Climate

The demise of a West Antarctic glacier poses the world’s biggest threat to raise sea levels before 2100 — and an ice shelf that’s holding it back from the sea could collapse within three to five years, scientists reported December 13 at the American Geophysical Union’s fall meeting in New Orleans.

Thwaites Glacier is “one of the largest, highest glaciers in Antarctica — it’s huge,” Ted Scambos, a glaciologist at the Boulder, Colo.–based Cooperative Institute for Research in Environmental Sciences, told reporters. Spanning 120 kilometers across, the glacier is roughly the size of Florida, and were the whole thing to fall into the ocean, it would raise sea levels by 65 centimeters, or more than two feet. Right now, its melting is responsible for about 4 percent of global sea level rise.

But a large portion of the glacier is about to lose its tenuous grip on the seafloor, and that will dramatically speed up its seaward slide, the researchers said. Since about 2004, the eastern third of Thwaites has been braced by a floating ice shelf, an extension of the glacier that juts out into the sea. Right now, the underbelly of that ice shelf is lodged against an underwater mountain located about 50 kilometers offshore. That pinning point is essentially helping to hold the whole mass of ice in place.

But data collected by researchers beneath and around the shelf in the last two years suggests that brace won’t hold much longer. Warm ocean waters are inexorably eating away at the ice from below (SN: 4/9/21; SN: 9/9/20). As the glacier’s ice shelf loses mass, it’s retreating inland, and will eventually retreat completely behind the underwater mountain pinning it in place. Meanwhile, fractures and crevasses, widened by these waters, are swiftly snaking through the ice like cracks in a car’s windshield, shattering and weakening it. 

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This deadly punch-jab-uppercut combination of melting from below, ice shattering and losing its grip on the pinning point is pushing the ice shelf to imminent collapse, within as little as three to five years, said Erin Pettit, a glaciologist at Oregon State University in Corvallis. And “the collapse of this ice shelf will result in a direct increase in sea level rise, pretty rapidly,” Pettit added. “It’s a little bit unsettling.”

Satellite data show that over the last 30 years, the flow of Thwaites Glacier across land and toward the sea has nearly doubled in pace. The collapse of this “Doomsday Glacier” alone would alter sea levels significantly, but its fall would also destabilize other West Antarctic glaciers, dragging more ice into the ocean and raising sea levels even more.

That makes Thwaites “the most important place to study for near-term sea level rise,” Scambos said. So in 2018, researchers from the United States and the United Kingdom embarked on a joint five-year project to intensively study the glacier and try to anticipate its imminent future by planting instruments atop, within, below it as well as offshore of it.

This pull-out-all-the-stops approach to studying Thwaites is leading to other rapid discoveries, including the first observations of ocean and melting conditions right at a glacier’s grounding zone, where the land-based glacier begins to jut out into a floating ice shelf. Scientists have also spotted how the rise and fall of ocean tides can speed up melting, by pumping warm waters farther beneath the ice and creating new melt channels and crevasses in the underside of the ice.

To better understand the rapid retreat of Thwaites Glacier, scientists drilled a hole through the ice at the glacier’s grounding zone, the region where the land-based glacier juts out into the sea to become a floating ice shelf. Heated water (heaters shown here) carved a borehole through the ice down to the grounding zone, allowing scientists to take the first ever measurements of ocean conditions in the region.PETER DAVIS/BAS

As Thwaites and other glaciers retreat inland, some scientists have pondered whether they might form very tall cliffs of ice along the edge of the ocean — and the potential tumble of such massive blocks of ice into the sea could lead to devastatingly rapid sea level rise, a hypothesis known as marine ice cliff instability (SN: 2/6/19). How likely researchers say such a collapse is depends on our understanding of the physics and dynamics of ice behavior, something about which scientists have historically known very little (SN: 9/23/20).

The Thwaites collaboration is also tackling this problem. In simulations of the further retreat of Thwaites, glaciologist Anna Crawford of the University of St. Andrews in Scotland and her colleagues found that if the shape of the land beneath the glacier dips deep enough in some places, that could lead to some very tall ice cliffs — but, they found, the ice itself might also deform and thin enough to make tall ice cliff formation difficult.

The collaboration is only at its halfway point now, but these data already promise to help scientists better estimate the near-term future of Thwaites, including how quickly and dramatically it might fall, Scambos said. “We’re watching a world that’s doing things we haven’t really seen before, because we’re pushing on the climate extremely rapidly with carbon dioxide emissions,” he added. “It’s daunting.” More

Wildfire smoke and urban air pollution bring out the worst in each other.

As wildfires rage, they transform their burned fuel into a complex chemical cocktail of smoke. Many of these airborne compounds, including ozone, cause air quality to plummet as wind carries the smoldering haze over cities. But exactly how — and to what extent — wildfire emissions contribute to ozone levels downwind of the fires has been a matter of debate for years, says Joel Thornton, an atmospheric scientist at the University of Washington in Seattle.

A new study has now revealed the elusive chemistry behind ozone production in wildfire plumes. The findings suggest that mixing wildfire smoke with nitrogen oxides — toxic gases found in car exhaust — could pump up ozone levels in urban areas, researchers report December 8 in Science Advances.

Atmospheric ozone is a major component of smog that can trigger respiratory problems in humans and wildlife (SN: 1/4/21). Many ingredients for making ozone — such as volatile organic compounds and nitrogen oxides — can be found in wildfire smoke, says Lu Xu, an atmospheric chemist currently at the National Oceanographic and Atmospheric Administration Chemical Sciences Laboratory in Boulder, Colo. But a list of ingredients isn’t enough to replicate a wildfire’s ozone recipe. So Xu and colleagues took to the sky to observe the chemistry in action.

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Through a joint project with NASA and NOAA, the researchers worked with the Fire Influence on Regional to Global Environments and Air Quality flight campaign to transform a jetliner into a flying laboratory. In July and August 2019, the flight team collected air samples from smoldering landscapes across the western United States. As the plane passed headlong through the plumes, instruments onboard recorded the kinds and amounts of each molecule detected in the haze. By weaving in and out of the smoke as it drifted downwind from the flames, the team also analyzed how the plume’s chemical composition changed over time.

Using these measurements along with the wind patterns and fuel from each wildfire sampled, the researchers created a straightforward equation to calculate ozone production from wildfire emissions. “We took a complex question and gave it a simple answer,” says Xu, who did the work while at Caltech.

As expected, the researchers found that wildfire emissions contain a dizzying array of organic compounds and nitrogen oxide species among other molecules that contribute to ozone formation. Yet their analysis showed that the concentration of nitrogen oxides decreases in the hours after the plume is swept downwind. Without this key ingredient, ozone production slows substantially.  

Air pollution from cities and other urban areas is chock full of noxious gases. So when wildfire smoke wafts over cityscapes, a boost of nitrous oxides could jump-start ozone production again, Xu says.

In a typical fire season, mixes like these could increase ozone levels by as much as 3 parts per billion in the western United States, the researchers estimate. This concentration is far below the U.S. Environmental Protection Agency’s health safety standard of 70 parts per billion, but the incremental increase could still pose a health risk to people who are regularly exposed to smoke, Xu says.

With climate change increasing the frequency and intensity of wildfires, this new ozone production mechanism has important implications for urban air quality, says Qi Zhang, an atmospheric chemist at the University of California, Davis who was not involved in the study (SN: 9/18/20). She says the work provides an “important missing link” between wildfire emissions and ozone chemistry.

The findings may also pose a challenge for environmental policy makers, says Thornton, who was not involved in the research. Though state and local authorities set strict regulations to limit atmospheric ozone, wildfire smoke may undermine those strategies, he says. This could make it more difficult for cities, especially in the western United States, to meet EPA ozone standards despite air quality regulations. More

It’s hard to imagine what Earth might look like in 2500. But a collaboration between science and art is offering an unsettling window into how ongoing climate change might transform now-familiar terrain into alien landscapes over the next few centuries.

These visualizations — of U.S. Midwestern farms overtaken by subtropical plants, of a dried-up Amazon rainforest, of extreme heat baking the Indian subcontinent — emphasize why researchers need to push climate projections long past the customary benchmark of 2100, environmental social scientist Christopher Lyon and colleagues contend September 24 in Global Change Biology.

Fifty years have passed since the first climate projections, which set that distant target at 2100, says Lyon, of McGill University in Montreal. But that date isn’t so far off anymore, and the effects of greenhouse gas emissions emitted in the past and present will linger for centuries (SN: 8/9/21).

To visualize what that future world might look like, the researchers considered three possible climate trajectories — low, moderate and high emissions as used in past reports by the United Nations’ Intergovernmental Panel on Climate Change — and projected changes all the way out to 2500 (SN: 1/7/20). The team focused particularly on impacts on civilization: heat stress, failing crops and changes in land use and vegetation (SN: 3/13/17).

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For all but the lowest-emission scenario, which is roughly in line with limiting global warming to “well under” 2 degrees Celsius relative to preindustrial times as approved by the 2015 Paris Agreement, the average global temperature continues to increase until 2500, the team found (SN: 12/12/15). For the highest-emissions scenario, temperatures increase by about 2.2 degrees C by 2100 and by about 4.6 degrees C by 2500. That results in “major restructuring of the world’s biomes,” the researchers say: loss of most of the Amazon rainforest, poleward shifts in crops and unlivable temperatures in the tropics.

The team then collaborated with James McKay, an artist and science communicator at the University of Leeds in England, to bring the data to life. Based on the study’s projections, McKay created a series of detailed paintings representing different global landscapes now and in 2500.

The team stopped short of trying to speculate on future technologies or cities to keep the paintings based more in realism than science fiction, Lyon says. “But we did want to showcase things people would recognize: drones, robotics, hybrid plants.” In one painting of India in 2500, a person is wearing a sealed suit and helmet, a type of garment that people in some high-heat environments might wear today, he says.

The goal of these images is to help people visualize the future in such a way that it feels more urgent, real and close — and, perhaps, to offer a bit of hope that humans can still adapt. “If we’re changing on a planetary scale, we need to think about this problem as a planetary civilization,” Lyon says. “We wanted to show that, despite the climate people have moved into, people have figured out ways to exist in the climate.”

2000 vs. 2500

High greenhouse gas emissions could increase average global temperatures by about 4.6 degrees Celsius relative to preindustrial times. As a result, extreme heat in India could dramatically alter how humans live in the environment. Farmers and herders, shown in 2000 the painting at left, may require protective clothing such as a cooling suit and helmet to work outdoors by 2500, as shown in the painting at right.

If greenhouse gas emissions remain high, the U.S. Midwest’s “breadbasket” farms, as seen below in 2000 in the painting at left, could be transformed into subtropical agroforestry regions by 2500, researchers say. The region might be dotted with some versions of oil palms and succulents, as envisioned in the painting at right, and rely on water capture and irrigation devices to offset extreme summer heat.

All: James McKay (CC-BY-ND) More

Over decades, centuries and millennia, the steady skyward climb of redwoods, the tangled march of mangroves along tropical coasts and the slow submersion of carbon-rich soil in peatlands has locked away billions of tons of carbon. 

If these natural vaults get busted open, through deforestation or dredging of swamplands, it would take centuries before those redwoods or mangroves could grow back to their former fullness and reclaim all that carbon. Such carbon is “irrecoverable” on the timescale — decades, not centuries — needed to avoid the worst impacts of climate change, and keeping it locked away is crucial.

Now, through a new mapping project, scientists have estimated how much irrecoverable carbon resides in peatlands, mangroves, forests and elsewhere around the globe — and which areas need protection.

The new estimate puts the total amount of irrecoverable carbon at 139 gigatons, researchers report November 18 in Nature Sustainability. That’s equivalent to about 15 years of human carbon dioxide emissions at current levels. And if all that carbon were released, it’s almost certainly enough to push the planet past 1.5 degrees Celsius of warming above preindustrial levels.

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“This is the carbon we must protect to avert climate catastrophe,” says Monica Noon, an environmental data scientist at Conservation International in Arlington, Va. Current efforts to keep global warming below the ambitious target of 1.5 degrees C require that we reach net-zero emissions by 2050, and that carbon stored in nature stays put (SN:12/17/18). But agriculture and other development pressures threaten some of these carbon stores.

To map this at-risk carbon, Noon and her colleagues combined satellite data with estimates of how much total carbon is stored in ecosystems vulnerable to human incursion. The researchers excluded areas like permafrost, which stores lots of carbon but isn’t likely to be developed (although it’s thawing due to warming), as well as tree plantations, which have already been altered (SN: 9/25/19). The researchers then calculated how much carbon would get released from land conversions, such as clearing a forest for farmland. 

That land might store varying amounts of carbon, depending on whether it becomes a palm oil plantation or a parking lot. To simplify, the researchers assumed cleared land was left alone, with saplings free to grow where giants once stood. That allowed the researchers to estimate how long it might take for the released carbon to be reintegrated into the land. Much of that carbon would remain in the air by 2050, the team reports, as many of these ecosystems take centuries to return to their former glory, rendering it irrecoverable on a timescale that matters for addressing climate change.

Releasing that 139 gigatons of irrecoverable carbon could have irrevocable consequences. For comparison, the United Nations’ Intergovernmental Panel on Climate Change estimates that humans can emit only 109 more gigatons of carbon to have a two-thirds chance of keeping global warming below 1.5 degrees C. “These are the places we absolutely have to protect,” Noon says.

Approximately half of this irrecoverable carbon sits on just 3.3 percent of Earth’s total land area, equivalent to roughly the area of India and Mexico combined. Key areas are in the Amazon, the Pacific Northwest, and the tropical forests and mangroves of Borneo. “The fact that it’s so concentrated means we can protect it,” Noon says.

Roughly half of irrecoverable carbon already falls within existing protected areas or lands managed by Indigenous peoples. Adding an additional 8 million square kilometers of protected area, which is only about 5.4 percent of the planet’s land surface, would bring 75 percent of this carbon under some form of protection, Noon says.

“It’s really important to have spatially explicit maps of where these irrecoverable carbon stocks are,” says Kate Dooley, a geographer at the University of Melbourne in Australia who wasn’t involved in the study. “It’s a small percentage globally, but it’s still a lot of land.” Many of these dense stores are in places at high risk of development, she says. 

“It’s so hard to stop this drive of deforestation,” she says, but these maps will help focus the efforts of governments, civil society groups and academics on the places that matter most for the climate. More

This year was supposed to be a turning point in addressing climate change. But the world’s nations are failing to meet the moment, states a new report by the United Nations Environment Programme.

The Emissions Gap Report 2021: The Heat Is On, released October 26, reveals that current pledges to reduce greenhouse gas emissions and rein in global warming still put the world on track to warm by 2.7 degrees Celsius above preindustrial levels by the end of the century.

Aiming for “net-zero emissions” by midcentury — a goal recently announced by China, the United States and other countries, but without clear plans on how to do so — could reduce that warming to 2.2 degrees C. But that still falls short of the mark, U.N. officials stated at a news event for the report’s release.

At a landmark meeting in Paris in 2015, 195 nations pledged to eventually reduce their emissions enough to hold global warming to well below 2 degrees C by 2100 (SN: 12/12/15). Restricting global warming further, to just 1.5 degrees C, would forestall many more devastating consequences of climate change, as the Intergovernmental Panel on Climate Change, or IPCC, reported in 2018 (SN: 12/17/18). In its latest report, released in August, the IPCC noted that extreme weather events, exacerbated by human-caused climate change, now occur in every part of the planet — and warned that the window to reverse some of these effects is closing (SN: 8/9/21).

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Despite these dire warnings, “the parties to the Paris Agreement are utterly failing to keep [its] target in reach,” said U.N. Secretary-General António Guterres. “The era of half measures and hollow promises must end.”

The new U.N. report comes at a crucial time, just days before world leaders meet for the 2021 U.N. Climate Change Conference, or COP26, in Glasgow, Scotland. The COP26 meeting — postponed from 2020 to 2021 due to the COVID-19 pandemic — holds particular significance because it is the first COP meeting since the 2015 agreement in which signatories are expected to significantly ramp up their emissions reductions pledges.

The U.N. Environment Programme has kept annual tabs on the still-yawning gap between existing national pledges to reduce emissions and the Paris Agreement target (SN: 11/26/19). Ahead of the COP26 meeting, 120 countries, responsible for emitting just over half of the world’s greenhouse gas emissions, announced their new commitments to address climate change by 2030.

The 2021 report finds that new commitments bring the world only slightly closer to where emissions need to be by 2030 to reach warming targets. With the new pledges, total annual emissions in 2030 would be 7.5 percent lower (about 55 gigatons of carbon dioxide equivalent) than they would have been with pledges as of last year (about 59 gigatons). But to stay on track for 2 degrees C of warming, emissions would have to be about 30 percent lower than the new pledges, or about 39 gigatons each year. To hold warming to 1.5 degrees C requires a roughly 55 percent drop in emissions compared with the latest pledges, to about 25 gigatons a year.

“I’m hoping that the collision of the science and the statistics in the gap analysis, and the voices of the people will promote a greater sense of urgency,” says Gabriel Filippelli, a geochemist at Indiana University–Purdue University Indianapolis.

On October 26, Filippelli, the editor of the American Geophysical Union journal GeoHealth, and editors in chief of other journals published by the organization coauthored a statement in Geophysical Research Letters. Theyurged world leaders at COP26 to keep the “devastating impacts” of climate change in check by immediately reducing global carbon emissions and shifting to a green economy. “We are scientists, but we also have families and loved ones alongside our fellow citizens on this planet,” the letter states. “The time to bridge the divide between scientist and citizen, head and heart, is now.”

Publishing that plea was a departure for some of the scientists, Filippelli says. “We have been publishing papers for the last 20 to 30 years, documenting the train wreck of climate change,” he says. “As you can imagine, behind the scenes there were some people who were a little uncomfortable because it veered away from the true science. But ultimately, we felt it was more powerful to write a true statement that showed our hearts.” More

The kids are not all right. Children born in 2020 could live through seven times as many extreme heat waves as people born in 1960.

That’s the projected generational disparity if global greenhouse gas emissions are curbed by the amount currently promised by the world’s nations, climate scientist Wim Thiery of Vrije Universiteit Brussel in Belgium and colleagues report September 26 in Science. Under current pledges, Earth’s average temperature is expected to increase by about 2.4 degrees Celsius relative to preindustrial times by 2100. While the older generation will experience an average of about four extreme heat waves during their lifetime, the younger generation could experience an average of about 30 such heat waves, the researchers say.

More stringent reductions that would limit warming to just 1.5 degrees C would shrink — but not erase — the disparity: Children born in 2020 could still experience four times as many extreme heat waves as people born in 1960.

Scientists have previously outlined how climate change has already amped up extreme weather events around the globe, and how those climate impacts are projected to increase as the world continues to warm (SN: 8/9/21). The new study is the first to specifically quantify how much more exposed younger generations will be to those events.

An average child born in 2020 also will experience two times as many wildfires, 2.8 times as many river floods, 2.6 times as many droughts and about three times as many crop failures as a child born 60 years earlier, under climate scenarios based on current pledges. That exposure to extreme events becomes even higher in certain parts of the world: In the Middle East, for example, 2020 children will see up to 10 times as many heat waves as the older cohort, the team found.

With this possible grim future in mind, student climate activists in the #FridaysforFuture movement have been among the most powerful voices of protest in recent years (SN: 12/16/19). Thiery and colleagues note that these findings come at a crucial time, as world leaders prepare to gather in Glasgow, Scotland, in late October for the 2021 United Nations Climate Change Conference to negotiate new pledges to reduce greenhouse gas emissions. More

Ice RiversJemma WadhamPrinceton Univ., $26.95

I’ve always been a sucker for glacier lingo, whimsical words for a harsh landscape gouged, smoothed and bulldozed by ice. Moulins, drumlins, eskers and moraines. Cirques and arêtes. Cold katabatic winds blowing down a mountain, huffed from a glacier’s snout and said to be its spirit.

Jemma Wadham’s Ice Rivers: A Story of Glaciers, Wilderness, and Humanity leans into this duality of whimsy and harshness, cheerfully pulling readers into this strange, icy world. Wadham, a glaciologist at the University of Bristol in England, confesses that her goal is to give readers a sense of connection to glaciers, which she knowingly anthropomorphizes: In her writing, glaciers have heavy bodies, dirty snouts and veins filled with water.

“When I’m with them, I feel like I’m among friends,” she writes. “It is, in many ways, a love story.” And knowing the glaciers, she reasons — perhaps coming to love them — is key to trying to save them.

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Accordingly, the book’s chapters are anchored by site, and each chapter documents a different field expedition or series of expeditions to a particular glacier. Wadham takes us from the Swiss Alps to Norway’s Svalbard islands, from India’s Himalayas to Antarctica’s McMurdo Dry Valleys. It’s a breezy read, with an eager party host vibe (“let me introduce to you my friend the glacier; I think you two will get along”).

While describing each site, Wadham dives into an engaging mishmash of personal recollections about her fieldwork, snippets of accessible glacier and climate science (I now know that these rivers of ice have three different manners of flow), a dash of alpine and polar exploration history, and many bits of local color. Ötzi the 5,300-year-old iceman, Erik the Red, Svalbard’s many polar bears and wild Patagonian horses all make an appearance, not to mention the mummified corpses of seals and penguins littering the Dry Valleys (SN: 7/12/18).

An interesting thread winding through the book concerns how the focus of glaciology as a field has shifted through time. After several years of not winning grants that would allow her to continue working on Svalbard, in 2008 Wadham got the opportunity to go to Greenland instead. “Valley glaciers were no longer considered quite as cutting-edge to the research council funders,” she writes. “Instead, glaciologists had become obsessed with the vast ice sheets,” for the potential of their meltwaters to raise sea levels and alter ocean currents. Several years later, funders began to call for projects looking at melting glaciers’ impacts on ocean life and the water cycle, opening up an opportunity for Wadham to study Patagonia’s fast-changing glacial region.

Where the book really comes alive is in its vivid snapshots of a scientist’s life in the field: making a bleary-eyed cup of coffee in Patagonia using a thin sock as a filter; fearfully skittering across fragile fjord ice on a Ski-Doo; consuming tins of bland fiskeboller, or fish balls, which were mostly used for food but sometimes for rifle practice; solo dancing away a gray mood on a pebbly beach on Svalbard, with a rifle ready to repel polar bears resting nearby on the stones.

These recollections are honest, funny and poignant, and reveal how the highs and lows of fieldwork are inextricably intertwined. Wadham writes, for example, of dreading the “hollow feeling caused by constant sleep deprivation” due to the midnight sun and the relentless roaring of winds and water, a feeling tempered by her fierce love for the open expanses of the wild and for pursuing a “big mission.”

She also writes wistfully of the “communal mirth of field-camp life” where she had never laughed as much before and, less wistfully, of the heavy, claustrophobic atmosphere of an Antarctic research station with its supercharged heating system and extreme politeness over meals with strangers. Against the backdrop of Patagonia’s swiftly shrinking glaciers, Wadham comes to grips with difficult personal losses, even as she wrestles with mysterious headaches. Months later, while recovering from emergency brain surgery, she secretly begins to write about her glaciers. Still more months pass before she finds her way back to the ice, this time in the Peruvian Andes.

“I quickly realized one key thing about fieldwork — if you think you are there to work, you’re gravely mistaken,” Wadham writes. “You’re actually there to survive, and perform some research along the way — if you’re lucky.… In some ways I found all this ‘surviving’ a grounding process.”

Every glacier Wadham has studied has shrunk since she first set foot on the ice over a quarter century ago. But Ice Rivers isn’t focused on mourning those glaciers so much as on celebrating the peace and purpose — the grounding line — Wadham found in them. It certainly makes me want to know them better.

Buy Ice Rivers from Bookshop.org. Science News is a Bookshop.org affiliate and will earn a commission on purchases made from links in this article. More

Under a midday summer sun in California’s Sacramento Valley, rice farmer Peter Rystrom walks across a dusty, barren plot of land, parched soil crunching beneath each step.

In a typical year, he’d be sloshing through inches of water amid lush, green rice plants. But today the soil lies naked and baking in the 35˚ Celsius (95˚ Fahrenheit) heat during a devastating drought that has hit most of the western United States. The drought started in early 2020, and conditions have become progressively drier.

Low water levels in reservoirs and rivers have forced farmers like Rystrom, whose family has been growing rice on this land for four generations, to slash their water use.

Rystrom stops and looks around. “We’ve had to cut back between 25 and 50 percent.” He’s relatively lucky. In some parts of the Sacramento Valley, depending on water rights, he says, farmers received no water this season.

California is the second-largest U.S. producer of rice, after Arkansas, and over 95 percent of California’s rice is grown within about 160 kilometers of Sacramento. To the city’s east rise the peaks of the Sierra Nevada, which means “snowy mountains” in Spanish. Rice growers in the valley below count on the range to live up to its name each winter. In spring, melting snowpack flows into rivers and reservoirs, and then through an intricate network of canals and drainages to rice fields that farmers irrigate in a shallow inundation from April or May to September or October.

If too little snow falls in those mountains, farmers like Rystrom are forced to leave fields unplanted. On April 1 this year, the date when California’s snowpack is usually at its deepest, it held about 40 percent less water than average, according to the California Department of Water Resources. On August 4, Lake Oroville, which supplies Rystrom and other local rice farmers with irrigation water, was at its lowest level on record.

Drought in the Sacramento Valley has forced Peter Rystrom and other rice farmers to leave swaths of land barren.N. Ogasa

Not too long ago, the opposite — too much rain — stopped Rystrom and others from planting. “In 2017 and 2019, we were leaving ground out because of flood. We couldn’t plant,” he says. Tractors couldn’t move through the muddy, clay-rich soil to prepare the fields for seeding.

Climate change is expected to worsen the state’s extreme swings in precipitation, researchers reported in 2018 in Nature Climate Change. This “climate whiplash” looms over Rystrom and the other 2,500 or so rice producers in the Golden State. “They’re talking about less and less snowpack, and more concentrated bursts of rain,” Rystrom says. “It’s really concerning.”

Farmers in China, India, Bangladesh, Indonesia, Vietnam — the biggest rice-growing countries — as well as in Nigeria, Africa’s largest rice producer — also worry about the damage climate change will do to rice production. More than 3.5 billion people get 20 percent or more of their calories from the fluffy grains. And demand is increasing in Asia, Latin America and especially in Africa.

To save and even boost production, rice growers, engineers and researchers have turned to water-saving irrigation routines and rice gene banks that store hundreds of thousands of varieties ready to be distributed or bred into new, climate-resilient forms. With climate change accelerating, and researchers raising the alarm about related threats, such as arsenic contamination and bacterial diseases, the demand for innovation grows.

“If we lose our rice crop, we’re not going to be eating,” says plant geneticist Pamela Ronald of the University of California, Davis. Climate change is already threatening rice-growing regions around the world, says Ronald, who identifies genes in rice that help the plant withstand disease and floods. “This is not a future problem. This is happening now.”

Saltwater woes

Most rice plants are grown in fields, or paddies, that are typically filled with around 10 centimeters of water. This constant, shallow inundation helps stave off weeds and pests. But if water levels suddenly get too high, such as during a flash flood, the rice plants can die.

Striking the right balance between too much and too little water can be a struggle for many rice farmers, especially in Asia, where over 90 percent of the world’s rice is produced. Large river deltas in South and Southeast Asia, such as the Mekong River Delta in Vietnam, offer flat, fertile land that is ideal for farming rice. But these low-lying areas are sensitive to swings in the water cycle. And because deltas sit on the coast, drought brings another threat: salt.

Salt’s impact is glaringly apparent in the Mekong River Delta. When the river runs low, saltwater from the South China Sea encroaches upstream into the delta, where it can creep into the soils and irrigation canals of the delta’s rice fields.

In Vietnam’s Mekong River Delta, farmers pull dead rice plants from a paddy that was contaminated by saltwater intrusion from the South China Sea, which can happen during a drought.HOANG DINH NAM/AFP VIA GETTY IMAGES

“If you irrigate rice with water that’s too salty, especially at certain [growing] stages, you are at risk of losing 100 percent of the crop,” says Bjoern Sander, a climate change specialist at the International Rice Research Institute, or IRRI, who is based in Vietnam.

In a 2015 and 2016 drought, saltwater reached up to 90 kilometers inland, destroying 405,000 hectares of rice paddies. In 2019 and 2020, drought and saltwater intrusion returned, damaging 58,000 hectares of rice. With regional temperatures on the rise, these conditions in Southeast Asia are expected to intensify and become more widespread, according to a 2020 report by the Economic and Social Commission for Asia and the Pacific.

Then comes the whiplash: Each year from around April to October, the summer monsoon turns on the faucet over swaths of South and Southeast Asia. About 80 percent of South Asia’s rainfall is dumped during this season and can cause destructive flash floods.

Bangladesh is one of the most flood-prone rice producers in the region, as it sits at the mouths of the Ganges, Brahmaputra and Meghna rivers. In June 2020, monsoon rains flooded about 37 percent of the country, damaging about 83,000 hectares of rice fields, according to Bangladesh’s Ministry of Agriculture. And the future holds little relief; South Asia’s monsoon rainfall is expected to intensify with climate change, researchers reported June 4 in Science Advances.

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A hot mess

Water highs and lows aren’t the entire story. Rice generally grows best in places with hot days and cooler nights. But in many rice-growing regions, temperatures are getting too hot. Rice plants become most vulnerable to heat stress during the middle phase of their growth, before they begin building up the meat in their grains. Extreme heat, above 35˚ C, can diminish grain counts in just weeks, or even days. In April in Bangladesh, two consecutive days of 36˚ C destroyed thousands of hectares of rice.

In South and Southeast Asia, such extreme heat events are expected to become common with climate change, researchers reported in July in Earth’s Future. And there are other, less obvious, consequences for rice in a warming world.

One of the greatest threats is bacterial blight, a fatal plant disease caused by the bacterium Xanthomonas oryzae pv. oryzae. The disease, most prevalent in Southeast Asia and rising in Africa, has been reported to have cut rice yields by up to 70 percent in a single season.

“We know that with higher temperature, the disease becomes worse,” says Jan Leach, a plant pathologist at Colorado State University in Fort Collins. Most of the genes that help rice combat bacterial blight seem to become less effective when temperatures rise, she explains.

And as the world warms, new frontiers may open for rice pathogens. An August study in Nature Climate Change suggests that as global temperatures rise, rice plants (and many other crops) at northern latitudes, such as those in China and the United States, will be at higher risk of pathogen infection.

Meanwhile, rising temperatures may bring a double-edged arsenic problem. In a 2019 study in Nature Communications, E. Marie Muehe, a biogeochemist at the Helmholtz Centre for Environmental Research in Leipzig, Germany, who was then at Stanford University, showed that under future climate conditions, more arsenic will infiltrate rice plants. High arsenic levels boost the health risk of eating the rice and impair plant growth.

Arsenic naturally occurs in soils, though in most regions the toxic element is present at very low levels. Rice, however, is particularly susceptible to arsenic contamination, because it is grown in flooded conditions. Paddy soils lack oxygen, and the microbes that thrive in this anoxic environment liberate arsenic from the soil. Once the arsenic is in the water, rice plants can draw it in through their roots. From there, the element is distributed throughout the plants’ tissues and grains.

Muehe and her team grew a Californian variety of rice in a local low-arsenic soil inside climate-controlled greenhouses. Increasing the temperature and carbon dioxide levels to match future climate scenarios enhanced the activity of the microbes living in the rice paddy soils and increased the amount of arsenic in the grains, Muehe says. And importantly, rice yields diminished. In the low-arsenic Californian soil under future climate conditions, rice yield dropped 16 percent.

According to the researchers, models that forecast the future production of rice don’t account for the impact of arsenic on harvest yields. What that means, Muehe says, is that current projections are overestimating how much rice will be produced in the future.

Managing rice’s thirst

From atop an embankment that edges one of his fields, Rystrom watches water gush from a pipe, flooding a paddy packed with rice plants. “On a year like this, we decided to pump,” he says.

Able to tap into groundwater, Rystrom left only about 10 percent of his fields unplanted this growing season. “If everybody was pumping from the ground to farm rice every year,” he admits, it would be unsustainable.

One widely studied, drought-friendly method is “alternate wetting and drying,” or intermittent flooding, which involves flooding and draining rice paddies on one- to 10-day cycles, as opposed to maintaining a constant inundation. This practice can cut water use by up to 38 percent without sacrificing yields. It also stabilizes the soil for harvesting and lowers arsenic levels in rice by bringing more oxygen into the soils, disrupting the arsenic-releasing microbes. If tuned just right, it may even slightly improve crop yields.

But the water-saving benefits of this method are greatest when it is used on highly permeable soils, such as those in Arkansas and other parts of the U.S. South, which normally require lots of water to keep flooded, says Bruce Linquist, a rice specialist at the University of California Cooperative Extension. The Sacramento Valley’s clay-rich soils don’t drain well, so the water savings where Rystrom farms are minimal; he doesn’t use the method.

Building embankments, canal systems and reservoirs can also help farmers dampen the volatility of the water cycle. But for some, the solution to rice’s climate-related problems lies in enhancing the plant itself.

Fourth-generation rice farmer Peter Rystrom (left) stands with his grandfather Don Rystrom (middle) and his father Steve Rystrom (right).CALIFORNIA RICE COMMISSION, BRIAN BAER

Better breeds

The world’s largest collection of rice is stored near the southern rim of Laguna de Bay in the Philippines, in the city of Los Baños. There, the International Rice Genebank, managed by IRRI, holds over 132,000 varieties of rice seeds from farms around the globe.

Upon arrival in Los Baños, those seeds are dried and processed, placed in paper bags and moved into two storage facilities — one cooled to 2˚ to 4˚ C from which seeds can be readily withdrawn, and another chilled to –20˚ C for long-term storage. To be extra safe, backup seeds are kept at the National Center for Genetic Resources Preservation in Fort Collins, Colo., and the Svalbard Global Seed Vault tucked inside a mountain in Norway.

All this is done to protect the biodiversity of rice and amass a trove of genetic material that can be used to breed future generations of rice. Farmers no longer use many of the stored varieties, instead opting for new higher-yield or sturdier breeds. Nevertheless, solutions to climate-related problems may be hidden in the DNA of those older strains. “Scientists are always looking through that collection to see if genes can be discovered that aren’t being used right now,” says Ronald, of UC Davis. “That’s how Sub1 was discovered.”

Over 132,000 varieties of rice seeds fill the shelves of the climate-controlled International Rice Genebank. Breeders from around the world can use the seeds to develop new climate-resilient rice strains.IRRI/FLICKR (CC BY-NC-SA 2.0)

The Sub1 gene enables rice plants to endure prolonged periods completely submerged underwater. It was discovered in 1996 in a traditional variety of rice grown in the Indian state of Orissa, and through breeding has been incorporated into varieties cultivated in flood-prone regions of South and Southeast Asia. Sub1-wielding varieties, called “scuba rice,” can survive for over two weeks entirely submerged, a boon for farmers whose fields are vulnerable to flash floods.

Some researchers are looking beyond the genetic variability preserved in rice gene banks, searching instead for useful genes from other species, including plants and bacteria. But inserting genes from one species into another, or genetic modification, remains controversial. The most famous example of genetically modified rice is Golden Rice, which was intended as a partial solution to childhood malnutrition. Golden Rice grains are enriched in beta-carotene, a precursor to vitamin A. To create the rice, researchers spliced a gene from a daffodil and another from a bacterium into an Asian variety of rice.

Three decades have passed since its initial development, and only a handful of countries have deemed Golden Rice safe for consumption. On July 23, the Philippines became the first country to approve the commercial production of Golden Rice. Abdelbagi Ismail, principal scientist at IRRI, blames the slow acceptance on public perception and commercial interests opposed to genetically modified organisms, or GMOs (SN: 2/6/16, p. 22).

Looking ahead, it will be crucial for countries to embrace GM rice, Ismail says. Developing nations, particularly those in Africa that are becoming more dependent on the crop, would benefit greatly from the technology, which could produce new varieties faster than breeding and may allow researchers to incorporate traits into rice plants that conventional breeding cannot. If Golden Rice were to gain worldwide acceptance, it could open the door for new genetically modified climate- and disease-resilient varieties, Ismail says. “It will take time,” he says. “But it will happen.”

Climate change is a many-headed beast, and each rice-growing region will face its own particular set of problems. Solving those problems will require collaboration between local farmers, government officials and the international community of researchers.

“I want my kids to be able to have a shot at this,” Rystrom says. “You have to do a lot more than just farm rice. You have to think generations ahead.” More