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If reducing carbon emissions fails to stop climate change, we may one day have the option of sending mirror-supporting satellites into space or filling the stratosphere with light-reflecting particles to block the sun’s rays. According to a new study, such measures could significantly cool Earth. But researchers caution that if they if they do not work or are suddenly halted, they could make matters worse. “As far as I know, this is the first century-scale, time-dependent simulation of a geoengineering scheme,” says Ken Caldeira, a climate scientist at the Carnegie Institution of Washington’s Department of Global Ecology in Stanford, Calif....

Every second, a vast quantity of cold, dense seawater equal to six times the combined flow of every land river on Earth streams over an ocean-floor ridge that stretches between Greenland and Scotland. This deep southbound current, flowing from the Norwegian, Iceland and Greenland seas into the North Atlantic, is the lower limb of the Gulf Stream and its northerly extension, a great conveyor belt of ocean heat and salt that transports warm tropical water north from the equator....

The ­generic line on dark matter is that nobody knows what it is because nobody has seen it. The former claim remains unassailable—any number of hypothetical particles could be dark matter. As to whether or not anybody has seen it, scientists are as divided as ever, and the discourse among rival dark matter hunters is getting chippy. The controversy centers on an Italy-based research group that runs DAMA, a particle detector that the researchers have claimed for years is picking up dark matter particles....

By Lawrence Hurley WASHINGTON (Reuters) - The Supreme Court appeared closely divided on Monday over whether the administration of President Barack Obama exceeded its authority in trying to regulate greenhouse gas emissions. Justice Anthony Kennedy would seem to hold the swing vote on the nine-member high court, with conservative justices skeptical of the U.S. Environmental Protection Agency’s approach and liberal justices generally supportive. During a 90-minute oral argument, Kennedy offered some criticism of the government’s position but did not indicate which way he would vote....

Henry Gustav Molaison was 27, a shy, intelligent young man, when he underwent an experimental operation to relieve his severe epilepsy. The surgeon extracted two slivers of gray matter from either side of his brain, including his hippocampus, which, at the time, no one knew was the center of memory consolidation. Henry’s amnesia was immediate and profound, and the “purity of his disorder”—he was otherwise cognitively normal—made him a much sought-after study subject....

Deep in the Nevada desert, halfway between Las Vegas and Reno, a lone white tower stands 195 meters tall, gleaming like a beacon. It is surrounded by more than 10,000 billboard-size mirrors focusing the sun’s rays on its tip. The Crescent Dunes “concentrating solar power” plant looks like some advanced communication device for aliens. But the facility’s innovation lies in the fact that it can store electricity and make it available on demand any time—day or night....

One of the most remarkable features of the solar system is the variety of planetary atmospheres. Earth and Venus are of comparable size and mass, yet the surface of Venus bakes at 460 degrees Celsius under an ocean of carbon dioxide that bears down with the weight of a kilometer of water. Callisto and Titan—planet-size moons of Jupiter and Saturn, respectively—are nearly the same size, yet Titan has a nitrogen-rich atmosphere thicker than our own, whereas Callisto is essentially airless....

If a breakthrough in developing an HIV vaccine occurred today, scientists and drug companies would need another decade to provide a commercial product. But, after a long struggle, researchers may indeed have made that breakthrough using a new vaccine approach that combines two prior ones. Given that the AIDS pandemic has been around for 30 years and has claimed 36 million lives, with 35 million more people currently infected with the HIV virus, the long-awaited goal might finally be attainable, according to researchers attending the 13th Aids Vaccine Conference last week in Barcelona....

A technique called optogenetics has transformed neuroscience during the past 10 years by allowing researchers to turn specific neurons on and off in experimental animals. By flipping these neural switches, it has provided clues about which brain pathways are involved in diseases like depression and obsessive-compulsive disorder. “Optogenetics is not just a flash in the pan,” says neuroscientist Robert Gereau of Washington University in Saint Louis. “It allows us to do experiments that were not doable before....

The human genome contains more than three billion base pairs of adenine (A), thymine (T), guanine (G) and cytosine (C)—some of the principal molecules that make up DNA. Found among those pairings are so-called single nucleotide polymorphisms (SNP), changes or mutations in the order of these molecules. A person of European descent typically has around eight million SNPs, many of which are shared widely throughout the population. By comparing some 500,000 of these common variations, a team of research groups discovered 24 genes and regions of the genome that raise a person’s risk of developing diseases ranging from clinical depression to diabetes....

Few consumer products have a poorer environmental image than the car tire. It is hard to escape the bleak sight of coal-colored mountains of used tires that blight the U.S. landscape. But like other parts of the automobile, the tire has been partially reworked during the past decade to make it more ecologically sustainable. As a result of efforts by tire industry chemists and engineers, many of today’s tires roll more easily to save fuel and contain fewer petroleum-based ingredients, both of which shrink this difficult technology’s carbon footprint....

Earlier this year Yaniv Erlich of the Whitehead Institute for Biomedical Research at M.I.T. sent bioethicists into a frenzy when he and his team uncovered the names of people whose anonymous genome profiles were published by the 1000 Genomes Project. Erlich and his co-workers found the identities entirely by connecting Y-chromosome data and other information from the database with publicly available records, including genealogy databases and lists of people living in particular locales....

Pop singer and wardrobe malfunction poster girl Janet Jackson has been diagnosed with vestibular migraines, a rare form of headache that her publicist blames for her recently canceled “Rock Witchu” concerts. Migraines affect nearly 30 million Americans, especially women, who suffer from them by a three to one ratio, according to the National Headache Foundation. Doctors aren’t sure exactly how many people are affected by vestibular migraines, but they know these headaches have a unique twist that run-of-the-mill, throbbing migraines don’t: a component of vertigo....

This story is a supplement to the feature “The Migration History of Humans: DNA Study Traces Human Origins Across the Continents” which was printed in the July 2008 issue of Scientific American. Looking Far and Wide High-powered genetic sequencing and computational techniques developed for the Human Genome Project and in its aftermath have furnished a wealth of data that lets researchers compare genomes drawn from distinct populations around the globe. A genomic map of the world (below), crafted by researchers at the University of Michigan at Ann Arbor, shows that genetic diversity decreases outside of Africa....

A close-up of a computer-simulated human eye during fixation, with an inset view of the visual scene. Although the eye is voluntarily “fixated” on the edge of a figure, it nevertheless makes tiny eye movements with distinct characteristics. The moving position of the very center of the retina is displayed as a line on the figure in the inset. This plot reveals three types of fixational eye movements: fast microsaccades, slow drift, and oscillatory tremor....

Earlier this week, Israeli media reported a person who was hospitalized with evidence of both seasonal flu and COVID at the same time. This unvaccinated and pregnant person had mild symptoms and was discharged without any complications. A person being infected with both the COVID-causing SARS-CoV2 virus and an influenza virus can happen; we just had one such person in our hospital last month whom we treated and discharged without a whole lot of fanfare....

A study published last week challenges the popular academic claim that crabs may have disappeared from Antarctica millions of years ago only to return thanks to warming seas, and one of the authors believes the finding indicates how unprepared scientists are to track the effects of global warming on Antarctic species. The study, published in the journal PLOS ONE, says previous theories of a recent king crab “invasion” were based on a poor fossil record and an insufficient number of samples....

People crossing the Mexican border into Nogales, Ariz., this week will have a chance to meet U.S. Customs and Border Protection’s newest officer—a polite yet no-nonsense bilingual gatekeeper with a thick shock of black hair and a striped gray tie. He may not have a name or join his fellow officers for coffee or lunch breaks, but his presence will likely be welcomed both by them and the commuters who regularly pass through this southern Arizona outpost on their way to and from Mexico....

As Japanese officials consider whether and when to reactivate most of the country’s 54 nuclear plants, a year after the Fukushima reactor disaster, they continue to face challenges to public confidence in the nuclear industry and its regulator. The latest comes from a new independent study of the accident to be released tomorrow by the Rebuild Japan Initiative Foundation, a nonprofit think tank. It describes the government’s failure to provide accurate and adequate warning of the mounting dangers as the Tokyo Electric Power Co....

If correct, researchers’ findings suggest the molecules of life on Earth may initially have come from elsewhere in the cosmos. The organic molecules that form the basis of life on Earth are often chiral, meaning they come in two forms that are mirror images, much as right and left hands appear identical but are reversed versions of each other. Strangely, the amino acids that make up proteins on Earth are virtually all “left-handed,” even though it should be as easy to make the right-handed kind....