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    How AI can help forecast how much Arctic sea ice will shrink

    In the next week or so, the sea ice floating atop the Arctic Ocean will shrink to its smallest size this year, as summer-warmed waters eat away at the ice’s submerged edges.

    Record lows for sea ice levels will probably not be broken this year, scientists say. In 2020, the ice covered 3.74 million square kilometers of the Arctic at its lowest point, coming nail-bitingly close to an all-time record low. Currently, sea ice is present in just under 5 million square kilometers of Arctic waters, putting it on track to become the 10th-lowest extent of sea ice in the area since satellite record keeping began in 1979. It’s an unexpected finish considering that in early summer, sea ice hit a record low for that time of year.

    The surprise comes in part because the best current statistical- and physics-based forecasting tools can closely predict sea ice extent only a few weeks in advance, but the accuracy of long-range forecasts falters. Now, a new tool that uses artificial intelligence to create sea ice forecasts promises to boost their accuracy — and can do the analysis relatively quickly, researchers report August 26 in Nature Communications.

    IceNet, a sea ice forecasting system developed by the British Antarctic Survey, or BAS, is “95 percent accurate in forecasting sea ice two months ahead — higher than the leading physics-based model SEAS5 — while running 2,000 times faster,” says Tom Andersson, a data scientist with BAS’s Artificial Intelligence lab. Whereas SEAS5 takes about six hours on a supercomputer to produce a forecast, IceNet can do the same in less than 10 seconds on a laptop. The system also shows a surprising ability to predict anomalous ice events — unusual highs or lows — up to four months in advance, Andersson and his colleagues found.

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    Tracking sea ice is crucial to keeping tabs on the impacts of climate change. While that’s more of a long game, the advanced notice provided by IceNet could have more immediate benefits, too. For instance, it could give scientists the lead time needed to assess, and plan for, the risks of Arctic fires or wildlife-human conflicts, and it could provide data that Indigenous communities need to make economic and environmental decisions.

    Arctic sea ice extent has steadily declined in all seasons since satellite records began in 1979 (SN: 9/25/19). Scientists have been trying to improve sea ice forecasts for decades, but success has proved elusive. “Forecasting sea ice is really hard because sea ice interacts in complex ways with the atmosphere above and ocean below,” Andersson says.

    [embedded content]
    In 2020, the sea ice in the Arctic shrank to its second lowest extent since satellite monitoring began in 1979. This animation uses those observations to show the change in sea ice coverage from March 5, when the ice was at its maximum, through September 15, when the ice reached its lowest point. The yellow line represents the average minimum extent from 1981 to 2010. Current forecasting tools can accurately predict these changes weeks in advance. A new AI-based tool can predict these changes with nearly 95 percent accuracy several months in advance.

    Existing forecast tools put the laws of physics into computer code to predict how sea ice will change in the future. But partly due to uncertainties in the physical systems governing sea ice, these models struggle to produce accurate long-range forecasts.

    Using a process called deep learning, Andersson and his colleagues loaded observational sea ice data from 1979 to 2011 and climate simulations covering 1850 to 2100 to train IceNet how to predict the state of future sea ice by processing the data from the past.

    To determine the accuracy of its forecasts, the team compared IceNet’s outputs to the observed sea ice extent from 2012 to 2020, and to the forecasts made by SEAS5, the widely cited tool used by the European Centre for Medium-Range Weather Forecasts. IceNet was as much as 2.9 percent more accurate than SEAS5, corresponding to a further 360,000 square kilometers of ocean being correctly labeled as “ice” or “no ice.”

    What’s more, in 2012, a sudden crash in summer sea ice extent heralded a new record low extent in September of that year. In running through past data, IceNet saw the dip coming months in advance. SEAS5 had inklings too but its projections that far out were off by a few hundred thousand square kilometers.

    “This is a significant step forward in sea ice forecasting, boosting our ability to produce accurate forecasts that were typically not thought possible and run them thousands of times faster,” says Andersson. He believes it’s possible that IceNet has better learned the physical processes that determine the evolution of sea ice from the training data while physics-based models still struggle to understand this information.

    “These machine learning techniques have only begun contributing to [forecasting] in the last couple years, and they’ve been doing amazingly well,” says Uma Bhatt, an atmospheric scientist at the University of Alaska Fairbanks Geophysical Institute who was not involved in the new study. She also leads the Sea Ice Prediction Network, a group of multidisciplinary scientists working to improve forecasting.

    Bhatt says that good seasonal ice forecasts are important for assessing the risk of Arctic wildfires, which are tied strongly to the presence of sea ice (SN: 6/23/20). “Knowing where the sea ice is going to be in the spring could potentially help you figure out where you’re likely to have fires — in Siberia, for example, as soon as the sea ice moves away from the shore, the land can warm up very quickly and help set the stage for a bad fire season.”

    Any improvement in sea ice forecasting can also help economic, safety and environmental planning in northern and Indigenous communities. For example, tens of thousands of walruses haul out on land to rest when the sea ice disappears (SN: 10/2/14). Human disturbances can trigger deadly stampedes and lead to high walrus mortality. With seasonal ice forecasts, biologists can anticipate rapid ice loss and manage haul-out sites in advance by limiting human access to those locations.

    Still, limitations remain. At four months of lead time, the system was about 91 percent accurate in predicting the location of September’s ice edge.IceNet, like other forecasting systems, struggles to produce accurate long-range forecasts for late summer due, in part, to what scientists call the “spring predictability barrier.” It’s crucial to know the condition of the sea ice at the start of the spring melting season to be able to forecast end-of-summer conditions.

    Another limit is “the fact that the weather is so variable,” says Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colo. Though sea ice seemed primed to set a new annual record low at the start of July, the speed of ice loss ultimately slowed due to cool atmospheric temperatures. “We know that sea ice responds very strongly to summer weather patterns, but we can’t get good weather predictions. Weather predictability is about 10 days in advance.” More

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    Clouds affected by wildfire smoke may produce less rain

    When smoke rises from wildfires in the western United States, it pummels clouds with tiny airborne particles. What happens next with these clouds has been largely unstudied. But during the 2018 wildfire season, researchers embarked on a series of seven research flights, including over the Pacific Northwest, to help fill this gap.

    Using airborne instruments to analyze small cumulus clouds affected by the smoke, the scientists found that these clouds contained, on average, five times as many water droplets as unaffected clouds. That in itself was not a huge surprise; it’s known that organic and inorganic particles in smoke can serve as tiny nuclei for forming droplets (SN: 12/15/20). But the sheer abundance of droplets in the affected clouds astounded the team. 

    Counterintuitively, those numerous droplets didn’t make the clouds more likely to produce rain. In fact, the opposite occurred. Because the droplets were about half as big as those found in a typical cloud, they were unlikely to collide and merge with enough other droplets to result in rain. The chances of rain were “virtually zero,” the researchers write in the August Geophysical Research Letters.

    The new research suggests that wildfires could lead to clouds producing less rain in the U.S. West, feeding into drought conditions and potentially increasing future wildfire risk.

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    But the environmental dynamics involved are complex, says Cynthia Twohy. She’s a San Diego–based atmospheric scientist at NorthWest Research Associates, a research organization specializing in geophysical and space sciences headquartered in Redmond, Wash. For instance, Twohy and her colleagues found that “the ratio of light-absorbing to light-scattering particles in the smoke was somewhat lower than measured in many prior studies,” she says.  

    “The take-home message is that while other studies have shown wildfire smoke has an absorbing (warming) influence that can be important for cloud formation and development, these impacts may be less in the western U.S., because the smoke is not as dark,” Twohy says. The impact of the lighter smoke is still an open question. “It’s just another way that smoke-cloud interactions are a wild card in the region.”  

    The team used onboard probes to sample clouds affected by wildfire smoke and compare them to their more pristine counterparts. The probes measured how many cloud droplets were present in the samples, the size range of those droplets and the liquid water content of the clouds.

    A special tube mounted on the exterior of the plane to collect and evaporate cloud droplets was used to “reveal the particles that the droplets were condensed on,” says Robert Yokelson, an atmospheric chemist at the University of Montana in Missoula who was not involved with the research. This process enabled the researchers to confirm what the original smoke particles were made of, a technique that Yokelson calls “neat.”

    The analysis detected the amounts of carbon, oxygen, nitrogen, sulfur and potassium found in residual particles evaporated from cloud droplets. These elements were present in similar amounts to those found in smoke particles sampled from below the clouds, “implying that the cloud droplets also formed on smoke particles,” Twohy says.

    Previous studies conducted in the Amazon have shown that “smoke will make the cloud droplets smaller and more numerous,” thereby reducing rainfall, Yokelson says. But this study provides robust evidence that the phenomenon isn’t isolated to the Amazon. It echoes the results of a much smaller 1974 study of smoke-filled clouds over the western United States, providing a crucial present-day snapshot of the challenges facing the region.

    Wildfires in the western United States have been breaking records in recent years — increasing in number and size due to climate change — a trend that scientists think will get worse as the globe continues to warm (SN: 12/21/20). As a result, Twohy says, it’s increasingly important that researchers continue to monitor these fires’ influence on the atmosphere. More

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    Greece’s Santorini volcano erupts more often when sea level drops

    When sea level drops far below the present-day level, the island volcano Santorini in Greece gets ready to rumble.

    A comparison of the activity of the volcano, which is now partially collapsed, with sea levels over the last 360,000 years reveals that when the sea level dips more than 40 meters below the present-day level, it triggers a fit of eruptions. During times of higher sea level, the volcano is quiet, researchers report online August 2 in Nature Geoscience.

    Other volcanoes around the globe are probably similarly influenced by sea levels, the researchers say. Most of the world’s volcanic systems are in or near oceans.

    “It’s hard to see why a coastal or island volcano would not be affected by sea level,” says Iain Stewart, a geoscientist at the Royal Scientific Society of Jordan in Amman, who was not involved in the work. Accounting for these effects could make volcano hazard forecasting more accurate.

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    Santorini consists of a ring of islands surrounding the central tip of a volcano poking out of the Aegean Sea. The entire volcano used to be above water, but a violent eruption around 1600 B.C. caused the volcano to cave in partially, forming a lagoon. That particular eruption is famous for potentially dooming the Minoan civilization and inspiring the legend of the lost city of Atlantis (SN: 2/1/12).

    To investigate how sea level might influence the volcano, researchers created a computer simulation of Santorini’s magma chamber, which sits about four kilometers beneath the surface of the volcano. In the simulation, when the sea level dropped at least 40 meters below the present-day level, the crust above the magma chamber splintered. “That gives an opportunity for the magma that’s stored under the volcano to move up through these fractures and make its way to the surface,” says study coauthor Christopher Satow, a physical geographer at Oxford Brookes University in England.

    According to the simulation, it should take about 13,000 years for those cracks to reach the surface and awaken the volcano. After the water rises again, it should take about 11,000 years for the cracks to close and eruptions to stop.

    When the sea drops at least 40 meters below the present-day level, the crust beneath the Santorini volcano (illustrated) starts to crack. As the sea level drops even further over thousands of years, those cracks spread to the surface, bringing up magma that feeds volcanic eruptions.Oxford Brookes University

    It may seem counterintuitive that lowering the amount of water atop the magma chamber would cause the crust to splinter. Satow compares the scenario to wrapping your hands around an inflated balloon, where the rubber is Earth’s crust and your hands’ inward pressure is the weight of the ocean. As someone else pumps air into the balloon — like magma building up under Earth’s crust — the pressure of your hands helps prevent the balloon from popping. “As soon as you start to release the pressure with your hands, [like] taking the sea level down, the balloon starts to expand,” Satow says, and ultimately the balloon breaks.

    Satow’s team tested the predictions of the simulation by comparing the Santorini Volcano’s eruption history — preserved in the rock layers of the islands surrounding the central volcano tip — with evidence of past sea levels from marine sediments. All but three of the volcano’s 211 well-dated eruptions in the last 360,000 years happened during periods of low sea level, as the simulation predicted. Such periods of low sea level occurred when more of Earth’s water was locked up in glaciers during ice ages.

    “It’s really intriguing and interesting, and perhaps not surprising, given that other studies have shown that volcanoes are sensitive to changes in their stress state,” says Emilie Hooft, a geophysicist at the University of Oregon in Eugene, who wasn’t involved in the work. Volcanoes in Iceland, for instance, have shown an uptick in eruptions after overlying glaciers have melted, relieving the volcanic systems of the weight of the ice.

    Volcanoes around the world are likely subject to the effects of sea level, Satow says, though how much probably varies. “Some will be very sensitive to sea level changes, and for others there will be almost no impact at all.” These effects will depend on the depth of the magma chambers feeding into each volcano and the properties of the surrounding crust.

    But if sea level controls the activity of any volcano in or near the ocean, at least to an extent, “you’d expect all these volcanoes to be in sync with one another,” Satow says, “which would be incredible.”

    As for Santorini, given that the last time sea level was 40 meters below the present-day level was about 11,000 years ago — and sea level is continuing to rise due to climate change — Satow’s team expects the volcano to enter a period of relative quiet right about now (SN: 3/14/12). But two major eruptions in the volcano’s history did happen amid high sea levels, the researchers say, so future violent eruptions aren’t completely off the table. More

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    A new book uses stories from tsunami survivors to decode deadly waves

    TsunamiJames Goff and Walter DudleyOxford Univ., $34.95

    On March 27, 1964, Ted Pederson was helping load oil onto a tanker in Seward, Alaska, when a magnitude 9.2 quake struck. Within seconds, the waterfront began sliding into the bay. As Pederson ran up the dock toward shore, a tsunami lifted the tanker and rafts of debris onto the dock, knocking him unconscious.

    Pederson survived, but more than 100 others in Alaska did not. His story is just one of more than 400 harrowing eyewitness accounts that bring such disasters to life in Tsunami. Written by geologist James Goff and oceanographer Walter Dudley, the book also weaves in accounts from researchers examining the geologic record to shed light on prehistoric tsunamis.

    Chapter by chapter, Goff and Dudley offer readers a primer on tsunamis: Most are caused by undersea earthquakes, but some are triggered by landslides, the sudden collapse of volcanic islands or meteorites hitting the ocean (SN: 3/6/04, p. 152). Readers may be surprised to learn that tsunamis need not occur on the coast: Lake Tahoe (SN: 6/10/00, p. 378) and New Zealand’s Lake Tarawera are just two of many inland locales mentioned that have experienced freshwater tsunamis.

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    Copiously illustrated and peppered with maps, the book takes readers on a world-spanning tour of ancient and recent tsunamis, from a deep-ocean impact off the coast of South America about 2.5 million years ago to numerous tsunamis of the 21st century. The authors’ somber treatment of the Indian Ocean tsunami of December 2004 stands out (SN: 1/8/05, p. 19). Triggered by a magnitude 9.1 earthquake, the megawave killed more than 130,000 people in Indonesia alone.

    The authors — Goff is a professor at the University of New South Wales in Sydney and Dudley is a researcher at the University of Hawaii at Hilo — help readers understand tsunamis’ power via descriptions of the damage they’ve wrought. For instance, the account of a huge wave in Alaska that scoured mature trees from steep slopes along fjords up to a height of 524 meters — about 100 meters taller than the Empire State Building — may leave readers stunned. But it’s the heart-thumping stories of survivors who ran to high ground, clambered up tall trees or clung to debris after washing out to sea that linger with the reader. They remind us of the human cost of living on the shore when great waves strike.

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    A spike in Arctic lightning strikes may be linked to climate change

    Climate change may be sparking more lightning in the Arctic.

    Data from a worldwide network of lightning sensors suggest that the frequency of lightning strikes in the region has shot up over the last decade, researchers report online March 22 in Geophysical Research Letters. That may be because the Arctic, historically too cold to fuel many thunderstorms, is heating up twice as fast as the rest of the world (SN: 8/2/19).

    The new analysis used observations from the World Wide Lightning Location Network, which has sensors across the globe that detect radio waves emitted by lightning bolts. Researchers tallied lightning strikes in the Arctic during the stormiest months of June, July and August from 2010 to 2020. The team counted everywhere above 65° N latitude, which cuts through the middle of Alaska, as the Arctic.

    The number of lightning strikes that the detection network precisely located in the Arctic spiked from about 35,000 in 2010 to about 240,000 in 2020. Part of that uptick in detections may have resulted from the sensor network expanding from about 40 stations to more than 60 stations over the decade.

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    And just looking at the 2010 and 2020 values alone may overstate the increase in lightning, because “there’s such variability, year to year,” and 2020 was a particularly stormy year, says Robert Holzworth, an atmospheric and space scientist at the University of Washington in Seattle. In estimating the increase in average annual lightning strikes, “I would argue that we have really good evidence that the number of strokes in the Arctic has increased by, say, 300 percent,” Holzworth says.

    That increase happened while global summertime temperatures rose from about 0.7 degrees Celsius above the 20th century average to about 0.9 degrees C above — hinting that global warming may create more favorable conditions for lightning in the Arctic.

    It makes sense that a warmer climate could generate more lightning in historically colder climes, says Sander Veraverbeke, an earth systems scientist at VU University Amsterdam who was not involved in the work. If it does, that could potentially ignite more wildfires (SN: 4/11/19). But the apparent trend in Arctic lightning strikes should be taken with a grain of salt because it covers such a short period of time and the detection network includes few observing stations at high latitudes, Veraverbeke says. “We need more stations in the high north to really accurately monitor the lightning there.” More

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    A drop in CFC emissions puts the hole in the ozone layer back on track to closing

    Good news for the ozone layer: After a recent spike in CFC-11 pollution, emissions of this ozone-destroying chemical are on the decline.
    Emissions of trichlorofluoromethane, or CFC-11, were supposed to taper off after the Montreal Protocol banned CFC-11 production in 2010 (SN: 7/7/90). But 2014 to 2017 saw an unexpected bump. About half of that illegal pollution was pegged to eastern China (SN: 5/22/19). Now, atmospheric data show that global CFC-11 emissions in 2019 were back down to the average levels seen from 2008 to 2012, and about 60 percent of that decline was due to reduced emissions in eastern China, two teams report online February 10 in Nature. 
    These findings suggest that the hole in Earth’s ozone layer is still on track to close up within the next 50 years — rather than being delayed, as it would have been if CFC-11 emissions had remained at the levels seen from 2014 to 2017 (SN: 12/14/16).
    One group analyzed the concentration of CFC-11, used to make insulating foams for buildings and household appliances, in the air above atmospheric monitoring stations around the globe. The team found that the world emitted about 52,000 metric tons of CFC-11 in 2019 — a major drop from the annual average of 69,000 metric tons from 2014 to 2018. The 2019 emissions were comparable to the average annual emissions from 2008 to 2012, Stephen Montzka, an atmospheric chemist at the U.S. National Oceanic and Atmospheric Administration in Boulder, Colo., and colleagues report.

    The new measurements imply that there has been a significant decrease in illicit CFC-11 production within the last couple of years, the researchers say, probably thanks to more rigorous regulation enforcement in China and elsewhere.
    Another group confirmed that emissions from eastern China have diminished since 2018 by analyzing air samples from Hateruma, Japan and Gosan, South Korea. The region emitted about 5,000 metric tons of CFC-11 in 2019, which was about 10,000 metric tons less than its average annual emissions from 2014 to 2017 and was similar to the 2008 to 2012 average. That analysis was led by Sunyoung Park, a geochemist at Kyungpook National University in Daegu, South Korea.

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    The recent downturn in CFC-11 pollution shows that “the Montreal Protocol is working,” says A.R. “Ravi” Ravishankara, an atmospheric scientist at Colorado State University in Fort Collins not involved in either study. When someone violates the treaty, “atmospheric sleuthing” can uncover the culprits and spur countries to take action, he says. “China clearly took action, because you can see the result of that action in the atmosphere.” 
    Montzka cautions that it might not always be so easy to point the finger at rogue emitters. “I think we got lucky this time,” he says, because atmospheric monitoring sites in Asia were able to trace the bulk of illegal emissions to eastern China and monitor the situation over several years. Many places around the world, such as in Africa and South America, lack atmospheric monitoring stations — so it’s still a mystery which countries besides China were responsible for the recent rise and fall of CFC-11 emissions. More

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    Three things to know about the disastrous flood in India

    A flash flood surged down a river in India’s Himalayan Uttarakhand state on February 7, killing at least 30 people and washing away two hydroelectric power stations.
    As rescue workers search for more than 100 people who are still missing, officials and scientists are trying to unravel the causes of the sudden flood. Did a glacier high up in the mountains collapse, releasing a huge plug of frigid meltwater that spilled into the river? Or was the culprit a landslide that then triggered an avalanche? And what, if any, link might these events have to a changing climate?
    Here are three things to know about what might have caused the disaster in Uttarakhand.
    1. One possible culprit was the sudden break of a glacier high in the mountains.
    News reports in the immediate wake of the disaster suggested that the floodwaters were caused by the sudden overflow of a glacial lake high up in the mountain, an event called a glacial lake outburst flood.
    “It’s likely too early to know what exactly happened,” says Anjal Prakash, the research director of the Bharti Institute of Public Policy at the Indian School of Business in Hyderabad. Satellite images show that a section of a glacier broke off, but how that break relates to the subsequent floods is still unknown. One possibility is that the glacier was holding back a lake of meltwater, and that heavy snowfall in the region two days earlier added enough volume to the lake that the water forced its way out, breaking the glacier and surging into nearby rivers.
    This scenario is certainly in line with known hazards for the region. “These mountains are very fragile,” says Prakash, who was also a lead author on the Intergovernmental Panel on Climate Change’s 2019 special report on oceans and the cryosphere, Earth’s icy places. But, he notes, there isn’t yet much on-the-ground data to help clarify events. “The efforts are still focused on relief at the moment.”
    2. A landslide may be to blame instead.
    Other researchers contend that the disaster wasn’t caused by a glacial lake outburst flood at all. Instead, says Daniel Shugar, a geomorphologist at the University of Calgary in Canada, satellite images snapped during the disaster show the telltale marks of a landslide: a dark scar snaking through the white snow and clouds of dust clogging the air above. “You could see this train of dust in the valley, and that’s common for a very large landslide,” Shugar says.
    “WOW,” he wrote on Twitter the morning of February 7, posting side-by-side satellite shots of a dark area of possible “massive dust deposition,” contrasted against the same snowy, pristine region just the day before.

    Landslides — the sudden failure of a slope, sending a rush of rocks and sediment downhill — can be triggered by anything from an earthquake to an intense deluge of rain. In high, snowy mountains, cycles of freezing and thawing and refreezing again can also begin to break the ground apart; the ice-filled cracks can slowly widen over time, setting the stage for sudden failure, and then, disaster.
    The satellite images seem to point clearly to such a landslide, rather than a typical glacial lake overflow, Shugar says. The force of the landslide may have actually broken off that piece of hanging glacier, he says. Another line of evidence against a sudden lake burst is that “there were no lakes of any size visible” in the satellite images taken over the region.
    However, an outlying question for this hypothesis is where the floodwaters came from. It might be that one of the rivers draining down the mountain was briefly dammed by the rockfall; a sudden release of that dam could send a large plug of water from the river swiftly and disastrously downhill. “But that’s a pure guess at the moment,” Shugar says.
    3. It’s not yet clear whether climate change played a role in the disaster.
    The risk of both glacial lake outburst floods and freeze-thaw-related landslides in Asia’s high mountains has increased due to climate change. At first glance, “it was a climate event,” Prakash says. “But the data are still coming.”
    The region, which includes the Hindu Kush Himalayan mountains and the Tibetan Plateau, “has been a climate change hot spot for a pretty long time,” Prakash says. The region is often called Earth’s third pole, because the stores of ice and snow in the Himalayan watershed amount to the largest reserves of freshwater outside of the polar regions. The region is the source of 10 major river systems that provide water to almost 2 billion people.
    Climate change reports have warned that warming is not only threatening this water supply, but also increasing the likelihood of natural hazards (SN: 5/29/19). In the Intergovernmental Panel on Climate Change’s 2019 special report on oceans and the cryosphere, scientists noted that glacier retreat, melting snow and thawing permafrost are making mountain slopes more unstable and also increasing the number of glacial lakes, upping the likelihood of a sudden, catastrophic failure (SN: 9/25/19).
    A 2019 comprehensive assessment focusing on climate change’s impacts in Asia’s high mountains found that the glaciers in the region have retreated much more quickly in the last decade than was anticipated, Prakash says, “and that is alarming for us.” Here’s another way to look at it: Glaciers are retreating twice as fast as they were at the end of the 20th century (SN: 6/19/19).
    Glacier-related landslides in the region have also become increasingly common in the last decade, as the region warms and destabilizing freeze-thaw cycles within the ground occur higher and higher up on the slopes.
    But in the case of this particular disaster, Shugar says, it’s just hard to say conclusively at this point what role climate change might have played, or even what specific event might have triggered a landslide. “Sometimes there is no trigger; sometimes it’s just time,” he says. “Or it’s that we just don’t understand the trigger.”

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    Fossil mimics may be more common in ancient rocks than actual fossils

    When it comes to finding fossils of very ancient microbial life — whether on Earth or on other worlds, such as Mars — the odds are just not in our favor.
    Actual microbial life-forms are much less likely to become safely fossilized in rocks compared with nonbiological structures that happen to mimic their shapes, new research finds. The finding suggests that Earth’s earliest rocks may contain abundant tiny fakers — minuscule objects masquerading as fossilized evidence of early life — researchers report online January 28 in Geology.
    The finding is “at the very least a cautionary tale,” says study author Julie Cosmidis, a geomicrobiologist at the University of Oxford.
    Tiny, often enigmatic structures found in some of Earth’s oldest rocks, dating back to more than 2.5 billion years, can offer tantalizing hints of the planet’s earliest life. And the hunt for ever-more-ancient signs of life on Earth has sparked intense debate — in part because the farther back in time you go, the harder it is to interpret tiny squiggles, filaments and spheres in the rock (SN: 1/3/20). One reason is that the movements of Earth’s tectonic plates over time can squeeze and cook the rocks, deforming and chemically altering tiny fossils, perhaps beyond recognition.

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    But an even more pernicious and contentious problem is that such tiny filaments or spheres may not be biological in origin at all. Increasingly, scientists have found that nonbiological chemical processes can create similar shapes, suggesting the possibility of “false positives” in the biological record.
    One such discovery led to the new study, Cosmidis says. A few years ago, she and others were trying to grow bacteria and make them produce sulfur. “We were mixing sulfides with organic matter, and we started forming these objects,” she says. “We thought they were formed by the bacteria, because they looked so biological. But then we realized they were forming in laboratory tubes that happened to have no bacteria in them at all.”
    That led her to wonder about such processes happening in the rocks themselves. So she and others decided to examine what would happen if they tried to re-create the early formation stages of chert, a kind of compact, silica-rich rock common on the early Earth. “Microfossils are often found in chert formations,” says study coauthor Christine Nims, a geobiologist now at the University of Michigan in Ann Arbor. “Anything hosted in [chert] will be well-preserved.”
    Chert forms out of silica-rich water; the silica precipitates out of the water and accumulates, eventually hardening into rock. Cosmidis, Nims and colleagues added sulfur-containing bacteria called Thiothrix to solidifying chert to see what might happen during actual fossilization. To other chert samples, they added sulfur-containing “biomorphs,” spheres and filaments made of tiny crystals but shaped like bacteria.
    At first, nanoparticles of silica encrusted the bacteria and the biomorphs, Nims says. But after a week or so, the bacteria started to deform, their cells deflating from cylinders into flattened, unrecognizable ribbons as the sulfur inside the cells diffused out and reacted with the silica outside the cells, forming new minerals.
    The biomorphs, on the other hand, “had this impressive resiliency,” she says. Although they, too, lost sulfur to the surrounding solution, they kept their silica crust. As a result, “they kept their shape and showed very little change over time.” That endurance suggests that enigmatic structures found in the early rock record have a better chance of being pseudofossils, rather than actual fossils, the team says.
    In a new study, researchers produced twisted filament-shaped biomorphs (top) from the reactions of sulfide with prebiotic organic compounds. The biomorphs resemble possible microbial fossils (bottom, filaments indicated by red arrows) found in rocks dating to 3.5 billion years ago.From top: C. Nims; R.J. Baumgartner et al/Geology 2019
    The idea that once-living creatures are harder to preserve makes sense, says Sean McMahon, an astrobiologist at the University of Edinburgh who was not involved in the new study. “It’s not totally surprising,” he says. “We know that biomass does tend to break down quite quickly.”
    In fact, scientists have known for centuries that certain chemical reactions can act as “gardens” that “grow” strange-shaped mineral objects, twisting into tubes or sprouting branches or otherwise mimicking the weirdness of life. “There’s a complacency about it, a misconception that we kind of know all this and it’s already been dealt with,” McMahon says.
    Strategies to deal with this conundrum have included looking for particular structures — such as mound-shaped stromatolites — or chemical compounds in a potential fossil that are thought to be uniquely formed or modified by the presence of life (SN: 10/17/18). Those criteria are the product of decades of field studies, through which scientists have amassed a vast reference dataset of fossil structures, against which researchers can compare and evaluate any new discoveries.
    “Anything we find, we can look at through that lens,” McMahon says. But what’s lacking is a similarly rich dataset for how such structures might form in the absence of life. This study, he says, highlights that attempts “to define criteria for recognizing true fossils in very ancient rocks are premature, because we don’t yet know enough about how nonbiological processes mimic true fossils.”
    It’s an increasingly urgent problem with rising stakes, as NASA’s Perseverance rover is about to set down on Mars to begin a new search for traces of life in ancient rocks (SN: 7/28/20), he adds. “Paleontologists and Mars exploration scientists should take [this study] very seriously.” More