How a warming climate may make winter tornadoes stronger

Though tornadoes can occur in any season, the United States logs the greatest number of powerful twisters in the warmer months from March to July. Devastating winter tornadoes like the one that killed at least 88 people across Kentucky and four other states beginning on December 10 are less common.

But climate change could increase tornado intensity in cooler months by many orders of magnitude beyond what was previously expected, researchers report December 13 in a poster at the American Geophysical Union’s fall meeting.

Tornadoes typically form during thunderstorms when warm, humid airstreams get trapped beneath cooler, drier winds. As the fast-moving air currents move past each other, they create rotating vortices that can transform into vertical, spinning twisters (SN: 12/14/18). Many tornadoes are short-lived, sometimes lasting mere minutes and with a width of only 100 yards, says Jeff Trapp, an atmospheric scientist at the University of Illinois at Urbana-Champaign.
Over the last 20 years, tornado patterns have shifted so that these severe weather events occur later in the season and across a broader range in the United States than before, Trapp says (SN: 10/18/18). But scientists have struggled to pin down a direct link between the twister changes and human-caused climate change.

Unlike hurricanes and other severe storm systems, tornadoes happen at such a small scale that most global climate simulations don’t include the storms, says Kevin Reed, an atmospheric scientist at Stony Brook University in New York who was not involved in the new research.

To see how climate change may affect tornadoes, Trapp and colleagues started with atmospheric measurements of two historical tornadoes and simulated how those storm systems might play out in a warmer future.

The first historical tornado took place in the cool season on February 10, 2013, near Hattiesburg, Miss., and the second occurred in the warm season on May 20, 2013, in Moore, Okla. The researchers used a global warming simulation to predict how the twisters’ wind speeds, width and intensity could change in a series of alternative climate scenarios.

Both twisters would likely become more intense in futures affected by climate change, the team found. But the simulated winter storm was more than eightfold as powerful as its historical counterpart, in part due to a predicted 15 percent increase in wind speeds. Climate change is expected to increase the availability of warm, humid air systems during cooler months, providing an important ingredient for violent tempests.

“This is exactly what we saw on Friday night,” Trapp says. The unseasonably warm weather in the Midwest on the evening of December 10 and in the early morning of December 11 probably contributed to the devastation of the tornado that traveled hundreds of miles from Arkansas to Kentucky, he speculates.

Simulating how historical tornados could intensify in future climate scenarios is a “clever way” to address the knowledge gap around the effects of climate change on these severe weather systems, says Daniel Chavas, an atmospheric scientist at Purdue University in West Lafayette, Ind., who was not involved in the new research.

But Chavas notes that this research is only one piece of a larger puzzle as researchers investigate how tornados might impact communities in the future.

One drawback of this type of simulation is it often requires direct measurements from a historical event, Reed says. That limits its prediction power to re-creating documented tornadoes rather than broadly forecasting shifts in large-scale weather systems.

Though the team based its predictions on only two previous tornados, Trapp says he hopes that adding more historical twisters to the analysis could provide more data for policy makers as well as residents of communities that may have to bear the force of intensifying tornadoes.

The earliest evidence of tobacco use dates to over 12,000 years ago

Ancient North Americans started using tobacco around 12,500 to 12,000 years ago, roughly 9,000 years before the oldest indications that they smoked the plant in pipes, a new study finds.

This discovery replaces the pipe-smoking report as the oldest direct evidence for the human use of tobacco anywhere in the world.

Excavations at the Wishbone site in Utah’s Great Salt Lake Desert uncovered four charred seeds of wild tobacco plants in a small fireplace, say archaeologist Daron Duke of Far Western Anthropological Research Group in Henderson, Nev., and colleagues.

Those seeds, dated based on radiocarbon dates of burned wood in the fireplace, likely came from plants gathered on foothills or mountains located 13 kilometers or more from the Wishbone area, Duke’s team reports October 11 in Nature Human Behavior.

The site was located in a sprawling marshland at the time of its occupation. Finds in and around the fireplace include bones of ducks and other waterfowl, a long, intact stone point and another point broken in two, a bone implement and seeds of several edible wetland plants.

It’s unclear how ancient North American hunter-gatherers used the tobacco, Duke says. Wads of tobacco leaves, stems and other plant fibers may have been twisted into balls and chewed or sucked, with attached seeds spit out or discarded. Ancestors of Pueblo people in what’s now Arizona chewed wild tobacco between around 1,000 and 2,000 years ago. Tobacco smoking can’t be ruled out at the Wishbone site, Duke adds.

The earliest evidence of domesticated tobacco, which comes from South America, dates to only about 8,000 years ago (SN: 10/29/18). Duke suspects various ancient American populations independently tamed the plant at different times. “Certain groups wound up domesticating particular [tobacco] species, typically alongside food crops,” he suggests.

Here’s how ice needles sculpt patterns into cold, rocky landscapes

Neat rings, stripes and swirls embellish many cold, rocky landscapes. Although these beautiful stone patterns look like humanmade artwork, they’re all natural. Scientists have long known that such rocky patterns result from freezing and thawing. But precisely how they develop has been a mystery — until now.

New experiments reveal that so-called “ice needles” can sort and organize rocks into many patterns, Anyuan Li of the University of Tsukuba in Japan and colleagues report the Oct. 5 Proceedings of the National Academy of Sciences.

“The beauty of [our] experiments is that you can actually see direct information on how the patterns form,” says Bernard Hallet of the University of Washington in Seattle, who has studied natural patterns in surface rocks around the world.
The researchers spread pebbles atop a pan holding moist, fine-grained soil, then froze and thawed this mini-landscape over and over. When the moist soil had not yet frozen but the air temperature dropped below freezing, tiny, needlelike columns of ice sprouted up from the soil. These ice needles, each up to a few centimeters high, lifted any stones atop them. When temperatures rose again, the ice collapsed and the stones tumbled off. Because the ice needles curved as they grew, the stones tended to fall off their icy pedestals to one side.

Over many freeze-thaw cycles, the ice needles cleared patches of exposed soil. Since needles could more easily form in spots where there were fewer rocks in the way, they more efficiently cleared out any remaining pebbles. Stones were gradually shuffled into clusters between stone-free areas to form larger patterns. The pattern that builds on a landscape “strongly depends on its [local stone] concentration,” says study coauthor Quan-Xing Liu, a theoretical ecologist at East China Normal University in Shanghai.
In lab experiments, the team “was able to able to get patterns after 30 freeze cycles,” says Hallet. That could equate to 30 cold nights — or 30 years, if each freeze lasted a whole winter. In the real world, Hallet says, some patterns might take “thousands, if not tens of thousands, of years to form.”

Using observations from their soil experiments, the researchers built a computer simulation of ice needle landscaping. This simulation could predict stone movement in the open environment under a range of conditions. The simulation confirmed that the rate of pattern formation depended on how dense the stone cover was, among other factors. The shapes and formation rates of patterns were also related to how moist the soil was, how the ground sloped and how tall the ice needles grew.

“We see identical patterns in different systems, such as fluids,” Hallet says of the rock formations. Materials with different characteristics or sizes often start all mixed together but don’t stay that way (SN: 4/22/21). Phase separation is the process that morphs these mixes into patterns. The new study is among the first to show how phase separation applies to landscapes.

The combination of experiments and computer modelling in this study provides a new way to connect how natural landscapes form and how their materials behave, says Rachel Glade, a geologist at the University of Rochester in New York who was not involved in the work. This approach “is vital for our understanding of complex materials,” she adds, and it could help us understand how landscapes may evolve differently in a changing climate.

The fastest-spinning white dwarf ever seen rotates once every 25 seconds

The sun turns once a month and the Earth once a day, but a white dwarf star 2,000 light-years away spins every 25 seconds, beating the old champ by five seconds. That makes it the fastest-spinning star of any sort ever seen — unless you consider such exotic objects as neutron stars and black holes, some of which spin even faster, to be stars (SN: 3/13/07).

About as small as Earth but roughly as massive as the sun, a white dwarf is extremely dense. The star’s surface gravity is so great that if you dropped a pebble from a height of a few feet, it would smash into the surface at thousands of miles per hour. The typical white dwarf takes hours or days to spin.

The fast-spinning white dwarf, named LAMOST J0240+1952 and located in the constellation Aries, got in a whirl because of its ongoing affair with a red dwarf star that revolves around it. Just as falling water makes a waterwheel turn, so gas falling from the red companion star made the white dwarf twirl.

The discovery occurred the night of August 7, when astronomer Ingrid Pelisoli of the University of Warwick in Coventry, England, and her colleagues detected a periodic blip of light from the dim duo. The blip repeated every 24.93 seconds, revealing the white dwarf star’s record-breaking rotation period, the researchers report August 26 at arXiv.org.

The star’s only known rival is an even faster-spinning object in orbit with the blue star HD 49798. But that rapid rotator’s nature is unclear, with some recent studies saying it is likely a neutron star, not a white dwarf.

Earth is reflecting less light. It’s not clear if that’s a trend

The amount of sunlight that Earth reflects back into space — measured by the dim glow seen on the dark portions of a crescent moon’s face — has decreased measurably in recent years. Whether the decline in earthshine is a short-term blip or yet another ominous sign for Earth’s climate is up in the air, scientists suggest.

Our planet, on average, typically reflects about 30 percent of the sunlight that shines on it. But a new analysis bolsters previous studies suggesting that Earth’s reflectance has been declining in recent years, says Philip Goode, an astrophysicist at Big Bear Solar Observatory in California. From 1998 to 2017, Earth’s reflectance declined about 0.5 percent, the team reported in the Sept. 8 Geophysical Research Letters.

Using ground-based instruments at Big Bear, Goode and his colleagues measured earthshine — the light that reflects off our planet, to the moon and then back to Earth — from 1998 to 2017. Because earthshine is most easily gauged when the moon is a slim crescent and the weather is clear, the team collected a mere 801 data points during those 20 years, Goode and his colleagues report.

Much of the decrease in reflectance occurred during the last three years of the two-decade period the team studied, Goode says. Previous analyses of satellite data, he and his colleagues note, hint that the drop in reflectance stems from warmer temperatures along the Pacific coasts of North and South America, which in turn reduced low-altitude cloud cover and exposed the underlying, much darker and less reflective seas.
“Whether or not this is a long-term trend [in Earth’s reflectance] is yet to be seen,” says Edward Schwieterman, a planetary scientist at University of California, Riverside, who was not involved in the new analysis. “This strengthens the argument for collecting more data,” he says.

Decreased cloudiness over the eastern Pacific isn’t the only thing trimming Earth’s reflectance, or albedo, says Shiv Priyam Raghuraman, an atmospheric scientist at Princeton University. Many studies point to a long-term decline in sea ice (especially in the Arctic), ice on land, and tiny pollutants called aerosols — all of which scatter sunlight back into space to cool Earth.

With ice cover declining, Earth is absorbing more radiation. The extra radiation absorbed by Earth in recent decades goes toward warming the oceans and melting more ice, which can contribute to even more warming via a vicious feedback loop, says Schwieterman.

Altogether, Goode and his colleagues estimate, the decline in Earth’s reflectance from 1998 to 2017 means that each square meter of our planet’s surface is absorbing, on average, an extra 0.5 watts of energy. For comparison, the researchers note in their study, planet-warming greenhouse gases and other human activity over the same period boosted energy input to Earth’s surface by an estimated 0.6 watts of energy per square meter. That means the decline in Earth’s reflectance has, over that 20-year period, almost doubled the warming effect our planet experienced.

What the Perseverance rover’s quiet landing reveals about meteor strikes on Mars

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.
But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”