One of the strangest things about growing a human being inside your body is the alien sensation of his movements. It’s wild to realize that these internal jabs and pushes are the work of someone else’s nervous system, skeleton and muscles. Someone with his own distinct, mysterious agenda that often includes taekwondoing your uterus as you try to sleep.
Around the 10-week mark, babies start to bend their heads and necks, followed by full-body wiggles, limb movement and breathing around 15 weeks. These earliest movements are usually undetectable by pregnant women, particularly first-timers who may not recognize the flutters until 16 to 25 weeks of pregnancy. These movements can be exciting and bizarre, not to mention uncomfortable. But for the developing baby, these kicks are really important, helping to sculpt muscles, bones and joints. While pregnant women can certainly sense a jab, scientists have largely been left in the dark about how normal fetuses move. “It’s extremely difficult to investigate fetal movements in detail in humans,” says Stefaan Verbruggen, a bioengineer formerly at Imperial College London who recently moved to Columbia University in New York.
Now, using relatively new MRI measurements of entire fetuses wiggling in utero, researchers have tracked these kicks across women’s pregnancies. The results, published January 24 in the Journal of the Royal Society Interface, offer the clearest look yet at fetal kicking and provide hints about why these moves are so important. Along with bioengineer Niamh Nowlan, of ICL, and colleagues, Verbruggen analyzed videos of fetal kicks caught on MRI scans. These scans, from multiple pregnant women, included clear leg kicks at 20, 25, 30 and 35 weeks gestation. Other MRI scans provided anatomical details about bones, joints and leg sizes. With sophisticated math and computational models, the researchers could estimate the strengths of the kicks, as well as the mechanical effects, such as stresses and strains, that those kicks put on fetal bones and joints. Kicks ramped up and became more forceful from 20 to 30 weeks, the researchers found. During this time, kicks shifted the wall of the uterus by about 11 millimeters on average, the team found. But by 35 weeks, kick force had declined, and the uterus moved less with each kick, only about 4 millimeters on average. (By this stage, things are getting pretty tight and tissues might be stretched taut, so this decrease makes sense.) Yet even with this apparent drop in force, the stresses experienced by the fetus during kicks kept increasing, even until 35 weeks. Increasing pressure on the leg bones and joints probably help the fetus grow, the researchers write.
Other work has found that the mechanical effects of movement can stimulate bone growth, which is why weight-bearing exercises, such as brisk walking and step aerobics, are often recommended for people with osteoporosis. In animal studies, stationary chick and mouse fetuses have abnormal bones and joints, suggesting that movement is crucial to proper development.
The results highlight the importance of the right kinds of movements for fetuses’ growth. Babies born prematurely can sometimes have joint disorders. It’s possible that bone growth and joints are affected when babies finish developing in an environment dominated by gravity, instead of the springy, tight confines of a uterus. Even in utero position might have an effect. Head-up breech babies, for instance, have a higher risk of a certain hip disorder, a link that hints at a relationship between an altered kicking ground and development. In fact, the researchers are now looking at the relationship between fetal movements and skeletal stress and strain in these select groups.
Mechanical forces in utero might have long-lasting repercussions. Abnormal joint shapes are thought to increase the risk of osteoarthritis, says Verbruggen, “which means that how you move in the womb before you’re even born can affect your health much later in life.”
There’s a lot more work to do before scientists fully understand the effects of fetal movements, especially those in less than ideal circumstances. But by putting hard numbers to squirmy wiggles, this new study is kicking things off right.
It’s another record for SpaceX. At 3:50 p.m. Eastern on February 6, the private spaceflight company launched the Falcon Heavy rocket for the first time.
The Heavy — essentially three SpaceX Falcon 9 rocket boosters strapped together — is the most powerful rocket launched since the Saturn V, which shot astronauts to the moon during the Apollo program. SpaceX hopes to use the Heavy to send humans into space. The company is developing another rocket, dubbed the BFR, to eventually send people to Mars. Another first for this launch: the synchronized return of two of the boosters. (The third, from the center core, didn’t descend properly, and instead of landing on a droneship, it hit the ocean at 300 mph.) Part of SpaceX’s program is to reuse rockets, which brings down the cost of space launches. The company has successfully landed the cores of its Falcon 9 rockets 21 times and reflew a rocket six times. The company landed a previously used rocket for the first time in March.
But the cargo for today’s launch is aimed at another planet. The rocket carried SpaceX CEO Elon Musk’s red Tesla Roadster with “Space Oddity” by David Bowie playing on the stereo. It is now heading toward Mars.
“I love the thought of a car drifting apparently endlessly through space and perhaps being discovered by an alien race millions of years in the future,” Musk tweeted in December. Editor’s note: This story was updated on February 7 to update the status of the booster landings, and again on February 9 to correct the rocket that SpaceX hopes to use to send people to Mars. The company intends to use its BFR rocket, not the Falcon Heavy.
Their poop contains a chemical called histamine, part of the suite of pheromones that the insects excrete to attract others of their kind. Human exposure to histamine can trigger allergy symptoms like itchiness and asthma. (Our bodies also naturally release histamine when confronted with an allergen.) Histamine stays behind long after the bedbugs disappear, scientists report February 12 in PLOS ONE.
Researchers from North Carolina State University in Raleigh collected dust from apartments in a building with a chronic bedbug infestation. After a pest control company treated the apartments by raising the temperature to a toasty 50° Celsius, the researchers sampled the dust again. They compared those two sample groups with a third, from area homes that hadn’t had bedbugs for at least three years.
Dust from the infested apartments had levels of histamine chemical that were 22 times as much as the low amount found in bedbug-free houses, the researchers found. And while the heat treatment got rid of the tiny bloodsuckers, it didn’t lower the histamine levels.
Future pest control treatments might need to account for bedbugs’ long-term effects.
AUSTIN, Texas — An analysis of the metals in dozens of Picasso’s bronze sculptures has traced the birthplace of a handful of the works of art to the outskirts of German-occupied Paris during World War II.
This is the first time that the raw materials of Picasso’s sculptures have been scrutinized in detail, conservation scientist Francesca Casadio of the Art Institute of Chicago said February 17 at the annual meeting of the American Association for the Advancement of Science. And the elemental “fingerprints” help solve a mystery surrounding the sculptures’ origins. “In collaboration with curators, we can write a richer history of art that is enriched by scientific findings,” Casadio said.
Casadio and colleagues from the Art Institute of Chicago and Northwestern University in Evanston, Ill., studied 39 bronzes in the collection of the Picasso Museum in Paris. The team used a portable X-ray fluorescence spectrometer to record the amount of copper, tin, zinc and lead at several points on each sculpture. Based on the percentage of tin versus zinc in the bronze, “we found that there are compositional groups that relate to a specific foundry,” Casadio said. Seventeen sculptures had a foundry mark on them, so the researchers could relate metal mixes to specific foundries. But seven sculptures lack foundry marks. Based on their composition, researchers pegged five to a specific foundry — that of Émile Robecchi, a craftsman whose workshop sat in the southern outskirts of Paris. Original invoices from the foundry surfaced two years ago and revealed when some of the pieces were cast. For instance, the description, weight and size written on one invoice confirmed that the bronze of Tête de femme de profil (MarieThérèse) — a portrait of one of Picasso’s mistresses originally sculpted in plaster in 1931 — was cast at the foundry in February 1941. At that time, the war had been under way for years and the Germans had just occupied Paris. Picasso worried that his fragile plaster sculptures could be easily destroyed and sought to have them cast in bronze.
The team’s analysis also found two distinct mixtures of bronze that came out of the Robbechi foundry. That difference makes sense in the context of 1940s occupied Paris, when the Germans instituted laws requiring that people turn in certain metals to go toward war efforts, Casadio said.
“A lot of [foundries’] archives are incomplete or nonexistent,” Casadio said. The new analysis “reinforces why it’s really important to collaborate and how science adds the missing piece of the puzzle.”
Chile’s Atacama Desert is so dry that some spots see rain only once a decade. Salt turns the sandy soil inhospitable, and ultraviolet radiation scorches the surface. So little can survive there that scientists have wondered whether snippets of DNA found in the soil are just part of the desiccated skeletons of long-dead microbes or traces of hunkered-down but still living colonies.
A rare deluge has solved that mystery. Storms that dumped a few centimeters of rain on the Atacama in March 2015 — a decade’s worth in one day — sparked a microbial superbloom, researchers report February 26 in Proceedings of the National Academy of Sciences. That storm initially threw a wrench into plans for scientists to get a snapshot of microbial life under normal, hyperarid conditions in the Atacama. “But in the end, it came back as a lucky stroke,” says study coauthor Dirk Schulze-Makuch, an astrobiologist at the Technische Universität Berlin. He and his colleagues drove mining vehicles into the desert to collect soil samples just a few weeks after the storm, and then returned again in 2016 and 2017 to track changes as the moisture dissipated.
The team found microbes — a mix of extremophile archaea, bacteria and fungi — that were tolerant of desiccation, salinity and UV radiation. The kinds of species were fairly consistent across sampling sites, which suggests there’s something of a native microbial community that can survive in this salty sand by going dormant between periods of moisture, says Schulze-Makuch.
Schulze-Makuch and his colleagues also found evidence for enzymes that are by-products of cellular metabolism. And traces of ATP, the molecule that cells use for energy, lingered inside cells. Those markers of life were the most bountiful at the first sampling time, and then declined as the soil dried out again.
Collectively, it’s evidence that microbes aren’t just dying and leaving their DNA behind in the Atacama — they’re laying low to live another day. That’s encouraging to Schulze-Makuch: He’s interested in the Atacama as a proxy for conditions on Mars. Armando Azua-Bustos, an astrobiologist at the Centro de Astrobiología in Madrid who was not part of this study, agrees. “If we’re finding that, on Earth, truly dry places are still inhabited,” he says. “That opens the door to finding life elsewhere in the universe.”
Researchers from Google are testing a quantum computer with 72 quantum bits, or qubits, scientists reported March 5 at a meeting of the American Physical Society — a big step up from the company’s previous nine-qubit chip.
The team hopes to use the larger quantum chip to demonstrate quantum supremacy for the first time, performing a calculation that is impossible with traditional computers (SN: 7/8/17, p. 28), Google physicist Julian Kelly reported. Achieving quantum supremacy requires a computer of more than 50 qubits, but scientists are still struggling to control so many finicky quantum entities at once. Unlike standard bits that take on a value of 0 or 1, a qubit can be 0, 1 or a mashup of the two, thanks to a quantum quirk known as superposition.
Nicknamed Bristlecone because its qubits are arranged in a pattern resembling a pinecone’s scales, the computer is now being put through its paces. “We’re just starting testing,” says physicist John Martinis of Google and the University of California, Santa Barbara. “From what we know so far, we’re very optimistic.” The quantum supremacy demonstration could come within a few months if everything works well, Martinis says.
Google is one of several companies working to make quantum computers a reality. IBM announced it was testing a 50-qubit quantum computer in November 2017 (SN Online: 11/10/17), and Intel announced a 49-qubit test chip in January.
And the winner is in. Of the roughly 34,000 submissions sent in by the public, NASA has finally chosen an official nickname for the New Horizons spacecraft’s next destination: Ultima Thule.
New Horizons is scheduled to visit the tiny Kuiper Belt object on New Year’s Day 2019. NASA announced in November that it was seeking public input for a catchier name than the object’s existing moniker: 2014 MU69. Submissions varied wildly, ranging from the mythological Olympus to the much less grandiose Nubbin, defined as a “small lump or residual part” (SN Online: 11/7/17).
The final choice, Ultima Thule (pronounced “thoo-lee”), was announced March 13. It means “beyond the borders of the known world.” The nickname is a nice fit since the object will be the most distant solar system body ever visited.
After the flyby, NASA will submit a formal name to the International Astronomical Union based on whether Ultima Thule is a single object, a binary pair or a multi-object system.
Location: The galaxy NGC1052–DF2, about 65 million light-years from Earth.
An unusual galaxy is surprisingly lacking in dark matter, scientists report March 28 in Nature.
In typical galaxies, normal matter is swamped by dark matter, an unidentified invisible substance that makes up most of the matter in the universe. The existence of dark matter explains the unexpectedly fast speeds at which stars swirl around galaxies, and how galaxies move within clusters. But one galaxy, NGC1052–DF2, appears to have less dark matter than normal matter, or potentially none at all. Given its mass — it holds stars with about 200 million times the mass of the sun — it would be expected to have about 300 times as much dark matter as normal matter. That adds up to about 60 billion times the sun’s mass in missing dark matter.
Using observations from several telescopes, Yale University astronomer Pieter van Dokkum and colleagues studied 10 bright clumps of stars within the galaxy, known as globular clusters, and measured their velocities. The more mass there is in the galaxy, the faster the clusters should move around it. So if dark matter were present, the clusters should cruise at a relatively rapid clip. Instead, the clusters were moving slowly, indicating a dark matter–free zone. In most galaxies, stars move faster than naïvely expected, which suggests dark matter lurks within them, providing an extra source of mass. Most physicists believe dark matter is an undetected type of particle. But some think that the hint of extra matter might be a mirage, caused by an incomplete understanding of the workings of gravity. These researchers favor a theory known as modified Newtonian dynamics, or MOND (SN: 3/31/07, p. 206), which adjusts the rules of gravity to make sense of stars’ motions, without requiring any new, elusive particles.
The new study, says van Dokkum, bolsters the idea that dark matter is real, instead of an illusion. “Until now, whenever we saw a galaxy, we also saw dark matter,” says van Dokkum. “We didn’t know for sure whether dark matter and galaxies were two separable things.”
Because MOND proposes tweaking the laws of physics, then — if correct — its effects should be felt in every galaxy across the cosmos. That makes it hard for MOND to explain the unusually slow speeds of the star clusters in NGC1052–DF2.
“It’s intriguing, but it’s not something I’m going to lose sleep over,” says Stacy McGaugh, an astrophysicist at Case Western Reserve University in Cleveland. He studies MOND and thinks the theory might still be able to explain this galaxy. That’s because NGC1052–DF2 is nestled close to another galaxy. That other galaxy could alter MOND’s predictions, perhaps explaining why the star clusters move slowly. The effect of that proximity needs to be taken into account to determine if MOND can explain the observations, he says.
Still, McGaugh acknowledges that NGC1052–DF2 is problematic for MOND. But it is also problematic for the standard dark matter picture, he says, as it’s not clear how such a galaxy could form in the first place. Most galaxies are thought to form around clumps of dark matter, so a galaxy devoid of the stuff is hard to explain.
NGC1052–DF2 is unusual in other ways. It’s a faint, ghostly blob known as an ultradiffuse galaxy. Although about the same volume as the Milky Way, NGC1052–DF2 contains many fewer stars. Scientists are struggling to understand why such galaxies look so different from most others (SN: 12/10/16, p. 18). Finding an ultradiffuse galaxy without dark matter further complicates the puzzle.
If scientists can explain how the galaxy formed, it might improve understanding of the properties of dark matter. “In physics we always want to find really extreme laboratories to test theories and ideas,” says astrophysicist James Bullock of the University of California, Irvine. This galaxy is extreme indeed.
Some victims were found at home. An 84-year-old woman who’d spent over half her life in the same Sacramento, Calif., apartment died near her front door, gripping her keys. A World War II veteran succumbed in his bedroom. Many died outside, including a hiker who perished on the Pacific Crest Trail, his water bottles empty.
The killer? Heat. Hundreds of others lost their lives when a stifling air mass settled on California in July 2006. And this repeat offender’s rap sheet stretches on. In Chicago, a multiday scorcher in July 1995 killed nearly 700. Elderly, black residents and people in homes without air conditioning were hardest hit. Europe’s 2003 heat wave left more than 70,000 dead, almost 20,000 of them in France. Many elderly Parisians baked to death in upper-floor apartments while younger residents who might have checked in on their neighbors were on August vacation. In 2010, Russia lost at least 10,000 residents to heat. India, in 2015, reported more than 2,500 heat-related deaths.
Year in and year out, heat claims lives. Since 1986, the first year the National Weather Service reported data on heat-related deaths, more people in the United States have died from heat (3,979) than from any other weather-related disaster — more than floods (2,599), tornadoes (2,116) or hurricanes (1,391). Heat’s victim counts would be even higher, but unless the deceased are found with a fatal body temperature or in a hot room, the fact that heat might have been the cause is often left off of the death certificate, says Jonathan Patz, director of the Global Health Institute at the University of Wisconsin–Madison.
As greenhouse gases accumulate in the atmosphere, heat’s toll is expected to rise. Temperatures will probably keep smashing records as carbon dioxide, methane and other gases continue warming the planet. Heat waves (unusually hot weather lasting two or more days) will probably be longer, hotter and more frequent in the future. Beyond deaths, researchers are beginning to document other losses: Heat appears to rob us of sleep, of smarts and of healthy births. “Heat has the ability to affect so many people,” says Rupa Basu, an epidemiologist with the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment in Oakland. “Everybody’s vulnerable.”
Many people see heat as more of an annoyance than a threat, but climate change, extreme heat and human health are entwined. “There might not be a huge burden of disease from heat-related illness right now in your community,” says Jeremy Hess, an emergency medicine physician and public health researcher at the University of Washington in Seattle. “But give it another 20 years, and it might be a more significant issue.” Adaptation has limits The human body can’t tolerate excessive heat. The biological and chemical processes that keep us alive are best carried out at a core temperature of 36° to 37° Celsius (96.8° to 98.6° Fahrenheit), with slight variation from person to person. Beyond that, “the body’s primary response to heat is to try and get rid of it,” says Jonathan Samet, dean of the Colorado School of Public Health in Aurora. Blood vessels in the skin dilate and heart rate goes up to push blood flow to the skin, where the blood can release heat to cool down. Meanwhile, sweating kicks in to cool the skin.
With repeated exposure to high temperatures, the body can become more efficient at shedding excess heat. That’s why a person can move from cold Minneapolis to steamy Miami and get used to the higher heat and humidity. But there is a limit to how much a person can adjust, which depends on the person’s underlying health and the ambient temperature and humidity. If the outside is hotter than the body, blood at the skin surface won’t release heat. If humidity is high, sweating won’t cool the skin. Two scientists proposed in 2008 that humans cannot effectively dissipate heat with extended exposure to a wet-bulb temperature, which combines heat and humidity, that is greater than 35° C. Forced to regulate heat without a break, the body gets worn out. Heat exhaustion leads to weakness, dizziness and nausea. If a person doesn’t cool off, heat stroke is likely — and likely fatal. The ability to regulate heat breaks down and core body temperature reaches or exceeds 40° C. A person suffering heat stroke may have seizures, convulsions or go into a coma.
No one is immune to heat, but it hits some groups harder than others. The elderly, considered the most vulnerable, have fewer sweat glands and their bodies respond more slowly to rising temperatures. Children haven’t fully developed the ability to regulate heat, and pregnant women can struggle due to the demands of the fetus. People with chronic diseases like diabetes, cardiovascular disease and obesity can have trouble dissipating heat. And, of course, people living in poverty often lack air conditioning and other resources to withstand sweltering conditions. Collateral damage Researchers are discovering more ways that heat can hurt. Take sleep: The onset and duration of sleep is sensitive to temperature. The body cools down as it prepares to sleep; this decrease in core temperature is a signal to bring on the z’s. Body temperature stays low throughout the night, then rises just before awakening. A good night’s rest is a cornerstone of health.
Hot nights make for bad sleep, according to a study combining responses to a U.S. Centers for Disease Control and Prevention sleep survey of 765,000 U.S. residents from 2002 to 2011 with data on nighttime temperatures during that period. The higher the nighttime temperatures, the more nights respondents reported getting too little shut-eye. The effect hit low-income respondents and the elderly hardest, the researchers reported in May 2017 in Science Advances.
The ability to think and calculate may take a beating in the heat, according to a small study presented in January in Austin, Texas, at the American Meteorological Society’s annual meeting. Researchers from Harvard University tested undergraduate students for 12 days — the time before, during and after a heat wave. Twenty-four lived in buildings with air conditioning and 20 in buildings without. The researchers assessed how quickly and accurately students performed an addition and subtraction test and a test that asked for the color of a written word, rather than the word itself. During the heat wave, the students without air conditioning got about 6 percent fewer correct answers on the math problems and 10 percent fewer on the color problems than the students with air conditioning.
Heat may even increase the risk of stillbirth. Researchers with the National Institute of Child Health and Human Development in Bethesda, Md., analyzed weather data and more than 223,000 U.S. births from 2002 to 2008. During the warm months of the year, a 1 degree C increase in temperature during the week before birth was associated with about four additional stillbirths per 10,000 births, the researchers reported in June 2017 in Environmental Health Perspectives. As heat gets vicious, it threatens to disrupt the fabric of society. Extreme heat — beyond a wet-bulb temperature of 35° C — could become more regular in South Asia and the Persian Gulf, rendering parts of those areas uninhabitable, according to studies in the August 2017 Science Advances (SN: 9/2/17, p. 10) and the February 2016 Nature Climate Change. It’s not hard to imagine that there will be profound societal and political instability “in a world where tens of millions of people have to move and are looking for cooler places to live,” says Howard Frumkin, a physician epidemiologist specializing in environmental health at the University of Washington.
Emerald cities Fifty-four percent of the world’s population — and around 80 percent of U.S. residents — live in urban areas. Cities are where some action to combat heat can be taken now, says Brian Stone Jr., an environmental planner and member of the Urban Climate Lab at Georgia Tech in Atlanta. “If we’re waiting for the national government to signal it’s time to do this, we’re going to wait too long,” he says. “We are well into a world that’s been altered by climate change.”
Heat thrives in cities. All of the nonreflective roofs, walls, roads and other surfaces absorb and retain heat during the day. Waste heat, emitted from air conditioners and vehicles, concentrates in cities too. Together, these factors contribute to what’s called an urban heat island, an amplification of heat that occurs within cities. On average, a city with at least a million residents can be 1 to 3 degrees C hotter than surrounding areas. At night, the temperature differences widen. Cities may be as much as 12 degrees C hotter than surrounding areas in the evening hours, because cities release built-up heat back out among buildings and avenues.
Hotlanta These Landsat satellite images show urban Atlanta on September 28, 2000. The core urban area is at the center of the images. The left side shows areas of vegetation (green), bare ground (brown) and roads and dense development (gray). The heat map on the right shows the areas of densest development also have the hottest land surface temperatures (red), near 30 degrees Celsius. The areas of heaviest vegetation are the coolest (yellow) due to evaporation of water and shade. City planners can rid their locales of some of this heat with several strategies. One is to plant more trees to create shade for residents and structures. Trees also lower the air temperature by transferring water from the soil through the tree to the air. The surrounding air is cooled as the water changes from a liquid to a vapor. The process is “much like the way sweating works for our bodies,” says George Ban-Weiss, an environmental engineer at the University of Southern California in Los Angeles.
Another strategy is to reduce the amount of sunlight that city surfaces absorb by using “cool” materials on exposed surfaces. The best known are cool roofs, which “reflect more sunlight than usual,” says Ronnen Levinson of Lawrence Berkeley National Laboratory in Berkeley, Calif., who studies cool surfaces and urban heat islands. In general, to make a surface cool, you make it lighter, with coatings or other light-colored materials. For example, a white roof that reflects 80 percent of the sun’s light on a typical summer afternoon will stay about 31 degrees C cooler than a gray roof that reflects only 20 percent. Giving buildings cool-surface makeovers counters the urban heat island effect and reduces the temperature inside a building. “In disadvantaged communities, people simply may not have air conditioning to help them ride out hot summers,” Levinson says. Cooling off the insides of buildings is “where I think the greatest potential benefits are for improving human comfort and health,” he says.
Stone has estimated how many heat-related deaths could be avoided by reducing urban heat island effects. In 2016, he and colleagues produced a report for the city of Louisville, Ky., that analyzed the impact of adding 450,000 trees, converting 168 square kilometers of surfaces to cool materials and more. The researchers estimated that areas of the city could reduce average summertime temperatures by as much as 1.7 degrees C or more. And based on the 53 deaths Stone attributed to the city’s unusually warm summer of 2012, there could be 11 fewer deaths from heat, a reduction of 21 percent. “When we get a big heat wave,” Stone says, “that could really translate into hundreds of lives.”
Many cities in the United States and abroad are working on tempering their urban heat islands with a variety of strategies, including programs to install cool roofs or plant more trees. The city of Los Angeles now requires that new or replaced roofs for homes and other residential buildings meet a solar reflectance index value — a measure of a materials’ ability to stay cool in the sun between zero (black surface) and 100 (white) — of at least 75 for flatter roofs and 16 for steeper ones. Through a provision in California’s building energy efficiency code, cities throughout the state have been converting flat, commercial roofs, like those on big-box stores, to light-colored cool roofs when a new topper is needed. New York City has planted a million new trees since 2007 and committed additional funds to adding even more to streets and parks. The city also has coated 0.62 square kilometers of roof surfaces white since 2009. The city of Ahmedabad, India, where about 25 percent of the residents live in slum communities, announced a heat action plan in 2017 that includes a cool roofs initiative to paint or otherwise convert at least 500 slum household roofs and to improve the reflectivity of roofs on government buildings and schools.
Measures that tackle the urban heat island effect also make cities more energy efficient (by reducing the cooling needs inside buildings) and more comfortable (by shading city residents). Individual cities need to implement strategies that make sense for their landscapes, their water resources, their usual climate and their populations, Ban-Weiss says.
But ameliorating urban heat can only do so much. There will still need to be a worldwide push to reduce emissions of greenhouse gases. Ban-Weiss and colleagues estimated how much cool roofs could counter warming from climate change in Southern California. Assuming that greenhouse gas emissions continue to increase, the widespread adoption of cool roofs in the Los Angeles metropolitan area would offset some of the warming expected by midcentury, the team reported in 2016 in Environmental Research Letters. But by the end of the century, Ban-Weiss says, the cool roof benefits “become mostly dwarfed by climate change.”
The world’s longest system of levees and floodways, meant to rein in the mighty Mississippi River, may actually make flooding worse.
Using tree rings and lake sediments, researchers re-created a history of flooding along the lower Mississippi River extending back to the 1500s. This paleoflood record suggests that the past century of river engineering — intended to minimize flood damage to people living along the river’s banks — has instead increased the magnitude of the largest floods by 20 percent, the researchers report April 5 in Nature. Climate patterns that bring extra rainfall to the region don’t account for the dramatic increase in flood size, the team found. “The obvious culprit is that we have really modified the river itself,” says Samuel Munoz, a geoscientist at Northeastern University in Boston.
Settlers built the first levees on the Mississippi in the early 1800s. After a massive flood displaced hundreds of thousands of people in 1927, the U.S. government built the current system of spillways and levees. The engineering projects profoundly altered the river’s shape and sediment content. But how these changes affected the size of the river’s largest floods has been unclear, in part because water gauges have tracked the river’s flow for just 150 years. “One of the difficult things about studying extreme floods is that you don’t get many,” says paleohydrologist Scott St. George of the University of Minnesota in Minneapolis, who wrote an accompanying commentary in Nature . “Floods like the one in 1927 don’t come around very often.” Munoz and his colleagues studied tree rings and sediments from oxbow lakes to create their 500-year record of Mississippi River floods. Oxbow lakes form as a river meanders and twists across its floodplain; sometimes, a large loop becomes cut off from the main channel, forming an isolated lake. When a river’s waters rise high enough, they can spill over into the lake, dropping loads of sand and silt.
“You get deposits of river material in which the coarse stuff settles out fastest and the finer stuff is on top,” Munoz says. As evidence of past floods, the team looked for this sediment pattern in cores from three oxbow lakes. Comparing recent flood sediment sequences with those floods’ actual size, the researchers created a template for assessing the magnitude of older floods.
Identifying “flood rings” in tree-ring samples from 35 oak trees along the lower river’s floodplain helped researchers pin down the timing of the floods. When a tree is inundated, tree ring vessels — cells that transport water and nutrients — may shrink or be distributed differently within that ring, compared with in rings not affected by floods.
The researchers next considered the influence of two large weather patterns known to bring wetter conditions to the central United States — the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation. The team analyzed historical data for these patterns back to the late 19th century, and reconstructed the patterns back to 1500. Those weather patterns are linked to warmer surface temperatures in the Pacific and Atlantic oceans, respectively, and correlated with the timing of observed floods on the lower Mississippi. But they weren’t the whole story. “The early 20th century got a lot of flooding,” but only 25 percent of the increase in flood magnitude over the past century can be explained by those climate patterns, Munoz says. The other 75 percent was probably due to the river modifications, the researchers found.
River modification is a plausible explanation for the increase in Mississippi flood extremes, St. George says. But there are other possible climate impacts, he notes, such as the fact that the area is warmer now than 150 years ago. These could also have affected rainfall and river flow in the Mississippi River basin.
Still, he says, the 500-year flood record is an important part of solving that puzzle. “It gives a long-term perspective on the Mississippi, which you really need to understand a river of its size and majesty.”
Munoz says this method of establishing a flood record that predates river gauges can be applied to other rivers, whether heavily managed or not. It could also help scientists understand how flood risks might change with increasing greenhouse gases in the atmosphere (SN: 9/2/19, p. 14). “This approach can help take the pulse of a river and determine how unprecedented such changes might be.”
