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Pliocene-Like Monsoons Are Returning to the American Southwest

Pliocene-Like Monsoons Are Returning to the American Southwest

Leaf waxes also predate climate records from Antarctic ice cores, which go back only about a million years and require a climate that can support ice. One study used leaf waxes to glimpse the climate of a warmer Spain some 15 to 17 million years ago. Another looked at the moisture history of Southwest Africa for the past 3.5 million years. 

Bhattacharya began using them while working as a postdoctoral fellow in Tierney’s lab. Five years ago, she and Ran Feng, a coauthor, came up with the idea of studying the Pliocene while riding a bus during a conference for young researchers. 

Their analysis started with marine sediments collected decades ago by the research vessel Joides Resolution, which roams the oceans drilling cores from as deep as 6 miles below the surface. The samples used for the study were taken off the coast of California: one off the Baja peninsula from a depth of more than 2,600 meters, and one from the East Cortes Basin at a depth of 1,700 meters. During the Pliocene, leaf waxes would have been transported west on the wind to become part of this marine sediment. 

The team got a cube of each core, freeze-dried them, and ran them through “a glorified espresso machine,” says Bhattacharya, using a solvent under pressure at high temperatures that extracted the waxes. Then they measured the hydrogen and carbon isotope composition using a gas chromatograph-isotope ratio mass spectrometer, which separated the waxes by their molecular mass. 

“The hydrogen that’s used to make the wax is coming from rainwater that the plant uses to grow. You can think of isotopes as like a fingerprint,” Tierney says. “These isotopes actually trace the kind of rainfall you have, which is pretty cool. They can also trace the amount of winter rainfall versus summer rainfall. So, it’s pretty powerful.”

For the second part of the study, climate modeler Ran Feng, a professor at the University of Connecticut’s Department of Geosciences, ran simulations to determine how sea temperatures influenced the stronger monsoons of the mid-Pliocene. Feng found that when marine temperatures—in an area that extends from Alaska to off the coast of Baja, California—were higher relative to the usually warmer tropical waters off Central America, they created conditions for stronger monsoons in the Southwest. Warmer local air acts like a heat pump, drawing the relatively cooler tropical air and warming it, pulling in moisture. “So it creates this loop,” she says. “That’s why this is able to drive moisture into the Southwest North America regions.”

That kind of marine heat wave has occurred off California in recent years and will become more prevalent as temperatures rise, feeding more intense monsoon storms. 

Monsoons will help with drought as the Southwest dries. But they will be stronger, dropping inches of rain in a short time and causing more frequent flooding. “The monsoon accounts here in Arizona for about 60 percent of our rainfall for the year,” Tierney says. “It’s an important source of water in the desert. It does, in certain hydrological systems, recharge the groundwater. But the flip side of that is that these monsoon storms can be so intense and so quick that a lot of the water can end up running off into the watersheds and off the landscape. So, it’s not always the case that it recharges groundwater.”

Those storms also threaten the built environment, and as the climate has changed, design standards for infrastructure like roads, bridges, dams, and stormwater systems have not kept pace. The National Oceanic and Atmospheric Association’s Atlas 14 reports for the US Southwest rely only on historical rainfall amounts, not a changing future, for its projections. The agency’s Southwest study was released in 2004 and last revised in 2011.

There is another troubling connection between more intense monsoons and disasters: wildfire. Stronger rainfall, Bhattacharya says, increases the growth of fuel loads by encouraging plant growth. Subsequent droughts set the stage for bigger fires. 

“We think a stronger monsoon season creates unanticipated hazards from fire and flooding,” she adds, noting that more research will bring the picture into focus. “We’re planning to go further and study this in the Pliocene to see how fire and flooding respond to a warmer climate.”

Scientists Reexamine Why Zebra Stripes Mysteriously Repel Flies

Scientists Reexamine Why Zebra Stripes Mysteriously Repel Flies

For the current study, Tombak, then a PhD candidate at Princeton, and her team wanted to test stripe width to see if narrower ones might be even more repulsive to flies—a potential evolutionary advantage that would explain the difference between zebra species. They also restricted their experiment to close-range encounters to rule out the theory that the repulsion required an illusion that could only happen at a distance. Hence the plexiglass box.

An undergraduate from the lab, Lily Reisinger, built the box and set up the experiment. For each trial, the team hung two pelts with clothespins, unleashed the flies, let them circle for a minute, and then counted how many landed on each pelt. First, they tested an impala pelt vs. one from a plains zebra, which has wide stripes. Then the impala vs. a Grevy’s zebra, which has narrower stripes. Finally, they pitted the skins from the two zebra species against each other. They tested 100 rounds for each pair.

The flies chose the impala skin about four times as often as they chose either zebra skin. And over the 100 rounds, the team found no obvious difference between stripes of different widths.

Why does it work? First, it’s helpful to know that flies don’t see the world as you do. Flies have “compound eyes” that combine input from thousands of photoreceptors, each pointing in slightly different directions from their eye’s rounded surface. Their sense of color is limited. And while they can sense motion and polarized light and process images 10 times faster than our eyes, those images are very low-res.

But like you, flies get fooled by the “barber pole” illusion—that famous diagonal red stripe that seems to spiral infinitely upwards. “Outside of a barber shop, there’s that rotating pole that looks like it’s going up, but it’s just rotating,” says Tombak. It creates a false perceived direction of motion, and false speed as well. A zebra’s stripes, she thinks, create a similarly disorienting sense of movement, which should make it harder for flies to gauge the timing and speed for a smooth landing. “You can imagine for a moving fly, just tons of objects are passing by at a very fast rate,” she says. And it makes sense that this illusion works close-up, as the fly is on approach to land.

Narrower stripes should create an even stronger barber pole illusion—“an enhanced perceived speed effect” as Tombak puts it—and thus stronger repulsion. But, she says, only a couple of previous studies examined stripe width, and they rarely involved real pelts; one tested painted stripes up to 5 inches wide, which is beyond what any real zebra has. Instead, she says, her team’s results show that “within the range of stripe widths that occurs naturally in zebras, width doesn’t make that much of a difference.”

That, of course, begs the question of why zebras have stripes of different widths—but Ted Stankowich, an evolutionary ecologist from California State University Long Beach who was not involved in the work, says all that really matters is that zebras have them. Additional variation could come from random genetic drift, or separate adaptations meant to confuse predators. “Once you’ve got stripes, you’ve got this anti-fly effect,” he says. “Selection from many other sources can impact that trait.”

America’s Billion-Dollar Tree Problem Is Spreading

America’s Billion-Dollar Tree Problem Is Spreading

Fast-growing, drought-tolerant trees are slowly spreading across grasslands on every continent except Antarctica. Given how desperate we are to reduce carbon in the atmosphere, millions of new saplings sprouting each year might seem like a good thing. But in reality, their spread across vulnerable grasslands and shrublands is upending ecosystems and livelihoods. As these areas transform into woodland, wildlife disappears, water supplies dwindle, and soil health suffers. The risk of catastrophic wildfire also skyrockets.

In a new study published in the Journal of Applied Ecology, researchers have shown how woodland expansion also takes an economic toll. American ranchers often depend on tree-free rangelands to raise their livestock. Between 1990 and 2019, landowners in the Western US lost out on nearly $5 billion worth of forage—the plants that cattle or sheep eat—because of the growth of new trees. The amount of forage lost over those three decades equates to 332 million tons, or enough hay bales to circle the globe 22 times.

“Grasslands are the most imperiled and least protected terrestrial ecosystem,” says Rheinhardt Scholtz, a global change biologist and affiliate researcher with the University of Nebraska-Lincoln. Also called steppes, pampas, or plains, our planet’s grasslands have dwindled drastically. According to Scholtz, less than 10 percent are still intact, as most have been plowed under for crops or bulldozed for human development. One of the most dire threats facing the grasslands that remain is woody encroachment. “It’s a slow and silent killer,” Scholtz says. 

Historically, tree expansion onto grasslands was checked by regular fires, which relegated woody species to wet or rocky places. But as European settlers suppressed fires and planted thousands of trees to provide windbreaks for their homes and livestock, trees proliferated. When trees invade grasslands, they outcompete native grasses and wildflowers by stealing the lion’s share of sunlight and water. Birds, often used as a bellwether for ecosystem health, are sounding the alarm: North America’s grassland bird populations have declined more than 50 percent since 1970, a 2019 study in Science found. 

According to University of Montana researcher Scott Morford, who led the study on rangeland forage loss, tree cover has increased by 50 percent across the western half of the US over the past 30 years, with tree cover expanding steadily year on year. In total, close to 150,000 km2 of once tree-free grasslands have been converted into woodland. “That means we’ve already lost an area the size of Iowa to trees,” says Morford, who emphasizes that an additional 200,000 km2 of tree-free rangelands—an area larger than the state of Nebraska—are “under immediate threat” because they are close to seed sources.

To figure out the amount of lost forage production due to woodland expansion, Morford and his team used satellite images in combination with meteorological data, topography, and information about soils and on-the-ground vegetation to estimate the change in herbaceous biomass (that is, non-woody plants, like grasses) in relation to tree cover over time. “Our computer models allow us to turn up or turn down the tree cover like a knob on your stereo to see how production is impacted,” explains Morford. 

The Future of Climate Activism Is Intergenerational—and on TikTok

The Future of Climate Activism Is Intergenerational—and on TikTok

When it comes to changing minds, nothing beats an experience. That’s how Sylvia Earle sees it. The scientist has spent years trying to get people to understand the impacts of climate change, and has found that showing them can be the best way to tell them about the problems the planet is facing. Problem is, you can’t take millions of people to the bottom of the ocean, or, for that matter, make them read a boring climate report. The solution? Actually, it might be TikTok.

At this week’s RE:WIRED Green, Earle talked with Sophia Kianni, a 20-year-old climate activist in her junior year at Stanford University, about the ways climate activism needs to be intergenerational. As Earle noted, older generations weren’t even convinced climate change was real, and research—the thing that could provide the evidence to prove that it is—”often stays in this nerdy community of scientists and doesn’t get out to the public.” Kianni’s generation, meanwhile, has grown up sharing messages on social media.

Portrait of Sylvia Earle against a green background

Sylvia Earle

Photograph: Aldo Chacon

“I’d like to know from you,” Earle said, “how to strengthen that bridge between the knowledge that is there and communicating it in a way that people listen.”

For Kianni, that bridge is social media. In 2020 she founded the Climate Cardinals, a nonprofit dedicated to translating information about the environment into as many languages as possible. It started as something she did with her family after seeing the effects of pollution in her parents’ home country of Iran. “The reason my nonprofit now has over 9,000 volunteers is because of TikTok,” Kianni said, “because we’ve been able to reach hundreds of thousands of people through organic, short-form video.”

Portrait of Sophia Kianni against a green background

Sophia Kianni

Photograph: Aldo Chacon

Mediums like TikTok aren’t just good for organizing volunteers; they’re also good for spreading information in a way people can easily ingest. “Instead of the traditional forms of media, where it would be a scientist or a politician getting on the news and droning on about the newest scientific updates or policy papers,” Kianni said, “we now have young people who are able to get in front of a camera and say in five seconds what they think the major headline is.” That, she adds, is a big differentiator between the climate activists of Earle’s generation and hers.

Both Kianni and Earle agreed the key factor is having communication between the generations that enables everyone to know what they personally can do about climate change. Like, for example, getting young people excited about green jobs. “That,” Kianni said, “is the most productive way we can have these conversations and actually equip people to build a future we want to inhabit, and have a sense of hope and optimism.”

The Sustainable Future of Food Must Bring Everyone to the Table

The Sustainable Future of Food Must Bring Everyone to the Table

How can we feed the world sustainably? Right now, 325 million people are acutely hungry. 35 million Americans don’t know where their next meal will come from. The world’s food systems are uneven, fragile, and only becoming more fragile with the climate crisis.

“When we talk about from farm-to-fork, we need to transform the food system in a way that, yes, it supports our environment, yes, it supports our health, but also that it provides the economic return to all of the stakeholders across the food system,” says Ertharin Cousin. Cousin is the CEO and managing director of Food Systems for the Future, a nutrition impact investment fund she founded. She has worked on resolving global food insecurity and hunger for two decades.

She spoke at RE:WIRED Green on Wednesday about her work, the need for more innovation, and the opportunity to lift up historically marginalized food entrepreneurs. She also announced a new coalition of investment entities resolving to minimize global hunger through technological innovation. The newly launched Food, Nutrition and Health Investor Coalition (FNHIC) will be led by S2G Ventures, FSF, and other partners. They plan to distribute $2.5 billion in new private investment over the next three years.

“We need to bring all of government together to ensure that we’re addressing access to more nutritious food by all Americans,” she said. “More importantly, we need to bring all of society together to address these issues.”

Cousin was joined in the session by other experts inspiring action on food insecurity: Doria Robinson, executive director of Urban Tilth, who spoke about community-based agriculture; Kayla Abe, cofounder of a climate-change-fighting restaurant and natural wine bar in San Francisco called Shuggie’s Trash Pie + Natural Wine; Isha Datar, executive director of cell-based foods nonprofit New Harvest; Beth Zotter, cofounder and CEO of Umaro Foods, which uses offshore seaweed farms to cultivate bacon; and Magi Richani, founder and CEO of plant-based dairy firm Nobell Foods.

Together, each painted a picture of the future of food that prioritized accessibility, innovation, and collaboration.

Each year, natural disasters and human conflicts threaten people with food insecurity and hunger. “People will say, ‘These are all natural disasters, we had these occurrences long before we were addressing a climate crisis,’” Cousin said. “But the reality is: They’re more erratic, the challenges are coming much more frequently, and impacting more of our food system, more people in their lives because of the climate crisis.”

Our food systems themselves also play a role—contributing about 25 percent of all greenhouse gases. And this feedback loop between climate change and food systems has motivated companies to cultivate food more sustainably, and without relying on livestock. Abe explained that for her part, eaters won’t find prime cuts of meat at her restaurant, and that the only meat products she uses are off-cuts like livers, gizzards, and chicken feet: things normally cast off from meat packing and production. Shuggies, her restaurant, uses upcycled ingredients, byproducts, and offcuts to minimize food waste and educate people about the link between climate and food.