and irritant gases.”
      The precise chemical makeup of the smoke varies by fire. It depends on “the type of fuel burned — including structures, intensity of the fire, atmospheric mixing, and distance or age of smoke,” says Tania Busch Isaksen, who studies public health effects of wildfire smoke at the University of Washington in Seattle.
      “Generally speaking, it’s a mixture of carbon dioxide, carbon monoxide, nitrogen oxides, particle matter — fine to coarse — hydrocarbons and other organic compounds,” she says. “Fine particulate matter, PM2.5, is what we are primarily concerned about when we consider impacts on health” (SN: 7/30/20).
      Those particles are 2.5 micrometers across or smaller, or about one-thirtieth the width of a human hair (SN: 8/22/18). Common in air pollution produced not only by wildfires, but also by power plants and cars, these particles are so tiny that they can be inhaled deeply into the lungs. There, they can trigger inflammation and possibly seep into the bloodstream.
      Can you see how much PM2.5 is in the air?
      No. These particles are so tiny and difficult to see that “even if the air seems clear, PM2.5 could be at levels that are dangerous,” says Perry Hystad, an environmental epidemiologist at Oregon State University in Corvallis. In the United States, the most reliable gauge of PM2.5 is the Air Quality Index, or AQI, which is based on data from air quality monitoring stations that measure the concentrations of pollutants in the air.
      The U.S. Environmental Protection Agency developed the index to grade levels of common air pollutants, such as ozone, PM2.5  and carbon monoxide. On a scale from 0 to 500, higher numbers indicate dirtier air. The EPA assigns AQI scores to different types of pollution based on studies of each contaminant’s health effects.
      The EPA considers scores up to 100 — indicating an average 35.4 micrograms of particulate matter per cubic meter of air over 24 hours  — generally safe. Scores from 101 to 200 may pose particular risk to people in sensitive groups, such as children and those with heart or lung diseases. Those people are advised to limit or avoid prolonged or vigorous outdoor activity. Above 200, everyone should cut down on physical activity outside. At scores 300 or above, with at least 250.4 micrograms of PM2.5 per cubic meter of air, everyone should avoid going outside.
      Smoke blanketing the western United States has created hazardous, and at times off-the-chart, levels of pollution in many places. For instance, on the morning of September 17, areas of Oregon near Portland showed PM2.5 AQI levels up to around a hazardous 380. In regions of central California northeast of Fresno, AQI levels reached a staggering 780.
      “Especially under conditions that we’re experiencing here in the western United States, it would be wise to check the AQI on a daily basis,” says Kent Pinkerton, a biologist at University of California, Davis.

      What happens when people breathe in wildfire smoke?
      “Wildfires, through the combustion process, create lots and lots of particles” in the size range of PM2.5, says Colleen Reid, an environmental epidemiologist and health geographer at the University of Colorado Boulder. A breath of these microscopic particles can send them all the way to the alveoli, the tiny sacs where the lungs and the blood swap oxygen and carbon dioxide.
      Research in lab dishes has found that the particles can lead to inflammation and oxidative stress, in which reactive molecules that contain oxygen build up and can damage cells. The smallest pollution particles may make their way into the bloodstream, possibly causing harm to the cardiovascular system.
      The research linking PM2.5 with health generally does not consider what types of materials are burning, so “at this point we are concerned about all PM2.5 regardless of source,” says Anthony Wexler, who studies particulate pollutants at the University of California, Davis. “But the source is likely important.”
      Historically, wildfires have burned mostly plant matter. But many of the recent devastating fires in the western U.S., such as the Camp Fire that destroyed the town of Paradise, Calif., in 2018, have devoured human-made structures (SN: 11/15/18). “Houses have paint and solvents and plastics and all this other terrible stuff going up in smoke, too, which may be increasing the toxicity of the material that’s being emitted,” says Wexler. He is currently preparing an experiment to compare the toxicity of the smoke from burnt household materials with that from woody materials.
      The impact of extended exposures to wildfire smoke also needs more research. Wildfires put a lot of pollution into the air, more than what’s generally produced from industrial and traffic sources, Reid says. But it’s often for a short period of time. “What’s going on right now in Oregon and Washington and California, where they’ve had essentially a week of very unhealthy levels of air pollution, is less common,” she says.
      Recent fires in the western United States have consumed not only trees but many buildings like this one, in Butte County, Calif., which went up in flames on September 9. Some researchers are concerned that plastics and other materials in homes may make smoke more toxic.Noah Berger/Associated Press
      What are the immediate health risks from wildfire smoke?
      Breathing in smoky air can irritate the respiratory tract, leading to coughing, sore throats and itchy, watery eyes. The foul air can also cause headaches and fatigue.
      Hospital visits for lung care go up during wildfires compared to periods without them, according to studies of emergency department traffic. For instance, an increase in PM2.5 exposure related to wildfires in northern California in 2008 was associated with an increase in risk for emergency department visits and hospitalizations for asthma, Reid and colleagues reported in Environmental Research in 2016. The 2012 wildfires in Colorado were linked to a rise in emergency department visits for asthma and chronic obstructive pulmonary disease, according to a 2016 study in Environmental Health. There’s some evidence of increased trips to the hospital for cardiovascular health problems during wildfires as well.
      Medical visits for kids go up during wildfires too. During the 2017 Lilac Fire in San Diego county, visits for respiratory problems to a children’s hospital rose due to increased exposure to PM2.5, according to a 2020 study in the Annals of the American Thoracic Society.
      Children, especially the very young and those with diseases like asthma, can be more vulnerable to health effects from wildfires. “They breathe more air per minute compared to adults” to meet their physiological needs, says Marissa Hauptman, a pediatrician at Boston Children’s Hospital. That can add up to more exposure. And developing lungs “are more susceptible to injury,” she says. 
      A developing fetus may also be at risk from exposure to PM2.5. In a 2012 study in Environmental Health Perspectives, Reid and colleagues reported a slight decrease in birth weight for infants from pregnancies that occurred during the 2003 wildfires in Southern California. Mothers exposed to smoke from Colorado wildfires during the second trimester were more likely to give birth prematurely, according to a 2019 study in the International Journal of Environmental Research and Public Health. Infants born early or smaller than usual can face developmental delays.
      What’s known about long-term health risks from wildfire smoke?
      Not much. But a few studies provide some initial clues.
      One examined how wildfires that scorched large areas of Indonesia in 1997 impacted health 10 years later. This population-wide study found that males and the elderly were worse off in 2007 for health measures such as lung function, the researchers reported in Economics & Human Biology in 2017.
      In the United States, the wildfire smoke that plagued the Seeley Lake community in Montana in 2017 has parallels to the prolonged, hazardous exposures happening now in the West. The wildfires produced extremely high levels of PM2.5 from July 31 to September 18 that year; the daily average was 221 micrograms per cubic meter of air. Christopher Migliaccio, a respiratory immunology researcher at the University of Montana in Missoula, and his colleagues screened adults in the community right after the last day of increased smoke and two more times in each of the following two years.
      Compared with members of a Montana community that hadn’t been exposed to the same levels of smoke, the participants from the Seeley Lake area had poorer lung function one and two years out, Migliaccio and his colleagues reported in Toxics in August. “I thought people might be worse right after,” he says, “but it’s a little bit of a delayed response.”
      Migliaccio and colleagues had planned to screen the participants again this year, but COVID-19 got in the way. Eventually they hope to see whether, in participants that still have worse lung function, the condition is treatable or if it’s “the new normal.”
      Can a mask protect you from wildfire smoke?
      It depends on the type of mask. “Cloth masks, which are effective at preventing transmission of SARS-CoV-2 [the virus that causes COVID-19] … don’t do anything to protect the wearer from exposure to wildfire smoke,” Balmes says (SN: 6/26/20). Surgical masks provide some protection. But “an N95 is the best protection.” N95 masks are designed to filter out at least 95 percent of airborne particles.
      But N95 masks are in short supply, and those masks have not been certified for use by children as they don’t fit properly. So the best protection is to avoid exposure. “People should stay indoors as much as possible with the windows closed,” Balmes says.

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      How can people keep indoor air clean?
      “If they have central ventilation, they should turn that to recirculation,” Balmes says. That can reduce the amount of smoke that enters the home. People can also use a High Efficiency Particulate Air, or HEPA purifier to smoke-proof a single room. And those who cannot afford a HEPA cleaner can put together a makeshift purifier using a MERV-13 furnace filter and a box fan, Balmes says. “They’re not as good as the proper devices, but they do provide some protection.”
      People hunkered down indoors can also keep the air clear by not burning gas stoves or candles, or even vacuuming — which can stir up particles inside the home.
      But some people don’t have a home to escape to. King County in Washington announced on September 11 the opening of a clean air shelter for people experiencing homelessness.
      How else might wildfires be harming health?
      The toll that the wildfires have on mental health could also be significant. The past month in the Pacific Northwest has brought images reminiscent of a science fiction novel: hazy, deep orange skies that sometimes completely obscured the sun, turning day to night.
      Extreme wildfires, with the potential for long periods of time in which the air is a danger, can upend people’s lives and add to stress levels. One of the few respites to the COVID-19 pandemic — going out for a breath of fresh air — has been shut off for millions of people. And there are many that have no choice but to work or live outdoors, exposed to hazardous air. “There could be a psychological impact of that,” says Reid. “That needs to be explored.” More

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      Underwater earthquakes’ sound waves reveal changes in ocean warming

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      Sound waves traveling thousands of kilometers through the ocean may help scientists monitor climate change.
      As greenhouse gas emissions warm the planet, the ocean is absorbing vast amounts of that heat. To monitor the change, a global fleet of about 4,000 devices called Argo floats is collecting temperature data from the ocean’s upper 2,000 meters. But that data collection is scanty in some regions, including deeper reaches of the ocean and areas under sea ice.
      So Wenbo Wu, a seismologist at Caltech, and colleagues are resurfacing a decades-old idea: using the speed of sound in seawater to estimate ocean temperatures. In a new study, Wu’s team developed and tested a way to use earthquake-generated sound waves traveling across the East Indian Ocean to estimate temperature changes in those waters from 2005 to 2016.
      Comparing that data with similar information from Argo floats and computer models showed that the new results matched well. That finding suggests that the technique, dubbed seismic ocean thermometry, holds promise for tracking the impact of climate change on less well-studied ocean regions, the researchers report in the Sept. 18 Science.

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      Sound waves are carried through water by the vibration of water molecules, and at higher temperatures, those molecules vibrate more easily. As a result, the waves travel a bit faster when the water is warmer. But those changes are so small that, to be measurable, researchers need to track the waves over very long distances.
      Fortunately, sound waves can travel great distances through the ocean, thanks to a curious phenomenon known as the SOFAR Channel, short for Sound Fixing and Ranging. Formed by different salinity and temperature layers within the water, the SOFAR channel is a horizontal layer that acts as a wave guide, guiding sound waves in much the same way that optical fibers guide light waves, Wu says. The waves bounce back and forth against the upper and lower boundaries of the channel, but can continue on their way, virtually unaltered, for tens of thousands of kilometers (SN: 7/16/60).
      In 1979, physical oceanographers Walter Munk, then at the Scripps Institution of Oceanography in La Jolla, Calif., and Carl Wunsch, now an emeritus professor at both MIT and Harvard University, came up with a plan to use these ocean properties to measure water temperatures from surface to seafloor, a technique they called “ocean acoustic tomography.” They would transmit sound signals through the SOFAR Channel and measure the time that it took for the waves to arrive at receivers located 10,000 kilometers away. In this way, the researchers hoped to compile a global database of ocean temperatures (SN: 1/26/1991).
      But environmental groups lobbied against and ultimately halted the experiment, stating that the human-made signals might have adverse effects on marine mammals, as Wunsch notes in a commentary in the same issue of Science.
      Forty years later, scientists have determined that the ocean is in fact a very noisy place, and that the proposed human-made signals would have been faint compared with the rumbles of quakes, the belches of undersea volcanoes and the groans of colliding icebergs, says seismologist Emile Okal of Northwestern University in Evanston, Ill., who was not involved in the new study.
      Still, Wu and colleagues have devised a work-around that sidesteps any environmental concerns: Rather than use human-made signals, they employ earthquakes. When an undersea earthquake rumbles, it releases energy as seismic waves known as P waves and S waves that vibrate through the seafloor. Some of that energy enters the water, and when it does, the seismic waves slow down, becoming T waves.
      Those T waves can also travel along the SOFAR Channel. So, to track changes in ocean temperature, Wu and colleagues identified “repeaters” — earthquakes that the team determined to originate from the same location, but occurring at different times. The East Indian Ocean, Wu says, was chosen for this proof-of-concept study largely because it’s very seismically active, offering an abundance of such earthquakes. After identifying over 2,000 repeaters from 2005 to 2016, the team then measured differences in the sound waves’ travel time across the East Indian Ocean, a span of some 3,000 kilometers. 
      The data revealed a slight warming trend in the waters, of about 0.044 degrees Celsius per decade. That trend is similar to, though a bit faster than, the one indicated by real-time temperatures collected by Argo floats. Wu says the team next plans to test the technique with receivers that are farther away, including off of Australia’s west coast.
      That extra distance will be important to prove that the new method works, Okal says. “It’s a fascinating study,” he says, but the distances involved are very short as far as T waves go, and the temperature changes being estimated are very small. That means that any uncertainty in matching the precise origins of two repeater quakes could translate to uncertainty in the travel times, and thus the temperature changes. But future studies over greater distances could help mitigate this concern, he says.
      The new study is “really breaking new ground,” says Frederik Simons, a geophysicist at Princeton University, who was not involved in the research. “They’ve really worked out a good way to tease out very subtle, slow temporal changes. It’s technically really savvy.”
      And, Simons adds, in many locations seismic records are decades older than the temperature records collected by Argo floats. That means that scientists may be able to use seismic ocean thermometry to come up with new estimates of past ocean temperatures. “The hunt will be on for high-quality archival records.” More

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      This moth may outsmart smog by learning to like pollution-altered aromas

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      Pollution can play havoc with pollinators’ favorite flower smells. But one kind of moth can learn how to take to an unfamiliar new scent like, well, a moth to a flame.
      Floral aromas help pollinators locate their favorite plants. Scientists have established that air pollutants scramble those fragrances, throwing off the tracking abilities of such beneficial insects as honeybees (SN: 4/24/08). But new lab experiments demonstrate that one pollinator, the tobacco hawkmoth (Manduca sexta), can quickly learn that a pollution-altered scent comes from the jasmine tobacco flower (Nicotiana alata) that the insect likes.
      That ability may imply that the moth can find food and pollinate plants, including crucial crops, despite some air pollution, researchers report September 2 in the Journal of Chemical Ecology. Scientists already knew that some pollinators can learn new smells, but this is the first study to demonstrate an insect overcoming pollution’s effects on odors.
      Chemical ecologist Markus Knaden and colleagues focused on one pollutant — ozone, the main ingredient in smog. Ozone reacts with flower aroma molecules, changing their chemical structure and therefore their fragrance.

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      In Knaden’s lab at the Max Planck Institute for Chemical Ecology in Jena, Germany, his team blew an ozone-altered N. alata scent from a tiny tube into a refrigerator-sized plexiglass tunnel, with a moth awaiting at the far end of the tunnel. Usually, when the moth smells the unaltered floral fragrance, it flies upwind and uses its long, skinny mouthparts to probe the tube the way that it would a blossom.
      The researchers expected that the modified scent might throw the moth off a little. But the insect wasn’t attracted at all to a flower aroma exposed to levels of ozone that are typical on some hot, sunny days.
      In addition to scent, tobacco hawkmoths track flowers visually, so Knaden’s team used that trait, along with a sweet snack, to train the moth to be attracted to a pollution-altered scent. The researchers wrapped a brightly-colored artificial flower around the tube to lure the moth back across the tunnel, despite the unfamiliar aroma. And the team added sugar water to the artificial flower. After a moth was given four minutes to taste the sweet stuff, it was attracted to the new smell when sent into the tunnel 15 minutes later, even when neither the sugar water nor the visual cue of the artificial flower was present. 
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      In the lab, researchers showed that tobacco hawkmoths can learn to drink from a fake flower whose scent has been scrambled by pollution. To train the moths to accept the altered scent, a visual cue — dressing up a tube emitting a fouled bouquet as an artificial flower — attracts the moth, and a sugar-water reward teaches the insect that it’s worth a return trip.
      Still, in an ozone-polluted environment in the wild, tobacco hawkmoths would have to be close enough to a tobacco flower to see it to learn its altered scent, and Knaden isn’t sure how often that will occur. The moths are difficult to observe in nature because they feed at twilight and are fast flyers.
      “This study is a clarion call to other scientists” to examine whether and how different pollinators might also adapt to human-driven changes to their environment, says chemical ecologist Shannon Olsson of the Tata Institute of Fundamental Research in Bangalore, India, who wasn’t involved with the work.
      Although the results suggest that some adaptation by insects to pollution is possible, Knaden is cautious about being too optimistic. “I don’t want the take-home message to be that pollution is not a problem,” he says. “Pollution is a problem.”
      This study focused on only one moth species, but Knaden’s team is now working on planning experiments with other pollinators that are easier to follow than tobacco hawkmoths. While he suspects honeybees might also be as adaptable as the moth was, that won’t be true of every pollinator. “The situation can become very bad for insects that are not as clever or cannot see that well.” More

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      New maps show how warm water may reach Thwaites Glacier’s icy underbelly

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      New seafloor maps reveal the first clear view of a system of channels that may be helping to hasten the demise of West Antarctica’s vulnerable Thwaites Glacier. The channels are deeper and more complex than previously thought, and may be funneling warm ocean water all the way to the underside of the glacier, melting it from below, the researchers found.
      Scientists estimate that meltwater from Florida-sized Thwaites Glacier is currently responsible for about 4 percent of global sea level rise (SN: 1/7/20). A complete collapse of the glacier, which some researchers estimate could happen within the next few decades, could increase sea levels by about 65 centimeters. How and when that collapse might occur is the subject of a five-year international collaborative research effort.
      Glaciers like Thwaites are held back from sliding seaward both by buttressing ice shelves — tongues of floating ice that jut out into the sea — and by the shape of the seafloor itself, which can help pin the glacier’s ice in place (SN: 4/3/18). But in two new studies, published online September 9 in The Cryosphere, the researchers show how the relatively warm ocean waters may have a pathway straight to the glacier’s underbelly.
      Channels carved into the seafloor, extending several kilometers wide and hundreds of meters deep, may act as pathways (red line with yellow arrows as seen in this 3-D illustration) to bring relatively warm ocean waters to the edges of vulnerable Thwaites Glacier, hastening its melting.International Thwaites Glacier Collaboration
      From January to March 2019 researchers used a variety of airborne and ship-based methods — including radar, sonar and gravity measurements — to examine the seafloor around the glacier and two neighboring ice shelves. From those data, the team was able to estimate how the seafloor is shaped beneath the ice itself.
      These efforts revealed a rugged series of high ridges and deep troughs on the seafloor, varying between about 250 meters and 1,000 meters deep. In particular, one major channel, more than 800 meters deep, could be funneling warm water all the way from Pine Island Bay to the submerged edge of the glacier, the team found.

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      Bering Sea winter ice shrank to its lowest level in 5,500 years in 2018

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      Sea ice in the Bering Sea, on the southern margin of the Arctic Ocean, dwindled to its smallest wintertime expanse in 5,500 years in 2018, new data show.  
      Summertime sea ice loss due to climate change has captured headlines, but winter ice in the region has also shown recent signs of decline. In both February 2018 and February 2019, the extent was 60 to 70 percent lower than the average February-to-May extent from 1979 to 2017. However, researchers thought that those declines might be linked to unusual short-term atmospheric conditions.
      Instead, the new study suggests that human-caused climate change is also helping to shrink Bering Sea ice during the winter. The findings, by geologist Miriam Jones of the U.S. Geological Survey in Reston, Va., and colleagues, were published September 2 in Science Advances.
      Jones and her team collected cores of peat from St. Matthew Island, a remote spot in the Bering Sea west of Alaska. Within the peat — packed remains of partially decomposed plants — oxygen-bearing organic compounds called cellulose contain clues to the climate history of the region.

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      Rain falling on the island contains two different isotopes, or forms, of oxygen: oxygen-18 and oxygen-16. The relative values of those isotopes in the rainfall change depending on atmospheric conditions, and as plants take up that oxygen from the air, they record those changes. By analyzing the amounts of those isotopes in the cellulose over time, the team was able to track changes in precipitation and atmospheric circulation going back 5,500 years.
      Then, the team established the link between this oxygen isotope record and sea ice extent.
      Bering Sea ice is known to be directly tied to shifts in wind direction. So the researchers created a computer simulation that included climate conditions from 1979 to 2018, oxygen isotope values from cellulose during that time and satellite observations of sea ice. When winds were strongly blowing from the south, and there was less sea ice, the relative amount of oxygen-18 increased. When winds from the north dominated, and there was more sea ice, there was less oxygen-18 in the cellulose.
      Next, the researchers used the oxygen isotopes in the peat to track the waxing and waning of the region’s sea ice over thousands of years. Most of the area’s rainfall occurs in winter and spring, so those oxygen isotopes are indicative of conditions between February and May, rather than summer. The peat cellulose oxygen-18 values recorded in winter 2018 were the highest, and the sea ice extent the smallest, in the last 5,500 years, the team found. 

      In preindustrial times, the researchers found, wintertime sea ice was gradually decreasing, largely due to natural changes in incoming sunlight during winter, related to changes in Earth’s orbit. But the team also found that atmospheric carbon dioxide concentrations, compiled from previous studies, were closely correlated to ice volume. As CO2 levels began to climb past 280 parts per million following the onset of the Industrial Revolution in the mid-1700s, the oxygen-18 values also began to rise, with corresponding sea ice decreases.
      How exactly increasing CO2 might be linked to winter ice volume is less clear. The losses may be directly due to greenhouse gas warming. Or more indirectly, changes to atmospheric circulation patterns due to increasing CO2 might also lead to those losses.
      The study demonstrates just how exceptional the recent winter sea ice losses in the region are, says Benjamin Gaglioti, an environmental scientist at the University of Alaska Fairbanks who was not involved in the study. “Although there [was] an overall trend towards less sea ice prior to anthropogenic warming, recent increases in human-derived greenhouse gases have enhanced this trend,” he says. And that is not good news for the region’s denizens.
      “Winter sea ice in this region serves as a critical habitat for unique marine wildlife like Pacific walrus and kittiwakes,” Gaglioti says. The ice also helps dampen the impacts of intense winter storms and flooding on coastal communities, he adds.
      Climate change due to CO2 and other climate-warming gases has already taken a visible toll on summertime sea ice in and around the Arctic; within 10 to 15 years, the region may be ice-free during the warmer months. Arctic sea ice in September 2019 tied for second-lowest on record with 2007 and 2016; first place still goes to 2012 (SN: 9/25/19). The loss of that ice is not just a bellwether for climate change in the Arctic, but is also speeding up the rate of warming in the region, a process called Arctic amplification (SN: 7/1/20). And the missing summer ice is also triggering a cascade of changes through Arctic ecosystems, including within the Bering Sea (SN: 3/14/19).
      But the new study suggests that winter sea ice losses might lag behind CO2 changes by decades, perhaps even a century — and that could mean a year-round ice-free Bering Sea by 2100. More