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      Why planting tons of trees isn’t enough to solve climate change

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      Trees are symbols of hope, life and transformation. They’re also increasingly touted as a straightforward, relatively inexpensive, ready-for-prime-time solution to climate change.

      When it comes to removing human-caused emissions of the greenhouse gas carbon dioxide from Earth’s atmosphere, trees are a big help. Through photosynthesis, trees pull the gas out of the air to help grow their leaves, branches and roots. Forest soils can also sequester vast reservoirs of carbon.

      Earth holds, by one estimate, as many as 3 trillion trees. Enthusiasm is growing among governments, businesses and individuals for ambitious projects to plant billions, even a trillion more. Such massive tree-planting projects, advocates say, could do two important things: help offset current emissions and also draw out CO2 emissions that have lingered in the atmosphere for decades or longer.

      Even in the politically divided United States, large-scale tree-planting projects have broad bipartisan support, according to a spring 2020 poll by the Pew Research Center. And over the last decade, a diverse garden of tree-centric proposals — from planting new seedlings to promoting natural regrowth of degraded forests to blending trees with crops and pasturelands — has sprouted across the international political landscape.

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      Trees “are having a bit of a moment right now,” says Joe Fargione, an ecologist with The Nature Conservancy who is based in Minneapolis. It helps that everybody likes trees. “There’s no anti-tree lobby. [Trees] have lots of benefits for people. Not only do they store carbon, they help provide clean air, prevent soil erosion, shade and shelter homes to reduce energy costs and give people a sense of well-being.”

      Conservationists are understandably eager to harness this enthusiasm to combat climate change. “We’re tapping into the zeitgeist,” says Justin Adams, executive director of the Tropical Forest Alliance at the World Economic Forum, an international nongovernmental organization based in Geneva. In January 2020, the World Economic Forum launched the One Trillion Trees Initiative, a global movement to grow, restore and conserve trees around the planet. One trillion is also the target for other organizations that coordinate global forestation projects, such as Plant-for-the-Planet’s Trillion Tree Campaign and Trillion Trees, a partnership of the World Wildlife Fund, the Wildlife Conservation Society and other conservation groups.

      Yet, as global eagerness for adding more trees grows, some scientists are urging caution. Before moving forward, they say, such massive tree projects must address a range of scientific, political, social and economic concerns. Poorly designed projects that don’t address these issues could do more harm than good, the researchers say, wasting money as well as political and public goodwill. The concerns are myriad: There’s too much focus on numbers of seedlings planted, and too little time spent on how to keep the trees alive in the long term, or in working with local communities. And there’s not enough emphasis on how different types of forests sequester very different amounts of carbon. There’s too much talk about trees, and not enough about other carbon-storing ecosystems.

      “There’s a real feeling that … forests and trees are just the idea we can use to get political support” for many, perhaps more complicated, types of landscape restoration initiatives, says Joseph Veldman, an ecologist at Texas A&M University in College Station. But that can lead to all kinds of problems, he adds. “For me, the devil is in the details.”

      The root of the problem

      The pace of climate change is accelerating into the realm of emergency, scientists say. Over the last 200 years, human-caused emissions of greenhouse gases, including CO2 and methane, have raised the average temperature of the planet by about 1 degree Celsius (SN: 12/22/18 & 1/5/19, p. 18).

      The litany of impacts of this heating is familiar by now. Earth’s poles are rapidly shedding ice, which raises sea levels; the oceans are heating up, threatening fish and food security. Tropical storms are becoming rainier and lingering longer, and out of control wildfires are blazing from the Arctic to Australia (SN: 12/19/20 & 1/2/21, p. 32).

      The world’s oceans and land-based ecosystems, such as forests, absorb about half of the carbon emissions from fossil fuel burning and other industrial activities. The rest goes into the atmosphere. So “the majority of the solution to climate change will need to come from reducing our emissions,” Fargione says. To meet climate targets set by the 2015 Paris Agreement, much deeper and more painful cuts in emissions than nations have pledged so far will be needed in the next 10 years.

      We invest a lot in tree plantings, but we are not sure what happens after that. Lalisa Duguma

      But increasingly, scientists warn that reducing emissions alone won’t be enough to bring Earth’s thermostat back down. “We really do need an all-hands-on-deck approach,” Fargione says. Specifically, researchers are investigating ways to actively remove that carbon, known as negative emissions technologies. Many of these approaches, such as removing CO2 directly from the air and converting it into fuel, are still being developed.

      But trees are a ready kind of negative emissions “technology,” and many researchers see them as the first line of defense. In its January 2020 report, “CarbonShot,” the World Resources Institute, a global nonprofit research organization, suggested that large and immediate investments in reforestation within the United States will be key for the country to have any hope of reaching carbon neutrality — in which ongoing carbon emissions are balanced by carbon withdrawals — by 2050. The report called for the U.S. government to invest $4 billion a year through 2030 to support tree restoration projects across the United States. Those efforts would be a bridge to a future of, hopefully, more technologies that can pull large amounts of carbon out of the atmosphere.

      The numbers game

      Earth’s forests absorb, on average, 16 billion metric tons of CO2 annually, researchers reported in the March Nature Climate Change. But human activity can turn forests into sources of carbon: Thanks to land clearing, wildfires and the burning of wood products, forests also emit an estimated 8.1 billion tons of the gas back to the atmosphere.

      That leaves a net amount of 7.6 billion tons of CO2 absorbed by forests per year — roughly a fifth of the 36 billion tons of CO2 emitted by humans in 2019. Deforestation and forest degradation are rapidly shifting the balance. Forests in Southeast Asia now emit more carbon than they absorb due to clearing for plantations and uncontrolled fires. The Amazon’s forests may flip from carbon sponge to carbon source by 2050, researchers say (SN Online: 1/10/20). The priority for slowing climate change, many agree, should be saving the trees we have.

      Just how many more trees might be mustered for the fight is unclear, however. In 2019, Thomas Crowther, an ecologist at ETH Zurich, and his team estimated in Science that around the globe, there are 900 million hectares of land — an area about the size of the United States — available for planting new forests and reviving old ones (SN: 8/17/19, p. 5). That land could hold over a trillion more trees, the team claimed, which could trap about 206 billion tons of carbon over a century.

      That study, led by Jean-Francois Bastin, then a postdoc in Crowther’s lab, was sweeping, ambitious and hopeful. Its findings spread like wildfire through media, conservationist and political circles. “We were in New York during Climate Week [2019], and everybody’s talking about this paper,” Adams recalls. “It had just popped into people’s consciousness, this unbelievable technology solution called the tree.”

      To channel that enthusiasm, the One Trillion Trees Initiative incorporated the study’s findings into its mission statement, and countless other tree-planting efforts have cited the report.

      But critics say the study is deeply flawed, and that its accounting — of potential trees, of potential carbon uptake — is not only sloppy, but dangerous. In 2019, Science published five separate responses outlining numerous concerns. For example, the study’s criteria for “available” land for tree planting were too broad, and the carbon accounting was inaccurate because it assumes that new tree canopy cover equals new carbon storage. Savannas and natural grasslands may have relatively few trees, critics noted, but these regions already hold plenty of carbon in their soils. When that carbon is accounted for, the carbon uptake benefit from planting trees drops to perhaps a fifth of the original estimate.

      Trees are having a bit of a moment right now. Joe Fargione

      There’s also the question of how forests themselves can affect the climate. Adding trees to snow-covered regions, for example, could increase the absorption of solar radiation, possibly leading to warming.

      “Their numbers are just so far from anything reasonable,” Veldman says. And focusing on the number of trees planted also sets up another problem, he adds — an incentive structure that is prone to corruption. “Once you set up the incentive system, behaviors change to basically play that game.”

      Adams acknowledges these concerns. But, the One Trillion Trees Initiative isn’t really focused on “the specifics of the math,” he says, whether it’s the number of trees or the exact amount of carbon sequestered. The goal is to create a powerful climate movement to “motivate a community behind a big goal and a big vision,” he says. “It could give us a fighting chance to get restoration right.”

      Other nonprofit conservation groups, like the World Resources Institute and The Nature Conservancy, are trying to walk a similar line in their advocacy. But some scientists are skeptical that governments and policy makers tasked with implementing massive forest restoration programs will take note of such nuances.

      “I study how government bureaucracy works,” says Forrest Fleischman, who researches forest and environmental policy at the University of Minnesota in St. Paul. Policy makers, he says, are “going to see ‘forest restoration,’ and that means planting rows of trees. That’s what they know how to do.”

      Counting carbon

      How much carbon a forest can draw from the atmosphere depends on how you define “forest.” There’s reforestation — restoring trees to regions where they used to be — and afforestation — planting new trees where they haven’t historically been. Reforestation can mean new planting, including crop trees; allowing forests to regrow naturally on lands previously cleared for agriculture or other purposes; or blending tree cover with croplands or grazing areas.

      In the past, the carbon uptake potential of letting forests regrow naturally was underestimated by 32 percent, on average — and by as much as 53 percent in tropical forests, according to a 2020 study in Nature. Now, scientists are calling for more attention to this forestation strategy.

      If it’s just a matter of what’s best for the climate, natural forest regrowth offers the biggest bang for the buck, says Simon Lewis, a forest ecologist at University College London. Single-tree commercial crop plantations, on the other hand, may meet the technical definition of a “forest” — a certain concentration of trees in a given area — but factor in land clearing to plant the crop and frequent harvesting of the trees, and such plantations can actually release more carbon than they sequester.

      Comparing the carbon accounting between different restoration projects becomes particularly important in the framework of international climate targets and challenges. For example, the 2011 Bonn Challenge is a global project aimed at restoring 350 million hectares by 2030. As of 2020, 61 nations had pledged to restore a total of 210 million hectares of their lands. The potential carbon impact of the stated pledges, however, varies widely depending on the specific restoration plans.

      In a 2019 study in Nature, Lewis and his colleagues estimated that if all 350 million hectares were allowed to regrow natural forest, those lands would sequester about 42 billion metric tons (gigatons in chart above) of carbon by 2100. Conversely, if the land were to be filled with single-tree commercial crop plantations, carbon storage drops to about 1 billion metric tons. And right now, plantations make up a majority of the restoration plans submitted under the Bonn Challenge.

      Striking the right balance between offering incentives to landowners to participate while also placing certain restrictions remains a tricky and long-standing challenge, not just for combating the climate emergency but also for trying to preserve biodiversity (SN: 8/1/20, p. 18). Since 1974, Chile, for example, has been encouraging private landowners to plant trees through subsidies. But landowners are allowed to use these subsidies to replace native forestlands with profitable plantations. As a result, Chile’s new plantings not only didn’t increase carbon storage, they also accelerated biodiversity losses, researchers reported in the September 2020 Nature Sustainability.

      The reality is that plantations are a necessary part of initiatives like the Bonn Challenge, because they make landscape restoration economically viable for many nations, Lewis says. “Plantations can play a part, and so can agroforestry as well as areas of more natural forest,” he says. “It’s important to remember that landscapes provide a whole host of services and products to people who live there.”

      But he and others advocate for increasing the proportion of forestation that is naturally regenerated. “I’d like to see more attention on that,” says Robin Chazdon, a forest ecologist affiliated with the University of the Sunshine Coast in Australia as well as with the World Resources Institute. Naturally regenerated forests could be allowed to grow in buffer regions between farms, creating connecting green corridors that could also help preserve biodiversity, she says. And “it’s certainly a lot less expensive to let nature do the work,” Chazdon says.

      Indeed, massive tree-planting projects may also be stymied by pipeline and workforce issues. Take seeds: In the United States, nurseries produce about 1.3 billion seedlings per year, Fargione and colleagues calculated in a study reported February 4 in Frontiers in Forests and Global Change. To support a massive tree-planting initiative, U.S. nurseries would need to at least double that number.

      A tree-planting report card

      From China to Turkey, countries around the world have launched enthusiastic national tree-planting efforts. And many of them have become cautionary tales.

      China kicked off a campaign in 1978 to push back the encroaching Gobi Desert, which has become the fastest-growing desert on Earth due to a combination of mass deforestation and overgrazing, exacerbated by high winds that drive erosion. China’s Three-North Shelter Forest Program, nicknamed the Great Green Wall, aims to plant a band of trees stretching 4,500 kilometers across the northern part of the country. The campaign has involved millions of seeds dropped from airplanes and millions more seedlings planted by hand. But a 2011 analysis suggested that up to 85 percent of the plantings had failed because the nonnative species chosen couldn’t survive in the arid environments they were plopped into.

      A woman places straw in March 2019 to fix sand in place before planting trees at the edge of the Gobi Desert in China’s Minqin County. Her work is part of a private tree-planting initiative that dovetails with the government’s decades-long effort to build a “green wall” to hold back the desert.WANG HE/GETTY IMAGES PLUS

      More recently, Turkey launched its own reforestation effort. On November 11, 2019, National Forestation Day, volunteers across the country planted 11 million trees at more than 2,000 sites. In Turkey’s Çorum province, 303,150 saplings were planted in a single hour, setting a new world record.

      Within three months, however, up to 90 percent of the new saplings inspected by Turkey’s agriculture and forestry trade union were dead, according to the union’s president, Şükrü Durmuş, speaking to the Guardian (Turkey’s minister of agriculture and forestry denied that this was true). The saplings, Durmuş said, died due to a combination of insufficient water and because they were planted at the wrong time of year, and not by experts.

      Some smaller-scale efforts also appear to be failing, though less spectacularly. Tree planting has been ongoing for decades in the Kangra district of Himachal Pradesh in northern India, says Eric Coleman, a political scientist at Florida State University in Tallahassee, who’s been studying the outcomes. The aim is to increase the density of the local forests and provide additional forest benefits for communities nearby, such as wood for fuel and fodder for grazing animals. How much money was spent isn’t known, Coleman says, because there aren’t records of how much was paid for seeds. “But I imagine it was in the millions and millions of dollars.”

      Coleman and his colleagues analyzed satellite images and interviewed members of the local communities. They found that the tree planting had very little impact one way or the other. Forest density didn’t change much, and the surveys suggested that few households were gaining benefits from the planted forests, such as gathering wood for fuel, grazing animals or collecting fodder.

      But massive tree-planting efforts don’t have to fail. “It’s easy to point to examples of large-scale reforestation efforts that weren’t using the right tree stock, or adequately trained workforces, or didn’t have enough investment in … postplanting treatments and care,” Fargione says. “We … need to learn from those efforts.”

      Speak for the trees

      Forester Lalisa Duguma of World Agroforestry in Nairobi, Kenya, and colleagues explored some of the reasons for the very high failure rates of these projects in a working paper in 2020. “Every year there are billions of dollars invested [in tree planting], but forest cover is not increasing,” Duguma says. “Where are those resources going?”

      In 2019, Duguma raised this question at the World Congress on Agroforestry in Montpellier, France. He asked the audience of scientists and conservationists: “How many of you have ever planted a tree seedling?” To those who raised their hands, he asked, “Have they grown?”

      Some respondents acknowledged that they weren’t sure. “Very good! That’s what I wanted,” he told them. “We invest a lot in tree plantings, but we are not sure what happens after that.”

      It comes down to a deceptively simple but “really fundamental” point, Duguma says. “The narrative has to change — from tree planting to tree growing.”

      The good news is that this point has begun to percolate through the conservationist world, he says. To have any hope of success, restoration projects need to consider the best times of year to plant seeds, which seeds to plant and where, who will care for the seedlings as they grow into trees, how that growth will be monitored, and how to balance the economic and environmental needs of people in developing countries where the trees might be planted.

      “That is where we need to capture the voice of the people,” Duguma says. “From the beginning.”

      Even as the enthusiasm for tree planting takes root in the policy world, there’s a growing awareness among researchers and conservationists that local community engagement must be built into these plans; it’s indispensable to their success.

      “It will be almost impossible to meet these targets we all care so much about unless small farmers and communities benefit more from trees,” as David Kaimowitz of the United Nations’ Food and Agriculture Organization wrote March 19 in a blog post for the London-based nonprofit International Institute for Environment and Development.

      For one thing, farmers and villagers managing the land need incentives to care for the plantings and that includes having clear rights to the trees’ benefits, such as food or thatching or grazing. “People who have insecure land tenure don’t plant trees,” Fleischman says.

      Fleischman and others outlined many of the potential social and economic pitfalls of large-scale tree-planting projects last November in BioScience. Those lessons boil down to this, Fleischman says: “You need to know something about the place … the political dynamics, the social dynamics.… It’s going to be very different in different parts of the world.”

      The old cliché — think globally, act locally — may offer the best path forward for conservationists and researchers trying to balance so many different needs and still address climate change.

      “There are a host of sociologically and biologically informed approaches to conservation and restoration that … have virtually nothing to do with tree planting,” Veldman says. “An effective global restoration agenda needs to encompass the diversity of Earth’s ecosystems and the people who use them.”

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      Human-driven climate change sent Pacific Northwest temperatures soaring

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      The deadly heat wave that baked the Pacific Northwest in late June would have been “virtually impossible” without human-caused climate change, an international team of scientists announced July 7.

      In fact, the temperatures were so extreme — Portland, Ore., reached a staggering 47° Celsius (116° Fahrenheit) on June 29, while Seattle surged to 42° C (108° F) — that initial analyses suggested they were impossible even with climate change, Geert Jan van Oldenborgh, a climate scientist with the Royal Netherlands Meteorological Institute in De Bilt, said at a news conference to announce the team’s findings. “This was an extraordinary event. I don’t know what English word covers it.”

      Climate change due to greenhouse gas emissions made the region’s heat wave at least 150 times more likely to occur, the team found. As emissions and global temperatures continue to rise, such extreme heat events could happen in the region as often as every five to 10 years by the end of the century.  

      It’s not just that numerous temperature records were broken, van Oldenborgh said. It’s that the observed temperatures were so far outside of historical records, breaking those records by as much as 5 degrees C in many places — and a full month before usual peak temperatures for the region. The observations were also several degrees higher than the upper temperature limits predicted by most climate simulations for the heat waves, even taking global warming into account.

      Coming just about a week after the heat wave broke, the new study is the latest real-time climate attribution effort by scientists affiliated with the World Weather Attribution network. Van Oldenborgh and University of Oxford climate scientist Friederike Otto founded the group in 2014 to conduct quick analyses of extreme events such as the 2020 Siberian heat wave (SN: 7/15/20).

      In the current study, 27 researchers focused on how the observed temperatures from June 27 to June 29 compared with annual maximum temperatures over the last 50 years for locations across the northwestern United States and southwestern Canada. The team then used 21 different climate simulations of temperatures to analyze the intensity of such a heat wave in the region with and without the influence of greenhouse gas warming.

      Earth has already warmed by about 1.2 degrees C relative to preindustrial times. That warming, the researchers determined, increased the intensity of the heat wave by about 2 degrees C. Once global warming increases to 2 degrees C, future heat waves may become even more intense (SN: 12/17/18). Those heat waves could be another 1.3 degrees C hotter, the researchers found.

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      That poses a real danger. The late June heat wave took a painful toll (SN: 6/29/21), killing several hundred people — “almost certainly” an underestimate, the researchers say. On June 29, Lytton, a small village in British Columbia, set an all-time Canadian temperature record of 49.6° C (121.3° F). The heat may have exacerbated wildfires that, a day later, swept through British Columbia’s Fraser Canyon region, burning 90 percent of the village, according to local officials. Meanwhile, the U.S. West and southwestern Canada are already bracing for another round of soaring temperatures.

      One possible reason for the startling intensity of this heat wave is that, while climate change amped up the temperatures, what happened was still a very rare, unlucky event for the region. How rare isn’t easy to say, given that the observed temperatures were so far off the charts, the researchers say. Under current climate conditions, simulations suggest that such a heat wave might occur once every 1,000 years — but these events will become much more common in future as the climate changes.

      By the end of June 2021, more than 40 wildfires burned across Canada’s British Columbia, exacerbated by extreme dryness and the intense heat. One fire burned 90 percent of the town of Lytton, which had set a new temperature record for the country the day before. The fire also generated a massive storm-producing plume of smoke called a pyrocumulonimbus cloud.NASA

      Another possibility is grimmer: Climate simulations may not accurately capture what really happens during extreme heat waves. “Climate science has been a bit complacent” about simulating heat waves, assuming that heat wave temperatures would increase linearly along with rising global temperatures, Otto said. But now, Earth’s climate system may have entered a new state in which other climatic factors, such as drier soils or changes to jet stream circulation, are exacerbating the heat in more difficult-to-predict, less linear ways.

      The new study didn’t seek to determine which of these possibilities is true, though the team plans to tackle this question over the next few months. However, many scientists have already noted the inability of current climate models to capture what’s really going on.  

      “I agree that it is virtually impossible that the [Pacific Northwest] heat wave would have occurred with the observed intensity in the absence of climate change,” Michael Mann, a climate scientist at Penn State who wasn’t involved in the attribution study, commented via e-mail. “But the models used don’t capture the jet stream phenomenon … that WE KNOW played an important role in this event.”

      Disproportionate warming of the Arctic region alters temperature gradients high in the atmosphere, which can lead to a wavier jet stream, Mann wrote in the New York Times June 29. That waviness can exacerbate and prolong extreme weather events, such as the heat dome centered over the Pacific Northwest in late June.

      This recent heat wave wasn’t just a major disaster, but also posed major scientific questions, van Oldenborgh said. Such an event “would have been judged impossible last year. All of us have just dialed down our certainty of how heat waves behave,” he added. “[We] are much less certain of how the climate affects heat waves than we were two weeks ago.” More

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      A tweaked yeast can make ethanol from cornstalks and a harvest’s other leftovers

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      When corn farmers harvest their crop, they often leave the stalks, leaves and spent cobs to rot in the fields. Now, engineers have fashioned a new strain of yeast that can convert this inedible debris into ethanol, a biofuel. If the process can be scaled up, this largely untapped renewable energy source could help reduce reliance on fossil fuels.

      Previous efforts to convert this fibrous material, called corn stover, into fuel met with limited success. Before yeasts can do their job, corn stover must be broken down, but this process often generates by-products that kill yeasts. But by tweaking a gene in common baker’s yeast, researchers have engineered a strain that can defuse those deadly by-products and get on with the job of turning sugar into ethanol.

      The new yeast was able to produce over 100 grams of ethanol for every liter of treated corn stover, an efficiency comparable to the standard process using corn kernels to make the biofuel, the researchers report June 25 in Science Advances.

      “They’ve produced a more resilient yeast,” says Venkatesh Balan, a chemical engineer at the University of Houston not involved in the research. The new strain may benefit biofuel producers trying to harness materials like corn stover, he says.

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      In the United States, most ethanol is made from corn, the country’s largest crop, and is mixed into most of the gasoline sold at gas stations. Corn ethanol is a renewable energy source, but it has limitations. Diverting corn to make ethanol can detract from the food supply, and expanding cropland just to plant corn for biofuel clears natural habitats (SN: 12/21/20). Converting inedible corn stover into ethanol could increase the biofuel supply without having to plant more crops.

      “Corn can’t really displace petroleum as a raw material for fuels,” says metabolic engineer Felix Lam of MIT. “But we have an alternative.”

      Lam and colleagues started with Saccharomyces cerevisiae, or common baker’s yeast. Like sourdough bakers and brewers, biofuel producers already use yeast: It can convert sugars in corn kernels into ethanol (SN: 9/19/17).

      But unlike corn kernels with easy-access sugars, corn stover contains sugars bound in lignocellulose, a plant compound that yeast can’t break down. Applying harsh acids can free these sugars, but the process generates toxic by-products called aldehydes that can kill yeasts.

      But Lam’s team had an idea — convert the aldehydes into something tolerable to yeast. The researchers already knew that by adjusting the chemistry of the yeast’s growing environment, they could improve its tolerance to alcohol, which is also harmful at high concentrations. With that in mind, Lam and colleagues homed in on a yeast gene called GRE2, which helps convert aldehydes into alcohol. The team randomly generated about 20,000 yeast variants, each with a different, genetically modified version of GRE2. Then, the researchers placed the horde of variants inside a flask that also contained toxic aldehydes to see which yeasts would survive.

      Multiple variants survived the gauntlet, but one dominated. With this battle-tested version of GRE2, the researchers found that the modified baker’s yeast could produce ethanol from treated corn stover almost as efficiently as from corn kernels. What’s more, the yeast could generate ethanol from other woody materials, including wheat straw and switchgrass (SN: 1/14/14). “We have a single strain that can accomplish all this,” Lam says.

      This strain resolves a key challenge in fermenting ethanol from fibrous materials like corn stover, Balan says. But “there are many more improvements that will have to happen to make this technology commercially viable,” he adds, such as logistical challenges in harvesting, transporting and storing large volumes of corn stover.

      “There are so many moving parts to this problem,” Lam acknowledges. But he thinks his team’s findings could help kick-start a “renewable pipeline” that harnesses underused, sustainable fuel sources. The vision, he says, is to challenge the reign of fossil fuels. More

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      Focusing on Asian giant hornets distorts the view of invasive species

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      Fingers crossed for finding nothing: July marks the main trapping season to check for Asian giant hornets still infesting Washington state.

      The first of these invasive hornets found in North America in 2021, in June, was probably not from a nest made this year, scientists say. So that find doesn’t say how well, or if, the pests might have survived the winter. Yet that hornet shows quite well the relentless risk of newly arriving insects.

      That initial specimen, a “crispy” dead male insect lying on a lawn in Marysville, Wash., belongs to the hefty species Vespa mandarinia. Nicknamed murder hornets, these were detected flying loose in Canada for the first time in 2019 and in the United States in 2020 (SN: 5/29/20). Yet the “dry, crispy” male is not part of known hornet invasions, said entomologist Sven Spichiger at a news conference on June 16.

      Testing shows the male “is definitely not the same genetic line as the ones we have found,” said Spichiger, of the Washington State Department of Agriculture in Olympia. Neither the U.S. finds, until now all from Washington’s Whatcom County, nor British Columbia’s on the other side of the border are closely related to the newfound hornet. It’s a separate incursion no one had noticed until now.

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      This oddball new specimen may help correct the skewed impression that sneaky invasive arrivals are rare. The hornets’ appearance in North America may have been a shock to some, but in reality, worrisome insects show up often, and will probably keep doing so. Fortunately making a permanent home is harder than getting here, scientists say.

      When news of the Asian giant hornets’ arrival first broke in 2019, one of the people who was not at all surprised at a foreign species was entomologist Doug Yanega of the University of California, Riverside. “It is very fair to say that there are many invasive species,” he emphasizes. “We just got a new African mantis species in California this past year in LA, and the expectation is that it is likely to spread.”

      But even alarming pest arrivals rarely kick up the fuss prompted by Asian giant hornets. At a peak in hornet news during May 2020, Yanega contrasted the new intruders with the South American palm weevil (Rhynchophorus palmarum). That big weevil had reached southern California and could “wipe out every palm tree in the state,” according to Yanega. Yet, “there have been ZERO [national] mainstream media reports about this, an insect that seriously threatens to have a VASTLY greater negative impact on the economy and our way of life than those hornets ever will,” he fumed in an e-mail.

      That relentless influx of invading insects may be one reason so few make it into the general news. For instance, U.S. Customs and Border Protection reported 31,785 incidents detecting some pest just for fiscal year 2020.

      For 2021, to pick just one example of worrisome arrivals that have not gone viral, inspectors at Washington Dulles International Airport in Virginia and later at Baltimore/Washington International noticed little brown pests called Khapra beetles (Trogoderma granarium) in Basmati rice and then in dried cow peas that travelers were trying to bring in from abroad. Officials banned the contaminated foodstuffs.

      The Dulles contraband had the bigger number of living insects: 12 larvae and four adults. Even that tiny number of tiny insects was unacceptable. This is the only insect species that U.S. customs officials act upon even when all specimens are found dead. The beetles nibble stored seeds but will also soil the goods with stray body parts and hairs that can make human babies fed dirty grain quite sick and adults uncomfortable. In 1953, a major California effort started to stamp out infestations of Khapra beetles and eventually preserved crop marketability. But the effort was expensive, costing the equivalent of about $90 million in today’s economy.

      Tiny but destructive Khapra beetles (shown, side and front view), which California eliminated at great expense, almost got into the United States at least twice in 2021 in air passenger luggage. Customs stopped those two incursions.Both: Pest and Diseases Image Library, Bugwood.org (CC BY-NC 3.0 US)

      Tiny but destructive Khapra beetles (shown, side and front view), which California eliminated at great expense, almost got into the United States at least twice in 2021 in air passenger luggage. Customs stopped those two incursions.Both: Pest and Diseases Image Library, Bugwood.org (CC BY-NC 3.0 US)

      Beetles aside, menacing hornets of other species have shown up before the latest Asian giants, says Paul van Westendorp, an apiculture specialist who now strategizes British Columbia’s fight against V. mandarinia. In May 2019, just months before the discovery of an Asian giant hornet’s arrival, a V. soror hornet appeared in Canada. It was “alive, but not for long,” van Westendorp says. “I had a chance to admire that specimen.” Not a frail beast, this species hunts down other insects and has been reported to catch prey as large as a gecko. V. soror looks very much like a V. mandarinia, he says.

      Even Asian giant hornets themselves have turned up at least once in the United States before 2020. An inspector in 2016 flagged a package coming into the San Francisco airport holding a papery insect nest but not mentioning insects on the label. The nest held Asian giant hornet larvae and pupae, some still alive when discovered. These and other species of hornets, including the ominously named V. bellicosa, accounted for about half of the 50 interceptions of hornets and yellow jackets flagged from 2010 to 2018 at U.S. ports of entry, researchers reported in 2020 in Insect Systematics and Diversity.  

      Only some stowaways will manage to make permanent homes in new territory. Of these, the real troublemakers seem to be a minority. For instance, out of 455 plant-attacking insects that settled into forests in the continental United States, 62 cause noticeable damage, according to a 2011 tally from U.S. Forest Service researcher Juliann Aukema and colleagues. Even a few rampaging invasive pests, though, can get expensive. Biologists are throwing themselves into the fight.

      Relentless as the onslaught of unwanted arrivals is, there’s hope for stamping out the more noticeable invasions if caught early. Vespa hornets are “very large-bodied and obvious, so people will see them,” says entomologist Lynn Kimsey of the University of California, Davis, one of the authors of the 2020 hornet overview. A Vespa affinis nest showed up in San Pedro, in Southern California at least a decade ago. However, she says, “it was killed and there’s been no sighting of the species since, as far as I’ve heard.”

      Catching such intrusions early isn’t always easy, however. The port of Oakland takes in about 1 million shipping containers from overseas a year, but at best U.S. Department of Agriculture inspectors can check maybe only 10 percent for stowaway insects, Kimsey says. Add to this all the cargo coming into Long Beach, San Diego and the other West Coast ports — plus all the cargo jets. “What’s amazing is that we don’t see more invasives,” she says. “I think this tells you how hard it is for exotic species to get established.”

      They’ll keep arriving though. All the more reason to keep an eye out for something funny on the lawn, even if it’s just a withered nugget. More

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      3 things to know about the record-smashing heat wave baking the Pacific Northwest

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      Like a lid on a steaming pot, a high-pressure system is sitting over the U.S. Pacific Northwest and British Columbia, Canada, sending temperatures in the region soaring to unprecedented heights.

      From a historic perspective, the event is so rare and extreme as to be a once in a millennium heat wave. But one consequence of Earth’s rapidly changing climate is that such extreme events will become much more common in the region in future, says Larry O’Neill, a climate scientist at Oregon State University in Corvallis.

      Temperatures in Portland, Ore., reached 115° Fahrenheit (46° Celsius) on June 29, the highest temperature recorded there since record-keeping began in 1940; average high temperatures for this time of year are about 73° F (23° C). Similar records were notched across the region and more are expected to be set as the high pressure system slowly slides east.

      The heat was so extreme it melted transit power cables for Portland’s cable cars and caused asphalt and concrete roads in western Washington to expand and crack. Such high temperatures are particularly dangerous in a normally cool region little used to or prepared for it, raising the risk of heat-related deaths and other health hazards (SN: 4/3/18). Ground-level ozone levels, for instance, also reached the highest seen yet in 2021, the chemical reactions that form the gas amped up by a potent mix of high heat and strong ultraviolet light.

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      O’Neill talked to Science News about three things to know about the heat wave.

      1. The heat wave is linked to a stalled kink in the jet stream.

      Jet streams, fast-moving currents of air high in the troposphere, encircle both poles, helping to push weather systems around Earth’s surface.  The current isn’t smooth and straight; it can meander and form large swirls, peaks and troughs surrounding zones of high- and low-pressure.

      Occasionally, these weather patterns stall, becoming stationary “blocking events” that keep a particular spate of weather in place for an extended period of time. One such stalled-out high-pressure zone — basically a large dome of hot, dry weather — is now sitting atop the Pacific Northwest.

      The punishing heatwave has an incredible jet stream pattern.The dome of heat will be encircled by the polar jet and this helps lift a sub-tropical jet branch almost into the Canadian Arctic. pic.twitter.com/uIWIIINlSc— Scott Duncan (@ScottDuncanWX) June 25, 2021
      London-based meteorologist Scott Duncan tweets about the unusual heat (top) and the jet stream pattern (bottom) that created that heat dome over the Pacific Northwest. In the jet stream image, hot, dry air (in orange) swirls around and maintains a high-pressure system over the region from June 24 to June 29, locking that hot, dry air in place.

      Historically, similar high-pressure patterns have brought heat waves to the region, O’Neill says. But this one is different. A typical severe heat wave in the past might lead to temperatures of about 100 °F, he says, “not 115 °F.”

      2. Climate change is making the heat wave more severe.

      Baseline temperatures were already higher than in the past, due to Earth’s changing climate. Globally, Earth’s average temperatures are increasing, with 2016 and 2020 tied for the hottest years on record (SN: 1/14/21).

      Those changes are reflected in what’s now officially considered “normal.” In May, for example, the U.S. National Oceanographic and Atmospheric Administration reported that the country’s new baseline reference temperature, or “climate normal,” will be the period from 1991 to 2020 — also now the hottest 30-year period on record for the country (SN: 5/26/21).

      That changing reference makes it tough to place such an unprecedented heat wave in any kind of historical context. “We have a historical data record that’s 100 years long,” O’Neill says. Saying that the heat wave is a once-in-a-millennium event means that “you would expect that, at random chance, this would occur once every 1,000 years. But we’ve never observed this. We have no basis to say this,” he adds. “This is a climate that we’re not accustomed to.”

      3. Climate change is likely to make such extreme events more common in the future.

      A week before the onset of the heat wave, forecasters were predicting such unprecedented temperatures for the region that many people dismissed those predictions as “being ridiculous,” O’Neill says. “Turns out, [the forecasters] were right.”

      Future climate change attribution studies may shed some more light on the ways in which this particular heat wave may be linked to climate change (SN: 7/15/20). Overall, it’s known that climate change is likely to make such extreme events more common in the future, O’Neill says. “We’re seeing these highs form more frequently, and more persistently.” Extreme heat and extreme drought in the U.S. West, for example, can create a reinforcing cycle that exacerbates both (SN: 4/16/20).  

      And that poses many dangers for the planet, not least for human health (SN: 4/3/18). In May, scientists reported in Nature Climate Change that 37 percent of heat-related deaths between 1991 and 2018 were attributable to human-caused climate change.  

      “When we talk about climate change, often the conversation is a little more abstract,” O’Neill says. “We’re experiencing it right now (SN: 11/25/19). And this question about whether we adapt and mitigate — that’s something we have to figure out right now.” More

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      ‘Fathom’ seeks to unravel humpback whales’ soulful songs

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      In an opening scene of the new film Fathom, Michelle Fournet sits at her computer in the dark, headphones on. The marine ecologist at Cornell University is listening to a humpback whale song, her fingers bobbing like a conductor’s to each otherworldly croak and whine. Software converts crooning whale sounds into the visual space of craggy valleys and tall peaks, offering a glimpse at a language millions of years in the making.

      Debuting June 25 on Apple TV+, Fathom follows two scientific teams studying the enigmatic songs of humpbacks. The film captivates, diving into the quest to unveil the inner world of these animals and their ever-changing song culture — one considered far older than our ancestors’ first upright steps.

      On opposite sides of the Pacific Ocean, scientists head out onto the water. In a mountain-fringed bay in Alaska, Fournet makes repeated attempts to talk to the whales, playing them a painstakingly reconstructed rendition of a yelp that she thinks may be a greeting. In French Polynesia, behavioral ecologist Ellen Garland of the University of St. Andrews in Scotland listens to humpback songs, mapping how they are tweaked, learned and shared by whales across the South Pacific. These settings are stark and gorgeous, their isolation artfully shown through silent, foggy mornings and endless cobalt seas. In a film fundamentally about oceans filled with sound, ample quiet rests on the surface.

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      Directed by Drew Xanthopoulos, Fathom portrays humpbacks and other whales as complex, highly social beings without overstated anthropomorphism. In one goose bump–inducing scene, Garland’s narration identifies whales’ social similarities to humans, but set in a totally different environment. Perceiving each other chiefly with sound cast over stupefying distances, “whales evolved to build relationships in the dark,” Garland says.

      Fathom also gives an intimate look at what scientists undertake to find humpbacks in the vast ocean. Equipment breaks. Whales prove unpredictable. Strategies must change on the fly. These moments communicate the tough realities of science and the resilience needed for successful research.

      Much of the film is immersed in scenes like these, between troubleshooting and long waits on boat surveys. At times, the film’s pace languishes; connections to greater perspectives, such as the possibility of a globally interlinked song culture, are touched on but not fully examined.

      Nonetheless, Fournet’s simple distillation of her complex quest lingers: “I’m trying to start a conversation.” Her words remind us that Fathom is inherently seated at the threshold of unfathomable territory.

      [embedded content]
      Watch a trailer for Fathom. More

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      Collapse may not always be inevitable for marine ice cliffs

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      When it comes to global warming and sea level rise, scientists have made some dire predictions. One of the most calamitous involves the widespread collapse of ice cliffs along the edges of Greenland and Antarctica, which could raise sea level as much as 4 meters by 2200 (SN: 2/6/19). Now, new simulations suggest that massive glaciers flowing into the sea may not be as vulnerable to such collapses as once believed.

      One hypothesis that projected calamitous sea level rise is called the marine ice cliff instability. It suggests that sea-facing bluffs of ice more than 100 meters tall will fail and then slough off to expose fresh ice. Those new cliffs will in turn disintegrate, fall into the sea and float away, setting off a relatively rapid retreat of the glacier that boosts sea level rise.

      Although discussed for years, the phenomenon hasn’t yet been seen in today’s glaciers, says Jeremy Bassis, a glaciologist at the University of Michigan in Ann Arbor. “But that may not be surprising, due to the relatively short record of observations in the field and by satellites,” he says.

      Because of the dearth of field data, Bassis and colleagues decided to use computer simulations to explore ice-cliff behavior. Unlike previous models, the researchers’ simulations considered how ice flows under pressure as well as how it fractures when highly stressed. This blended model is “a pioneering composite,” says Nicholas Golledge, a glaciologist at the Victoria University of Wellington in New Zealand, who wasn’t involved in the study.

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      First, the researchers simulated the collapse of a 135-meter-tall ice cliff on dry land. Over a virtual period of weeks, the face of the cliff shattered and then slumped down to the base, where the icy rubble helped buttress the cliff against further collapse. Researchers have often seen this result in the field, Bassis says.

      Then, the team simulated a 400-meter-tall glacier flowing into water that was 290 meters deep. These dimensions are typical of some of the massive glaciers in Greenland flowing into deep fjords, Bassis says. When the cybercliff collapsed, ice that fell into the water at the cliff’s base floated away, leading to repeated failures and rapid, runaway collapse of the glacier. But adding even a small amount of back pressure at the base of the cliff — as would happen if icebergs got stuck and couldn’t waft away, or if they froze in place — prevented a runaway collapse, Bassis and his team reports in the June 18 Science. “We didn’t expect this to be the case,” Bassis says. “But if small bergs got stuck in the shallows ahead of the ice cliff, it was enough to buttress the [cliff] face,” he says.

      Simulations of an 800-meter-tall glacier flowing into 690 meters of water, comparable to the dimensions of the Thwaites and Pine Island glaciers in Antarctica, yielded similar results. The researchers also found that in relatively warm ambient temperatures, ice flow upstream of the cliff thins the glacier and reduces the height of the cliff, thus reducing the likelihood of runaway collapses.

      The team’s simulations “capture what I think of as realistic behavior,” says Golledge, who coauthored a commentary on the study in the same issue of Science. Future fieldwork may help validate the group’s results. If the simulations hold, Golledge says, the less dire results may mean slower sea level rise in the short term than otherwise predicted.

      Bassis and his colleagues’ analysis “is an important piece of work,” says Ted Scambos, a glaciologist at the University of Colorado Boulder, who was not involved in the study. The results, he says, “provide a balance between the possibilities for extreme runaway collapse and some that are more realistic.” More

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      A new book uses stories from tsunami survivors to decode deadly waves

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      TsunamiJames Goff and Walter DudleyOxford Univ., $34.95

      On March 27, 1964, Ted Pederson was helping load oil onto a tanker in Seward, Alaska, when a magnitude 9.2 quake struck. Within seconds, the waterfront began sliding into the bay. As Pederson ran up the dock toward shore, a tsunami lifted the tanker and rafts of debris onto the dock, knocking him unconscious.

      Pederson survived, but more than 100 others in Alaska did not. His story is just one of more than 400 harrowing eyewitness accounts that bring such disasters to life in Tsunami. Written by geologist James Goff and oceanographer Walter Dudley, the book also weaves in accounts from researchers examining the geologic record to shed light on prehistoric tsunamis.

      Chapter by chapter, Goff and Dudley offer readers a primer on tsunamis: Most are caused by undersea earthquakes, but some are triggered by landslides, the sudden collapse of volcanic islands or meteorites hitting the ocean (SN: 3/6/04, p. 152). Readers may be surprised to learn that tsunamis need not occur on the coast: Lake Tahoe (SN: 6/10/00, p. 378) and New Zealand’s Lake Tarawera are just two of many inland locales mentioned that have experienced freshwater tsunamis.

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      Copiously illustrated and peppered with maps, the book takes readers on a world-spanning tour of ancient and recent tsunamis, from a deep-ocean impact off the coast of South America about 2.5 million years ago to numerous tsunamis of the 21st century. The authors’ somber treatment of the Indian Ocean tsunami of December 2004 stands out (SN: 1/8/05, p. 19). Triggered by a magnitude 9.1 earthquake, the megawave killed more than 130,000 people in Indonesia alone.

      The authors — Goff is a professor at the University of New South Wales in Sydney and Dudley is a researcher at the University of Hawaii at Hilo — help readers understand tsunamis’ power via descriptions of the damage they’ve wrought. For instance, the account of a huge wave in Alaska that scoured mature trees from steep slopes along fjords up to a height of 524 meters — about 100 meters taller than the Empire State Building — may leave readers stunned. But it’s the heart-thumping stories of survivors who ran to high ground, clambered up tall trees or clung to debris after washing out to sea that linger with the reader. They remind us of the human cost of living on the shore when great waves strike.

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