Suicide rates have increased across the United States — and in dozens of states by more than 30 percent, according to a new report from the U.S. Centers for Disease Control and Prevention based on public health data from 1999 to 2016.
Among suicide victims counted in 2015 in 27 states, 54 percent had no known mental health condition, researchers say in the June 8 report. For those who died, circumstances surrounding their suicide included relationship or job problems, the loss of a home, legal troubles and physical health issues. These factors played a role whether suicide victims had a diagnosed medical condition or not. With suicide, “there’s no one cause. It’s a confluence of contributors at a particular stress point in time,” says clinical psychologist Jill Harkavy-Friedman, the vice president of research at the American Foundation for Suicide Prevention in New York City. “It’s very important to know that it’s not just mental illness; it’s many factors.”
Overall, close to 45,000 Americans died by suicide in 2016. Suicide is one of three top causes of death on the rise in the country, and has contributed to a drop in U.S. life expectancy (SN Online: 12/21/07). By state or jurisdiction, the rates of suicide in the most recent period studied (2014 to 2016) ranged from 6.9 per 100,000 people in the District of Columbia to 29.2 per 100,000 for Montana. “Suicide is a public health problem that can be prevented,” said Anne Schuchat, the CDC’s principal deputy director, in a news conference on June 7. “That’s why it’s so important to understand the range of factors and circumstances that contribute to suicide risk.”
Starting that prevention early by teaching elementary school kids problem-solving and coping skills and how to take care of their mental and physical health is key, Harkavy-Friedman says.
To reach the National Suicide Prevention Lifeline, call 1-800-273-TALK (8255).
The story of how some of the massive stone statues on Rapa Nui, also known as Easter Island, ended up wearing stone hats involves ramps, ropes and remarkably few workers, a contested new analysis suggests.
No more than 15 people were needed to manipulate ropes that rolled stone cylinders, or pukao, up ramps to the top of forward-leaning statues, say archaeologist Sean Hixon of Penn State and his colleagues. The hatlike cylinders were then tipped over to rest atop statues, the researchers propose online May 31 in the Journal of Archaeological Science. After clearing the ramp away, workers then carved statues’ bases flat so that the figures assumed their iconic, upright positions.
Several possible ways in which Rapa Nui inhabitants put pukao on statues have previously been proposed, including sliding pukao up wooden ramps.
“Our group is the first to consider which pukao transport and placement scenario is most consistent with the archaeological record of these multi-ton objects,” Hixon says. The researchers accounted for possible ways in which stone cylinders with the physical features of pukao could have been leveraged onto statues’ heads.
Covering just 164 square kilometers, Rapa Nui sits in the Pacific Ocean about 3,700 kilometers west of Chile. Polynesian travelers first reached the island by the 1200s (SN Online: 1/5/15). Those people made nearly 1,000 human statues from volcanic rock. Hundreds of them, measuring up to 10 meters tall and weighing up to 74 metric tons, were moved to stone platforms, many on the coast. A team led by study coauthor Carl Lipo of Binghamton University in New York concluded in 2013 that islanders used ropes to rock upright statues enough so that the huge stones waddled down prepared dirt roads to display sites. Some statues fell along the way and were left on the side of the road. Those left-behind rocks reveal bases carved on a slight diagonal rather than flat. The pukao were carved from a distinctive, red-hued rock. Weighing up to nearly 12 metric tons, the cylinders were probably laid on their sides and rolled down dirt roads to statue sites, where they were carved into their final shapes, the researchers say. Rock chips are still scattered around the statue sites from that activity.
Ramps made of soil and stones provided access to the tops of statues, Hixon’s group proposes. A technique called parbuckling would have enabled a small group of people to roll cylinders up ramps. In that scenario, islanders would have wrapped a long, doubled-over rope made from a local shrub around a cylinder placed on its side. One of the rope’s ends would be anchored at or near the ramp’s top and held in place by several individuals. Another group would have pulled on the rope’s free end to roll the cylinder uphill.
At the top of the ramp, islanders would have tipped the pukao into place on a statue’s head, although it’s unclear precisely how the tipping was done. Shallow indentations on the bottoms of cylinders, identified on 3-D models of 10 pukao left at a quarry site, enabled a snug fit atop the statues, the researchers say.
Archaeologist Jo Anne Van Tilburg of UCLA regards the new scenario as dubious. Base angles on Rapa Nui statues varied considerably, making them difficult and dangerous to maneuver upright, Van Tilburg says. And parbuckling pukao up long ramps would not have reduced the total effort required to move the massive cylinders to where they needed to be, she contends.
A more plausible plan, in Van Tilburg’s view, involved transporting statues and pukao together. Van Tilburg directed a 1998 experiment in which a tree-trunk frame was used to transport a replica stone statue and pukao to an experimental platform. Ropes were used to pull the frame-encased replicas, lying prone, across the rungs of a wooden, ladderlike ramp up to the platform. Six to eight families could have completed this process, she estimates.
However Rapa Nui’s statues and pukao were moved and set up, they along with other impressive stone monuments, such as England’s Stonehenge (SN Online: 9/6/12), were built by small communities rather than states or kingdoms, Lipo says.
A new kind of artificial diamond is a cut above the rest for quantum memory.
Unlike other synthetic diamonds, which could either store quantum information for a long time or transmit it clearly, the new diamond can do both. This designer crystal, described in the July 6 Science, could be a key building block in a quantum internet. Such a futuristic communications network would allow people to send supersecure messages and connect quantum computers around the world (SN: 10/15/16, p. 13). Synthetic diamond can serve as quantum storage thanks to a type of flaw in its carbon lattice, where two neighboring carbon atoms are replaced with one noncarbon atom and an empty space (SN: 4/5/08, p. 216). This pairing exhibits a quantum property known as spin, which can be in an “up” state, a “down” state or both at once. Each of those states reflects a bit of quantum data, or qubit, that may be 1, 0 or both at once. A diamond transmits qubits by encoding them in light particles, or photons, that travel through fiber-optic cables.
Qubit-storing diamond defects are typically made with nitrogen atoms, which can store quantum data for milliseconds — a relatively long time in the quantum realm (SN: 4/23/11, p. 14). But nitrogen defects can’t communicate that data clearly. They emit light particles at a broad range of frequencies, which muddles the quantum information written into the photons.
Defects made with silicon atoms emit light more precisely, but until now haven’t been able to store qubits for longer than several nanoseconds due to their electrical interactions with nearby particles, explains Nathalie de Leon, an electrical engineer at Princeton University.
De Leon and colleagues got around this problem by forging silicon defects in a diamond infused with boron. This extra chemical ingredient shielded the delicate silicon defects from electrical interactions with nearby particles, extending the defects’ quantum memory. The boron-infused crystal nearly rivaled the long-term quantum memory of nitrogen defects, storing qubits for about a millisecond. And it gave a clean photon readout, emitting about 90 percent of its photons at the exact same frequency — compared to just 3 percent of photons spat out by nitrogen defects. Tweaking the environment of the silicon defects was “an extremely creative way” to help keep a better grip on qubits, says Evelyn Hu, an applied physicist and electrical engineer at Harvard University not involved in the work.
This new artificial diamond could be used to construct devices called quantum repeaters for long-distance quantum communications, says David Awschalom, a physicist and quantum engineer at the University of Chicago who wasn’t involved in the work. Qubit-carrying photons can travel only up to about 100 kilometers through optical fiber before their signal gets scrambled (SN: 9/30/17, p. 8). Quantum repeaters that catch, store and re-emit photons could serve as stepping stones between fiber-optic cables to extend the reach of future networks.
When you hear the word bee, the image that pops to mind is probably a honeybee. Maybe a bumblebee. But for conservation biologist Thor Hanson, author of the new book Buzz, the world is abuzz with thousands of kinds of bees, each as beautiful and intriguing as the flowers on which they land.
Speaking from his “raccoon shack” on San Juan Island in Washington — a backyard shed converted to an office and bee-watching space, and named for its previous inhabitants — Hanson shares what he’s learned about how bees helped drive human evolution, the amazing birds that lead people to honey, and what a Big Mac would look like without bees. The following conversation has been edited for length and clarity. SN: This bee book is unusual — it isn’t mainly about honeybees. Why did you write about lesser-known bees?
Hanson: I made a deliberate decision because I thought the celebrity bees, the honeybees, would steal the show. It was high time to turn a stage light onto these 20,000 other species of bees, which have habits that are less familiar but just as fascinating. For example, most people think of hives when they think of bees, but actually most bees are solitary.
SN: You write that this book is an “exploration of how the very nature of bees makes them so utterly necessary.” So let’s cut to the chase: Why are bees necessary? Hanson: First is the deep connection between bees and flowering plants. They’ve had a partnership from an early stage; each spurs the other in terms of diversity. It’s an incredible role that bees have played in shaping the natural world. They’re also important to our lifestyle, first for their role in the human diet. It’s often said that one of every three bites of food depends on bees.
But there are all these other connections that we don’t think about: Bees have provided light from beeswax candles and sweetness from honey. Early industrial uses of wax included making bronze sculptures with wax molds, batiks in Indonesia and wax tablets to write on.
You can trace our relationship with bees back not hundreds, but hundreds of thousands of years. The role of honey in the human diet goes back into prehistory. That source of sugar may have even helped fuel the expansion of our brain size. It may have helped us become who we are. SN: One of the most astonishing examples of our relationship with bees has to do with a bird called the honeyguide. Tell me about that.
Hanson: Hunter-gatherers in Africa follow this bird to bees’ nests, and have for generations (SN: 8/20/16, p. 10). The honeyguide is very good at locating a hive. But on its own, it can’t access the nest. So once it locates one, the next thing it does is look for people. It hops around on branches and makes a piercing cry to get attention, then leads a person to the honey. People climb the tree or dig out the nest, and honeyguides feed on the remains.
What’s funny is how long it took biologists to figure out this relationship. The original explanation was that the honeyguide coevolved with the honey badger, which also raids nests for honey. Then a biologist pointed out that badgers are nocturnal, and the birds aren’t. Also, no one has ever seen a honeyguide leading a badger. It makes more sense that the relationship evolved on the savannah with people out looking for honey every day.
SN: One of the book’s most hilariously geeky moments is when you go to McDonald’s and pick apart a Big Mac. Why did you do that?
Hanson: I wanted to look for the significance of bees in an unexpected place. And you don’t think of bees when you go into McDonald’s — you just don’t! I didn’t care how much people stared. I sat there with my tweezers, pulling all the seeds off the bun. I ended up with one pile you could have without bees [meat and bun] and one you couldn’t [including not only the veggies, but also the cheese and special sauce]. We could still eat, but it would be pretty dull.
SN: You’re worried about bees. Why?
Hanson: It’s the four p’s: pesticides, pathogens, parasites and poor nutrition. Poor nutrition is one that people don’t think of. We ship honeybees all over the place, and they get force-fed almond blossoms for three weeks, then they’re packed onto trucks and shipped off to pollinate apples. It’s not a healthy lifestyle, and not a varied diet.
SN: You say that bees are one of the few insects that inspire fondness instead of fear. Why do you think that is?
Hanson: Bees have been with us from the beginning. Our primordial sweet tooth led us to follow these creatures, then we domesticated bees very early on, setting out hives and reusing good sites in baobab trees. I think we have a very deep connection to these creatures.
Marathoners queuing up for a big race tend to go with the flow, surging toward the start line like a fluid.
Using footage of runners moving in groups toward the start of the Chicago Marathon, researchers developed a theory that treats the crowd like a liquid to explain its movement. The theory correctly predicted the motion of crowds of runners at marathons in two other locations, physicists report in the Jan. 4 Science.
Previous studies have devised rules for how individuals act within a crowd and used that behavior to describe crowd motion (SN: 1/10/15, p. 15). But to understand how wine swirls in a glass, you don’t need to know the behavior of each molecule. So physicists Nicolas Bain and Denis Bartolo of École Normale Supérieure de Lyon in France considered the crowd as a whole.
At the start of a marathon, runners arrange themselves into groups known as corrals, which individually advance to the starting line. Marathon staff members form a line in front of each corral, periodically holding participants back until there’s space to move forward. The researchers filmed this start-and-stop process at four marathons, including the Chicago Marathon in 2016 and 2017. The movements of the staff set off a change in crowd density and speed that traveled through the throng akin to waves produced when water is pushed, the team found. Similar effects occurred at marathons in Paris and Atlanta in 2017.
Marathon crowds are a special type in that everyone travels in the same direction. Eventually, this type of research could lead to new insight into other crowd formations, including those packed more tightly than marathon crowds, with pedestrians literally shoulder to shoulder. Such crowds sometimes result in deadly stampedes, such as the 2015 event at the hajj in Mecca, Saudi Arabia (SN: 4/7/07, p. 213). Better understanding of these crowd dynamics could help prevent similar tragedies.
A drug that treats a rare form of cystic fibrosis may have even better results if given before birth, a study in ferrets suggests.
The drug, known by the generic name ivacaftor, can restore the function of a faulty version of the CFTR protein, called CFTRG551D. The normal CFTR protein controls the flow of charged atoms in cells that make mucus, sweat, saliva, tears and digestive enzymes. People who are missing the CFTR gene and its protein, or have two copies of a damaged version of the gene, develop the lung disease cystic fibrosis, as well as diabetes, digestive problems and male infertility. Ivacaftor can reduce lung problems in patients with the G551D protein defect, with treatment usually starting when a patient is a year old. But if the results of the new animal study carry over to humans, an even earlier start date could prove more effective in preventing damage to multiple organs.
Researchers used ferret embryos with two copies of the G551D version of the CFTR gene. Giving the drug to mothers while the ferrets were in the womb and then continuing treatment of the babies after birth prevented male infertility, pancreas problems and lung disease in the baby ferrets, called kits, researchers report March 27 in Science Translational Medicine. The drug has to be used continuously to prevent organ damage — when the drug was discontinued, the kits’ pancreases began to fail and lung disease set in.
Cystic fibrosis affects about 30,000 people in the United States and 70,000 worldwide. But only up to 5 percent of patients have the G551D defect.
Other researchers are testing combinations of three drugs, including ivacaftor, aimed at helping the roughly 90 percent of cystic fibrosis patients afflicted by another genetic mutation that causes the CFTR protein to lack an amino acid (SN: 11/24/18, p. 11). Those drug combos, if proven effective, might also work better if administered early, cystic fibrosis researcher Thomas Ferkol of Washington University School of Medicine in St. Louis writes in a commentary published with the study.
Black holes are extremely camera shy. Supermassive black holes, ensconced in the centers of galaxies, make themselves visible by spewing bright jets of charged particles or by flinging away or ripping up nearby stars. Up close, these behemoths are surrounded by glowing accretion disks of infalling material. But because a black hole’s extreme gravity prevents light from escaping, the dark hearts of these cosmic heavy hitters remain entirely invisible.
Luckily, there’s a way to “see” a black hole without peering into the abyss itself. Telescopes can look instead for the silhouette of a black hole’s event horizon — the perimeter inside which nothing can be seen or escape — against its accretion disk. That’s what the Event Horizon Telescope, or EHT, did in April 2017, collecting data that has now yielded the first image of a supermassive black hole, the one inside the galaxy M87.
“There is nothing better than having an image,” says Harvard University astrophysicist Avi Loeb. Though scientists have collected plenty of indirect evidence for black holes over the last half century, “seeing is believing.”
Creating that first-ever portrait of a black hole was tricky, though. Black holes take up a minuscule sliver of sky and, from Earth, appear very faint. The project of imaging M87’s black hole required observatories across the globe working in tandem as one virtual Earth-sized radio dish with sharper vision than any single observatory could achieve on its own. Putting the ‘solution’ in resolution Weighing in around 6.5 billion times the mass of our sun, the supermassive black hole inside M87 is no small fry. But viewed from 55 million light-years away on Earth, the black hole is only about 42 microarcseconds across on the sky. That’s smaller than an orange on the moon would appear to someone on Earth. Still, besides the black hole at the center of our own galaxy, Sagittarius A* or Sgr A* — the EHT’s other imaging target — M87’s black hole is the largest black hole silhouette on the sky. Only a telescope with unprecedented resolution could pick out something so tiny. (For comparison, the Hubble Space Telescope can distinguish objects only about as small as 50,000 microarcseconds.) A telescope’s resolution depends on its diameter: The bigger the dish, the clearer the view — and getting a crisp image of a supermassive black hole would require a planet-sized radio dish. Even for radio astronomers, who are no strangers to building big dishes (SN Online: 9/29/17), “this seems a little too ambitious,” says Loeb, who was not involved in the black hole imaging project. “The trick is that you don’t cover the entire Earth with an observatory.” Instead, a technique called very long baseline interferometry combines radio waves seen by many telescopes at once, so that the telescopes effectively work together like one giant dish. The diameter of that virtual dish is equal to the length of the longest distance, or baseline, between two telescopes in the network. For the EHT in 2017, that was the distance from the South Pole to Spain.
Telescopes, assemble! The EHT was not always the hotshot array that it is today, though. In 2009, a network of just four observatories — in Arizona, California and Hawaii — got the first good look at the base of one of the plasma jets spewing from the center of M87’s black hole (SN: 11/3/12, p. 10). But the small telescope cohort didn’t yet have the magnifying power to reveal the black hole itself.
Over time, the EHT recruited new radio observatories. By 2017, there were eight observing stations in North America, Hawaii, Europe, South America and the South Pole. Among the newcomers was the Atacama Large Millimeter/submillimeter Array, or ALMA, located on a high plateau in northern Chile. With a combined dish area larger than an American football field, ALMA collects far more radio waves than other observatories.
“ALMA changed everything,” says Vincent Fish, an astronomer at MIT’s Haystack Observatory in Westford, Mass. “Anything that you were just barely struggling to detect before, you get really solid detections now.” More than the sum of their parts EHT observing campaigns are best run within about 10 days in late March or early April, when the weather at every observatory promises to be the most cooperative. Researchers’ biggest enemy is water in the atmosphere, like rain or snow, which can muddle with the millimeter-wavelength radio waves that the EHT’s telescopes are tuned to.
But planning for weather on several continents can be a logistical headache.
“Every morning, there’s a frenetic set of phone calls and analyses of weather data and telescope readiness, and then we make a go/no-go decision for the night’s observing,” says astronomer Geoffrey Bower of the Academia Sinica Institute of Astronomy and Astrophysics in Hilo, Hawaii. Early in the campaign, researches are picky about conditions. But toward the tail end of the run, they’ll take what they can get.
When the skies are clear enough to observe, researchers steer the telescopes at each EHT observatory toward the vicinity of a supermassive black hole and begin collecting radio waves. Since M87’s black hole and Sgr A* appear on the sky one at a time — each one about to rise just as the other sets — the EHT can switch back and forth between observing its two targets over the course of a single multi-day campaign. All eight observatories can track Sgr A*, but M87 is in the northern sky and beyond the South Pole station’s sight.
On their own, the data from each observing station look like nonsense. But taken together using the very long baseline interferometry technique, these data can reveal a black hole’s appearance.
Here’s how it works. Picture a pair of radio dishes aimed at a single target, in this case the ring-shaped silhouette of a black hole. The radio waves emanating from each bit of that ring must travel slightly different paths to reach each telescope. These radio waves can interfere with each other, sometimes reinforcing one another and sometimes canceling each other out. The interference pattern seen by each telescope depends on how the radio waves from different parts of the ring are interacting when they reach that telescope’s location. For simple targets, such as individual stars, the radio wave patterns picked up by a single pair of telescopes provide enough information for researchers to work backward and figure out what distribution of light must have produced those data. But for a source with complex structure, like a black hole, there are too many possible solutions for what the image could be. Researchers need more data to work out how a black hole’s radio waves are interacting with each other, offering more clues about what the black hole looks like.
The ideal array has as many baselines of different lengths and orientations as possible. Telescope pairs that are farther apart can see finer details, because there’s a bigger difference between the pathways that radio waves take from the black hole to each telescope. The EHT includes telescope pairs with both north-south and east-west orientations, which change relative to the black hole as Earth rotates.
Pulling it all together In order to braid together the observations from each observatory, researchers need to record times for their data with exquisite precision. For that, they use hydrogen maser atomic clocks, which lose about one second every 100 million years.
There are a lot of data to time stamp. “In our last experiment, we recorded data at a rate of 64 gigabits per second, which is about 1,000 times [faster than] your home internet connection,” Bower says.
These data are then transferred to MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy in Bonn, Germany, for processing in a special kind of supercomputer called a correlator. But each telescope station amasses hundreds of terabytes of information during a single observing campaign — far too much to send over the internet. So the researchers use the next best option: snail mail. So far, there have been no major shipping mishaps, but Bower admits that mailing the disks is always a little nerve-wracking.
Though most of the EHT data reached Haystack and Max Planck within weeks of the 2017 observing campaign, there were no flights from South Pole until November. “We didn’t get the data back from the South Pole until mid-December,” says Fish, the MIT Haystack astronomer.
Filling in the blanks Combining the EHT data still isn’t enough to render a vivid picture of a supermassive black hole. If M87’s black hole were a song, then imaging it using only the combined EHT data would be like listening to the piece played on a piano with a bunch of broken keys. The more working keys — or telescope baseline pairs — the easier it is to get the gist of the melody. “Even if you have some broken keys, if you’re playing all the rest of them correctly, you can figure out the tune, and that’s partly because we know what music sounds like,” Fish says. “The reason we can reconstruct images, even though we don’t have 100 percent of the information, is because we know what images look like” in general. There are mathematical rules about how much randomness any given picture can contain, how bright it should be and how likely it is that neighboring pixels will look similar. Those basic guidelines can inform how software decides which potential images, or data interpretations, make the most sense.
Before the 2017 observing campaign, the EHT researchers held a series of imaging challenges to make sure their computer algorithms weren’t biased toward creating images to match expectations of what black holes should look like. One person would use a secret image to generate faux data of what telescopes would see if they were peering at that source. Then other researchers would try to reconstruct the original image.
“Sometimes the true image was not actually a black hole image,” Fish says, “so if your algorithm was trying to find a black hole shadow … you wouldn’t do well.” The practice runs helped the researchers refine the data processing techniques used to render the M87 image.
Black holes and beyond So, the black hole inside M87 finally got its closeup. Now what?
The EHT’s black hole observations are expected to help answer questions like how some supermassive black holes, including M87’s, launch such bright plasma jets (SN Online: 3/29/19). Understanding how gas falls into and feeds black holes could also help solve the mystery of how some black holes grew so quickly in the early universe, Loeb says (SN Online: 3/16/18).
The EHT could also be used, Loeb suggests, to find pairs of supermassive black holes orbiting one another — similar to the two stellar mass black holes whose collision created gravitational waves detected in 2015 by the Advanced Laser Interferometer Gravitational-Wave Observatory, or Advanced LIGO (SN: 3/5/16, p. 6). Getting a census of these binaries may help researchers identify targets for the Laser Interferometer Space Antenna, or LISA, which will search from space for gravitational waves kicked up by the movement of objects like black holes (SN Online: 6/20/17). The EHT doesn’t have many viable targets other than supermassive black holes, says astrophysicist Daniel Marrone, at the University of Arizona in Tucson. There are few other things in the universe that appear as tiny but luminous as the space surrounding a supermassive black hole. “You have to be able to get enough light out of the really tiny patches of sky that we can detect,” Marrone says. “In principle, we could be reading alien license plates or something,” but they’d need to be super bright.
Too bad for alien seekers. Still, even if the EHT is a one-trick pony, spying supermassive black holes is a pretty neat trick.
The Chugach people of southern Alaska’s Kenai Peninsula have picked berries for generations. Tart blueberries and sweet, raspberry-like salmonberries — an Alaska favorite — are baked into pies and boiled into jams. But in the summer of 2009, the bushes stayed brown and the berries never came.
For three more years, harvests failed. “It hit the communities very hard,” says Nathan Lojewski, the forestry manager for Chugachmiut, a nonprofit tribal consortium for seven villages in the Chugach region. The berry bushes had been ravaged by caterpillars of geometrid moths — the Bruce spanworm (Operophtera bruceata) and the autumnal moth (Epirrita autumnata). The insects had laid their eggs in the fall, and as soon as the leaf buds began growing in the spring, the eggs hatched and the inchworms nibbled the stalks bare.
Chugach elders had no traditional knowledge of an outbreak on this scale in the region, even though the insects were known in Alaska. “These berries were incredibly important. There would have been a story, something in the oral history,” Lojewski says. “As far as the tribe was concerned, this had not happened before.”
At the peak of the multiyear outbreak, the caterpillars climbed from the berry bushes into trees. The pests munched through foliage from Port Graham, at the tip of the Kenai Peninsula, to Wasilla, north of Anchorage, about 300 kilometers away. In summer, thick brown-gray layers of denuded willows, alders and birches lined the mountainsides above stretches of Sitka spruce. Two summers ago, almost a decade after the first infestation, the moths returned. “We got a few berries, but not as many as we used to,” says Chugach elder Ephim Moonin Sr., whose house in the village of Nanwalek is flanked by tall salmonberry bushes. “Last year, again, there were hardly any berries.” For more than 35 years, satellites circling the Arctic have detected a “greening” trend in Earth’s northernmost landscapes. Scientists have attributed this verdant flush to more vigorous plant growth and a longer growing season, propelled by higher temperatures that come with climate change. But recently, satellites have been picking up a decline in tundra greenness in some parts of the Arctic. Those areas appear to be “browning.” Like the salmonberry harvesters on the Kenai Peninsula, ecologists working on the ground have witnessed browning up close at field sites across the circumpolar Arctic, from Alaska to Greenland to northern Norway and Sweden. Yet the bushes bereft of berries and the tinder-dry heaths (low-growing shrubland) haven’t always been picked up by the satellites. The low-resolution sensors may have averaged out the mix of dead and living vegetation and failed to detect the browning.
Scientists are left to wonder what is and isn’t being detected, and they’re concerned about the potential impact of not knowing the extent of the browning. If it becomes widespread, Arctic browning could have far-reaching consequences for people and wildlife, affecting habitat and atmospheric carbon uptake and boosting wildfire risk.
Growing greenbelt The Arctic is warming two to three times as fast as the rest of the planet, with most of the temperature increase occurring in the winter. Alaska, for example, has warmed 2 degrees Celsius since 1949, and winters in some parts of the state, including southcentral Alaska and the Arctic interior, are on average 5 degrees C warmer.
An early effect of the warmer climate was a greener Arctic. More than 20 years ago, researchers used data from the National Oceanic and Atmospheric Administration’s weather satellites to assess a decade of northern plant growth after a century of warming. The team compared different wavelengths of light — red and near-infrared — reflecting off vegetation to calculate the NDVI, the normalized difference vegetation index. Higher NDVI values indicate a greener, more productive landscape. In a single decade — from 1981, when the first satellite was launched, to 1991 — the northern high latitudes had become about 8 percent greener, the researchers reported in 1997 in Nature.
The Arctic ecosystem, once constrained by cool conditions, was stretching beyond its limits. In 1999 and 2000, researchers cataloged the extent and types of vegetation change in parts of northern Alaska using archival photographs taken during oil exploration flyovers between 1948 and 1950. In new images of the same locations, such as the Kugururok River in the Noatak National Preserve, low-lying tundra plants that once grew along the riverside terraces had been replaced by stands of white spruce and green alder shrubs. At some of the study’s 66 locations, shrub-dominated vegetation had doubled its coverage from 10 to 20 percent. Not all areas showed a rise in shrub abundance, but none showed any decrease.
In 2003, Howard Epstein, a terrestrial ecologist at the University of Virginia in Charlottesville, and colleagues looked to the satellite record, which now held another decade of data. Focusing on Alaska’s North Slope, which lies just beyond the crown of the Brooks Range and extends to the Beaufort Sea, the researchers found that the highest NDVI values, or “peak greenness,” during the growing season had increased nearly 17 percent between 1981 and 2001, in line with the warming trend. Earth-observing satellites have been monitoring the Arctic tundra for almost four decades. In that time, the North Slope, the Canadian low Arctic tundra and eastern Siberia have become especially green, with thicker and taller tundra vegetation and shrubs expanding northward. “If you look at the North Slope of Alaska, if you look at the overall trend, it’s greening like nobody’s business,” says Uma Bhatt, an atmospheric scientist at the University of Alaska Fairbanks.
Yet parts of the Arctic, including the Yukon-Kuskokwim Delta of western Alaska, the Canadian Arctic Archipelago (the islands north of the mainland that give Canada its pointed tip) and the northwestern Siberian tundra, show extensive browning over the length of the satellite record, from the early 1980s to 2016. “It could just be a reduction in green vegetation. It doesn’t necessarily mean the widespread death of plants,” Epstein says. Scientists don’t yet know why plant growth there has slowed or reversed — or whether the satellite signal is in some way misleading.
“All the models indicated for a long time that we would expect greening with warmer temperatures and higher productivity in the tundra, so long as it wasn’t limited in some other way, like [by lower] moisture,” says Scott Goetz, an ecologist and remote-sensing specialist at Northern Arizona University in Flagstaff. He is also the science team lead for ABoVE, NASA’s Arctic-Boreal Vulnerability Experiment, which is tracking ecosystem changes in Alaska and western Canada. “Many of us were quite surprised … that the Arctic was suddenly browning. It’s something we need to resolve.”
Freeze-dried tundra While global warming has propelled widespread trends in tundra greening, extreme winter weather can spur local browning events. In recent years, in some parts of the Arctic, extraordinary warm winter weather, sometimes paired with rainfall, has put tundra vegetation under enormous stress and caused plants to lose freeze resistance, dry up or die — and turn brown.
Gareth Phoenix, a terrestrial ecologist at the University of Sheffield in England, recalls his shock at seeing a series of midwinter timelapse photos taken in 2001 at a research site outside the town of Abisko in northern Sweden. In the space of a couple of days, the temperature shot up from −16° C to 6° C, melting the tundra’s snow cover. “As an ecologist, you’re thinking, ‘Whoa! Those plants would usually be nicely insulated under the snow,’ ” he says. “Suddenly, they’re being exposed because all the snow has melted. What are the consequences of that?”
Arctic plants survive frigid winters thanks to that blanket of snow and physiological changes, known as freeze resistance, that allow plants to freeze without damage. But once the plants awaken in response to physical cues of spring — warmer weather, longer days — and experience bud burst, they lose that ability to withstand frigid conditions. That’s fine if spring has truly arrived. But if it’s just a winter heat wave and the warm air mass moves on, the plants become vulnerable as temperatures return to seasonal norms. When temporary warm air covers thousands of square kilometers at once, plant damage occurs over large areas. “These landscapes can look like someone’s gone through with a flamethrower,” Phoenix says. “It’s quite depressing. You’re there in the middle of summer, and everything’s just brown.”Jarle Bjerke, a vegetation ecologist at the Norwegian Institute for Nature Research in Tromsø, saw browning across northern Norway and Sweden in 2008. The landscape — covered in mats of crowberry, an evergreen shrub with bright green sausagelike needles — was instead shades of brown, red-brown and grayish brown. “We saw it everywhere we went, from the mountaintops to the coastal heaths,” Bjerke says. Bjerke, Phoenix and other researchers continue to find brown vegetation in the wake of winter warming events. Long periods of mild winter weather have rolled over the Svalbard archipelago, the cluster of islands in the Arctic Ocean between Norway and the North Pole, in the last decade. The snow melted or blew away, exposing the ground-hugging plants. Some became encrusted in ice following a once-unheard-of midwinter rainfall. In 2015, the Arctic bell heather, whose small white flowers brighten Arctic ridges and heaths, were brown that summer, gray the next and then the leaves fell off. “It’s not new that plants can die during mild winters,” Bjerke says. “The new thing is that it is now happening several winters in a row.”
Insect invasion The weather needn’t always be extreme to harm plants in the Arctic. With warmer winters and summers, leaf-eating insects have thrived, defoliating bushes and trees beyond the insects’ usual range. “They’re very visual events,” says Rachael Treharne, an Arctic ecologist who completed her Ph.D. at the University of Sheffield and now works at ClimateCare, a company that helps organizations reduce their climate impact. She remembers being in the middle of an autumnal moth outbreak in northern Sweden one summer. “There were caterpillars crawling all over the plants — and us. We’d wake up with them in our beds.”
In northernmost Norway, Sweden and Finland in the mid-2000s, successive bursts of geometrid moths defoliated 10,000 square kilometers of mountain birch forest — an area roughly the size of Puerto Rico. The outbreak was one of Europe’s most abrupt and large-scale ecosystem disturbances linked to climate change, says Jane Jepsen, an Arctic ecologist at the Norwegian Institute for Nature Research. “These moth species benefit from a milder winter, spring and summer climate,” Jepsen says. Moth eggs usually die at around −30° C, but warmer winters have allowed more eggs of the native autumnal moth to survive. With warmer springs, the eggs hatch earlier in the year and keep up with the bud burst of the mountain birch trees. Another species — the winter moth (O. brumata), found in southern Norway, Sweden and Finland — expanded northward during the outbreak. The spring and summer warmth favored the larvae, which ate more and grew larger, and the resulting hardier female moths laid more eggs in the fall.
While forests that die off can grow back over several decades, some of these mountain birches may have been hammered too hard, Jepsen says. In some places, the forest has given way to heathland. Ecological transitions like this could be long-lasting or even permanent, she says.
Smoldering lands Once rare, wildfires may be one of the north’s main causes of browning. As grasses, shrubs and trees across the region dry up, they are being set aflame with increasing frequency, with fires covering larger areas and leaving behind dark scars. For example, in early 2014 in the Norwegian coastal municipality of Flatanger, sparks from a power line ignited the dry tundra heath, destroying more than 100 wooden buildings in several coastal hamlets.
Sparsely populated places, where lightning is the primary cause of wildfires, are also seeing an uptick in wildfires. Scientists say lightning strikes are becoming more frequent as the planet warms. The number of lightning-sparked fires has risen 2 to 5 percent per year in Canada’s Northwest Territories and Alaska over the last four decades, earth system scientist Sander Veraverbeke of Vrije Universiteit Amsterdam and his colleagues reported in 2017 in Nature Climate Change.
In 2014, the Northwest Territories had 385 fires, which burned 34,000 square kilometers. The next year, 766 fires torched 20,600 square kilometers of the Alaskan interior — accounting for about half the total area burned in the entire United States in 2015.
In the last two years, wildfires sent plumes of smoke aloft in western Greenland (SN: 3/17/18, p. 20) and in the northern reaches of Sweden, Norway and Russia, places where wildfires are uncommon. Wildfire activity within a 30-year period could quadruple in Alaska by 2100, says a 2017 report in Ecography. Veraverbeke expects to see “more fires in the Arctic in the future.”
The loss of wide swaths of plants could have wide-ranging local effects. “These plants are the foundation of the terrestrial Arctic food webs,” says Isla Myers-Smith, a global change ecologist at the University of Edinburgh. The shriveled landscapes can leave rock ptarmigan, for example, which rely heavily on plants, without enough food to eat in the spring. The birds’ predators, such as the arctic fox, may feel the loss the following year.
The effects of browning may be felt beyond the Arctic, which holds about half of the planet’s terrestrial carbon. The boost in tundra greening allows the region to store, or “sink,” more carbon during the growing season. But carbon uptake may slow if browning events continue, as expected in some regions.
Treharne, Phoenix and colleagues reported in February in Global Change Biology that on the Lofoten Islands in northern Norway, extreme winter conditions cut in half the heathlands’ ability to trap carbon dioxide from the atmosphere during the growing season.
Yet there’s still some uncertainty about how these browned tundra ecosystems might change in the long-term. As the land darkens, the surface absorbs more heat and warms up, threatening to thaw the underlying permafrost and accelerate the release of methane and carbon dioxide. Some areas might switch from being carbon sinks to carbon sources, Phoenix warns.
On the other hand, other plant species — with more or less capacity to take up carbon — could move in. “I’m still of the view that [these areas] will go through these short-term events and continue on their trajectory of greater productivity,” Goetz says.
A better view The phenomena that cause browning events — extreme winter warming, insect outbreaks, wildfires — are on the rise. But browning events are tough to study, especially in winter, because they’re unpredictable and often occur in hard-to-reach areas. Ecologists working on the ground would like the satellite images and the NDVI maps to point to areas with unusual vegetation growth — increasing or decreasing. But many of the browning events witnessed by researchers on the ground have not been picked up by the older, lower-resolution satellite sensors, which scientists still use. Those sensors oversimplify what’s on the ground: One pixel covers an area 8 kilometers by 8 kilometers. “The complexity that’s contained within a pixel size that big is pretty huge,” Myers-Smith says. “You have mountains, or lakes, or different types of tundra vegetation, all within that one pixel.” At a couple of recent workshops on Arctic browning, remote-sensing experts and ecologists tried to tackle the problem. “We’ve been talking about how to bring the two scales together,” Bhatt says. New sensors, more frequent snapshots, better data access and more computing power could help scientists zero in on the extent and severity of browning in the Arctic.
Researchers have begun using Google Earth Engine’s massive collection of satellite data, including Landsat images at a much better resolution of 30 meters by 30 meters per pixel. Improved computational capabilities also enable scientists to explore vegetation change close up. The European Space Agency’s recently launched Sentinel Earth-observing satellites can monitor vegetation growth with a pixel size of 10 meters by 10 meters. Says Myers-Smith: “That’s starting to get to a scale that an ecologist can grapple with.”
In other star systems, some moons could escape their planets and start orbiting their stars instead, new simulations suggest. Scientists have dubbed such liberated worlds “ploonets,” and say that current telescopes may be able to find the wayward objects.
Astronomers think that exomoons — moons orbiting planets that orbit stars other than the sun — should be common, but efforts to find them have turned up empty so far (SN Online: 4/30/19). Astrophysicist Mario Sucerquia of the University of Antioquia in Medellín, Colombia and colleagues simulated what would happen to those moons if they orbited hot Jupiters, gas giants that lie scorchingly close to their stars (SN: 7/8/17, p. 4). Many astronomers think that hot Jupiters weren’t born so close, but instead migrated toward their star from a more distant orbit. As the gas giant migrates, the combined gravitational forces of the planet and the star would inject extra energy into the moon’s orbit, pushing the moon farther and farther from its planet until eventually it escapes, the researchers report June 27 at arXiv.org.
“This process should happen in every planetary system composed of a giant planet in a very close-in orbit,” Sucerquia says. “So ploonets should be very frequent.”
Some ploonets may be indistinguishable from ordinary planets. Others, whose orbits keep them close to their planet, could reveal their presence by changing the timing of when their neighbor planet crosses, or transits, in front of the star. The ploonet should stay close enough to the planet that its gravity can speed or slow the planet’s transit times. Those deviations should be detectable by combining data from planet-hunting telescopes like NASA’s TESS or the now-defunct Kepler, Sucerquia says. Ploonethood may be a relatively short-lived phenomenon, though, making the worlds more difficult to spot. About half of the ploonets in the researchers’ simulations crashed into either their planet or star within about half a million years. And half of the remaining survivors crashed within a million years.
Even with few visible survivors, ploonets could help explain some bizarre exoplanetary features. Moon debris from such crashes could lead to giant ring systems around planets, like the 37 rings that encircle exoplanet J1407b, the team says.
Or, if the ploonet had an icy surface or an atmosphere before moving close to its star, the star’s heat would evaporate it, giving the ploonet a tail like a comet’s. Evaporating ploonets zipping by with a long light-blocking tail could explain strangely flickering stars like Tabby’s star, Sucerquia says (SN: 12/22/18, p. 9).
“Those structures [rings and flickers] have been discovered, have been observed,” Sucerquia says. “We just propose a natural mechanism to explain [them].”
While the solar system doesn’t have any hot Jupiters, ploonethood may be possible here, too. Earth’s moon is moving slowly away from the Earth, at a rate of about 4 centimeters per year. When it eventually breaks free, “the moon is a potential ploonet,” Sucerquia says — although that won’t happen for about 5 billion years.
The study is a good first step for thinking about what would happen to exomoons in real planetary systems, says planetary astrophysicist Natalie Hinkel of the Southwest Research Institute in San Antonio, who wasn’t involved in the new work. “Nobody’s looked at the problem quite like this,” she says. “It adds to the layers of how complex these systems are.”
Plus, ploonet is “a wonderful name,” Hinkel says. “Normally I sort of eye-roll at these made-up names, but this one is a keeper.”
A praying mantis depends on precision targeting when hunting insects. Now, scientists have identified nerve cells that help calculate the depth perception required for these predators’ surgical strikes.
In addition to providing clues about insect vision, the principles of these cells’ behavior, described June 28 in Nature Communications, may also lead to advances in robot vision or other automated systems.
So far, praying mantises are the only insects known to be able to see in 3-D. In the new study, neuroscientist Ronny Rosner of Newcastle University in England and colleagues used a tiny theater that played praying mantises’ favorite films — moving disks that mimic bugs. The disks appeared in three dimensions because the insects’ eyes were covered with different colored filters, creating minuscule 3-D glasses. As a praying mantis watched the films, electrodes monitored the behavior of individual nerve cells in the optic lobe, a brain structure responsible for many aspects of vision. There, researchers found four types of nerve cells that seem to help merge the two different views from each eye into a complete 3-D picture, a skill that human vision cells use to sense depth, too.
One cell type called a TAOpro neuron possesses three elaborate, fan-shaped bundles that receive incoming visual information. Along with the three other cell types, TAOpro neurons are active when each eye’s view of an object is different, a mismatch that’s needed for depth perception.
The details of the various types of nerve cells, and how they might receive, combine and send visual information, suggest that these insects’ vision may be more sophisticated than some scientists had thought, the team writes. And the principles guiding praying mantis depth perception may be useful to researchers working on improving machine vision, perhaps allowing artificial systems to better sense the depths of objects.
