Wishing all my readers and blog followers a very Happy Maha Shiv Ratri. Today is the day of Lord Shiva.
A 3-D-printed vortex-maker may improve understanding of braided fluids in nature, such as in the sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields
More than a century after the idea was first floated, physicists have finally figured out how to tie water in knots in the laboratory. The gnarly feat, described today in Nature Physics, paves the way for scientists to experimentally study twists and turns in a range of phenomena — ionized gases like that of the Sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields that describe elementary particles.
Lord Kelvin proposed that atoms were knotted “vortex rings” — which are essentially like tornado bent into closed loops and knotted around themselves, as Daniel Lathrop and Barbara Brawn-Cinani write in an accompanying commentary. In Kelvin’s vision, the fluid was the theoretical ‘aether’ then thought to pervade all of space. Each type of atom would be represented by a different knot.
Kelvin’s interpretation of the periodic table never went anywhere, but his ideas led to the blossoming of the mathematical theory of knots, part of the field of topology. Meanwhile, scientists also have come to realize that knots have a key role in a host of physical processes.
Creating a knot in a fluid bears little resemblance to tying a knot in a shoelace, say Dustin Kleckner and William Irvine, physicists at the University of Chicago in Illinois. The entire three-dimensional (3D) volume of a fluid within a confined region, such as a vortex, must be twisted. Kleckner and Irvine have now created a knotted vortex using a miniature version of an airplane wing built with a 3D printer.
During an airplane’s flight, a wing induces a rotational or vortex-like motion of air currents that gives lift to an airplane. When a wing at rest suddenly accelerates, it creates two vortices of air circulating in opposite directions. The researchers submerged their tiny wings in a tank of water and gave it a sudden acceleration to create a knotted structure (videos below and at top).
Capturing images of the knot was another technical tour-de-force. Fluid dynamicists often use colored dye to trace the motion of fluids, but Kleckner and Irvine injected tiny gas bubbles into the water that were drawn to the center of the knotted vortex by buoyancy forces. A high-speed laser scanner capable of producing CT-scan views of the fluid at 76,000 frames per second enabled the researchers to reconstruct the 3D arrangement of the bubbles, thus revealing the knots.
“The authors have managed a remarkable achievement to be able to images these vortex knots,” says Mark Dennis, an optical physicist at the University of Bristol, UK, who has made knotted vortices from light beams. The new study, he adds, transforms abstract notions about physical processes involving knots into testable ideas in the laboratory.
“Knotted vortices are an ideal model system for allowing us to study the precise way in which knots untie themselves in a real physical field,” says Irvine.
Knotted vortices show up in several branches of physics. Particle physicists, for example, have proposed that ‘glueballs’, hypothetical agglomerations of gluons — the elementary particles that bind quarks to form protons and neutrons — are tightly knotted quantum fields.
And in January, scientists reported evidence of ‘unbraiding’ or relaxation of knotted magnetic fields that may help to transfer heat to the Sun’s corona, or outer atmosphere, explaining why the plasma in this region is much hotter than the Sun’s surface.
Source: Scientific American.
The rare ships that have ventured through the harsh, icebound Arctic Ocean require reinforced hulls and ice-breaking bows that allow them to plow through dense ice as much as two meters deep, and face hazardous conditions in remote locations for long periods of time. Arctic sea ice now is melting so rapidly each summer due to global warming, however, that ships without ice-breaking hulls will be able to cross previously inaccessible parts of the Arctic Ocean by 2050. And light-weight ships equipped to cut through one meter of ice will be able to travel over the North Pole regularly in late summer, according to a new study published March 4 in Proceedings of the National Academy of Sciences Plus.
That’s good news for economic development because it offers many new and faster routes from east to west, shaving 40 percent off transportation time and fuel costs compared with shipments via the Suez Canal. But the geographic extent of trade routes across the Arctic is worrisome for scientists who study invasive species.
Ships traveling regularly in the Northwest Passage, beyond the Northern Sea Route and through the central Arctic Ocean, will likely bring new invaders to the Arctic as well as to northern ports. Mosquitoes and forest beetles are expected to survive hidden in cargo, for example. Hearty marine organisms, such as mussels and barnacles, will likely tag along as larvae in ballast tanks or in niche areas on vessel hulls. When new species flourish in a new environment they can become harmful, damaging local ecosystems and threatening native plants and animals, much as the Japanese vine known as kudzu has overrun the southern U.S. Economic costs associated with new pests have been significant—for example, the influx of zebra mussels into the Great Lakes has been estimated at $1 billion annually.
“The temptation for many new ships to enter [the Arctic] will be huge,” says University of California, Los Angeles, geographer Laurence Smith, lead author of the new study. Arctic shipping already has grown by leaps and bounds in just the past few years. In 2012, which set a record for lowest sea ice extent, a total of 46 ships—the most ever—traversed the Arctic Ocean. Thirty-four ships made the passage in 2011 whereas just four had done so the year before. For context, 19,000 ships pass through the Suez Canal annually.
Sea ice has long been a barrier to shipping across the Arctic Ocean as well as to species. Already, shipping is by far the most common pathway for marine invasive species, responsible for 69 percent of species introductions to marine areas, followed by aquaculture at 41 percent (non-native species can have more than one pathway of introduction, meaning some double counting.) The most common transport method is ships’ ballast water. Organisms can also hitch a ride in nooks and crannies on a ship’s hull, known as hull fouling. And organisms such as forest pests and mosquitoes can survive long trips in pallets and in cargo such as tires.
“Invasive species are one of those things that once the genie is out of the bottle, it’s hard to put her back in,” says climate scientist Jessica Hellmann of the University of Notre Dame who was not involved with this study. Hellmann studies the impact of climate change on invasive species and ecological systems. As Arctic ice melts, new ports will be connected and shorter passages between existing ports will lead to new opportunities for invasive species to spread, she says.
Mario Tamburri, a marine scientist and director of the Maritime Environment Resource Center at the University of Maryland Center for Environmental Science, has been researching survivorship and reproduction of organisms likely to be transported by ships by mimicking the conditions of shipping traffic. New colder, shorter routes afforded by the retreat of ice help invaders, such as mussels, barnacles and crabs, on a biological level, Tamburri says. Cold water slows metabolism of organisms, which can sustain themselves in low food conditions. “It’s like putting your groceries on ice,” he says.
Shorter routes also mean more organisms either attached to the hull or in ballast water are now more likely to survive the journey. Previously, the high heat and lack of light of longer trips outside the Arctic killed them off. “When ships now transport goods through the Panama Canal, for instance, through warm water and freshwater, natural barriers to invasive species are built into the shipping routes,” Tamburri says. “In the Arctic, those barriers go away.”
Ballast water and bivalves
Murmansk, Russia, a leading global port and the largest city north of the Arctic Circle, is one area that ice-free routes will likely open up further this summer. As more ships exchange ballast water for cargo, native species in places like Murmansk can quickly lose out against new species that have no checks and balances, such as marine species like bivalves that can be dispersed by larvae in ballast water as well as cold-water adapted adults, including green crabs.
Lewis Ziska, a plant physiologist with the U.S. Department of Agriculture’s Agricultural Research Service, says that once introduced, a new species can outcompete everything that has evolved over millennia. Although some nonnative species are innocuous, others thrive because there have no predators. Nothing controls them in the natural system, and they are better at filtering food out of the water than their native cousins. “Invasives use up the lion’s share of resources, and whatever biodiversity that was there falls apart,” Ziska says.
When new interlopers take hold, one or two tend to become very well suited for that environment and dominate it. The natural biodiversity diminishes, Ziska says. Scientists are beginning to catalogue and classify native and nonnative species at ports near oil facilities in Alaska. No large obvious invasions by marine traffic have occurred yet in the high latitude environment but Ziska and others scientists say no one can be sure. Scientists are only now beginning to look closely.
“We weren’t expecting the Arctic to change this quickly,” Ziska notes, adding that the implications for not only human traffic but also for biology are worrisome. “It’s basically opening up the entire Arctic region as a huge playground for invasive species. New things, new biological organisms are going into the area where they have never been seen before. The consequences of that are, quite frankly, are completely unknown.”
Source: Scientific American.
Nanowires used to disarm single genes in cells without harming or altering them were used to reveal that sodium chloride might cause harmful T cell growth
The incidence of autoimmune diseases, such as multiple sclerosis and type 1 diabetes, has spiked in developed countries in recent decades. In three studies published today in Nature, researchers describe the molecular pathways that can lead to autoimmune disease and identify one possible culprit that has been right under our noses — and on our tables — the entire time: salt.
To stay healthy, the human body relies on a careful balance: too little immune function and we succumb to infection, too much activity and the immune system begins to attack healthy tissue, a condition known as autoimmunity. Some forms of autoimmunity have been linked to overproduction of TH17 cells, a type of helper T cell that produces an inflammatory protein called interleukin-17.
But finding the molecular switches that cause the body to overproduce TH17 cells has been difficult, in part because conventional methods of activating native immune cells in the laboratory often harm the cells or alters the course of their development.
So when researchers heard a talk by Hongkun Park, a physicist at Harvard University in Cambridge, Massachusetts, about the use of silicone nanowires to disarm single genes in cells, they approached him immediately, recalls Aviv Regev, a biologist at the Massachusetts Institute of Technology (also in Cambridge) and a co-author on two of the studies.
Park showed last year that these nanowires can be used to manipulate genes in immune cells without affecting the cells’ functions. For the first of the Nature studies, Regev and her colleagues used Park’s technology to piece together a functional model of how TH17 cells are controlled, she says. “Otherwise,” she says, they would have been only “guessing in the dark.”
In the second study, an affiliated team of researchers observed immune cell production over 72 hours. One protein kept cropping up as a TH17-signal: serum glucocorticoid kinase 1 (SGK1), which is known to regulate salt levels in other types of cells. The researchers found that mouse cells cultured in high-salt conditions had higher SGK1 expression and produced more TH17 cells than those grown in normal conditions.
“If you incrementally increase salt, you get generation after generation of these TH17 cells,” says study co-author Vijay Kuchroo, an immunologist at Brigham and Women’s Hospital in Boston, Massachusetts.
In the third study, researchers confirmed Kuchroo’s findings, in mouse and human cells. It was “an easy experiment — you just add salt”, says David Hafler, a neurologist at Yale University in New Haven, Connecticut, who led the research.
But could salt change the course of autoimmune disease? Both Kuchroo and Hafler found that in a mouse model of multiple sclerosis, a high-salt diet accelerated the disease’s progression.
All this evidence, Kuchroo says, “is building a very interesting hypothesis [that] salt may be one of the environmental triggers of autoimmunity”.
But Kuchroo and other researchers say that evidence so far cannot predict the effect of salt on human autoimmunity. “As a physician, I’m very cautious,” Hafler says. “Should patients go on a low-salt diet? Yes,” he says, adding that “people should probably already be on a low-salt diet” for general health concerns.
Other experts are intrigued by the findings. “They have a very clear effect in vitro,” says John O’Shea, scientific director of the National Institute of Arthritis and Musculoskeletal and Skin Diseases Intramural Research Program in Bethesda, Maryland. But Hafler and others note that there are likely many cell types and environmental factors involved in triggering autoimmunity.
The results offer tantalizing leads for drug targets for autoimmune conditions. But O’Shea notes that it is unclear whether TH17 proliferation is a factor in all autoimmune disease. A targeted drug that might work to relieve psoriasis might not subdue rheumatoid arthritis. “When we say autoimmunity, we’re implying that it’s one thing,” O’Shea says. “But it’s not one thing — it’s heterogeneous.”
Source: Scientific American.
Materials that flip from insulator to conductor could make more energy-efficient transistors, although the metals are not yet close to competing with silicon
The switches in most electronic circuits are made of silicon, one of the commonest elements. But their successors might contain materials that, for now, are lab-grown oddities: strongly correlated metal oxides.
The allure of these materials lies in the outer shells of electrons surrounding their metal atoms. The shells are incomplete, leaving the electrons free to participate in coordinated quantum-mechanical behavior. In some materials, electrons pair up to produce superconductivity, or coordinate their spins to produce magnetism. Other materials can switch from being an insulator to a conductor.
Unlike transitions to superconductivity, which happen as temperatures approach absolute zero, the insulating-to-conducting transition typically happens as temperature increases, and sometimes occurs near room temperature. That has raised hopes that metal oxides could be used instead of silicon to make transistors. A spate of results is now making that look feasible. “People are interested in seeing if oxides can make it to applications,” says Manuel Bibes, a physicist at the Joint Physics Unit in Palaiseau, France, which is run by the French National Research Center and electronics company Thales.
Metal oxide transistors have the potential to consume less power than silicon switches, because the phase transition frees electrons from their localized state near each atom, without moving them through the bulk material. By contrast, silicon switches work by pulling electrons through the material to a channel where they conduct current (see ‘Go with the flow’).
In the past 5–10 years, researchers have succeeded in growing high-quality thin films of the metal oxides — overcoming one of the major barriers to applications. In July 2012, for example, a group in Japan reported that it had deposited a thin film of vanadium dioxide that underwent a phase transition in response to an applied electric field — proof that the material could be used as an electronic switch.
And last month, a group led by Shriram Ramanathan, a materials scientist at Harvard University in Cambridge, Massachusetts, addressed a fabrication challenge by growing a thin film of samarium nickelate on top of a substrate made of silicon and silicon dioxide.
The nickelate was deposited at a relatively low temperature that did not disturb the underlying silicon layers, raising the possibility of manufacturing metal oxides on top of silicon wafers to form three-dimensional chips, says Andrew Millis, a solid-state theorist at Columbia University in New York. Not only would that allow computing power to be packed much more densely, says Millis, but it would also permit metal oxide switches to be built on top of existing circuit architectures.
Other groups are trying to understand the nature of the phase transition. In January, Ivan Schuller, a solid-state physicist at the University of California, San Diego, and his colleagues showed that in vanadium oxide, the transition is in large part caused by micrometer-scale heating by the applied electric field.
Some point to Schuller’s work as evidence that metal oxides will never make fast switches, because heating effects are usually quite slow. But Ramanathan says that his own measurements on vanadium oxide demonstrate that the phase transition is quite fast — less than a few nanoseconds — and that it should not hinder applications.
Some physicists are finding further examples of potentially useful materials. Bernhard Keimer at the Max Planck Institute for Solid State Research in Stuttgart, Germany, alternates thin layers of metal oxides to form composites that often turn out to have serendipitous properties. His group layered conducting lanthanum nickelate and insulating lanthanum aluminate and found that the composite underwent a transition between the two properties.
The highest phase-transition temperature for the composite was 150 kelvin above absolute zero — too low for practical applications. But the group is now trying to replicate the phenomenon in other materials that might have higher transition temperatures.
Sandip Tiwari, an applied physicist at Cornell University in Ithaca, New York, acknowledges that metal oxides are not yet close to competing with silicon. But given recent progress, he feels that researchers need to start trying to implement them in devices. That way, he says, all the properties needed for a good transistor will be developed in tandem. “If you just look at whatever property is your favorite, you won’t get them all.”
Source: Scientific American.
As debate over the use of unmanned aerial vehicles in the U.S. rages on, a fashion designer introduces clothing that blocks drone-mounted infrared cameras
As the U.S. government draws up plans to use surveillance drones in domestic airspace, opposition to what many consider an unwarranted and significant invasion of privacy is mounting across the country, from rural Virginia to techopolis Seattle. Although officials debate anti-drone legislation at federal, state and local levels, one man is fighting back with high-tech apparel.
A New York City privacy advocate-turned-urban-guerilla fashion designer is selling garments designed to make their wearers invisible to infrared surveillance cameras, particularly those on drones. And although Adam Harvey admits that his three-item Stealth Wear line of scarves and capes is more of a political statement than a money-making venture, the science behind the fashion is quite sound.
“Fighting drones is not my full-time job, but it could be,” says Harvey, an instructor of physical computing at Manhattan’s School of Visual Arts and the creator of the CV Dazzle project, which seeks to develop makeup and hairstyles that camouflage people from face-recognition cameras and software.
Harvey’s newest medium, metalized fabric, has been around for more than 20 years. It holds in body heat that would burn bright for infrared cameras—a characteristic that could prove attractive to those who do not want unmanned aerial vehicles spying on them.
Metal is very good at absorbing and scattering infrared light, says Cheng Sun, a Northwestern University assistant professor of mechanical engineering. In that sense there is nothing exotic in how metalized fabric works—it “would strongly attenuate the [infrared] light,” he says. The metal would dissipate heat to surroundings as well, making the wearer harder to pinpoint.
To date, the fabric has primarily been used in tape and gaskets to protect electronics and communications equipment from static electricity and electromagnetic interference, according to Larry Creasy, director of technology for metalized fabric-maker Laird Technologies, based in Saint Louis.
Here’s how metalizing works, at least at Laird: Woven fabric, commonly nylon or polyester, is coated with a special catalyst—a precious metal Creasy declined to specify—that helps copper bind to the fiber. Once dry, the fabric is submerged in a copper sulfate–plating bath and dried. A nickel sulfamate bath follows to help the finished fabric withstand the elements and abrasions. The result is a flexible, breathable fabric that can be cut with ordinary tools but that protects against electromagnetic interference and masks infrared radiation, Creasy says. The process adds weight to the original fabric. An untreated square yard of nylon weighs about 42.5 grams. Treated, the same patch weighs more than 70 grams.
Harvey’s fabric is coated with copper, nickel and silver, a combination that gives his scarves, head-and-shoulders cloak and thigh-length “burqa” a silvery and “luxurious” feel. The material blocks cell signals, as well, adding an element of risk to tweeting, texting and other mobile activities, as the wearer must break cover to communicate.
Stealth Wear is sold only via a U.K. Web site. The burqa goes for about $2,300, the “hoodie” is $481 and the scarf is $565—luxury items, but so, too, is privacy today, Harvey says.
The high cost and limited availability are significant drawbacks—Harvey says he’s only sold one Stealth Wear item online, a scarf. But the Federal Aviation Administration (FAA) predicts 10,000 commercial drones will ply domestic airspace by 2017—almost twice the that of the U.S. Air Force’s current fleet of unmanned aircraft. The number of drones flying in the U.S. today is hard to pin down because not every company and agency that gets FAA approval to fly a drone actually puts one in the air. In fact, 1,428 private-sector and government requests have been approved since 2007, according to the FAA. A Los Angeles Times report states that 327 of those permits are still active. Meanwhile, President Obama signed a law in February 2012 that gives the FAA until September 2015 to draw up rules that dictate how law enforcement, the military and other entities may use drones in U.S. airspace.
As of October 2012, 81 law agencies, universities, an Indian tribal agency and other entities had applied to the FAA to fly drones, according to documents released by the FAA to the Electronic Freedom Frontier following a Freedom of Information Act lawsuit. Government entities as diverse as the U.S. Department of State and Otter Tail County, Minn., are among them.
Although Harvey’s anti-drone fashions are not currently flying off the shelves, he could soon find himself leading a seller’s market if recent events are any metric:
- The Charlottesville, Va., city council has passed a watered-down ordinance that asks the federal and commonwealth governments not to use drone-derived information in court. Proponents had sought to make the city drone-free (pdf).
- Virginia, Minnesota, Oregon, Montana, Arizona (pdf) and Idaho legislators are trying to at least regulate or even prohibit, drones in their skies.
- Seattle Mayor Mike McGinn returned the city’s two surveillance drones after a hostile public reception.
- A bipartisan pair of U.S. Representatives has introduced legislation to limit information-gathering by government-operated drones as well as prohibit weapons on law-enforcement and privately owned unmanned aerial vehicles.
Drone advocates defend the use of the technology as a surveillance tool. “We clearly need to do a better job of educating people about the domestic use of drones,” says Ben Gielow, government relations manager for the Association for Unmanned Vehicle Systems International. Gielow says U.S. voters must decide the acceptability of data collection from all sources, adding, “Ultimately, an unmanned aircraft is no different than gathering data from the GPS on your phone or from satellites.”
GPS does not use infrared cameras, however, and satellites are not at the center the current privacy debate brewing in Washington—factors that could make Harvey’s designs all the more fashionable.
Source: Scientific American.
The last time I visited Boston’s Museum of Fine Arts was in 2004 to see a Rembrandt exhibition. But I might have wandered away from the works of the Dutch master in search of an ancient Greek artifact, had I known at the time that the object in question, a wine vessel, was in the museum’s collection. According to the 2012 Christmas issue of the BMJ (preacronymically known as the British Medical Journal), the 2,500-year-old cup, created by one of the anonymous artisans who helped to shape Western culture, is adorned with the image of a man wiping his butt.
That revelation appears in an article entitled “Toilet Hygiene in the Classical Era,” by French anthropologist and forensic medicine researcher Philippe Charlier and his colleagues. Their report examines tidying techniques used way back—and the resultant medical issues. Such a study is in keeping with the BMJ‘s tradition of offbeat subject matter for its late December issue—as noted in this space five years ago: “Had the Puritans never left Britain for New England, they might later have fled the British Medical Journal to found the New England Journal of Medicine.”
The toilet hygiene piece reminds us that practices considered routine in one place or time may be unknown elsewhere or elsetime. The first known reference to toilet paper in the West does not appear until the 16th century, when satirist François Rabelais mentions that it doesn’t work particularly well at its assigned task. Of course, the ready availability of paper of any kind is a relatively recent development. And so, the study’s authors say, “anal cleaning can be carried out in various ways according to local customs and climate, including with water (using a bidet, for example), leaves, grass, stones, corn cobs, animal furs, sticks, snow, seashells, and, lastly, hands.” Sure, aesthetic sensibility insists on hands being the choice of last resort, but reason marks seashells as the choice to pull up the rear. “Squeezably soft” is the last thing to come to mind about, say, razor clams.
Charlier et al. cite no less an authority than philosopher Seneca to inform us that “during the Greco-Roman period, a sponge fixed to a stick (tersorium) was used to clean the buttocks after defecation; the sponge was then replaced in a bucket filled with salt water or vinegar water.” Talk about your low-flow toilets. The authors go on to note the use of rounded “fragments of ceramic known as ‘pessoi’ (meaning pebbles), a term also used to denote an ancient board game.” (The relieved man on the Museum of Fine Arts’s wine cup is using a singular pessos for his finishing touches.) The ancient Greek game pessoi is not related to the ancient Asian game Go, despite how semantically satisfying it would be if one used stones from Go after one Went.
According to the BMJ piece, a Greek axiom about frugality cites the use of pessoi and their purpose: “Three stones are enough to wipe.” The modern equivalent is probably the purposefully self-contradictory “toilet paper doesn’t grow on trees.”
Some pessoi may have originated as ostraca, pieces of broken ceramic on which the Greeks of old inscribed the names of enemies. The ostraca were used to vote for some pain-in-the-well-you-know to be thrown out of town—hence, “ostracized.” The creative employment of ostraca as pessoi allowed for “literally putting faecal matter on the name of hated individuals,” Charlier and company suggest. Ostraca have been found bearing the name of Socrates, which is not surprising considering they hemlocked him up and threw away the key. (Technically, he hemlocked himself, but we could spend hours in Socratic debate about who took ultimate responsibility.)
Putting shards of a hard substance, however polished, in one’s delicate places has some obvious medical risks. “The abrasive characteristics of ceramic,” the authors write, “suggest that long term use of pessoi could have resulted in local irritation, skin or mucosal damage, or complications of external haemorrhoids.”
To quote Shakespeare, “There’s a divinity that shapes our ends.” Sadly, for millennia the materials used to clean our divinely shaped ends were decidedly rough-hewn.
Source: Scientific American.
Global average temperatures are now higher than they have been for about 75% of the past 11,300 years, a study suggests. And if climate models are any indication, by the end of this century they will be the highest ever since the end of the most recent ice age.
Instrumental records of climate extend back to only the late nineteenth century. Beyond that, scientists depend on analyses of natural chronicles such as tree rings and isotope ratios in cave formations.
But even these archives have their limits: many detailed reconstructions of climate, particularly of temperature, apply to only limited regions or extend back at most a couple of millennia, says Shaun Marcott, a climate scientist at Oregon State University in Corvallis.
Marcott and his colleagues set about reconstructing global climate trends all the way back to 11,300 years ago, when the Northern Hemisphere was emerging from the most recent ice age. To do so, they collected and analyzed data gathered by other teams. The 73 overlapping climate records that they considered included sediment cores drilled from lake bottoms and sea floors around the world, along with a handful of ice cores collected in Antarctica and Greenland.
Each of these chronicles spanned at least 6,500 years, and each included a millennium-long baseline period beginning in the middle of the post-ice-age period at 3550 BC.
For some records, the researchers inferred past temperatures from the ratio of magnesium and calcium ions in the shells of microscopic creatures that had died and dropped to the ocean floor; for others, they measured the lengths of long-chain organic molecules called alkenones that were trapped in the sediments.
After the ice age, they found, global average temperatures rose until they reached a plateau between 7550 and 3550 BC. Then a long-term cooling trend set in, reaching its lowest temperature extreme between ad 1450 and 1850.
Since then, temperatures have been increasing at a dramatic clip: from the first decade of the twentieth century to now, global average temperatures rose from near their coldest point since the ice age to nearly their warmest, Marcott and his team report today in Science.
The temperature trends that the team identified for the past 2,000 years are statistically indistinguishable from results obtained by other researchers in a previous study, says Marcott. “That gives us confidence that the rest of our record is right too,” he adds.
Marcott and his colleagues “have put together a pretty impressive set of climate proxies”, says Gavin Schmidt, a climate scientist at the NASA Goddard Institute for Space Studies in New York. “The overall climate picture has been clear for a long time, mostly from the Northern Hemisphere, but this compilation really puts the rest of the world in context,” he adds.
“Prior to this study, researchers could only guess whether global temperatures had exceeded the warmest part of the present interglacial period,” says Darrell Kaufman, a geologist at Northern Arizona University in Flagstaff. The latest findings show that the recent high temperatures are not necessarily the warmest, but they are unusually high, he notes.
The temperature trends during most of the post-ice-age period match those expected from natural factors such as the long-term variation in the tilt of Earth’s axis, says Marcott. But in the past century and a half, industrial emissions of the greenhouse gas carbon dioxide have increased — which helps to explain why global temperatures have risen so quickly in recent decades, he suggests.
Climate models from the Intergovernmental Panel on Climate Change suggest that by the end of this century, regardless of future carbon dioxide emissions, temperatures will be at their highest since the end of the most recent ice age, the researchers say.
Source: Scientific American.
In December 2005, when winter the bottlenose dolphin was just a few months old, she was swimming with her mother in Mosquito Lagoon, along central Florida’s Atlantic coast. Somehow she got herself tangled in a crab trap. An eagle-eyed fisherman spotted her struggling and called in a wildlife rescue team. The volunteers gently positioned the dolphin on a stretcher, carried her out of the water and drove her across the state to the Clearwater Marine Aquarium.
She was in bad shape when she arrived—exhausted, dehydrated, and sporting numerous cuts and abrasions. She could barely swim, and trainers stood in the tank with her, holding her little body up in the water. No one knew whether she would make it through the night. But she was a survivor, enduring that first night and the next one, too.
- A bottlenose dolphin named Winter lost her tail after getting tangled up in a crab trap. She was forced to swim from side to side like a fish, which warped her spine.
- Two prosthetists decided to build Winter a whole new tail, something that had never been done before. In the process, they invented a new kind of gel.
- Today Winter’s false tail is helping to straighten her spine, and “dolphin gel” cushioning has proved useful for human athletes who have lost limbs.
Source: Scientific American.