Galaxies may grow by swiping gas from their neighbors.

New simulations suggest that nearly half the matter in the Milky Way may have been siphoned from the gas of other galaxies. That gas provides the raw material that galaxies use to build their bulk. The finding, scheduled to appear in the Monthly Notices of the Royal Astronomical Society, reveals a new, unexpected way for galaxies to acquire matter and could give clues to how they evolve.
“These simulations show a huge amount of interaction among galaxies, a huge dance that’s going on,” says astronomer Romeel Davé of the University of Edinburgh. That dance, and the subsequent exchange of atoms, could be what establishes a galaxy’s character — whether it’s small or big, elliptical or spiral, quiet or bursting with star formation. If the simulation results are confirmed with observations, it could be a major advancement in understanding galaxy formation, Davé says.

It makes sense that much of the material in one galaxy actually came from other galaxies, says study coauthor Claude-André Faucher-Giguère, a theoretical astrophysicist at Northwestern University in Evanston, Ill. “Still, the result was really unexpected,” he says.

Astronomers thought galaxies got their matter in two main ways. First, atoms clumped together to form stars and then galaxies, not long after the Big Bang about 13.8 billion years ago. Then some of those atoms were eventually ejected by supernovas but rained back onto the same galaxy, recycling the gas again and again.

The new simulations showed a third way galaxies could score gas. Powerful supernova explosions would eject atoms, in the form of gas, far from their home galaxies into intergalactic space. Those atoms would then travel through space, pushed toward other galaxies by galactic winds that move at several hundred kilometers per second. When the particles neared a galaxy’s gravitational pull, they would get sucked in, where they would serve as the basis for stars, planets, dust and other material in their new galactic home. Still, this exchange of atoms is extremely difficult to spot in space because the gas atoms, don’t give off light like stars do.
Faucher-Giguère and colleagues spotted the exchange in computer simulations that show how galaxies formed just after the Big Bang and how they have evolved over time. The team tracked gas atoms as they moved through the model universe, formed stars and then were ejected from galaxies as those stars exploded.

In the simulations, up to half of the atoms in large galaxies were pulled in from other galaxies. Because more massive galaxies have more gravity, they tended to pull atoms from the ejected material of small galaxies. The exchange appears to take billions of years as atoms travel the vast space between galaxies, the team notes.

“It’s that not surprising to see a galaxy kick out matter, which is then pulled in by other galaxies,” Davé says. What is surprising, he says, is the amount of material that’s transferred. Before seeing the simulations, he would have guessed that about 5 percent of gas was transferred among galaxies this way. “To see that it is up to 50 percent is pretty remarkable,” he says.

Already, astronomers are searching for evidence of this material-swapping behavior among galaxies. Faucher-Giguère and colleagues, working with researchers using the Hubble Space Telescope, hope to observe intergalactic transfer of gas among galaxies soon.

The largest marsupial to ever walk the Earth just got another accolade: It’s also the only marsupial known to migrate seasonally.

Diprotodon optatum was a massive wombat-like herbivore that lived in what’s now Australia and New Guinea during the Pleistocene, until about 40,000 years ago. Now, an analysis of one animal’s teeth suggests that it undertook long, seasonal migrations like those made by zebras and wildebeests in Africa.

Animals pick up the chemical element strontium through their diet, and it leaves a record in their teeth. The ratio of different strontium isotopes varies from place to place, so it can provide clues about where an animal lived. Strontium isotope ratios in an incisor from one D. optatum revealed a repeating pattern. That suggests the animal migrated seasonally — it moved around, but generally hit up the same rest stops each year, researchers report September 27 in the Proceedings of the Royal Society B.

It’s the first evidence to show a marsupial — living or extinct — migrating in this way, says study coauthor Gilbert Price, a paleoecologist at the University of Queensland in Brisbane, Australia. It’s not clear exactly why this mega-marsupial might have migrated, but an analysis of the carbon isotopes in its teeth suggests it ate a fairly limited diet. So it might have migrated to follow food sources that popped up seasonally in different places, the authors suggest.

What looks like a spider, but with a segmented rear plus a long spike of a tail, has turned up in amber that’s about 100 million years old.

Roughly the size of a peppercorn (not including the tail, which stretches several times the body length), this newly described extinct species lived in forests in what is now Myanmar during the dinosaur-rich Cretaceous Period.

Spiders as their own distinctive group had evolved long before. Whether this tailed creature should be considered a true spider (of the group Araneae) is debatable though, researchers acknowledge February 5 in two studies in Nature Ecology & Evolution. In one of the papers, the fossils’ chimeric mash-up of traits both spidery and nonspidery inspired Bo Wang of the Chinese Academy of Sciences in Nanjing and colleagues to name the species Chimerarachne yingi.
C. yingi indeed has some anatomy that, among living animals, would be unique to spiders, says Gonzalo Giribet of Harvard University, a coauthor of the other paper. The fossils have what look like little structures that could have exuded spider silk, as well as distinctive male spider sex organs. Called pedipalps, these modified legs have no direct connection to a sperm-producing organ. Spiders need to load them before mating, for instance by ejaculating a sperm droplet and dipping pedipalps in it, so the structures can deliver the sperm a bit like a syringe.

But the abdomen-like end of a true spider’s body isn’t segmented and certainly doesn’t have a tail. Giribet and his colleagues’ analysis puts C. yingi in an ancient sister group of spiders. That’s startling in itself, Giribet says, because researchers have speculated that this Uraraneida group had gone extinct much earlier. So, spider or not, C. yingi remains intriguing.

Underwater grasses are growing back in the Chesapeake Bay. The plants now carpet three times as much real estate as in 1984, thanks to more than 30 years of efforts to reduce nitrogen pollution. This environmental success story shows that regulations put in place to protect the bay’s health have made a difference, researchers report the week of March 5 in Proceedings of the National Academy of Sciences.

Rules limiting nutrient runoff from farms and wastewater treatment plants helped to decrease nitrogen concentrations in the bay by 23 percent since 1984. That decline in nitrogen has allowed the recovery of 17,000 hectares of grasses, the new study shows — enough to cover roughly 32,000 football fields.
“This is one of the best examples we have of linking long-term research data with management to show how important that is in restoring this critical habitat,” says Karen McGlathery, an environmental scientist at the University of Virginia in Charlottesville who wasn’t involved in the research. ”I don’t know of any other system that’s so large and so complicated where these connections have been made.”

The bay’s aquatic vegetation, including seagrasses and freshwater grasses, is an important part of coastal ecosystems, says study coauthor Jonathan Lefcheck, a marine ecologist at the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine. Beds of underwater grasses act as nurseries that shelter young fish and aquatic invertebrates. The plants clean the water by trapping particulates, and stabilize shorelines by preventing erosion. But the once-lush grasses began dying off in the 1950s when the region’s human population boomed, and cities and farms dumped increasing amounts of nitrogen and other nutrients into the bay.

In the late 1970s and early 1980s, state and federal agencies took action, limiting the amount of nutrients that could enter the bay from farms, water treatment facilities and other sources. Those groups also instituted programs to monitor the bay’s health, building up the stockpile of information that Lefcheck and his colleagues have now analyzed.

The researchers looked at aerial surveys of the bay, data on water temperature and nutrient levels, as well as land and fertilizer use. Using mathematical equations to test which variables had the biggest impact on seagrass regrowth, the team pinned down nitrogen reduction as the driving force. That makes sense: Too much nitrogen in water promotes the growth of plankton, which can block sunlight, and algae, which can settle on the grass blades and smother them.
Now, though, researchers are seeing just the opposite. Grasses need clean water to get a foothold, but once they settle in, they “modify their own environment and make it better,” Lefcheck says. “Once you get a little bit established, it can take off.”

As I’ve been reporting a story about the opioid epidemic, I’ve sorted through a lot of tragic numbers that make the astronomical spike in deaths and injuries related to the drugs feel more real.

The rise in the abuse of opioids — powerfully addictive painkillers — is driven by adults. But kids are also swept up in the current, a new study makes clear. The number of children admitted to pediatric intensive care units at hospitals for opioid-related trouble nearly doubled between 2004 and 2015, researchers report in the March Pediatrics.
Researchers combed through medical records from 46 hospitals around the United States, looking for opioid-related reasons for admission to the hospital. When the researchers looked at children who landed in pediatric intensive care units for opioid-related crises, the numbers were grim, nearly doubling. In the period including 2004 to 2007, 367 children landed in the PICU for opioid-related trouble. In the period including 2012 to 2015, that number was 643. (From 2008 to 2011, 554 kids were admitted to the PICU for opioid-related illnesses.)
Most opioid-related hospital admissions were for children ages 12 to 17, the researchers found. The available stats couldn’t say how many of those events were accidental ingestions versus intentional drug use. (Though for older kids, there’s a sliver of good news from elsewhere: Prescription opioid use among teenagers is actually down, a recent survey suggests.)
But about a third of the hospitalizations were for children younger than 6. And among these young kids, about 20 percent of the poisonings involved methadone, a drug that’s used to treat opioid addiction. That means that these young kids are getting into adults’ drugs (illicit or prescribed) and accidentally ingesting them.

Lots of parents don’t store their prescription opioid painkillers safely away from their young children, a survey last year suggests. Drugs, prescription or otherwise, should be kept out of sight and out of reach, ideally locked away. Some kids are great climbers, and some are crafty bottle openers who can, with persistence, work around supposedly child-resistant packaging.

These are tips for everyone living with small kids — not just those who may have opioids in the house. Children are curious, persistent and, sadly, extra vulnerable to powerful drugs, which means that we should all do our best to keep them away from these potentially dangerous drugs.

To quickly unfurl and refold their wings, earwigs stretch the rules of origami.

Yes, those garden pests that scurry out from under overturned flowerpots can also fly. Because earwigs spend most of their time underground and only occasionally take to the air, they pack their wings into packages with a surface area more than 10 times smaller than when unfurled, using an origami-like series of folds. Springy wing joints let the insects bypass some of the mathematical constraints that normally limit the way a rigid two-dimensional material can be folded, researchers report March 23 in Science.
Earwig wings’ folding pattern should be impossible according to mathematical equations that predict the three-dimensional designs that can be made by folding a two-dimensional material like a sheet of paper, says study coauthor Andres Arrieta, a mechanical engineer at Purdue University in West Lafayette, Ind.

Origami theory assumes that the material being folded is perfectly rigid. But the joints of earwigs’ wings — where creases form — are rich in a rubbery polymer called resilin. This little bit of stretch lets earwig wings do what a regular origami structure can’t: lock into two different conformations, open or folded up, and transition between the two.
It’s an example of a bistable structure — something like the slap bracelets, popular in the 1980s and 1990s, which switch from a flat conformation to a curved one when whacked against a wrist, says study coauthor André Studart, a materials scientist at ETH Zürich. When locked open, earwig wings store energy in the springy resilin joints. When that strain is released, the wings rapidly crumple back to their folded position.
Such constructions can inform robotics design. Inspired by the wings, the researchers created a prototype gripper. Its rigid pieces are held together by rubbery, strategically placed joints. Within fractions of a second, the structure can snap from its mostly flat conformation to one that can grip a small object and hold it without constant external force.
While other materials scientists have pushed the limits of origami by making flat pieces bendable, this design instead stretches the hinges, says Jesse Silverberg, a physicist at Harvard University who wasn’t part of the study. Such a design has been observed and discussed, but never before been implemented in this way.

The earwig “is a beautiful example of how nature uses slight extensions to ideal mathematical origami to do something amazing,” says Itai Cohen, a physicist at Cornell University who wasn’t part of the study.

Perhaps that’s a slight redemption for the much-maligned insect.

A genetic hack to make photosynthesis more efficient could be a boon for agricultural production, at least for some plants.

This feat of genetic engineering simplifies a complex, energy-expensive operation that many plants must perform during photosynthesis known as photorespiration. In field tests, genetically modifying tobacco in this way increased plant growth by over 40 percent. If it produces similar results in other crops, that could help farmers meet the food demands of a growing global population, researchers report in the Jan. 4 Science.
Streamlining photorespiration is “a great step forward in efforts to enhance photosynthesis,” says Spencer Whitney, a plant biochemist at Australian National University in Canberra not involved in the work.

Now that the agricultural industry has mostly optimized the use of yield-boosting tools like pesticides, fertilizers and irrigation, researchers are trying to micromanage and improve plant growth by designing ways to make photosynthesis more efficient (SN: 12/24/16, p. 6).

Photorespiration is a major roadblock to achieving such efficiency. It occurs in many plants, such as soybeans, rice and wheat, when an enzyme called Rubisco — whose main job is to help transform carbon dioxide from the atmosphere into sugars that fuel plant growth — accidentally snatches an oxygen molecule out of the atmosphere instead.

That Rubisco-oxygen interaction, which happens about 20 percent of the time, generates the toxic compound glycolate, which a plant must recycle into useful molecules through photorespiration. This process comprises a long chain of chemical reactions that span four compartments in a plant cell. All told, completing a cycle of photorespiration is like driving from Maine to Florida by way of California. That waste of energy can cut crop yields by 20 to 50 percent, depending on plant species and environmental conditions.Streamlining photorespiration is “a great step forward in efforts to enhance photosynthesis,” says Spencer Whitney, a plant biochemist at Australian National University in Canberra not involved in the work.

Now that the agricultural industry has mostly optimized the use of yield-boosting tools like pesticides, fertilizers and irrigation, researchers are trying to micromanage and improve plant growth by designing ways to make photosynthesis more efficient (SN: 12/24/16, p. 6).

Photorespiration is a major roadblock to achieving such efficiency. It occurs in many plants, such as soybeans, rice and wheat, when an enzyme called Rubisco — whose main job is to help transform carbon dioxide from the atmosphere into sugars that fuel plant growth — accidentally snatches an oxygen molecule out of the atmosphere instead.

That Rubisco-oxygen interaction, which happens about 20 percent of the time, generates the toxic compound glycolate, which a plant must recycle into useful molecules through photorespiration. This process comprises a long chain of chemical reactions that span four compartments in a plant cell. All told, completing a cycle of photorespiration is like driving from Maine to Florida by way of California. That waste of energy can cut crop yields by 20 to 50 percent, depending on plant species and environmental conditions.
Using genetic engineering, researchers have now designed a more direct chemical pathway for photorespiration that is confined to a single cell compartment — the cellular equivalent of a Maine-to-Florida road trip straight down the East Coast.

Paul South, a molecular biologist with the U.S. Department of Agriculture in Urbana, Ill., and colleagues embedded genetic directions for this shortcut, written on pieces of algae and pumpkin DNA, in tobacco plant cells. The researchers also genetically engineered the cells to not produce a chemical that allows glycolate to travel between cell compartments to prevent the glycolate from taking its normal route through the cell.
Unlike previous experiments with human-designed photorespiration pathways, South’s team tested its photorespiration detour in plants grown in fields under real-world farming conditions. Genetically altered tobacco produced 41 percent more biomass than tobacco that hadn’t been modified.
“It’s very exciting” to see how well this genetic tweak worked in tobacco, says Veronica Maurino, a plant physiologist at Heinrich Heine University Düsseldorf in Germany not involved in the research, but “you can’t say, ‘It’s functioning. Now it will function everywhere.’”

Experiments with different types of plants will reveal whether this photorespiration fix creates the same benefits for other crops as it does for tobacco. South’s team is currently running greenhouse experiments on potatoes with the new set of genetic modifications, and plans to do similar tests with soybeans, black-eyed peas and rice.

The vetting process for such genetic modifications to be approved for use on commercial farms, including more field testing, will probably take at least another five to 10 years, says Andreas Weber, a plant biochemist also at Heinrich Heine University Düsseldorf who coauthored a commentary on the study that appears in the same issue of Science. In the meantime, he expects that researchers will continue trying to design even more efficient photorespiration shortcuts, but South’s team “has now set a pretty high bar.”

THE WOODLANDS, Texas — Grains of dust from the edge of the solar system could be finding their way to Earth. And NASA may already have a handful of the debris, researchers report.

With an estimated 40,000 tons of space dust settling in Earth’s stratosphere every year, the U.S. space agency has been flying balloon and aircraft missions since the 1970s to collect samples. The particles, which can be just a few tens of micrometers wide, have long been thought to come mostly from comets and asteroids closer to the sun than Jupiter (SN Online: 3/19/19).

But it turns out that some of the particles may have come from the Kuiper Belt, a distant region of icy objects orbiting beyond Neptune, NASA planetary scientist Lindsay Keller said March 21 at the Lunar and Planetary Science Conference. Studying those particles could reveal what distant, mysterious objects in the Kuiper Belt are made of, and perhaps how they formed (SN Online: 3/18/19).

“We’re not going to get a mission out to a Kuiper Belt object to actually collect [dust] samples anytime soon,” Keller said. “But we have samples of these things in the stratospheric dust collections here at NASA.”
One way to find a dust grain’s home is to probe the particle for microscopic tracks where heavy charged particles from solar flares punched through. The more tracks a grain has, the longer it has wandered in space — and the more likely it originated far from Earth, says Keller, who works at the Johnson Space Center in Houston.

But to determine precisely how long a dust grain has spent traveling space, Keller first needed to know how many tracks a grain typically picks up per year. Measuring that rate required a sample with a known age and known track density — criteria met only by moon rocks brought back on the Apollo missions. But the last track-rate estimate was done in 1975 and with less precise instruments than are available today.
So Keller and planetary scientist George Flynn of SUNY Plattsburgh reexamined that same Apollo rock with a modern electron microscope. They found that the rate at which rocks pick up flare tracks was about 20 times lower than the previous study estimated.

That means it takes longer for dust flakes to pick up tracks than astronomers assumed. When Keller and Flynn counted the number of tracks in 14 atmospheric dust grains, the pair found that some of the particles must have spent millions of years out in space — far too long to have come just from between Mars and Jupiter.

Grains specifically from the Kuiper Belt would have wandered 10 million years to reach Earth’s stratosphere, the researchers calculated. That’s “pretty solid evidence that we’re collecting Kuiper Belt dust right here,” Keller says.
Four of the particles contained minerals that had to have formed through interactions with liquid water. That’s surprising; the Kuiper Belt is thought to be too cold for water to be liquid.

“Many of these particles, if they in fact are from the Kuiper Belt, tell you that some of the minerals in Kuiper Belt objects formed in the presence of liquid water,” Keller says. The water probably came from collisions between Kuiper Belt objects that produced enough heat to melt ice, he says.

“I think it’s incredible if Lindsay Keller has shown that he has pieces of Kuiper Belt dust in his lab,” says planetary scientist Carey Lisse of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. But more work needs to be done to confirm that the dust really came from the Kuiper Belt, he says, and wasn’t just sitting on an asteroid for millions of years. “Lindsay needs to get a lot more samples,” Lisse says. “But I do think he’s on to something.”

Lisse works on NASA’s New Horizons mission, which found plenty of dust in the outer solar system and measured its abundance near Pluto when the spacecraft flew past the dwarf planet in 2015. Based on those results, he finds it unsurprising that some of that dust has made it to Earth. But it is “really cool,” he says. “We can actually try to figure out what the Kuiper Belt is made of.”

Editor’s note: This story was updated April 8, 2019, to correct that the newly calculated flare track rate was about 20 times lower than the rate calculated in 1975, not two orders of a magnitude lower.

A new member of the human genus has been found in a cave in the Philippines, researchers report.

Fossils with distinctive features indicate that the hominid species inhabited the island now known as Luzon at least 50,000 years ago, according to a study in the April 11 Nature. That species, which the scientists have dubbed Homo luzonensis, lived at the same time that controversial half-sized hominids named Homo floresiensis and nicknamed hobbits were roaming an Indonesian island to the south called Flores (SN: 7/9/16, p. 6).
In shape and size, some of the fossils match those of corresponding bones from other Homo species. “But if you take the whole combination of features for H. luzonensis, no other Homo species is similar,” says study coauthor and paleoanthropologist Florent Détroit of the French National Museum of Natural History in Paris.

If the find holds up to further scientific scrutiny, it would add to recent fossil and DNA evidence indicating that several Homo lineages already occupied East Asia and Southeast Asian islands by the time Homo sapiens reached what’s now southern China between 80,000 and 120,000 years ago (SN: 11/14/15, p. 15). The result: an increasingly complicated picture of hominid evolution in Asia.

Excavations in 2007, 2011 and 2015 at Luzon’s Callao Cave yielded a dozen H. luzonensis fossils at first — seven isolated teeth (five from the same individual), two finger bones, two toe bones and an upper leg bone missing its ends, the scientists say. Analysis of the radioactive decay of uranium in one tooth suggested a minimum age of 50,000 years. Based on those fossils, a hominid foot bone found in 2007 in the same cave sediment was also identified as H. luzonensis. It dates to at least 67,000 years ago.
had molars that were especially small, even smaller than those of hobbits, with some features similar to modern humans’ molars. The hominid also had relatively large premolars that, surprisingly, had two or three roots rather than one. Hominids dating to several hundred thousand years ago or more, such as Homo erectus , typically had premolars with multiple roots. H. luzonensis finger and toe bones are curved, suggesting a tree-climbing ability comparable to hominids from 2 million years ago or more.
It’s unclear whether H. luzonensis was as small as hobbits, Détroit says. The best-preserved hobbit skeleton comes from a female who stood about a meter tall. Based on the length of the Callao Cave foot bone, Détroit’s team suspects that H. luzonensis was taller than that, although still smaller than most human adults today.

As with hobbits, H. luzonensis’ evolutionary origins are unknown. Scientists think that hobbits may have descended from seagoing H. erectus groups, and perhaps H. luzonensis did too, writes paleoanthropologist Matthew Tocheri of Lakehead University in Thunder Bay, Canada, in a commentary published with the new report. Evidence suggests that hominids reached Luzon by around 700,000 years ago (SN Online: 5/2/18). So H. erectus may have also crossed the sea from other Indonesian islands or mainland Asia to Luzon and then evolved into H. luzonensis with its smaller body and unusual skeletal traits, Détroit speculates, a process known as island dwarfing.

But some scientists not involved in the research say it’s too soon to declare the Luzon fossils a brand-new Homo species. Détroit’s group, so far, has been unable to extract ancient DNA from the fossils. So “all [evolutionary] possibilities must remain open,” says archaeologist Katerina Douka of the Max Planck Institute for the Science of Human History in Jena, Germany.

The mosaic of fossil features that the team interprets as distinctive, for instance, may have been a product of interbreeding between two or more earlier Homo species, creating hybrids, but not a new species.

Or perhaps a small population of, say, H. erectus that survived on an isolated island like Luzon for possibly hundreds of thousands of years simply acquired some skeletal features that its mainland peers lacked, rather than evolving into an entirely new species, says paleoanthropologist María Martinón-Torres.

Those questions make the new fossils “an exciting and puzzling discovery,” says Martinón-Torres, director of the National Research Centre on Human Evolution in Burgos, Spain.

If the unusual teeth and climbing-ready hand and foot bones found at Callao Cave occurred as a package among Luzon’s ancient Homo crowd, “then that combination is unique and unknown so far” among hominids, Martinón-Torres says. Only a more complete set of fossils, ideally complemented by ancient DNA, she adds, can illuminate whether such traits marked a new Homo member.

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.”